Aus der Universitätsklinik für Zahn-, Mund-, und Kieferheilkunde der
Albert-Ludwigs-Universität Freiburg
Abteilung Poliklinik für zahnärztliche Prothetik
(Ärztl. Direktor: Prof. Dr. J. R. Strub)
Fracture resistance of molars restored with different
types of ceramic partial coverage restorations.
An in-vitro study
INAUGURAL-DISSERTATION
zur Erlangung des
Zahnmedizinischen Doktorgrades
Der Medizinischen Fakultät der Albert-Ludwigs-Universität
Freiburg
Vorgelegt 2003
Von Wael ATT
Geboren in Damaskus, Syrien
Dekan:
Prof. Dr. J. Zentner
1. Gutachter:
Prof. Dr. J. R. Strub
2. Gutachter:
PD Dr. P. Hahn
Promotionsjahr:
2003
I
Table of contents
1.
Introduction
1
2.
Literature review
4
2.1
History of porcelain and its use in dentistry
4
2.2
Definition of inlay/ onlay restoration
5
2.3
Development of ceramic inlay and onlay restorations
6
2.4
Classification of contemporary all-ceramic systems
used for the fabrication of inlays and onlays
7
2.4.1 sintered ceramics (powder-slurry ceramics)
7
2.4.2 Pressable ceramics
9
2.4.3 Infiltrated ceramics
12
2.4.4 Machinable ceramics
13
2.4.4.1
CAD/CAM systems
13
2.4.4.2
Copy-milling technique
15
2.4.4.3
Procera® all-ceramic system
17
2.5
Occlusal forces affecting posterior restorations
18
2.6
Fracture strength test data of ceramic inlays and onlays 19
2.7
Factors responsible for the failure of all-ceramic restorations 20
2.7.1 Microstructure of ceramics
20
2.7.2 Thickness and surface roughness of ceramics
21
2.7.3 Oral environment
21
II
2.7.4 Parafunctional loads
22
2.7.5 Cementation methods of ceramic materials
22
2.8
Guidelines for ceramic inlay and onlay preparation
24
2.9
Factors that influence longevity of ceramic inlays and onlays 25
2.10
Survival rate of ceramic inlays and onlays
26
3.
Aim of the study
29
4.
Outline of the study
30
5.
Materials and methods
31
5.1
Materials
31
5.1.1 Experiment teeth
31
5.1.2 Materials used for the fabrication of ceramic inlays
and onlays
5.2
31
5.1.3 Materials used in cementation procedures
33
5.1.4 Impression and die materials
34
5.1.5 Additional materials
35
Methods
36
5.2.1 Experiment teeth
36
5.2.2 Fabrication of models before preparation
36
5.2.3 Tooth preparation
36
5.2.4 Final impressions and fabrication of master models
40
5.2.5 Fabrication of ceramic inlays and onlays (EPC)
40
5.2.6 Luting procedures
42
5.2.7 Artificial periodontal membrane
43
III
5.3
6.
43
5.2.9 Embedding the experiment teeth in the sample holders
44
Tests
44
5.3.1 Exposure of the test samples to the artificial mouth
44
5.3.2 Fracture strength test
45
5.3.3 Statistics
45
Results
6.1
7.
5.2.8 Preparing the representative model of a clinical case
48
Survival rate of the test samples after exposure to the
artificial mouth
48
6.2
Fracture strength test of the test samples
48
6.3
Fracture patterns of the test samples
50
Discussion
53
7.1
Materials and Methods
53
7.1.1 The use of natural teeth
53
7.1.2 Artificial periodontal membrane
54
7.1.3 Tooth preparation
54
7.1.4 Adhesive cementation
56
7.1.5 Clinical relevance and influence of using the artificial
mouth on the survival rate and fracture strength
of ceramic onlays
7.1.6 The clinical relevance of fracture strength tests
57
59
IV
7.2
Results
60
7.2.1 Survival rate of the test samples after exposure to
the artificial mouth
60
7.2.2. Fracture strength tests after exposure to the artificial
mouth
61
7.2.3 Influence of the preparation design on the fracture
strength of the ceramic inlays and onlays
7.2.4 Patterns of fracture of the samples
62
63
8.
Conclusions
64
9.
Summary
65
10.
Zusammenfassung
66
11.
Appendix
67
11.1
Results of the fracture strength test (N) after exposure to
the artificial mouth
67
12.
References
68
13.
Acknowledgements
85
14.
Curriculum vitae
86
1
1. Introduction
Dental caries is one of the most common diseases, affecting approximately 80% of
the population in developed countries (Agerholm & Sidi 1988, Burke et al. 1999).
Finding a material that could restore the lost tooth structure and combine physical,
chemical and aesthetic properties which are optimal has been the goal of research
for many years. The science of dental materials is considered one of the most
important issues in contemporary dentistry, and has led to the development of many
alternatives for restoring lost tooth structure particularly in the posterior region.
Amalgam is one of the most frequently used materials in dentistry, with an annual
failure rate between 0% to 7% over an observation period of up to 20 years (Hickel &
Manhart 2001). Despite the controversy about its safety and efficacy (al-Nazhan et
al. 1988, Lindberg et al. 1994), amalgam has been around for more than 100 years.
Among its advantages are the relative low cost, ease of handling and placement and
the longevity of the restoration (Roulet 1997b, Chen et al. 2000, Grobler et al. 2000).
Although recent studies have proven that the use of dental amalgam has little or no
adverse effects (Ganss et al. 2000), an intensive public debate about the alleged
adverse effects of dental amalgam led to a significant limitation of its use and to
patients feeling a deep sense of insecurity (Eley 1997a, b, c).
Since the beginning of the twentieth century cast gold restorations have made up a
significant portion of all posterior tooth restorations. This is due to the superior
physical and chemical properties of the material. When dentists are asked about
their favorite restoration for their own teeth, gold cast restorations are most often the
preferred choice (Christensen 1989). Studies of the longevity of cast gold
restorations have produced conflicting results (Kerschbaum & Voss 1981, Presern &
Strub 1983, Jahn & Gonschorek 1986, Frtiz et al. 1992, Studer et al. 2000).
However, recently published data show that cast gold restorations have an annual
failure rate of only 0% to 5.9% with observation periods of up to 15 years (Hickel &
Manhart 2001). With such results cast gold remains a standard restorative material
for posterior teeth (Christensen 1989, 1996a, Eley 1997c, Stoll et al. 1999, Studer et
al. 2000, Hickel & Manhart 2001).
2
Increasing demands for alternative restorative materials that are aesthetically
pleasing has led to the development of tooth-coloured restorative materials.
Materials available until 1978 were very inadequate and had short clinical longevity.
Since 1978, various materials have shown the ability to serve more than 10 years
(Christensen 1989). Glass-ionomer cements are not considered to process
adequate mechanical properties for general use as definitive restorations in stressbearing posterior teeth (Caughman et al. 1990, Eley 1997c, van Dijken & Sjostrom
1998, Hickel & Manhart 2001). Recently developed resin composites are superior to
the earlier versions in regard to wear, resistance and colour stability, but the
predominant shortcoming of the composites is the polymerisation shrinkage
(Davidson et al. 1984, Feilzer et al. 1987, Ciucchi et al. 1997). During recent years
several techniques have been introduced to solve existing problems with resin
composites, such as multiple increment techniques, replacement of the dentin with
glass ionomer cement in the sandwich technique, or the use of ceramic inserts
(Krejci et al. 1987, van Dijken et al. 1999). However, these techniques still suffer
from imperfections and are very technique sensitive (Roulet 1997a, van Dijken
2000). A promising method, the inlay/onlay technique, has also been introduced to
reduce the shrinkage problem (Mörmann 1982, James & Yarovesky 1983,
Blankenau et al. 1984). The form of the restoration can be established by a direct,
indirect or semidirect method. Unfortunately, with only one exception (Roulet 1994),
no clinical studies fulfilled the criteria of a long-term study (5 years) on the success
rate of this technique (James & Yarovesky 1983, Füllemann et al. 1992, Krejci
1992). Furthermore, clinical studies have demonstrated a failure of the compositecomposite bond (60% marginal openings after 6 months) (Krejci 1992, Roulet
1997a).
Along with metals and polymers, ceramics are one of the basic groups of materials.
For decades they have been recognized as one of the earliest and most
environmentally-durable materials known to man. Developing dental ceramics is one
of the most important subjects in the field of dental materials.
In the last few years, several new all-ceramic systems, which offered good
aesthetics and simplified fabrication procedures, have been introduced. With these
systems it is possible to fabricate single crowns, inlays, onlays and veneers. These
all-ceramic restorations represent an interesting option to aesthetic restorative
3
treatment of lost tooth structure and can be made by using a variety of fabrication
techniques.
However, in vitro and in vivo investigations of new all-ceramic systems should be
undertaken before introducing them into routine clinical use.
4
2.
2.1
Literature review
History of porcelain and its use in dentistry
The word ceramic is derived from the Greek word “Keramos”, meaning of or
pertaining to pottery, especially as an art form. Porcelain is defined as a fine kind of
earthenware, having a translucent body and a transparent glaze, or as an article or
vessel made of porcelain (Qualtrough et al. 1990). Ceramics were probably the first
materials to be artificially made by humans, and porcelain was among the first
materials to be the subject of early laboratory research by scientists. Primitive man
would have become aware of the plastic properties of mud and clay and might have
accidentally discovered that molded shapes baked in fire became hard. Examples of
the early fabrication of ceramic articles have been found and dated as far back as
23,000 years BC. However, the earliest examples of porcelain known, date back a
thousand years to the Sung dynasty (960 to 125 AD) (Jones 1985).
Although dental technology existed in Etruria as early as 700 BC and during the
Roman first century (Kelly et al. 1996), the history of porcelain as a dental material
only goes back approximately 200 years (Jones 1985). It was found that, by using
this material, it was possible to reproduce the color and translucency of natural
teeth, and the first porcelain teeth were thus manufactured (Qualtrough et al. 1990).
In 1774, Alexis Duchateau and Nicholas Dudois de Chemant fabricated the first
successful porcelain dentures. Dubois de Chemant, who improved porcelain
formulations continually, was awarded both French and British patents. In 1808,
individually-formed porcelain teeth which contained embedded platinum foils were
introduced in Paris by Giuseppangelo Fonzi. Their aesthetic and mechanical
versatility provided a major advance in prosthetic dentistry (Kelly et al. 1996,
Pröbster 1997). Single-tooth porcelain restorations were first introduced in 1844. The
porcelain jacket crown is said to have originated from the gold shell crown, the idea
which was credited to Beers of California in 1873. The porcelain crown was
constructed on the same principle and basic theory, but was capable of better
esthetic results regarding shades and translucency. The preparation and fabrication
5
procedures for porcelain crowns were more complex in comparison to inlays; for this
reason, the major use of dental porcelain between 1900 and 1920 was for inlay work
(Jones 1985).
The technique for making individual porcelain inlays and crowns was not developed
until the late 1800s. An early technique, described by Herbst in 1882, was one in
which porcelain rods were ground, fitted and cemented into prepared cavities in the
natural tooth (Jones 1985, Touati 1996). The first successful fused inlays and
crowns were said to be made by Land of Detroit, in about 1886. A patent was taken
out by Land in 1887 covering the method of a burnishing platinum foil in order to
make a matrix for fusing the porcelain with the aid of a gas furnace. Land also
experimented with producing a low-fusing porcelain that would be compatible with a
gold matrix. However, he had little success with the low-fusing porcelain (Jones
1985, Qualtrough et al. 1990).
During the late 1950s and 1960s there were marked advances in the development of
new techniques, materials, and equipment, such as furnaces, alloys and porcelain
frits. Improved tooth-cavity preparation, using techniques based upon new, highspeed instrumentation and burs combined with the introduction of improved and
more accurate impression techniques, vastly changed clinical approaches and
attitudes regarding porcelain restorations (Qualtrough et al. 1990, Pröbster 1997).
One of the most significant advances occurred with the successful introduction of the
acid-etch technique by Buonocore (1955), which opened a new era for adhesive
dentistry and development of new dental materials (Qualtrough et al. 1990).
2.2 Definition of Inlay/ onlay restorations
According to the Glossary of Prosthodontic terms (The Academy of Prosthodontics
1999), an inlay is a dental restoration made outside of a tooth to correspond to the
form of the prepared cavity, which is then luted into the tooth. An onlay is a
restoration that restores the entire occlusal surface and is retained by mechanical or
adhesive means.
6
2.3 Development of ceramic inlay and onlay restorations
Formulating an ideal strength-aesthetic combination in a ceramic material has been
a battle for many years. Traditional porcelain is a blend of three minerals: quartz,
feldspar and pure white clay (Al2O3.2SiO2.xH2O). Pigments and opacifying agents
are added to this type of porcelain in order to produce various shades and
translucencies. After baking, the porcelain contains similar components: small
crystals (leucite) and/or alumino-silicate crystals embedded in a silicate glass (a noncrystalline, amorphous matrix). Leucite, a reaction product of potassium feldspar and
glass, is responsible for optical properties, thermal expansion, strength, and
hardness of the porcelain (Rosenblum & Schulman 1997).
In the early 1980s, castable glass-ceramic and refractory die techniques were
introduced. The disadvantages of the refractory die system are that the particles are
sintered together, resulting in microporosities and inhomogeneities between the
ceramic particles. It is well known that these microporosities can initiate crack
propagation, leading to early failure of such all-ceramic restorations (Kelly et al.
1996). Many castable glass-ceramic systems have been described in which the
porosities could be reduced to a minimum by the casting technique (Dicor,
Dentsply, York, Pennsylvania, USA/ Cerapearl, Kyocera Bioceramics, Kyoto,
Japan/). However, the casting process is followed by a ceramming procedure
(controlled crystallization using an appropriate heat treatment), resulting in additional
ceramic shrinkage (Kelly et al. 1996).
In 1990, the IPS Empress all-ceramic system was developed (Beham 1990). It is a
leucite-reinforced glass-ceramic material, which can be deformed at elevated
temperatures and can be pressed into a mould. This method provides a high degree
of homogeneity, high precision and good aesthetic appearance (Beham 1990, 1991,
Dong et al. 1992). With a flexural strength of 200 MPa, the system is considered one
of the most preferred restorative options for the fabrication of single crowns,
inlays/onlays, and veneers. (Dong et al. 1992, Kelly et al. 1996).
7
2.4
Classification of contemporary all-ceramic systems used
for the fabrication of inlays and onlays
Contemporary all-ceramic systems can be classified either by material composition
or by fabrication procedures (Kelly et al. 1996, Rosenblum & Schulman 1997, van
Dijken 1999).
2.4.1 Sintered ceramics (powder slurry ceramics)
Stronger all-ceramic systems were developed by increasing the crystalline content of
conventional feldspathic porcelain. All systems used the refractory die technique.
o
Optec HSP (Jeneric/Pentron, Wellingford, USA, Connecticut)
The material is a feldspathic porcelain containing 40% leucite crystals. With the
increased amount of leucite, the material has a flexural strength of 146 MPa
(Rosenblum & Schulman 1997). The manufacturer disperses the leucite crystals in a
glassy matrix by controlling their nucleation and crystal growth during the initial
production of the porcelain powder. In the so-called refractory die technique, the
porcelain is built up on a model in layers, using a powder-water slurry. The layering
technique produces a less controlled crystallization (van Dijken 1999). Optec
ceramic is indicated for inlays, onlays, and veneers (Garber & Goldstein 1994). The
marginal integrity of Optec inlays was rated excellent for 67% in a clinical follow-up
study of 8.1 months (Molin & Karlsson 1992). The failure rate of 145 Optec inlays
was 13% after 3 years of function (Molin & Karlsson 1996). The main reason for
failure was fracture of the inlays. Due to the high leucite content, the material’s
abrasiveness against a natural tooth is greater than that of conventional feldspathic
porcelain (Rosenblum & Schulman 1997).
o
Duceram LFC (Ducera Dental, D-Rosbach)
The material is a hydrothermal low-fusing ceramic material with a flexural strength of
110 MPa. It is composed of an amorphous glass containing hydroxyl ions. The
8
material’s hardness is close to the hardness of natural teeth owing to the absence of
leucite (Rosenblum & Schulman 1997). The application of the material is limited to
inlays, onlays, veneers and crowns. The restoration is made in two layers; the base
layer is Duceram Metal Ceramic (a leucite containing porcelain), which is placed on
a refractory die using standard powder-slurry technique; the veneering layer is
Duceram LFC (Rosenblum & Schulman 1997). It has been reported that Duceram
inlays have a marginal gap of 72 µm (Gemalmaz et al. 1997). The survival rate of 53
inlays was 90% after three years of function (Haas et al. 1992).
o
Hi Ceram (Vita Zahnfabrik, D-Bad Säckingen)
Hi-Ceram is an alumina-based ceramic material. It is indicated for the fabrication of
inlays, onlays and veneers. Fabrication procedures of restorations using this
material are the same procedures when using other sintered ceramic systems. In a
longitudinal study, 30 inlays showed a survival rate of 80% over an observation
period of 3 years. The main reasons for failure were either fracture of the inlays or
secondary caries (Haas et al. 1992).
o
Mirage / Mirage II (Chameleon Dental Products, USA, Kansas city)
Mirage and Mirage II are feldspathic ceramic materials reinforced with zirconia
fibers. The size of the fibers differentiate the two materials. In a clinical study, 25
inlays showed a survival rate of 52% after 4.5 years of function (Isidor & Brondum
1995). The main reasons for failure were fractures of the inlays. In a three-year
comparative study, 118 inlays (59 each group) were either luted with glass-ionomer
cement or composite resin cement and examined intraindividually . They showed
survival rates of 84.7% and 96.6%, respectively (Aberg et al. 1994). In another 6year comparative study, the survival rate was 74% for 59 inlays luted with glassionomer cement and 88% for 59 inlays luted with composite resin cement (van
Dijken et al. 1998). It was concluded from this study that higher failure rates could be
expected in restorations luted with glass-ionomer cement.
9
Fifty inlays fabricated with Mirage II showed a survival rate of 100% after an
observation period of 4 years. 64% of the margins were clinically perceptible after 4
years (Friedl et al. 1997).
The disadvantage of all-ceramic restorations, made with sintering techniques, is that
sintering the particles together can result in microporosities and inhomogeneties
between the particles, which can initiate crack formation (van Dijken 1999).
2.4.2 Pressable ceramics
o
IPS Empress I (Ivoclar-Vivadent, FL-Schaan)
To overcome the processing of inhomogeneities and porosity during ceramming, a
heat-press technique (IPS-Empress) was developed in 1983 by faculty members of
the Department of Fixed and Removable Prosthodontics and Dental Materials at the
University of Zurich. Since 1986 the development has proceeded in conjunction with
a dental company (Ivoclar-Vivadent, FL-Schaan).
The IPS Empress I material is a type of leucite-reinforced glass-ceramic material
supplied in ingot form. The glass-ceramic ingot is precerammed and precolored
(Dong et al. 1992). This material is derived from the SiO2-Al2O3-K2O chemical
system. Leucite crystals represent framework silicates with the chemical formula
KalSi2O6. Depending on the type of the IPS Empress I product, the content of the
crystal phase ranges between 30 and 40 vol%. The material has a flexural strength
of 182 MPa following heat treatment. Therefore, the IPS Empress I system is
designed for the fabrication of single units, inlays, onlays and veneers (Dong et al.
1992). The strengthening mechanism of leucite is attributed to the higher percentage
volume reduction of leucite particles compared to the surrounding glass matrix upon
cooling (Seghi et al. 1995). The higher percentage volume reduction of leucite is
accounted for by its higher coefficient of thermal expansion in comparison to the
glass matrix and a high-to-low temperature phase transformation. The volume
differential between the leucite particles and the glass matrix causes residual
stresses that place the surrounding glass matrix in compression, which must be
counteracted by tensile stresses before cracks propagate (Dong et al. 1992, Seghi
10
et al. 1995). It has also been shown that flexural strength improves under
subsequent heat treatments as a result of the growth of additional leucite crystals
(Dong et al. 1992).
A full-contour restoration is waxed-up on a conventional die system. The wax-up is
then sprued, invested and placed in a special mold that has an alumina plunger. The
ring is placed in a cold burn-out oven and progressively heated to 850 °C and held at
this temperature for 90 minutes for wax burnout and heat saturation. The ring is then
ready for placement in the EP 500 (Ivoclar-Vivadent, FL-Schaan) pressing furnace,
which is in a standby mode at a temperature of 700 °C. One or two precerammed
ingots of the desired color are placed in the center of the sprue former. Once the
process is initiated, the entire assembly is heated to 1150 °C under a vacuum and
the plunger presses the molten ceramic into the mold. Afterwards, the final shade of
the restoration is adjusted by staining or veneering. In the veneering technique, the
original wax-up is cut back by about 0.3 mm. After molding and baking as described,
feldspathic porcelain is added to the surface to obtain full contour and the correct
shade.
Short- and long-term clinical studies on Empress I inlays and onlays showed very
good survival rates (Table 2.1).
Author (year)
Krejci et al. (1992)
Tidehag & Gunne
(1995)
Studer et al.
(1996)
Thonemann et al.
(1997)
Fradeani et al.
(1997)
Lehner et al.
(1998)
Scheibenbogen et
al. (1998)
Observation
period
Type (No.)
Survival
rate
Complications
1.5 years
Inlays class II (10)
100%
Inlay fracture
2 years
Inlays & onlays (62)
98.4%
1 onlay fractured
2 years
Inlays & onlays (130)
97.5%
Inlay fracture
2 years
Inlays (51)
100%
4.5 years
Inlays & onlays (125)
95.6%
Restoration fracture
94.9%*
7 onlays fractured
100%
-
6 years
1 year
Inlays (138)
Onlays (17)
Inlays class I (24)
Significant deterioration of
marginal quality over time
11
Krämer et al.
(1999)
Frankenberger et
al. (2000)
Manhart et al.
Inlays (96)
93%
6 years
Inlays (96)
93%*
7 inlays failed
100%
-
Inlays class I & II
3 years
(2001)
Inlay fracture
4 years
(24)
caries
92% with
chemical
van Dijken et al.
(2001)
5 years
Total coverage
cured resin
restorations without
composite)
macromechanical
95% with
retention (182)
dual-cured
Restoration fracture
resin
composite
* Estimated survival (Kaplan-Meier analysis)
Table 2.1
o
Survival rates of Empress I inlays and onlays
Optec OPC (Jeneric/Pentron, Wellingford, USA, Connecticut)
This material is a type of feldspathic porcelain with increased leucite content,
processed by molding under pressure and heat. The OPC system can be used for
full-contour restorations (inlays, onlays, veneers, full crowns). Alternatively, it can be
used as a core material, which is veneered using conventional powder-slurry
techniques with a high-leucite-content feldspathic porcelain, similar to Optec HSP
porcelain. The manufacturer reports that the crystalline leucite particle size has been
reduced and the leucite content increased, resulting in an overall increase in flexural
strength of OPC (165 MPa) (Kappert 1993, Rosenblum & Schulman 1997).
There are no published clinical studies on Optec OPC (van Dijken 1999). However,
because of its high leucite content, it can be expected that this porcelain’s abrasion
against natural teeth will be greater than that of conventional feldspathic porcelain
(Rosenblum & Schulman 1997).
12
2.4.3 Infiltrated ceramics
o
In-Ceram (Vita Zahnfabrik, D-Bad Säckingen)
The restoration is composed of an infiltrated core veneered with feldspathic
porcelain. The core is extremely porous, and is composed of either alumina oxide or
spinel, a composition containing aluminum oxide and magnesium oxide. The core is
made from fine insoluble particles that are mixed with water to form a suspension
referred to as slip and then painted on a gypsum die. Water, flowing under capillary
pressure into the gypsum die, compacts the particles against the die. The procedure
is called slip-casting. Afterwards, the compacted particles are partially sintered
together to form necks between touching particles for 10 hours at 1120°C. The result
is an opaque, porous core. The spinel core is more than twice as translucent as the
alumina coping and is more suited for esthetically critical areas and inlays (Kelly et
al. 1996, van Dijken 1999). After choosing an appropriate shade, the porous,
partially sintered alumina (or spinel) core, is then infiltrated with a low-viscosity glass
(Lanthanum glass) by baking again at 1120°C for 4 hours to yield a ceramic coping
of high density and strength. The coping contains at least 70% aluminum oxide or
spinel and is currently one of the strongest ceramics available with a flexural
strength between 236 and 446 MPa depending on the test method used (Seghi &
Sorensen 1995, Giordano et al. 1995b). The densely stacked particles and the
different thermal expansion coefficients of glass and alumina (or spinel) contribute to
the high strength of the material. The In-Ceram material is then veneered with a
feldspathic ceramic for the final aesthetics. The core of aluminum oxide or spinel is
so dense that conventional etching with hydrofluoric acid is not possible and does
not increase the surface roughness and bond of the restoration to the tooth.
Adhesive luting is possible after sandblasting and the use of a resin cement
containing a phosphate monomer, i.e., Panavia 21 (Kern & Thompson 1995, Kern &
Strub 1998). The material has a hardness equal to that of conventional feldspathic
porcelain (Rosenblum & Schulman 1997).
The fabrication of inlays and onlays using the In-Ceram ceramic can be successfully
made with the help of CAD/CAM technology. No clinical data are available on the
performance of inlays and onlays utilizing the conventional technique.
13
2.4.4 Machinable ceramics
The development of the machinable technology took place in the 1980’s. At that time
the application of this method was only indicated for the fabrication of inlays and
onlays (Isenberg et al. 1992). Nowadays, machining has become a viable option as
a forming method in the fabrication of all-ceramic restorations. Both CAD/CAM
systems and the precision copy-milling machine are commercially available (Kelly et
al. 1996).
2.4.4.1
CAD/CAM systems
ο
Cerec (Sirona, D-Bensheim)
The
introduction
of
computer-aided
design/
computer-aided
manufacture
(CAD/CAM) systems to restorative dentistry represents a major technological
breakthrough. This technology is implemented in the Cerec system, which was
developed in 1984 (Mörmann & Bindl 2000). The system mills ceramic restorations
from industrial blocks of ceramic material which are prefabricated under optimum
and controlled conditions (Martin & Jedynakiewicz 1999). It is possible to obtain a
high and uniform ceramic quality without the inevitable material variations seen in
manually-produced restorations (Sjögren et al. 1992). It is possible with this system
to generate a restoration without taking an impression, to fabricate a temporary
restoration, and to avoid any laboratory assistance (chair side). The entire procedure
can be preformed in one appointment. The annual failure rates of CAD/CAM ceramic
inlays and onlays range from 0% to 4.4% (Hickel & Manhart 2001).
Technically, the cavity is coated with a light-reflecting powder, mapped
stereophotogramatrically using a mini hand-held, 3-dimensional intraoral video
camera (Sidexis/Sirocam 2, Sirona, Bensheim, D). This procedure is called optical
impression (Mörmann & Brandestini 1989). The obtained information is fed to a
computer that stores the 3-dimensional pattern depicted on the screen. The video
display serves as a format for the necessary manual construction via an electrical
signal. Then the integrated microprocessor develops the final 3-dimensional
restoration from the 2-dimensional construction. After that the electronic information
14
is transferred numerically to the linked miniature 3-axis milling device. The milling
unit driven by a water turbine device generates a restoration from the standard
ceramic block. The blocks are cast and ceramed by several manufacturers
(Mörmann & Bindl 2000).
The available types of ceramic blocks are as follows:
Cerec Vitablocs Mark I (Vita Zahnfabrik, D-Bad Säckingen)
The ceramic material of these blocks is a feldspathic porcelain with a fracture
strength of 93 MPa and a hardness similar to that of conventional feldspathic
porcelain (Rosenblum & Schulman 1997). This material was the first composition
used with the Cerec system. It is recommended for the fabrication of veneers,
inlays/onlays and single crowns (Otto 1995).
Cerec Vitablocs Mark II (Vita Zahnfabrik, D-Bad Säckingen)
This is a feldspathic porcelain of increased strength (up to 152 MPa), and it has a
finer grain size than the Mark I compositions. The hardness of the material is equal
to that of tooth enamel (Rosenblum & Schulman 1997). The material is indicated for
the fabrication of veneers, inlays/onlays and single crowns (Otto 1995).
ProCAD (Ivoclar-Vivadent, FL-Schaan)
It is a leucite reinforced glass ceramic with a fracture strength of 140-200 MPa which
also indicates it for the fabrication of inlays, onlays, and single crowns (Gaglio 2001).
No data are available on the performance of inlays and onlays made out of this
ceramic.
Since the introduction of the Cerec system, a large number of in-vitro and in-vivo
studies have been published. Reiss & Walther (1991) reported that the survival rate
of 426 Cerec inlays was 95% after observation period of 3 years. The main reasons
for replacement were fractures and postoperative symptoms. In a longitudinal clinical
study Walther et al. (1994) reported that the success rate for 1011 Cerec inlays was
15
95% after 5 years. The main reasons for failure were either inlay, tooth fractures or
caries. Otto (1995) reported a survival rate of 98% for 100 Cerec inlays after 5 years.
In this study, 2 teeth required endodontic therapy. In a four-year follow-up Heymann
et al. (1996) showed a survival rate of 100% for 19 Cerec inlays and 31 Dicor MGC
inlays. Berg and Derand (1997) reported a survival rate of 94.1% for 51 Cerec I
inlays after an observation period of 5 years. All inlays in this study showed marginal
defects after 5 years. In a 7.5-year clinical trial, the survival rate of 1011 Cerec inlays
was 91.6% (Reiss & Walther 1998). Premolars exhibited a better performance than
molars. In another study, 36 inlays, made out of Cerec Vita Mark II blocks, have
been observed for 3 years. Twenty eight inlays were luted with resin cement and 9
with glass-ionomer cement. Survival-rate results were 96.4% after 3 years for inlays
luted with resin cement and 100% for inlays luted with glass-ionomer cement
(Zuellig-Singer & Bryant 1998). In an 8-year follow-up clinical study, 32 Cerec inlays
have been evaluated. Half of the inlays were fabricated from Vita Mark II block and
the other half were fabricated from Dicor MGC blocks. Only 3 fractures were
observed in this study (2 Dicor MGC and 1 Vitablocs Mark II) after 8 years and the
survival rate was 90.6%. No difference was found between the two blocks used
regarding degree of color matching, marginal integrity and general clinical
performance (Pallesen & van Dijken 2000). Reiss & Walther (2000) reported a
success rate of 90% for Cerec inlays after 10 years and 84.9% success rate after 12
years of observation. This study also showed that premolars exhibited a better
performance than molars. In a short-term clinical study, 10 Cerec inlays were
fabricated from Vitablocs Mark II. After two years, all onlays were recorded to be
successful (Denissen et al. 2000). Unfortunately, no long-term clinical data are
available on onlays using the Cerec technique.
2.4.4.2
o
Copy-milling technique
Celay (Mikrona Technologies AG, CH-Spreitenbach)
The Celay technique is a variation of the direct-indirect restoration concept but
without the need for a laboratory technician (Eidenbenz et al. 1994). After the tooth
preparation is completed, a precision imprint composite material (Espe-Celay-Dent,
16
Espe, D-Seefeld) is molded directly in the cavity, where it is adjusted for occlusion,
contact relations, and marginal integrity. The material then undergoes a light- or
chemical curing process. Afterwards, it is removed from the cavity, and it serves as a
prototype model to be copied and reproduced in ceramics using the milling system
(Eidenbenz et al. 1994, Garber & Goldstein 1994). The milling center has two
distinct aspects. In one part, the model to be copied is centered in a holder, where it
is manually scanned. A second part of the milling machine contains a rotary turbine
with various cutting tools. The directly-formed pattern in the vice is manually
scanned with a sensor. This sensor is directly connected to the milling aspect. Any
form scanned is thus simultaneously reproduced in all three dimensions in a block of
ceramic by the rotary turbine. The gross form is developed with a diamond disc and
refined with a diamond point. The same type of ceramic blocks that are available for
the CAD/CAM systems can be used with this technique (van Dijken 1999). An
appropriately-sized block is selected and inserted in the holder of the milling center.
The system can also be used as a purely indirect process, in which an impression is
made and a die fabricated in the laboratory. The composite resin imprint prototype
material is precisely formed in the die to represent the desired restoration. The
composite resin prototype inlay is then placed in the left side of the milling unit in a
bipoint metallic vise. The surface of the prototype is then similarly scanned manually
and reproduced in ceramic on the milling unit, which carves out an exact replica of
the plastic prototype in ceramic. A thin white powder coating is used as a control of
the tracing. Contact of the stylus will remove the white powder, and the blue color of
the pre-inlay/onlay is visible. The occlusal scheme developed inside the oral cavity is
reproduced identically, so that after completion of the milling process, the inlay is
ready to be inserted with minor corrections. Additional characterization or
colorization of the inlay can be accomplished in the laboratory by refiring the inlay
prior to final finishing (Eidenbenz et al. 1994, Garber & Goldstein 1994).
An In-Ceram-like ceramic block (Alumina Celay Blank, Vita, D-Bad Säckingen) is
also available for the Celay technique. The material is a feldspathic porcelain, in
which a porous perform of alumina is manufactured under factory conditions.
Celay ceramic inlays were considered clinically acceptable by traditional criteria.
Marginal fit was reported to differ slightly depending on whether the inlay pattern
was fabricated directly on the prepared tooth or on a laboratory die (Siervo et al.
17
1994). In only one clinical study 12 out of 15 Celay machined inlays survived after 3
years of function (Thordrup et al. 1999).
Both the Cerec and the Celay systems mill the ceramics with diamond burs,
producing initially rough surfaces. It is the responsibility of the dentist to bring these
surfaces to a high gloss with aluminum-oxide-coated flexible discs and felt cones
impregnated with diamond particles to avoid wear of the opposing tooth (Roulet
1997a).
Two advantages are provided by the availability of CAD/CAM or other machining
routes to all-ceramic restorations. Firstly, these systems remove the processing of
ceramics, and hence microstructural control, from the dental laboratory and place it
within jurisdiction of the manufacturer. Secondly, the manufacturer merely provides a
few sizes of simple blocks; complex shaping is controlled by the machining process
(Kelly et al. 1996).
2.4.4.3
Procera® all-ceramic system (Noble Biocare, S-Göteborg)
The Procera® all-ceramic system, which was developed in 1993, consists of a
computer-controlled scanning and design station located in the dental laboratories
that are connected via modem to Procera Scandivk AB in Stockholm, Sweden
(Andersson & Oden 1993). The system is mainly indicated for the fabrication of allceramic crowns and abutments for single tooth restorations (Andersson et al. 1998).
The restoration is composed of a densely sintered, high-purity aluminum oxide
coping that is combined with low-fusing AllCeram® (Noble Biocare, S-Göteborg)
veneering porcelain. The fabrication of the coping takes into account the sintering
shrinkage of approximately 20% by enlarging a model of the preparation that is used
in the manufacturing process. The scanner, which is located in a local dental
laboratory, digitizes a conventional die. The digital image is sent by the modem to
the central production unit, where the computer-controlled milling machines fabricate
refractory dies compensating for the sintering shrinkage. The high-purity aluminum
oxide powder (>99.5%) is compacted against the enlarged preparation model,
milled, and sintered to full density (Andersson et al. 1998). The coping material has
a flexural strength of 678 MPa ( Ottl et al. 2000). The high-purity aluminum oxide
system promotes the densification of alumina during melting and solidification,
18
hence eliminating most porosities and increasing the strength of the material
(Andersson & Oden 1993).
Denissen et al. (2000) evaluated 7 Procera onlays after 2 years of clinical function.
They had a survival rate of 100%. The average marginal gap width for the onlays
was 68 µm. The authors reported that fabricating onlays using this technique is
difficult due to problems faced when trying to do the surface measurements by the
Procera contact probe. The orientation of the sapphire tip toward the preparation
surface was reported to be critical. It was necessary to apply wax to smooth internal
edges and make it easier for scanning the dies.
2.5 Occlusal forces affecting posterior restorations
Occlusal forces are forces created by the dynamic action of the muscles during the
physiologic act of mastication. The bite forces increase with growth. Men bite with
greater force compared to women. This difference between sexes is due to the fact
that men have bigger muscles than women. It has been reported that there is a
positive correlation between the maximal bite force in the incisor region and the
vertical proportions of the anterior facial morphology; subjects with a high bite force
have a relatively short lower anterior height. Higher biting loads are measured on
molar teeth than on other teeth in the dental arch. No relation was found between
facial characteristics and the maximal bite force in the molar region or the maximal
bite force endurance (Kiliaridis et al. 1993). Published data on bite forces indicate
that the maximum biting force that may occur in the posterior dental area vary
between 300 and 880 N. (Bates et al. 1976, Gibbs et al. 1986, Kiliaridis et al. 1993).
Some bruxers and clenchers presented biting forces that are six times higher than
that of non bruxers. It was also reported that the maximum chewing forces in the
molar region are approximately 400 N (Schwickerath & Coca 1987). It has been
suggested that a force of 500 N, as used for cracking a hazelnut, seems to be the
maximum limit for natural teeth (Kappert 1996). Thus, it can be concluded that in
order to achieve a good clinical long-term result, it is important for the posterior
restorations to be able to withstand the maximum stress created in this region.
When comparing the maximal biting forces exerted by the stomatognathic system, it
is obvious that average functional chewing forces are lesser. It has been reported by
19
several authors that the normal physiological chewing forces around posterior teeth
range from 2 to 150 N (Eichner 1963, Bates et al. 1976, De Boever et al. 1978,
Jäger 1989). In several simulated clinical conditions, a load of 49 N is set for the
chewing simulator to imitate the physiological biting force (Krejci et al. 1990, Behr et
al. 1999, Kern et al. 1999).
2.5
Fracture strength test data of ceramic inlays and
onlays
Fracture strength values are often relied upon as indicators of structural
performance for brittle dental materials. However, strength is more of a conditional
than an inherent material property, and strength data alone cannot be directly
extrapolated to predict structural performance.
Extrapolation of strength data of clinical performance, considered alone, must be
approached cautiously. Proper use of strength data for predicting the life expectancy
of restorations in clinical situations requires knowledge of the following; (1) that the
critical flaw in the test specimen is the same as the one involved in clinical failure; (2)
that environmental influences have been replicated in the laboratory; (3) that failure
parameters describing the flaw size, distribution, and crack growth rates have been
measured; and (4) that stress distribution in the clinical structure is well
characterized (Kelly 1995).
Typically, the fracture strength of ceramics is checked by using bend bars with three
or four point loading and/or discs tested in biaxial flexure (Campbell 1989, Giordano
et al. 1995b, Seghi & Sorensen 1995). Measured strengths vary as a function of
specimen preparation and testing methodology, including surface condition, threepoint versus four-point bending and different stress rates.
Homogeneous all-ceramic restorations consist of a layer of ceramic (approximately
1.0-2.0 mm thick) atop a layer of cement (approximately 30 to 120 µm thick)
supported by a layer of dentin. This structure is not well represented by simple barshaped specimens, such as those used in 3-point or 4-point bending tests (Kelly
1999). Furthermore, the surface of a restoration is sophisticated and not represented
by the typical test methods. Therefore, in order for strength testing to be relevant, it
20
is generally recommended that the mode of loading be chosen to closely simulate
the actual component in service (Ritter 1995a, Kelly 1999).
While most laboratory studies have evaluated the strength of all-ceramic crowns and
bridges placed on plastic abutments, metal abutments or natural abutments, only
few studies tested the strength of all-ceramic inlays and onlays:
Dietschi et al. (1990) compared the fracture strength of natural teeth restored with
inlays made out of Vitadur N and inlays made out of Ceramco II and luted with
composite resin cement. Results of the fracture strength test for natural teeth
(control), Vitadur N and Ceramco II all-ceramic inlays were 3547 N, 2680 N and
1662 N, respectively.
Esquivel-Upshaw et al. (2001) compared the fracture resistance of metal-ceramic
inlays made of Goldtech Bio 2000 metal and Ceramco porcelain with Empress 2 allceramic inlays. The inlay preparation was made on 60 plastic teeth, with 30 teeth
allocated for metal-ceramic inlays and 30 teeth for all-ceramic inlays. Each group
was further divided into 5-, 10-, and 20-degree taper preparation. The mean fracture
load for Empress 2 inlays and metal-ceramic inlays at 5°, 10°, and 20° was 70 N, 48
N, 33 N, and 40 N, 29 N, and 14 N, respectively.
2.7
Factors
responsible
for
the
failure
of
all-ceramic
restorations
2.7.1 Microstructure of ceramics
It is well known that fractures always progress from the area that is subjected to the
highest tensile stress. Porosities and microcracks have been shown to be sites of
fracture initiation (van Dijken 1999). They can considerably increase internal stress,
which initiates a crack that progresses from the inner surface and finally damages
the restoration (Anusavice & Hojjatie 1992, Peters et al. 1993, van Dijken 1999). The
initial cracks may form during processing, due to incomplete densification, which
leaves angular pores behind, or due to differences in thermal expansion or a
modulus between grains or inclusion particles (Jung et al. 2000). They also
frequently form in the surface of ceramics through abrasion by abrasive particles or
21
corrosion by water (Kelly 1995). These cracks, coupled with a low fracture
toughness, not only limit the strength of ceramics but also cause variation in strength
and a time-dependency (Ritter 1995b). Most all-ceramic single restorations fail from
the inner aspect outward (Kelly et al. 1990, Thompson et al. 1994, White et al. 1996,
Kelly 1999), indicating that the interface is both a location of high tensile stress and
an important source of flaws (Kelly 1995).
2.7.2 Thickness and surface roughness of ceramics
The thickness of a ceramic restoration can also affect fracture resistance. Under
normal circumstances, a thick ceramic restoration would be assumed to
demonstrate a higher degree of fracture resistance than a thin one (Tsai et al. 1998).
Unfortunately, this relationship between the thickness of ceramic material and its
susceptibility or resistance has not been examined conclusively.
It has been shown that roughness produced by the finishing procedure and the
introduction of surface flaws may be accompanied by a reduction in strength of
ceramic restorations. This was demonstrated by Williamson et al. (1996). They
found that specimens with a coarsely ground surface were significantly weaker than
those with polished surfaces. Giordano et al. (1994, 1995a) have reported that
sequential polishing significantly improved the flexural strength of feldspathic
porcelain. A similar effect has been demonstrated in an experimental study, where
biaxial flexural strength of different ceramic materials was measured with and
without glazing. A significant correlation was found between the roughness of the
surface and the biaxial flexural strength: the smoother the surface, the stronger the
sample. This correlation, however, couldn’t be found where the ceramic material had
an inner structure which caused an even larger stress concentration than that
caused by the combination of surface roughness and flaws (De Jager et al. 2000).
2.7.3 Oral environment
In the oral environment, the influence of water and changing temperature, called
stress corrosion, can promote crack propagation and decrease the fracture strength
of an all-ceramic restoration (Kelly 1995). In-vitro investigations showed that storage
22
in water for extended periods and/ or changing temperature will alter the failure load
data (Schwickerath 1986, Mante et al. 1993, Kern et al. 1994)
2.7.4 Parafunctional loads
Posterior teeth are loaded vertically during centric occlusion. Eccentric or
parafunctional forces can increase the shear resistance of the ceramic material,
thereby accelerating their fatigue rate (Hojjatie & Anusavice 1990). The intensity and
duration of loading may have more influence on the fracture strength of single allceramic posterior restorations than the previous eccentric forces. However, the
vertically-loaded all-ceramic restorations can withstand greater chewing forces;
therefore, it would seem that they might have a better prognosis than restorations
loaded more horizontally (Kelly 1999, Cotert et al. 2001).
2.7.5 Cementation methods of ceramic materials
In vivo, the forces of occlusion applied to the enamel surface create stresses that
are transferred through the dentino-enamel junction to the supporting dentin where
they are effectively distributed and absorbed. The transfer and distribution of
stresses in an efficient manner are probably of equal importance to strength and
toughness in a restorative system (Banks 1990).
The enamel of natural teeth has the greatest surface toughness. Its flexural-, and
crack-formation strength equal 20 MPa and 1 MPa.m½, respectively, whereas dentin
has 80 MPa flexural strength and 3 MPa.m½ crack-formation strength. These values
are comparable to those of the weakest all-ceramic materials (Kappert & Krah
2001). The system dentin-enamel obtains its strength from the cohesive force
between the two components that have values ranging from 10 to 30 MPa (Roulet
1997a, Kappert & Krah 2001). Therefore, the adhesion strength value between allceramic restoration and tooth structure should be more than 10 MPa (Kappert &
Krah 2001).
Ceramic materials demonstrate a low tensile and shear resistance. Therefore, the
fracture load of ceramic restorations depends on the cementation method. The first
23
all-ceramic restorative materials used in the posterior part of the mouth relied on
conventional zinc phosphate cements and, later, on glass ionomer cements for
retention (Banks 1990). In-vitro studies have shown that the fracture strength of allceramic restorations, which have been placed with the adhesive technique, is
significantly greater than that of restorations placed with the conventional technique
using phosphate or glass ionomer cements (Burke 1995, Burke et al. 2002). Based
on the knowledge of microcrack formation, the internal surface of all-ceramic crowns
has to be etched and coated with a polymer. This layer significantly helps to
increase the strength of the restoration, as microcracks and small defects are
covered (Rosenstiel et al. 1993). Non-reinforced ceramic materials exhibit very low
fracture resistance. The pretreated dentin, in conjunction with the bonding medium,
provides the ceramic restoration with the necessary strength. A bonding medium,
which has a modulus of elasticity similar to that of dentin, can increase fracture
resistance because the stress is reduced (Platt 1999). The elimination, blunting, or
bridging of cracks may cause this strengthening effect, or a coating may act to
reduce the ability of water to be transported to the crack tip, which lessens the
stress-corrosion. Furthermore, polymerization shrinkage may actually increase the
strength of all-ceramic restorations by creating compressive stresses within the
ceramic (Magne et al. 1999, Platt 1999). Chemical bonding using hydrophobic silane
treatments, has been shown to significantly increase the strength of feldspathic
dental porcelain (Rosenstiel et al. 1993).
Two groups of dentinal adhesions are available: glass ionomer cements (Wilson &
McLean 1988, Croll 1993) and dentin bonding agents together with resin composites
(Krejci et al. 1993, Retief et al. 1993).
Glass ionomer cements are hybrids of silicate and polycarboxylate cements
designed to combine the optical and fluoride-releasing properties of silicate particles.
Compared to the extremely acidic matrix of silicate cement, glass ionomer cements
have chemically-adhesive and more biocompatible characteristics of the polyacrylic
acid matrix (Sturdevant et al. 1999). It has been found that glass ionomer cements
have some disadvantageous physical properties, controversial biocompatibility and
insufficient adhesion to porcelain (Moscovich et al. 1998).
24
Light-cured resin-modified glass ionomers (RMGIC) were developed to combine
some advantages of glass ionomers and composite resins (Thonemann et al. 1995,
Moscovich et al. 1998). These materials have a variety of different chemistries and
setting behaviors (Thonemann et al. 1995). The mechanical properties of RMGICs,
compared to the conventional glass ionomer cements, have been improved (Crim
1993, Croll 1993). RMGICs have been used as lining materials and as luting
materials for composite or ceramic inlays (Thonemann et al. 1995). Platt (1999)
have reported that RMGIC/ compomer has a hygroscopic expansion, which leads to
failure of all-ceramic crowns when the material is used for both build-up or adhesive
luting.
Glass ionomers, RMGICs or compomers are now acceptable only for use as a filler,
because they are too weak (Christensen 1996b, Burke et al. 2002).
Nowadays, adhesive luting, using resin cements along with dentin bonding agents,
is highly recommended to improve survival rate and fracture strength of all-ceramic
inlays and onlays (Roulet 1997a, van Dijken et al. 1998, Kappert & Krah 2001, Burke
et al. 2002)
2.8
Guidelines for ceramic inlay and onlay preparation
Many advantages can be obtained by retaining as much as possible of the healthy
tooth structure. This can best be achieved by using minimally-invasive tooth
preparation. The general benefits of using inlay and onlay preparations can be
summarized as follows: (Braunwarth & Hellge 1991)
o
Preserving healthy tooth structure.
o
Facilitating superior periodontal health.
o
Facilitating cementation without hydrolic behavior.
o
Preserving the pulp’s health.
o
Preserving the anatomical shape.
o
Facilitating visual margin control.
o
Facilitating efficient and effective oral hygiene for the patient.
o
Improving testing of the tooth’s vitality.
25
The principles of cavity preparation designs for tooth-colored inlays and onlays are
different from those for cast metal ones (Banks 1990, Jackson & Ferguson 1990,
Hickel & Manhart 2001). Two requirements should be considered: (1) provide an
adequate thickness for the restoration and (2) create a passive seating pattern
(Ritter & Baratieri 1999).
The recommended preparation design for tooth-colored inlays and onlays is as
follows: The walls should be divergent with up to 15°. All internal line angles should
be rounded with a chamfer proximal box margin and no bevels. The depth should be
1.5 mm to 2 mm (Banks 1990, Jackson & Ferguson 1990, Lehmann & Hellwig
1998). The isthmus width should be 2 mm. For onlays, cusps should be reduced at
least 1.5 mm (Banks 1990, Jackson & Ferguson 1990).
Some clinicians prefer to use the classical preparation form, as described for the
metal partial crowns, which consists of an MOD box form retention with a modified
finishing line in the shape of a shoulder with a rounded internal line angle (Banks
1990, Lehmann & Hellwig 1998). Because of the introduction of new generations of
dentin bonding agents and composite resin cements, other preparation designs,
which have less or no retention form, were suggested (Broderson 1994, Freedman
1998, King & Aboush 1999, van Dijken et al. 2001).
2.9
Factors that influence longevity of ceramic inlays and
onlays
Factors that affect the survival rate of all-ceramic inlays and onlays can be divided
into patient-related and processing- or operator-related factors (Hickel & Manhart
2001):
Patient-related factors include:
o Oral hygiene
o Preventive measures
o Compliance during recall
o Oral environment (quality of tooth structure, saliva, etc.)
26
o Size, shape, location of the lesion and tooth (number of surfaces, vital versus
nonvital tooth, premolar versus molar)
o Cooperation during treatment
o Bruxism
o Habits (high sugar intake, smoking, frequent chewing of hard foods, etc.)
o Participation in contact sports
Processing- and Operator-related factors include:
o Correct indication
o Cavity preparation (size, type, finishing)
o Impression technique
o Handling and application
o Correct occlusion
o Experience (with material and technique)
o Recall schedule
2.10 Survival rate of ceramic inlays and onlays
The longevity of a dental restoration is an important concern. Informed insight into
the longevity of these restorations is best provided by longitudinal studies (Leempoel
et al. 1989, Hickel & Manhart 2001, Blatz 2002). Any prosthetic restorative system
can be considered successful if it demonstrates a clinical survival rate of 95% after 5
years and 85% after 10 years (Pröbster 1996).
The survival rates of all-ceramic inlays and onlays with an observation periods of 5
years and longer are listed in table (2.2):
27
Author (year)
Observation
Survival rate
Material
Type (No. of restorations)
5
Cerec Vita Mk I & II
Inlays (8)
100
Walther et al. (1994)
5*
Cerec Vita blocks
Inlays (1011)
95
Hofman et al. (1995)
5
Cerec Vita blocks
Inlays (59)
90
Otto (1995)
5
Cerec Vita blocks
Inlays (100)
98
Berg & Derand(1997)
5
Cerec I
Inlays (51)
94.1
Roulet (1997b)
6*
Dicor
Inlays (123)
76
Inlays & onlays (287)
94.2
Mörmann & Krejci
(1992)
period (y)
(%)
Dicor, Empress,
Felden et al. (1998)
7*
Mirage II, Cerec Vita
Mark I, Duceram LFC
Hayashi et al. (1998)
6
Fired ceramic
Inlays (49)
92
Lehner et al. (1998)
6*
Empress
Inlays & onlays (138/ 17)
94.9
7.5*
Cerec Vita blocks
Inlays (1011)
91.6
Inlays (33)
94
Inlays (33)
85
Inlays (58)
88
Inlays (57)
74
Inlays (182)
97
Inlays (60)
92
Reiss & Walther
(1998)
Cerec (chemical
Sjögern et al. (1998)
5
cure)
Cerec (dual cure)
Van Dijken et al.
(1998)
Mirage (resin
6
Mirage (GI cement)
Fuzzi & Rappelli
(1999)
Molin & Karlsson
(2000)
10*
Fired ceramic
Mirage
5
Cerec
IPS Empress
Pallesen & van
Dijken (2000)
8
Reiss & Walther
10
(2000)
12*
Thordrup et al.
(2001)
Van Dijken et al.
(2001)
cement)
Cerec Vita MK II
Inlays (16)
Dicor MGC
Inlays (16)
Cerec Vita blocks
Inlays (1010)
90.6
90
84.9
5
Cerec Cos 2.0
Inlays (15)
92.9
5
IPS Empress
Onlays (182)
92.9
* Estimated survival (Kaplan-Meier analysis)
Table (2.2)
Survival rates of all-ceramic inlays and onlays
These studies illustrate that the survival rate of all-ceramic inlays and onlays ranges
between 74% to 100% with observation periods of up to 12 years. With the
exception of two studies (Roulet 1997b, van Dijken et al. 1998), all other studies
28
showed very good clinical successes. Long-term clinical success of all-ceramic
onlays was evaluated in only 4 studies (Felden et al. 1998, Lehner et al. 1998, van
Dijken et al. 2001). Other studies with shorter observation periods between 2 to 4.4
years have evaluated all-ceramic onlays and reported good results as well (Tidehag
& Gunne 1995, Studer et al. 1996, Fradeani et al. 1997, Denissen et al. 2000).
29
3.
Aim of the study
The aim of this in-vitro study was to evaluate the survival rate and fracture strength
of ceramic onlays fabricated out of an Experimental Heat-Press All-Ceramic material
(EPC) with different preparation designs luted on upper first molars after exposure to
the artificial mouth, and to compare the data with ceramic inlays and unprepared
teeth (control).
30
4.
Outline of the study (Fig. 4.1)
Ninety-six human upper molars were used for the experiment. They were randomly
divided into one control group and 5 test groups, using sixteen samples of each (AF). In the control group A, teeth were left with no preparation. In group B, inlay
preparations were made (6° MOD taper box, 3 mm deep). The isthmus was 3 mm
wide. A mesial and distal finishing 1 mm above the cemento-enamel junction was
made. In group C, teeth were prepared in the same manner as described for group
B, but in addition, the mesio-palatal cusps were reduced 2 mm with 45° on the
occlusal plane, and the margins were left in an overlapping form. In group D, teeth
were prepared in the same manner as in group B, and both palatal cusps were
reduced 2 mm with 45° on the horizontal plane. In group E, teeth were prepared in
the same manner as described for group B, then the palatal and disto-buccal cusps
were reduced 2 mm with 45° on the horizontal plane. In group F, teeth were
prepared in the same manner as in group B, then all cusps were reduced. Sixteen
all-ceramic inlays and 64 onlays were fabricated out of an Experimental PressCeramic (EPC) material and adhesively luted. Afterwards, all of the samples, along
with the control group, were placed in the artificial mouth for 1.2 million cycles. Then
all samples were loaded in the universal testing machine until fracture occurred.
96 human upper molars
Group A (Control)
Group B
Group C
Group D
Group E
Group F
16 teeth
No preparation
16 restored teeth
Inlay preparation
MOD
16 restored teeth
Onlay preparation
mesio-palatal cusp red.
16 restored teeth
Onlay preparation
Palatal cusps red.
16 restored teeth
Onlay preparation
Palatal+disto-buccal cusps red.
16 restored teeth
Onlay preparation
Palatal+buccal cusps red.
loaded in chewing machine
loaded in chewing machine
loaded in chewing machine
loaded in chewing machine
loaded in chewing machine
loaded in chewing machine
Fracture strength test
Fracture strength test
Fracture strength test
Fracture strength test
Fracture strength test
Fracture strength test
Fig. (4.1)
Outline of the study
31
5.
Materials and methods
5.1 Materials
5.1.1 Experiment teeth
Ninety-six caries-free human upper molars were used for the experiment. The teeth
were obtained directly after extraction, cleaned and stored in 0.1% thymol solution at
room temperature throughout the study. All teeth were inspected with a 10X
magnifying glass to detect cracks before including them in the study.
5.1.2
Materials used for the fabrication of ceramic inlays and
onlays
EPC (Ivoclar-Vivadent AG, FL-Schaan) (Table 5.1)
The experimental press ceramic (EPC) consists of lithium disilicate glass and
sintered apatite glass. The chemical basis of the material is the same as the
chemical basis of IPS Empress® 2 (Si2O – Li2O).
According to the manufacturer, these 2 different glass ceramic materials exhibit
substantially improved physical properties and higher translucency. The framework
is a lithium disilicate glass in which the glass layer is a new type of fluoroapatite
porcelain. The framework material, representing the high strength component of the
system, is pressed in the EP 500 press furnace (Ivoclar-Vivadent AG, FL-Schaan) at
910-920 °C. The crystalline phase of the material consists of elongated lithium
disilicate crystals, measuring approximately 0.5 to 4 µm in length, and small lithium
orthophosphate crystals (Li3PO4).
The glass layer is fired on the lithium disilicate framework at 740 °C. This sintering
temperature is lower than the one needed for sintering the glass layer of IPS
Empress® 2 (Table 5.2). The crystalline phase of the glass layer enhances the
biocompatibility of the material. Additionally, the glass layer is responsible for
32
excellent aesthetics because it guarantees translucency, brightness and light
scattering.
Components
ma. %
SiO2
57 – 80
Al2O3
0–5
La2O3
0.1 – 6
MgO
0–5
ZnO
0–8
K2O
0 – 13
Li2O
11 – 19
P2O5
0 – 11
Additional ingredients 0 – 8
Table 5.1
Composition of EPC
Properties
EPC
Mechanical:
● Flexural strength
525 ± 75 MPa
● Fracture toughness
3.0 ± 0.5 MPa ● m 0.5
Optical:
● Translucency
Very high translucency, similar to the natural tooth
Thermal:
● Coefficient of thermal expansion
10.6 ± 0.5 ● 10-6 K-1 m/m
Chemical:
< 100 µg/cm2
● Solubility
Technical:
● Press temperature
920 °C
● Firing temperature of sinter
800 °C
ceramic resp.
sinter glass ceramic (Dentin and
(new type of material:
Incisal)
740 °C)
Table 5.2
Properties and technical data of EPC (Information obtained from manufacturer)
33
5.1.3 Materials used in cementation procedures
Variolink ®II (Ivoclar-Vivadent AG, FL-Schaan) (Table 5.3)
The Variolink
®
system is a micro-filled light/dual curing adhesive luting composites.
It is available in 5 shades, 3 degrees of translucency, as well as 3 consistencies (low
viscosity, high viscosity, and ultra-high viscosity for application of the ultrasonic
technique). Barium glass is used as a filler in this system. It demonstrates excellent
radiopacity and permits a clear distinction between the restoration, the cement and
caries on X-rays.
Variolink ®II is indicated for the adhesive cementation of all-ceramic, Ceromer, and
composite restorations and is especially recommended by the manufacturer for the
placement
of
IPS
Empress®
all-ceramic
and
Targis/Vectris
Ceromer/FRC
restorations.
In weight %
Standard composition
Base
Catalyst
Catalyst low
high
Bis-GMA
13.1
11.0
13.9
Urethane dimethacrylate
6.6
5.5
7.0
Triethylenglycloe dimethacrylate
6.6
5.5
7.0
Barium glass filler, silanized
38.4
42.2
36.2
Ytterbiumtrifluoide (YbF3)
25.0
25.0
25.0
Mixed oxide, silanized
5.0
5.0
5.0
Ba-Al-Fluoro-Silicateglass
5.0
5.0
5.0
Catalysts and Stabilizers
0.3
0.8
0.9
Pigments
<0.1
<0.1
<0.1
Table 5.3
Composition of Variolink® II
34
Variolink ®II professional set consists of:
Total Etch® is a gel for enamel etching and dentin conditioning. It contains
phosphoric acid (37% wt. % in water), silicon dioxide and pigments.
Syntac® is a two-phase adhesive system, which mediates a chemically-stable bond
between the composite and the tooth structure. Syntac primer is composed of
polyethylene glycol dimethacrylate, maleic acid and ketone in an aqueous solution.
Syntac adhesive is composed of polyethylene glycol dimethacrylate and
glutaraldehyde in an aqueous solution. This system can be used with both light- and
self-curing composites. A light-curing bonding agent (Heliobond®) must be used prior
to application of the composite.
Heliobond® is a light-curing, single component bonding material for optimizing the
enamel etching technique. It contains Bis-GMA 60% wt. and Triethylene glycol
dimethacrylate 40% wt.
Monobond S® is a single-component material mediating a stable bond between the
ceramic material and the composite. It contains a water/ethanol solution with acetic
acid set to pH 4 (99% wt.) and 3-methacryloxypropyl-trimethoxysilane 1% wt.
Liquid strip® is a glycerine gel. It is impermeable to oxygen and therefore can be
used for the try-in of the luting material and ceramic restorations.
IPS Ceramic etching gel® is a hydrofluoric acid that creates an excellent retentive
etching pattern in the IPS Empress® 2 material.
5.1.4 Impression and die materials
Dimension® Garant L (Espe, D-Seefeld)
This is an additional hydrophilic low consistency polymerization silicone material
which is recommended for impression taking for partial crowns, crowns and bridges.
35
This material presents 4.5% deformation under load (ISO), 99.9% elasticity after
deformation (ISO), and –0.20% linear dimensional change (ISO, after 24 h). The
setting time is 5½ minutes after mixing.
Permagum® Putty Soft (Espe, D-Seefeld)
It is an additional cross-linking high viscosity silicone impression material with a 0.05 % dimensional change and a 0.3% compression set. The mixing time is 45
seconds and the setting time is 5 minutes.
GC Fujirock®(GC, B-Brussel)
This is a type 4 dental stone with improved physical properties and workability. The
recommended water/powder ratio is 20 ml/100g. The setting expansion is 0.08%
and the compressive strength is 53 MPa.
5.1.5 Additional materials (Table 5.4)
Material / Equipment
Anti-Rutsch Lack
Manufacturer
Wenko-Wenselaar GmbH, D-Hilden
Artificial oral environment /Thermocycling Willytech, D-Munich / Gebrüder Haake
system
GmbH, D-Karlsruhe
Diamond burs No. 8837KR, No. 847KREF Gebr. Brasseler, D-Lemgo
023, No. 8847KR 023, No. 379EF 016
Steatite ceramic ball
Hoechst Ceram Tec, D-Wunsiedel
Technovit 4000
Kulzer, D-Wehrheim
Zwick Z010/TN2S
Zwick, D-Ulm
Table 5.4
Additional materials
36
5.2 Methods
5.2.1 Experiment teeth
See outline of study.
5.2.2 Fabrication of models before preparation
Sample holders were made from small blocks of dental stone for the fabrication of
models of the teeth before preparation. Two holes were burred into each block in
order to fix the teeth inside. Two teeth were fixed inside each block using Formasil®
Xact (Heraeus Kulzer GmbH, D-Wehrheim). Teeth were numbered, and the
numbers were carved on the blocks using a burr and a hand piece. Afterwards,
impressions were taken of the blocks containing the teeth using Dimension® Garant
L (Espe, D-Seefeld), Permagum® Putty Soft (Espe, D-Seefeld) and perforated
custom-made plastic trays (Minitrays, Hager & Werken GmbH, D-Duisburg) with the
Putty-Soft-Wash-Technique. A thin layer of polyvinyl siloxane adhesive was applied
on the tray. After 5 minutes, Dimension® Garant was applied around the tooth, and
Permagum® Putty Soft was put on the tray. The tray was then placed parallel to the
tooth line, and held without pressure until the impression material was set
(approximately 7 minutes). Afterwards, the impression was removed from the teeth
and one hour later the master model was poured. A silicon surfactant was used to
avoid introducing bubbles into the model and then GC Fujirock® type 4 dental stone
was mixed with water. The recommended water/powder ratio is 20 ml/100 g. The
powder was added to the water within 10 seconds, then mixed uniformly for 60
seconds by mechanical spatulation under vacuum. After a setting time of at least 45
minutes, the model was removed from the impression and trimmed.
Creating the models before the preparation, assures that the final product will most
closely resemble the original shape of the tooth.
5.2.3 Tooth preparation (see outline of study) (Fig. 5.1-7)
In group A, teeth were left with no preparation (control group).
37
Preparation for group B (Fig. 5.3 a & b)
A 6° taper box form, with rounded and soft internal line angles, was prepared to
represent an MOD cavity. It was 3 mm deep and the isthmus was 3 mm wide. The
mesial and distal finishing line was 1 mm above the cemento-enamel junction.
Preparation for group C (Fig. 5.2, 5.4 a & b)
Teeth were prepared in the same manner as in group B. In addition, the mesiopalatal cusps were reduced by 2 mm with an angle of 45° on the occlusal plane. The
margins were left in an overlapping form without a bevel.
Preparation for group D (Fig. 5.1, 5.5 a & b)
Teeth were prepared in the same manner as group B. In addition, the palatal cusps
were reduced by 2 mm with an angle of 45° on the occlusal plane and the margins
were left in an overlapping form without a bevel.
Preparation for group E (Fig. 5.6 a & b)
Teeth were prepared in the same manner as group B. In addition, the palatal and
disto-buccal cusps were reduced by 2 mm with an angle of 45° on the occlusal plane
and the margins were left in an overlapping form without a bevel.
Preparation for group F (Fig. 5.7 a & b)
Teeth were prepared in the same manner as group B. In addition, both palatal and
buccal cusps were reduced by 2 mm with an angle of 45° on the occlusal plane and
the margins were left in an overlapping form without a bevel.
38
6° taper box form with internal rounded line angle
Buccal
Palatal
2mm reduction of the cusps (45°)
Mesial and distal finishing 1mm above
the CEJ
Fig. 5.1 Preparation of group D
Buccal
3mm isthmus width, finishing
without bevels, rounded internal
line angles
Palatal
Fig. 5.2 Preparation of group C
39
Fig. 5.3 (a & b) Preparation of group B
Fig. 5.4 (a & b) Preparation of group C
Fig. 5.5 (a & b) Preparation of group D
Fig. 5.6 (a & b) Preparation of group E
40
Fig. 5.7 (a & b) Preparation of group F
5.2.4 Final impressions and fabrication of master models
The prepared teeth were fixed again inside the marked holders, which were already
made for taking impressions before preparation. Impressions were taken with the
same impression materials used before and with the Putty-Soft-Wash-Technique.
After setting, the impressions were removed from the teeth, and one hour later the
master models were poured. Both the same technique used for pouring models and
the same dental stone (GC Fujirock® type 4) were used before preparation. After a
setting time of at least 45 minutes, the models were removed from the impressions.
5.2.5 Fabrication of ceramic inlays and onlays (EPC)
All models before and after preparation from the different groups were sent to the
manufacturer (Ivoclar-Vivadent AG, Schaan, FL), in order to fabricate the ceramic
inlays and onlays. The following procedures were performed by the manufacturer:
A surface hardening agent (Margidur, Benzer Dental AG, Zurich, CH) was applied
on the master models. Afterwards, one layer of dye spacer (Purargent, Benzer
Dental AG, Zurich, CH) was painted on the inner surfaces of the dies, but only up to
approximately 0.5 mm above the preparation margin.
Using the silicone key from the models before preparation as a guide, full wax-ups of
the inlays and onlays were fabricated using dental wax (Pro Art Sculpturing Wax,
Williams AG). The silicone keys were helpful in restoring the original surface
structure of the teeth before preparation. A 3 mm round wax sprue was then
41
attached to each wax-up at an approximately 45° angle. The sprues had the
following dimensions: round profile, 3-8 mm length, 2-3 mm diameter, 8 gauges. The
investment was carried out with the IPS Empress® 2 Speed investment material.
Each of the 4 pieces was invested together with a 200 g investment material. The
investment was mixed with its liquid for 1 minute in a vacuum, according to
instructions. After a setting time of one hour the ring gauge and ring base were
removed with a turning movement, and the paper ring and rough spots on the
bottom side of the investment cylinder were removed.
The investment ring was preheated without the ingot, but including the plunger, in a
conventional preheating furnace (KaVo Type 5636, KaVo AG, D) beginning at room
temperature and increasing to 850°C. Preheating the IPS Empress investment ring
together with casting objects is not recommended, because oxides may settle in the
investment ring. The following parameters were checked:
o Temperature increase (beginning at room temperature): 5°C per minute
o Final temperature: 850°C
o Holding time: 60 minutes at 850°C
The investment cylinder was then removed from the furnace and the corresponding
cold ingot (EPC VP1989 / 4 g) was placed into the cylinder. The following press
parameters were observed. (Table 5.5)
P
Table 5.5
B
t↑
T
H
V1
V2
N
700°C
60°C/min
915°C
20 min.
500 °C
915°C
0
Pressing parameters for EPC using the EP 500 / V2.9 press furnace
After setting the exact parameters, the investment cylinder with the ingot was placed
in the center of the EP 500 / V2.9 press furnace. After manual closing of the furnace
head the program was activated, and the press process ran automatically. An
acoustic signal indicated the end of the pressing cycle.
The investment cylinders were removed from the press furnace after approximately
60 minutes. Due to the difference in the coefficient of thermal expansion of the
42
various materials, cylinders occasionally show cracks. These cracks do not
compromise the results of the pressing. The investment cylinder was separated
using a separating disc to create a predetermined breaking point. Rough divestment
was carried out with sand particles at 2-bar pressure. Subsequently, the pressed
frameworks were cleaned in Invex liquid (Ivoclar-Vivadent AG, FL-Schaan) in an
ultrasonic unit for 10 minutes, rinsed with water, and blow dried. The white reaction
layer was then removed with Al2O3 (type 100) at 1 bar pressure. The pressed
frameworks were cut from the sprues using a fine diamond disc. The attachment
points were removed with ceramic burs. The ceramic frameworks were cleaned with
steam, dried with oil-free air, and fitted on the master models.
Subsequently, two glaze firings were performed in the Programat P 100 furnace
(Ivoclar-Vivadent AG, FL-Schaan) using glazing liquid (Empress Universal Glasur
C27688, Ivoclar-Vivadent AG, FL-Schaan). The following firing parameters were
considered: (Table 5.6)
P
Table 5.6
B
t↑
T
S
H
V1
V2
403°C
60°C
770°C
6 min.
2min.
450°C
769°C
L
Firing parameters for EPC using the EP 500 / V2.9 press furnace
Then the fitting surfaces of the inlays and onlays were sandblasted with Al2O3 (type
100) at 1-bar pressure.
The finished ceramic inlays and onlays made out of EPC were delivered with the
master models and the models pre-testing models.
5.2.6 Luting procedures
After 2 minutes of ultrasonic cleaning, each tooth was dipped in 96% alcohol. The
inner surfaces of the restorations were etched for 20 seconds with IPS Ceramic etch
gel, rinsed with water for 30 seconds and dried. Monobond S was then applied with
a brush, and after 60 seconds, dried with air. Then Heliobond was applied with a
brush and dispersed with air. All prepared teeth were cleaned using a prophylaxis
paste (non-fluoride) with a rotary brush. The prepared teeth were etched with 37%
43
phosphoric acid for 30-60 seconds, and Syntac Primer was applied and dispersed
with an air syringe after 15-20 seconds. Then Syntac Adhesive was applied and
dispersed with air after 10 seconds. Afterwards, Heliobond was applied and
dispersed with air. Variolink® II was mixed and applied to the inner surfaces of the
inlays, onlays and prepared teeth and then the restorations were placed on the teeth
and held in place on the central fossa of the restoration using a plastic stick and
under finger pressure (approx. 10-15 N). Any excess cement was removed and
glycerine gel was applied in the marginal area of the restorations. Then all surfaces
of the restorations were light-cured for 1 minute occlusally, mesially, distally,
lingually, and buccally.
After setting, test samples were cleaned using a prophylaxis paste (non-fluoride)
with a rotary brush.
5.2.7 Artificial periodontal membrane
In order to imitate physiological tooth mobility, all roots of the selected teeth were
covered with an artificial periodontal membrane made out of gum resin (0.25 mm
thickness) (Anti-Rutsch-Lack, Wenko-Wenselaar GmbH, D-Hilden) (Kern et al.
1993). In order to conform to the biological width, each tooth was coronally covered
with wax, 2 mm short of the cemento-enamel junction, and then dipped once in the
gum resin. After the gum resin had dried, the excess resin on the root tip was
removed using a scalpel so that a uniform coating remained on the root surface.
5.2.8 Preparing the representative model of a clinical case
An upper molar was selected as a representative model of a clinical case. The
model was embedded in a sample holder of the artificial oral environment (Willytech,
D-Munich) using a silicone putty material (Optosil®, Kulzer, D-Wehrheim). The
occlusal surface of the sample was set to be parallel to the horizontal plane. A
silicone mold of the representative model was then fabricated with a polysiloxane
impression material (Putty Soft, D-Seefeld,) covering at least 2 mm above the edge
of the sample holder. This silicone mold was then used as the negative form for
fixing the test specimens in the sample holder.
44
5.2.9 Embedding the experiment teeth in the sample holders
Using wax, all teeth were fixed vertically at 90° into the silicone mold. The wax
covered the whole crown, and it was extended 2 mm apically. The sample holder
was then isolated with Vaseline (Weißes Vaseline, FL-Schaan) and attached to the
prepared silicone mold with the tooth in place. Then self-curing plolyester resin
(Technovit 4000®, Kulzer, D-Wehrheim) was mixed and poured into the sample
holder. After the resin had set, the silicone was removed, and the crowns of the
teeth were cleaned.
5.3
Tests
5.3.1 Exposure of the test samples to the artificial mouth
(Fig. 5.8-11)
The artificial oral environment (Willytec, D-Munich) consists of eight identical sample
chambers, two stepper motors controlling vertical and horizontal movement of the
samples against the antagonist, a hot and cold water circulation system (Haake, DKarlsruhe) and a computerized control unit (Kern et al. 1999). All of the samples in
each group were subjected to 1,2 million cycles by a reproducible dynamic occlusal
load. Instead of following the standard protocol of applying 49 N load (De Boever et
al. 1978, Krejci et al. 1990), the applied load here was 98 N, and the thermo-cycling
was 5°C to 55°C for 60 seconds each with an intermediate pause of 12 seconds,
maintained by the thermostatically-controlled liquid circulator (Haake, D-Karlsrue). A
6 mm in diameter ceramic antagonist Steatit® ball (Höchst Ceram Tec, D-Wunsiedel)
was applied vertically onto the occlusal surface of the restorations.
All samples were examined twice a day. Fractures of the teeth or of the porcelain
were recorded as a failure.
45
Test parameters of the artificial mouth (Table 5.7)
Cold/hot bath temperature
5 °C/55 °C
Dwell time
60 s
Vertical movement
6 mm
Horizontal movement
0.5 mm
Descending speed
60 mm/s
Rising speed
55 mm/s
Forward speed
60 mm/s
Backward speed
55 mm/s
Applied weight per sample
10 kg (98 N)
Cycle frequency
1.6 Hz
Table 5.7
Parameters used for the experiment in the artificial mouth
5.3.2 Fracture strength test (Fig. 5.13)
Using a universal-testing machine (Zwick, Z010/TN2S, D-Ulm), all samples were
loaded until fracture occurred. A 1-mm thick tin foil was placed over the occlusal
surface of the teeth to achieve homogenous stress distribution. A perpendicular load
was applied to the occlusal surface of samples, under a stroke control of 2 mm/min.
The loads required for fracturing the samples were recorded with the Zwick
testXpert® V 7.1 software.
5.3.3 Statistics
Data after dynamic loading of the test samples in the artificial mouth were analyzed
by the Kaplan-Meier method (survival rate).
The statistical analysis of the fracture strength tests was preformed at the Institute of
Medical Biometry and Medical Informatics, Albert Ludwigs University, Freiburg,
Germany using pair-wise comparisons with the Wilcoxon test (Splus statistic
program, version 3.4 release 1 for Sun SPARC) at a significance level 0.05.
46
Fig. 5.8 Schematic drawing of the dual-axis chewing simulator with eight sample chambers
(Willytech, Munich, D) from (Kern et al. 1999).
(1) upper crossbeam, (2) lower crossbeam, (3a) water reservoir (in), (3b) water
reservoir (out), (4) filter for cold water, (5) filter for warm water, (6) pump for removal
of cold water, (7) pump for removal of warm water, (8) pump for application of cold
water, (9) pump for application of warm water, (10) motor block, (11) table.
Fig. 5.9 Chewing simulator (Willytech, D-Munich)
47
Fig. 5.10
Schematic drawing of one chewing chamber (Kern et al. 1999).
Fig. 5.11 Sample in the chewing chamber
Fig. 5.12 fracture strength test of a sample
48
6.
Results
6.1 Survival rate of test samples after exposure to the
artificial mouth
All the test samples survived 1,200,000 dynamic loading cycles and thermocycling in
the artificial oral environment.
6.2 Fracture strength of the test samples (Table 6.1)
For each group, statistics were computed for fracture strength values after artificial
aging. These results are represented in the box plot (Fig. 6.1).
The fracture strength values of all test samples after simulation in the artificial oral
environment were over 800 N. The smallest value was observed in test group F
(852.4 N), whereas the highest value was observed in the control group A (3616.0
N).
Results of the comparison of the fracture strengths of all test groups showed no
statistically significant differences between different groups (Table 6.2).
Group
Minimum
A (control) : Natural
teeth with no preparation
B: MOD inlays
C: MOD with mesiopalatal cusp
D: MOD with palatal
cusps
E: MOD with palatal and
disto-buccal cusps
F: MOD with palatal and
buccal cusps
Table 6.1
1st
Quartile
Median
Mean
3rd
Quartile
Maximum
871.5
1480.0
1960.0
2041.0
2228.0
3616.0
1023.0
1463
1567.0
1700
1948
2831.0
880.7
1489.0
1870.0
1789.0
2116.0
2547.0
858.4
1365.0
1687.0
1594.0
1789.0
2462.0
963
1577
1705
1836
2049
3486
852.4
1306.0
1842.0
1796.0
2343.0
2612.0
Statistical analysis of the fracture strength results in N (fracture strength of each
sample is listed in the appendix)
49
Fracture strength (N)
Fig.6.1 Box plot of the fracture strength test results in N.
The central box shows data between the 1st-quartile and the 3rd-quartile, the median
is represented by a line. “Whiskers” represent the extremes of the data, and very
extreme values are shown by themselves.
A= Natural teeth with no preparation
B= MOD Inlay preparation
C= MOD preparation with reduction of the mesio-palatal cusp
D= MOD preparation with reduction of palatal cusps
E= MOD preparation with reduction of palatal and disto-buccal cusps
F= MOD preparation with reduction of all cusps
50
Wilcoxon
Group A
test
(control)
Group B
Group C
Group D
Group E
Group F
1.000
0.318
0.665
0.062
0.510
0.638
0.318
1.000
0.462
0.925
0.337
0.559
0.655
0.462
1.000
0.169
0.895
0.955
0.062
0.925
0.169
1.000
0.365
0.337
Group E
0.510
0.337
0.895
0.356
1.000
0.865
Group F
0.638
0.559
0.955
0.337
0.865
1.000
Group A
(control)
Group B
Group C
Group D
Table 6.2:
Results of the multiple pair-wise comparisons of the fracture strength of
test groups after loading in the artificial oral environment using the Wilcoxon test
(significantly different when value < 0.05)
6.2 Fracture patterns of the test samples
Group A (teeth with no preparation) (Fig 6.2 a & b)
All test samples of the control group fractured in a homogenous manner. The
fracture always initiated in the enamel where it had contact with the testing head in
the crown. No root fractures were noticed.
Group B (Fig. 6.3 a, b, c)
Most samples fractured in a homogenous manner. No debonding of the ceramic
restorations occurred. In only two test samples the teeth fractured with the
restorations.
51
In most of the test samples, the fracture initiated in the restoration where it had
contact with the testing head starting at the cement interface and extending towards
the occlusal surface. In only one test sample, it was noticed that the crack initiation
occurred externally at the approximal incline near the loading site.
Group C
Most samples fractured in a homogenous manner. No debonding of the ceramic
restorations occurred. Fracture of the teeth with the restorations occurred in 4 test
samples.
The fracture always occurred in the same manner as in group B. All fracture patterns
went horizontally through the whole restoration surface (MOD). In only two test
samples, the crack initiation was situated in the occlusal region of the external
surface of the inlay near the occluso-axial line angle
Group D
Most samples fractured in a homogenous manner. No debonding of the ceramic
restorations occurred. In three test samples the teeth fractured with the restorations.
The fracture always occurred in the same manner as in other groups. In only one
test sample, it was noticed that the crack initiation occurred externally at the
approximal incline near the loading site.
Group E
Most samples fractured in a fairly homogenous manner. No debonding of the
ceramic restorations occurred. In only two test samples the teeth fractured with the
restorations.
The fracture always occurred in the same manner as in other groups. All fracture
patterns were going through the whole restoration (MOD). Crack initiation occurred
at the occlusal surface in only one test sample.
52
Group F (Fig 6.4 a, b, c)
Most samples fractured in a homogenous manner. No debonding of the ceramic
restorations occurred. In three test samples the teeth fractured with the restorations.
The fracture always occurred in the same manner as the fracture in group B. All
fracture patterns went through the whole restoration (MOD). In only one test sample,
did the crack initiation occur at the occlusal surface.
Fig. 6.2 (a & b) Fracture pattern of group A (control)
Fig. 6.3 (a, b, c) Fracture pattern for group B
Fig. 6.4 (a, b, c) Fracture pattern of group F
53
7.
Discussion
7.1 Materials and methods
7.1.1 The use of natural teeth
Extracted human teeth were used in this study because their bonding
characteristics, thermal conductivity, modulus of elasticity and strength are closer to
the clinical situation than metal, plastic replicas or animal teeth. Attention was paid to
the selection of teeth with comparable sizes. Teeth which were too big or too small,
as well as teeth with caries, cracks or deformities, were discarded. The extracted
teeth were stored in 0.1% thymol solution to prevent them from drying out and
thereby becoming brittle (Helfer et al. 1972). This storage solution also inhibited
microbial activity (Sparrius & Grossman 1989).
The fracture strength of ceramic inlays and onlays, placed on extracted natural teeth
, was evaluated in several in vitro studies (Geurtsen et al. 1989, Dietschi et al. 1990,
1995, Krejci et al. 1993, Cotert et al. 2001).
Bovine teeth have also been used for testing the fracture strength of ceramics
(Mesaros et al. 1994) and the bonding strength of luting materials (Hosoya &
Tominaga 1999). Bovine teeth have similar bonding characteristics, modulus of
elasticity and tensile strength to human teeth (Sano et al. 1994). However, because
of their size, they are not used for fracture strength tests of inlays and onlays.
Metal samples offer other advantages. They have identical dimensions and physical
properties. However, testing the fracture strength of inlays and onlays on metal
samples is inappropriate because of the difficulties in preparing the test samples and
because the elastic and bonding properties of these abutments cannot be compared
to those of natural teeth. Moreover, metal abutments do not reproduce the actual
force distribution that occurs on restorations cemented on natural teeth.
Plastic samples made out of resin have also been used for fracture strength testing
of inlays and onlays (Esquivel-Upshaw et al. 2001). They have a modulus of
54
elasticity that is similar to human dentin and they can be etched with 34%
phosphoric acid (Neiva et al. 1998). The disadvantages of plastic teeth are that resin
materials tend to absorb water (Soderholm 1981) which will weaken the luting
condition and thereby reduce the fracture strength value of the restorations.
Moreover, the bonding characteristics cannot be simulated when using plastic teeth,
because they do not consist of water and organic substances.
7.1.2 Artificial periodontal membrane
In the present study, a thin layer of gum resin (Anti-Rutsch-Lack ®) was painted on
the roots of the teeth. This layer served to mimick the physiological mobility of teeth
during chewing simulation and fracture strength testing. Kern et al. (1993) showed
that, when using this method, the artificial tooth mobility under a force of 5 N was
100 ± 30 µm in the horizontal direction and 65 ± 21 µm in the vertical direction.
These values are similar to the physiological tooth mobility as described by
Mühlemann (1951).
In several studies, ceramic inlays and onlays were embedded directly into dental
stone, resin or rigid metal before fracture strength testing was performed (Dietschi et
al. 1990, 1995, Cotert et al. 2001, Esquivel-Upshaw et al. 2001).
It has been demonstrated that sample mobility is a decisive factor in the evaluation
of fracture strength (Kelly 1995), and when a small amount of tooth rotation is
allowed, failure of the restoration is more relevant to the clinical situation (Kelly et al.
1995).
7.1.3 Tooth preparation
Two mm is the recommended depth for a cavity in all-ceramic inlays and onlays
(Banks 1990, Lehmann & Hellwig 1998). In this study, a depth of 3 mm was used in
the preparation cavity at the occlusal portion.
In the MOD inlay preparation, a width of one third of the intercuspal distance is
recommended for the occlusal portion of the preparation (Joynt et al. 1987). This
value, which is usually 3 mm in molars, guarantees an adequate thickness for the
55
restorative material and does not weaken the tooth (Jackson & Ferguson 1990,
Garber & Goldstein 1994, Cotert et al. 2001).
The interproximal finishing lines should extend into the facial and lingual embrasures
for ease of finishing after bonding (Presern & Strub 1983, Christensen 1988, Banks
1990). For the width of the proximal portion of the cavity, one third of the total
faciolingual distance is recommended (Joynt et al. 1987, Lehmann & Hellwig 1998,
Cotert et al. 2001).
All teeth prepared for ceramic inlays or onlays should exhibit a smooth internal
surface with rounded line and point angles to minimize stress-concentrating effects
that can lead to crack propagation and failure of the restoration (Banks 1990, Garber
& Goldstein 1994, Lehmann & Hellwig 1998, Denissen et al. 2000). The walls of the
preparation should be slightly divergent to the occlusal between 5° to 15° to assure a
properly fitted restoration and increase fracture resistance of both the restorative
material and the tooth structure (Jackson 1999). Esquivel-Upshaw et al. (2001)
compared the fracture resistance of metal-ceramic inlays made of Goldtech Bio
2000 metal and Ceramco porcelain with Empress® 2 all-ceramic inlays. The inlay
preparation was made on 60 plastic teeth, with 30 teeth allocated for metal-ceramic
inlays and 30 teeth for all-ceramic inlays. Each group was further divided into 5-, 10-,
and 20-degree taper preparations. The mean fracture load for Empress® 2 inlays
was significantly higher than that for metal-ceramic inlays, and inlays with a 5° taper
were significantly more fracture resistant than those with a 20° taper.
The reduction of weak cusps not only lessens the risk of ceramic fractures, but also
lessens the risk of problems such as hypersensitivity. A tendency towards a
reduction in fracture frequency could be seen when weak cusps were protected by
reducing them (Milleding et al. 1995). An approximately 1.5 to 2 mm of occlusal cusp
reduction is recommended in the literature for ceramic onlays (Hobo & Iwata 1986,
Malament & Grossman 1987, Malament 1988, Christensen 1988, Banks 1990,
Jackson & Ferguson 1990, Garber & Goldstein 1994, Denissen et al. 2000).
The design of the marginal finish line of inlays or onlays can influence the prognosis
of the restoration. Farah et al. (1977) studied the effect of cavity wall taper and
margin preparation on stress distribution using finite element analysis. They found
that inlays with 7° taper and no occlusal bevel had better stress distribution than
56
cavities with more taper or a longer bevel. Taleghani & Leinfelder (1987) advocated
a butt joint preparation margin for inlays while Jensen et al. (1987) recommended a
0.5 mm bevel for inlay and onlay preparations.
In a recent finite element analysis study, onlay restorations with three different types
of marginal finish lines, i.e., shoulder, chamfer and bevel, were subjected to vertical
and horizontal load at three different sites. The results showed that horizontal forces
acting on the restoration generated the highest tensile stresses (Abu-Hassan et al.
2000).
It can be concluded from the above-mentioned studies that preparing the margins
with bevels or chamfers is not recommended when using all-ceramic restorations.
Thin layers of ceramic material covering the bevels or thin chamfers cannot
withstand stresses that form during chewing, can easily fracture and lead to failure of
the restoration. Although shoulder preparation enhances the fracture resistance of
ceramic inlays and onlays, it requires additional removal of healthy tooth structure.
Moreover, the advances in luting and bonding procedures and the increased use of
adhesive techniques result in less extensive tooth preparations. Therefore, shoulder
preparation was avoided in this study in order to minimize tooth structure removal.
7.1.4 Adhesive cementation
In this study, a dual-cured resin cement was used to lute the restorations on the
teeth. Several studies showed a strong enhancement of the fracture strength of allceramic restorations bonded to dies or teeth versus non bonded restorations.
In an in-vitro investigation, Dietschi et al. (1990) found that ceramic inlays cemented
with composite resin were more resistant to fracture than those luted with glass
ionomer, although no statistically significant difference was found.
Stenberg & Matsson (1993) reported a failure rate of 23% for 25 Dicor inlays luted
with glass-ionomer cement after 2 years.
Van Dijken et al. (1998) evaluated 118 feldspathic ceramic inlays luted with dualcured resin composite or glass ionomer cement (GIC) over a 6-year follow-up.
57
Twelve percent of the resin composite group and 26% of the GIC group were
assessed as failures.
Mitchell et al. (1999) tested the fracture toughness of six different luting cements
(four conventional glass-ionomer cements, one resin-modified glass ionomer and
one resin cement), in order to determine their tendency to fail cohesively when
loaded. The results indicated that the fracture toughness of the resin-modified glassionomer cement was greater than any of the four conventional glass-ionomer
cements, and that the fracture toughness of the resin composite cement was
significantly greater than any of the other cements tested.
It can be concluded from the above-mentioned studies that the adhesive luting of
ceramic inlays and onlays using resin cements has a better prognosis than luting
with other materials.
Resin luting cements are available as light-/ dual-cured systems, dual-cured
systems, or chemical-cured systems. Although chemically cured resin cements
harden sufficiently, they allow only a short working time, which can be stressful for
the operator and lead to failures in cementation. The light-cured systems provide the
benefit of controlled working time. Color is more easily controlled because no mixing
of components is required and try-in without polymerization is possible. However,
obtaining a thorough polymerization through ceramic materials is not always
accomplished. The critical thickness of ceramic restorations for polymerization is 2-3
mm (Blackman et al. 1990, Platt 1999).
7.1.5 Clinical relevance and influence of the artificial mouth
on the survival rate and fracture strength of ceramic onlays
Before performing in-vivo studies or applying new dental materials for clinical use,
in-vitro tests are recommended in order to prove their applicability and performance.
In-vitro tests can be performed in a short period of time and have the advantages of
reproducibility and the possibility of standardizing the test parameters (Krejci & Lutz
1990, Kern et al. 1999). However, each in-vitro test represents only one approach to
a clinical situation. The more closely a test simulates the clinical situation, the more
clinically relevant the results (Krejci et al. 1990). In the past, different chewing
58
simulators have been used to simulate clinical conditions and have saved evaluation
time for inlays and onlays (Krejci & Lutz 1990, Krejci et al. 1993, Mehl et al. 1998,
Behr et al. 1999). It has been shown that ceramic restorations accumulate damage
during cyclic loading and thermocycling. The accumulated subsurface damage
weakens the ceramic restorations and can cause clinical failures (Kelly 1999).
Schwickerath (1996) reported that the flexural strength of In-Ceram, IPS Empress
and Dicor ceramics was approximately 50% of the initial strength after 100,000fatigue loading cycles. Intraoral occlusal forces create dynamic repetitive loading.
Therefore, instead of monotonic static loading, it is more clinically relevant to test the
specimens under physiological fatigue load in a chewing simulator, which will allow
evaluation of the dental restorative systems under clinically relevant conditions
(DeLong & Douglas 1983, Krejci et al. 1990, Kelly 1999). However, no data is
available on the effect of cyclic and dynamic loading on the fracture strength of
ceramic inlays and onlays.
Adding moisture and controlled temperature to the environment was found to be
important when measuring the fracture or fatigue strength of dental ceramics.
Exposure to water was been found to affect the mechanical properties of all-ceramic
restorations. Also, storage in water for extended periods has been shown to alter the
failure of all-ceramic materials (Kelly 1999) and to weaken the bond strength (Roulet
et al. 1995). Furthermore, temperature changes also lead to slow flaw propagation
(Kelly 1999). Although some authors used a median temperature of 37°C for testing
dental material in the artificial oral environment (Brantley et al. 1986, Kappert &
Altvater 1991), most of the authors used temperatures varying from 5°C to 55°C for
their tests (Kern & Thompson 1993, Kern et al. 1999). In this study temperatures
varying from 5° to 55°C were used simultaneously with the cyclic loading. No studies
are available on the effect of thermocycling on the fracture strength of ceramic inlays
and onlays.
Clinical studies showed that humans have an average of 250,000 masticatory cycles
per year (DeLong & Douglas 1983, Sakaguchi et al. 1986). Therefore, to simulate a
service time of 5 years, about 1,200,000 masticatory cycles have to be performed in
the chewing simulator (Krejci & Lutz 1990, Kern et al. 1999). The artificial chewing
cycle in the artificial oral environment is designed to correspond as closely as
possible to physiological conditions. The magnitude, duration and frequency of the
59
force applied in the artificial mouth are comparable to values reported in the
literature (Bates et al. 1976, Bradley 1996).
In this study, balls made of Steatite (a ceramic enamel analogue) were used as
antagonists for the test samples in the chewing machine. It has been shown that
antagonists made out of enamel are not suitable for standardized wear tests,
because they differ in morphology, microstructure and composition (Wassell et al.
1994b). Metals and composites are also not acceptable as antagonists (Krejci & Lutz
1990). The advantages of a Steatite antagonist are that it has a Vickers hardness
that is very similar to enamel, and is accurate, reproducible and cost-effective
(Wassell et al. 1994a, b).
The parameters used for the chewing machine were limited to the physiological
values found in the literature. A cycle loading force of 49 N was used in several
studies (Krejci & Lutz 1990, Kern et al. 1999). However, clinical studies showed that
biting forces can easily exceed the 49 N loading force (Gibbs et al. 1986,
Schwickerath & Coca 1987). Therefore, it is more realistic, for purposes of
experimental design, to consider higher loading forces than the functional forces that
arise during chewing or swallowing. In this study, a cycle loading force of 98 N was
used in order to approach a clinical situation comparable to the posterior area of the
dental arch. Unfortunately, no studies are available on the performance of ceramic
inlays and onlays in the artificial mouth.
7.1.6 The clinical relevance of fracture strength tests
In the presented study, the fracture strength of molars and molars with ceramic
inlays and onlays was evaluated after exposure to the artificial oral environment.
The physical properties and performance of newly-developed dental materials must
be tested before they can be recommended for clinical use (Ritter 1995b). The
traditional fracture strength tests (biaxial flexural tests or 3-, 4-point bending tests)
cannot be used to predict the performance of a restoration in the mouth, because
they do not simulate a clinical mode of failure (Kelly 1995, Ritter 1995a). Also,
traditional fracture strength tests can fail from their edges during processing, raising
the possibility that premature failures occur from the uncharacteristic processing
60
flaws (Kelly 1995). Therefore, in order for testing to be relevant, test specimens must
have the same type and distribution of flaws as the target structure when placed into
service (Kelly et al. 1995, Ritter 1995a, b).
Kelly (1999) questioned the relevance of traditional load-to-failure tests of allceramic restorations. He mentioned that the elementary beam theory cannot be
used to examine a cemented full coverage restoration or to predict its clinical
behavior. Homogeneous all-ceramic restorations consist of a layer of ceramic, a
layer of cement and are supported by a thickness of dentin. This structure of
different materials having different modulus of elasticity is not well represented by
simple bar-shaped specimens, such as those used in 3-point or 4-point bending
tests. These tests also do not create failure mechanisms seen in retrieved clinical
specimens (Kelly 1999). Moreover, no conclusion regarding longevity of the
restoration can be drawn from fracture strength results alone. Furthermore, water
showed that it can act chemically at crack tips and decrease the strength of glass
and ceramics. Temperature change also affects the fracture strength of those
materials. (Kern et al. 1994)
For the strength test to accurately reflect the variability and time dependency of a
ceramic component in service, the test environment must be the same as the
service environment, and the strength-controlling flaw population must be the same
as that responsible for failure in service. Therefore, it is generally recommended that
the test specimens and mode of loading be chosen to closely simulate the actual
components in service (Ritter 1995a, b, Kelly 1999).
7.2
Results
7.2.1 Survival rate of test samples after exposure to the artificial
mouth
The objective of the artificial mouth test, as already indicated, was to introduce a
comparable cycle fatigue component. In the present study all of the samples have
been exposed to the artificial mouth to simulate 5 years of service before the fracture
61
strength test was performed. All the samples survived the exposure to the artificial
mouth.
Historically, ceramic inlays and onlays were exposed to the artificial mouth in only
two in-vitro studies (Krejci et al. 1993, Mehl et al. 1998). However, for the present
study, no comparison data is available in the literature regarding the performance of
ceramic inlays and onlays.
7.2.2 Fracture strength tests after exposure to the artificial mouth
In the present study all of the samples were loaded until fracture occurred in the
universal testing machine after exposure to the artificial mouth. The observed
median fracture strength values of the groups were, A (control) 1960 N, B 1567 N, C
1870 N, D 1687 N, E 1705 N and F 1842 N. Data from fracture strength tests of
ceramic onlays using natural teeth as abutments after exposure to the artificial
mouth are not available in the literature. Despite different preparation and extension
designs, the statistical analysis demonstrated no significant differences in the
fracture strength values between the test groups and the control group. The fracture
strength values of the five groups were comparable to those of natural teeth. All test
samples had fracture strength values of more than 800 N. These values exceeded
the maximum limit of natural teeth (500 N), as suggested by Kappert (1996). The
findings in this study are greater than the fracture strength values of Vitadur N inlays
(2680 N) and Ceramco II inlays (1662) luted on natural teeth and unprepared natural
teeth (3547 N) as reported by Dietschi et al. (1990). Deviations in the reported
fracture forces may be explained by the use of: different types of ceramics, different
test methods and different preparation designs. Compared to the study of Dietschi et
al. (1990), the testing procedures used in this study were harder, because dynamic
loading with thermocycling was performed and tooth mobility was simulated.
The measurement of the fracture strength resulted in an asymmetric distribution of
the data. Therefore, instead of the mean, the median was used for the statistical
analysis of the fracture resistance data. The small sample size (n = 16), used in the
present study, may affect the interpretation of the statistical analysis in this study.
62
7.2.3 Influence of preparation design on the fracture strength of the
ceramic inlays and onlays
In the present study, the statistical analysis showed no significant differences in the
fracture strength values between the test groups and the control group (natural
teeth). Despite different preparation designs and extensions, the fracture strength of
all test specimens in this study reached values that were comparable to those of
natural teeth.
The fracture strength of a natural tooth is compromised after tooth preparation or
caries as reported by Geurtsen et al. (1989). They examined the fracture strength of
148 extracted human molars after having performed different types of cavity
preparations and fillings with various materials (amalgam, direct composite and
composite inlays). Unprepared teeth were used as a control group in the study.
Results of the fracture tests showed that the prepared-only teeth had the lowest
fracture strength value (733 N), while the teeth in the control group had the highest
fracture strength value (2088 N). Cotert et al. (2001) compared the cuspal fracture
resistance of eighty-four molars restored with five different adhesive materials. The
teeth were divided into seven groups. The first five received MOD cavity
preparations and were restored with amalgam, composite, composite inlay, castmetal inlay and ceramic inlay. The sixth and the seventh groups were used as
controls. Samples of group 6 were prepared without restoring them. Samples of
group 7 were intact teeth and were tested as unprepared. All samples were loaded
axially until failure. Results showed that the unprepared teeth had a significantly
higher resistance than all other groups, while the prepared-only group was the
weakest. In the same study, no significant differences were found in resistance to
cuspal fracture among the different restoration groups (Cotert et al. 2001).
It seems in the present study that the different preparation designs of different test
groups, along with adhesive cementation, have succeeded in supporting the rest of
the tooth structure, have applied an appropriate distribution of stresses generated by
the artificial mouth, and enabled the prepared tooth to again reach the fracture
strength that it had before preparation. However, no comparison data is available in
the literature regarding the effect of preparation design on the fracture strength of
63
ceramic inlays and onlays placed on natural teeth after exposure to the artificial
mouth.
7.2.4 Patterns of fracture of the samples
In the present study, the recorded patterns of fracture of samples of the test groups
were typical for ceramic inlays and onlays. Fractures were found mostly in the
ceramic material, with the exception of 14 samples (17.5%) where the fracture
pattern extended to the tooth structure. This failure of both restoration and tooth can
be explained by the fact that the ceramic material (EPC) had almost the same
tensile strength values as that of natural teeth. Therefore, when applying the load-tofailure test, both the restoration and the tooth failed. However, it is preferred that the
restoration fails alone to preserve the remaining tooth structure (Peters et al. 1993).
The crack initiation for almost all test samples in the present study started at the
cement interface to the occlusal aspect of the restoration. This is in agreement with
data from Kelly (1999), who reported that crack initiation starts at the cement
interface. When a ceramic layer is uniformly supported by, and bonded to, a less stiff
material, high tensile stresses develop in the ceramic at its interface with the
cement, directly below the loaded area. These interfacial stresses arise from strain
differences in the ceramics, cement and dentin because of the ceramic material
having a higher modulus of elasticity. Therefore, cracks usually initiate at the
interface level, leading to a subsequent total failure of the restoration (Kelly et al.
1990, Kelly 1999). The form of crack initiation and the failure pattern provide strong
evidence that the in-vitro test model selected in this study is clinically relevant.
64
8.
Conclusions
Within the limits of this study it can be concluded that:
1.
The different preparation designs of ceramic onlays seem to have no
influence on the survival rate and fracture strength of these restorations.
2.
Clinical data is needed before recommending the EPC material for clinical
use.
65
9.
Summary
In this study, the survival rate and fracture strength of ceramic inlays, different types
of onlays and unprepared teeth were compared, after exposure to the artificial
mouth.
Ninety-six caries-free human upper first molars were used for the experiment. The
teeth were randomly divided into five groups of 16 samples each and a control group
(A) with no preparation. In group B, inlay preparation was made in a 6° MOD taper
box form with rounded and soft internal line angle and 3 mm deep. The isthmus was
3 mm wide. A mesial and distal finishing 1 mm above cemento-enamel junction has
been made. In group C, teeth were prepared in the same manner as the first group,
then the mesio-palatal cusp was reduced 2 mm with 45° on the occlusal plane and
margins were left in an overlapping form. In group D, teeth were prepared in the
same manner as the first group, then both palatal cusps were reduced 2 mm with
45° on the horizontal plane. In group E, teeth were prepared in the same manner as
the first group, then the palatal and disto-buccal cusps were reduced. In group F,
teeth were prepared in the same manner as the first group, then all cusps were
reduced. 16 ceramic inlays (group B) and 64 onlays were fabricated using
Experimental Press Ceramic material (EPC). The ceramic inlays and onlays were
luted to the teeth using Variolink® II. All test and control samples, were loaded in an
artificial mouth to simulate 5 years of clinical work (1.2 million chewing cycles). All
test samples survived the exposure to the artificial mouth. Then all samples were
loaded until fracture occurred in the universal testing machine. The median fracture
strength values (in N), were as follows: group B 1567, group C 1870, group D 1687,
group E 1705, group F 1842 and group A (control) 1960.
All test groups demonstrated fracture strength values above the maximum
suggested load of 500 N. No statistically significant differences in the fracture
strength values between the inlay group, the different types of onlay restorations and
the natural teeth were recorded. Within the limits of this study, it can be concluded
that the different preparation designs of ceramic onlays seem to have no influence
on the survival rate and fracture strength of these restorations. However, clinical
data is needed before recommending the EPC material for clinical use.
66
10. Zusammenfassung
In dieser Studie wurde die Überlebensrate und Bruchfestigkeit keramischer Inlays
und unterschiedlicher keramischer Teilkronen mit denen von unpräparierten Zähnen
nach Simulation im künstlichen Mund verglichen.
96 kariesfreie menschliche obere Molaren wurden für die Untersuchung verwendet.
Die Zähne wurden auf 5 Testgruppen und eine Kontrollgruppe (A) ohne Präparation
je 16 randomisiert verteilt. In Gruppe B wurde eine Inlay-Kastenpräparation (MOD)
mit 6° Abschrägung, weichen internen Winkeln, bei 3mm Tiefe, präpariert. Der
Isthmus war 3mm breit. Die Präparation endete 1mm über der Schmelz-ZementGrenze. Die Inlaypräparation diente als Grundlage für die Präparation der Gruppen
C-F. In Gruppe C wurde zusätzlich der mesio-palatinale Höcker in einem 45° Winkel
zur okklusalen Fläche um 2mm reduziert. Die Präparationsränder endeten im
rechten Winkel. In Gruppe D wurden beide palatinalen Höcker mit 45° Winkel zur
horizontalen Ebene um 2mm reduziert. In Gruppe E wurden beide palatinale und der
disto-bukkale Höcker reduziert. In Gruppe F wurden alle Höcker reduziert. 16
Keramikinlays (Gruppe B) und 64 Teilkronen wurden aus einem experimentellen
presskeramischen Material (EPC) hergestellt. Die keramischen Inlays und
Teilkronen wurden adhäsiv mit Variolink® II befestigt. Dann wurden alle Test- und
Kontrollprüfkörper einer Kausimulation von 5 Jahren im künstlichen Mund (1.2
Millionen Kauzyklen), ausgesetzt. Alle Prüfkörper überlebten die künstliche
Kaubelastung. Danach wurden alle Prüfkörper in der Universal Testmaschine bis
zum
Bruch
belastet.
Die
Bruchfestigkeitswerte
(Median)
zeigten
folgende
Ergebnisse (in N): Gruppe B 1567, Gruppe C 1870, Gruppe D 1687, Gruppe E 1705,
Gruppe F 1842 und Gruppe A (Kontrollgruppe) 1960. Alle Testgruppen zeigten
Bruchfestigkeitswerte, die über der beschriebenen Maximalkaukraft von 500N lagen.
Es zeigten sich keine statistisch signifikanten Unterschiede in den Bruchfestigkeitswerten zwischen der Inlaygruppe, den unterschiedlichen Onlayrestaurationen und
den natürlichen Zähnen. Im Rahmen dieser Studie konnte gezeigt werden, dass die
unterschiedlichen Präparationsformen der keramischen Teilkronen keinen Einfluss
auf die Überlebensrate und Bruchfestigkeit dieser Restaurationen zeigten. Allerdings
werden weitere Daten aus klinischen Untersuchungen benötigt, bevor das EPC
Material für die klinische Anwendung allgemein empfohlen werden kann.
67
11. Appendix
11.1 Results of the fracture strength test (N) after exposure to the
artificial mouth
Group
Control
A
B
C
D
E
1
2212.26
1592.26
1394.54
1239.46
1929.93
2599.71
2
3328.48
2599.71
1526.70
1782.19
2007.49
2332.89
3
1402.09
1521.93
2081.43
1689.74
1594.01
2372.97
4
1831.36
2288.28
1378.74
2004.29
1793.99
2611.86
5
2051.56
1022.90
1083.31
1807.64
1609.44
2498.25
6
1506.60
1605.76
1854.14
858.35
3485.74
1706.05
7
1067.49
1350.47
1885.41
1683.83
1217.04
1319.68
8
1821.84
1118.35
2219.50
1277.72
2226.51
1465.42
9
3615.53
2201.89
2546.76
1569.84
1526.66
852.40
10
1977.96
1520.13
1785.72
2461.51
2172.29
1688.78
11
2273.24
1863.67
880.67
866.04
963.03
1978.88
12
2158.11
2326.65
2408.18
1778.29
1515.92
2078.03
13
1061.51
1501.04
2318.29
1611.79
2306.66
1056.19
14
871.53
1668.42
1896.82
1732.30
1635.94
2053.00
15
1942.61
1542.02
1525.25
1852.80
1774.31
863.36
16
3533.08
1252.09
2000.21
1130.01
1616.16
1264.88
Sample
68
12. References
Aberg CH, van Dijken JW, Olofsson AL (1994). Three-year comparison of fired
ceramic inlays cemented with composite resin or glass ionomer cement. Acta
Odontol Scand 52(3):140-9.
Abu-Hassan MI, Abu-Hammad OA, Harrison A (2000). Stress distribution associated
with loaded ceramic onlay restorations with different designs of marginal
preparation. An FEA study. J Oral Rehabil 27(4):294-8.
Agerholm DM, Sidi AD (1988). Reasons given for extraction of permanent teeth by
general dental practitioners in England and Wales. Br Dent J 164(11):345-8.
al-Nazhan S, Sapounas G, Spangberg L (1988). In vitro study of the toxicity of a
composite resin, silver amalgam, and Cavit. J Endod 14(5):236-8.
Andersson M, Oden A (1993). A new all-ceramic crown. A dense-sintered, highpurity alumina coping with porcelain. Acta Odontol Scand 51(1):59-64.
Andersson M, Razzoog ME, Oden A, Hegenbarth EA, Lang BR (1998). Procera: a
new way to achieve an all-ceramic crown. Quintessence Int 29(5):285-96.
Anusavice KJ, Hojjatie B (1992). Tensile stress in glass-ceramic crowns: effect of
flaws and cement voids. Int J Prosthodont 5(4):351-8.
Banks RG (1990). Conservative posterior ceramic restorations: a literature review. J
Prosthet Dent 63(6):619-26.
Bates JF, Stafford GD, Harrison A (1976). Masticatory function - a review of the
literature. III. Masticatory performance and efficiency. J Oral Rehabil 3(1):57-67.
Beham G (1990). IPS-Empress: A new ceramic technology. Ivoclar-Vivadent Report
6:1-13.
Beham G (1991). IPS-Empress: Eine neue Keramik-Technologie. Zwr 100(6):404-8.
Behr M, Rosentritt M, Leibrock A, Schneider-Feyrer S, Handel G (1999). In-vitro
study of fracture strength and marginal adaptation of fibre-reinforced adhasive fixed
partial inlay dentures. J Dent 27(2):163-8.
69
Berg NG, Derand T (1997). A 5-year evaluation of ceramic inlays (CEREC). Swed
Dent J 21(4):121-7.
Blackman R, Barghi N, Duke E (1990). Influence of ceramic thickness on the
polymerization of light-cured resin cement. J Prosthet Dent 63(3):295-300.
Blankenau RJ, Kelsey WP, 3rd, Cavel WT (1984). A direct posterior restorative resin
inlay technique. Quintessence Int 15(5):515-6.
Blatz MB (2002). Long-term clinical success of all-ceramic posterior restorations.
Quintessence Int 33(6):415-26.
Bradley M (1996). Physiologie des stomatognathen Systems. Mosby, Ullstein,
Berlin.
Brantley CF, Kanoy BE, Jr., Sturdevant JR (1986). Thermal effects on retention of
resin-bonded retainers. Dent Mater 2(2):67-71.
Braunwarth J, Hellge A (1991). Die vollkeramische Teilkrone: II. Die Herstellung.
Quintessenz Zahntech 17(2):157-67.
Broderson SP (1994). Complete-crown and partial-coverage tooth preparation
designs for bonded cast ceramic restorations. Quintessence Int 25(8):535-9.
Buonocore MG (1955). A simple method of increasing the adhesion of acrylic filling
materials to enamel surfaces. J Dent Res 34(2):849-53.
Burke FJ (1995). The effect of variations in bonding procedure on fracture resistance
of dentin-bonded all-ceramic crowns. Quintessence Int 26(4):293-300.
Burke FJ, Cheung SW, Mjor IA, Wilson NH (1999). Reasons for the placement and
replacement of restorations in vocational training practices. Prim Dent Care 6(1):1720.
Burke FJ, Fleming GJ, Nathanson D, Marquis PM (2002). Are adhesive technologies
needed to support ceramics? An assessment of the current evidence. J Adhes Dent
4(1):7-22.
Campbell SD (1989). A comparative strength study of metal ceramic and all-ceramic
esthetic materials: modulus of rupture. J Prosthet Dent 62(4):476-9.
70
Caughman WF, Caughman GB, Dominy WT, Schuster GS (1990). Glass ionomer
and composite resin cements: effects on oral cells. J Prosthet Dent 63(5):513-21.
Chen RS, Liu CC, Cheng MR, Lin CP (2000). Bonded amalgam restorations: using a
glass-ionomer as an adhesive liner. Oper Dent 25(5):411-7.
Christensen GJ (1988). Tooth-colored inlays and onlays. J Am Dent Assoc
117(4):12E-17E.
Christensen GJ (1989). Alternatives for the restoration of posterior teeth. Int Dent J
39(3):155-61.
Christensen GJ (1996a). The coming demise of the cast gold restoration? J Am Dent
Assoc 127(8):1233-6.
Christensen GJ (1996b). When to use fillers, build-ups or posts and cores. J Am
Dent Assoc 127(9):1397-8.
Ciucchi B, Bouillaguet S, Delaloye M, Holz J (1997). Volume of the internal gap
formed under composite restorations in vitro. J Dent 25(3-4):305-12.
Cotert HS, Sen BH, Balkan M (2001). In vitro comparison of cuspal fracture
resistances of posterior teeth restored with various adhesive restorations. Int J
Prosthodont 14(4):374-8.
Crim GA (1993). Marginal leakage of visible light-cured glass ionomer restorative
materials. J Prosthet Dent 69(6):561-3.
Croll TP (1993). Management of dental trauma using bonded adhesive material.
Dent Econ 83(7):78-9.
Davidson CL, de Gee AJ, Feilzer A (1984). The competition between the compositedentin bond strength and the polymerization contraction stress. J Dent Res
63(12):1396-9.
De Boever JA, McCall WD, Jr., Holden S, Ash MM, Jr. (1978). Functional occlusal
forces: an investigation by telemetry. J Prosthet Dent 40(3):326-33.
De Jager N, Feilzer AJ, Davidson CL (2000). The influence of surface roughness on
porcelain strength. Dent Mater 16(6):381-8.
71
DeLong R, Douglas WH (1983). Development of an artificial oral environment for the
testing of dental restoratives: bi-axial force and movement control. J Dent Res
62(1):32-6.
Denissen H, Dozic A, van der Zel J, van Waas M (2000). Marginal fit and short-term
clinical performance of porcelain-veneered CICERO, CEREC, and Procera onlays. J
Prosthet Dent 84(5):506-13.
Dietschi D, Maeder M, Meyer JM, Holz J (1990). In vitro resistance to fracture of
porcelain inlays bonded to tooth. Quintessence Int 21(10):823-31.
Dietschi D, Magne P, Holz J (1995). Bonded to tooth ceramic restorations: in vitro
evaluation of the efficiency and failure mode of two modern adhesives. Schweiz
Monatsschr Zahnmed 105(3):299-305.
Dong JK, Luthy H, Wohlwend A, Scharer P (1992). Heat-pressed ceramics:
technology and strength. Int J Prosthodont 5(1):9-16.
Eichner K (1963). Messung der Kaukräfte bei Kauvorgängen. Dtsch Zahnarztl Z
18(17):915-24.
Eidenbenz S, Lehner CR, Schärer P (1994). Copy milling ceramic inlays from resin
analogs: a practicable approach with the CELAY system. Int J Prosthodont 7(2):13442.
Eley BM (1997a). The future of dental amalgam: a review of the literature. Part 5:
Mercury in the urine, blood and body organs from amalgam fillings. Br Dent J
182(11):413-7.
Eley BM (1997b). The future of dental amalgam: a review of the literature. Part 6:
Possible harmful effects of mercury from dental amalgam. Br Dent J 182(12):455-9.
Eley BM (1997c). The future of dental amalgam: a review of the literature. Part 7:
Possible alternative materials to amalgam for the restoration of posterior teeth. Br
Dent J 183(1):11-4.
Esquivel-Upshaw JF, Anusavice KJ, Yang MC, Lee RB (2001). Fracture resistance
of all-ceramic and metal-ceramic inlays. Int J Prosthodont 14(2):109-14.
72
Farah JW, Dennison JB, Powers JM (1977). Effects of design on stress distribution
of intracoronal gold restorations. J Am Dent Assoc 94(6):1151-4.
Feilzer AJ, De Gee AJ, Davidson CL (1987). Setting stress in composite resin in
relation to configuration of the restoration. J Dent Res 66(11):1636-9.
Felden A, Schmalz G, Federlin M, Hiller KA (1998). Retrospective clinical
investigation and survival analysis on ceramic inlays and partial ceramic crowns:
results up to 7 years. Clin Oral Investig 2(4):161-7.
Fradeani M, Aquilano A, Bassein L (1997). Longitudinal study of pressed glassceramic inlays for four and a half years. J Prosthet Dent 78(4):346-53.
Frankenberger R, Petschelt A, Kramer N (2000). Leucite-reinforced glass ceramic
inlays and onlays after six years: clinical behavior. Oper Dent 25(5):459-65.
Freedman G (1998). Ultraconservative dentistry. Dent Clin North Am 42(4):683-93,
ix.
Friedl KH, Hiller KA, Schmalz G, Bey B (1997). Clinical and quantitative marginal
analysis of feldspathic ceramic inlays at 4 years. Clin Oral Investig 1:163-168.
Frtiz U, Fischbach H, Harke I (1992). Langzeitverweildauer von Goldgußfüllungen.
Dtsch Zahnärztl Z 47(10):714-16.
Füllemann J, Krejci I, Lutz F (1992). Kompositinlays: Klinische und Rasterelektronenmikroskopische
Untersuchung
nach
einjähriger
Funktionszeit.
Schweiz
Monatsschr Zahnmed 102(3):292-8.
Fuzzi M, Rappelli G (1999). Ceramic inlays: clinical assessment and survival rate. J
Adhes Dent 1(1):71-9.
Gaglio MA (2001). Esthetic restorations designed with confidence and predictability.
Compend Contin Educ Dent 22(6 Suppl):30-4.
Ganss C, Gottwald B, Traenckner I, Kupfer J, Eis D, Monch J, Gieler U, Klimek J
(2000). Relation between mercury concentrations in saliva, blood, and urine in
subjects with amalgam restorations. Clin Oral Investig 4(4):206-11.
73
Garber AD, Goldstein ER (1994). Porcelain and composite inlays and onlays:
Esthetic posterior restorations. Quintessence, Illinois, St Louis
Gemalmaz D, Ozcan M, Yoruc AB, Alkumru HN (1997). Marginal adaptation of a
sintered ceramic inlay system before and after cementation. J Oral Rehabil
24(9):646-51.
Geurtsen W, Orth M, Gartner A (1989). Die Frakturfestigkeit menschlicher
Oberkiefermolaren mit einer MOD-Amalgam- oder -Kompositfüllung. Dtsch Zahnarztl
Z 44(2):108-10.
Gibbs CH, Mahan PE, Mauderli A, Lundeen HC (1986). Limits of human bite
strength. J Prosthet Dent 56(2):226-29.
Giordano RA, 2nd, Campbell S, Pober R (1994). Flexural strength of feldspathic
porcelain treated with ion exchange, overglaze, and polishing. J Prosthet Dent
71(5):468-72.
Giordano R, Cima M, Pober R (1995a). Effect of surface finish on the flexural
strength of feldspathic and aluminous dental ceramics. Int J Prosthodont 8(2):31119.
Giordano RA, 2nd, Pelletier L, Campbell S, Pober R (1995b). Flexural strength of an
infused ceramic, glass ceramic, and feldspathic porcelain. J Prosthet Dent
73(5):411-8.
Grobler SR, Oberholzer TG, Rossouw RJ, Grobler-Rabie A, Van Wyk Kotze TJ
(2000). Shear bond strength, microleakage, and confocal studies of 4 amalgam alloy
bonding agents. Quintessence Int 31(7):501-8.
Haas M, Arnetzl G, Wegscheider WA, Konig K, Bratschko RO (1992). Klinische und
werkstoffkundliche Erfahrungen mit Komposit-, Keramik-, und Goldinlays. Dtsch
Zahnarztl Z 47:18-22.
Hayashi M, Tsuchitani Y, Miura M, Takeshige F, Ebisu S (1998). 6-year clinical
evaluation of fired ceramic inlays. Oper Dent 23(6):318-26.
Helfer AR, Melnick S, Schilder H (1972). Determination of the moisture content of
vital and pulpless teeth. Oral Surg Oral Med Oral Pathol 34(4):661-70.
74
Heymann HO, Bayne SC, Sturdevant JR, Wilder AD, Jr., Roberson TM (1996). The
clinical performance of CAD-CAM-generated ceramic inlays: a four-year study. J Am
Dent Assoc 127(8):1171-81.
Hickel R, Manhart J (2001). Longevity of restorations in posterior teeth and reasons
for failure. J Adhes Dent 3(1):45-64.
Hobo S, Iwata T (1986). Gussfähiges Apatit-Porzellan: Ein neues biokompatibles
Material für Zahnersatz Teil II: Herstellung des Zahnersatzes. Quintessenz
37(12):2047-63.
Hofmann N, Popp M, Klaiber B (1995). Klinische und rasterelektronenmikroskopische Nachuntersuchung von Cerec inlays nach fünf Jahren Liegedauer. Dtsch
Zahnärztl Z 50:835-39.
Hojjatie B, Anusavice KJ (1990). Three-dimensional finite element analysis of glassceramic dental crowns. J Biomech 23(11):1157-66.
Hosoya Y, Tominaga A (1999). A comparison of five adhesive systems to primary
enamel. Pediatr Dent 21(1):46-52.
Isenberg BP, Essig ME, Leinfelder KF (1992). Three-year clinical evaluation of
CAD/CAM restorations. J Esthet Dent 4(5):173-6.
Isidor F, Brondum K (1995). A clinical evaluation of porcelain inlays. J Prosthet Dent
74(2):140-4.
Jackson RD (1999). Indirect resin inlay and onlay restorations: a comprehensive
clinical overview. Pract Periodontics Aesthet Dent 11(8):891-900, 902.
Jackson RD, Ferguson RW (1990). An esthetic, bonded inlay/onlay technique for
posterior teeth. Quintessence Int 21(1):7-12.
Jäger K (1989). Aufbau und Test einer Messkette zur Kaukraftmessung. Schweiz
Monatsschr Zahnmed 99(6):670-75.
Jahn KR, Gonschorek E (1986). Untersuchungen zur Standzeit von Füllungen.
Stomatol DDR 36(3):124-8.
75
James DF, Yarovesky U (1983). An esthetic inlay technique for posterior teeth.
Quintessence Int 14(7):725-31.
Jensen ME, Redford DA, Williams BT, Gardner F (1987). Posterior etched-porcelain
restorations: an in vitro study. Compendium 8(8):615-7, 620-2.
Jones DW (1985). Development of dental ceramics. An historical perspective. Dent
Clin North Am 29(4):621-44.
Joynt RB, Wieczkowski G, Jr., Klockowski R, Davis EL (1987). Effects of composite
restorations on resistance to cuspal fracture in posterior teeth. J Prosthet Dent
57(4):431-5.
Jung YG, Peterson IM, Kim DK, Lawn BR (2000). Lifetime-limiting strength
degradation from contact fatigue in dental ceramics. J Dent Res 79(2):722-31.
Kappert HF, Altvater A (1991). Feldstudie über die Passgenauigkeit und das
Randschlussverhalten von In-Ceram-Kronen und -Brücken. Dtsch Zahnarztl Z
46(2):151-3.
Kappert HF (1993). I-Ceram: testing a new ceramic material. Quintessence Dent
Technol Special reprint(1).
Kappert HF (1996). Perspektiven für metalfreie Seitenzahnversorgung mit Kronen
und Brücken. In: Werkstoffkunde - Zahntechnik - Klinische Erfahrung. Kappert HF
editor. Quintessenz, Berlin, pp. 231-36.
Kappert HF, Krah M (2001). Keramiken- eine Übersicht. Quintessenz Zahntech
27(6):668-704.
Kelly JR, Giordano R, Pober R, Cima MJ (1990). Fracture surface analysis of dental
ceramics: clinically failed restorations. Int J Prosthodont 3(5):430-40.
Kelly JR (1995). Perspectives on strength. Dent Mater 11(2):103-10.
Kelly JR, Tesk JA, Sorensen JA (1995). Failure of all-ceramic fixed partial dentures
in vitro and in vivo: analysis and modeling. J Dent Res 74(6):1253-8.
Kelly JR, Nishimura I, Campbell SD (1996). Ceramics in dentistry: historical roots
and current perspectives. J Prosthet Dent 75(1):18-32.
76
Kelly JR (1999). Clinically relevant approach to failure testing of all-ceramic
restorations. J Prosthet Dent 81(6):652-61.
Kern M, Douglas WH, Fechtig T, Strub JR, DeLong R (1993). Fracture strength of
all-porcelain, resin-bonded bridges after testing in an artificial oral environment. J
Dent 21(2):117-21.
Kern M, Thompson VP (1993). Sandblasting and silica-coating of dental alloys:
volume loss, morphology and changes in the surface composition. Dent Mater
9(3):151-61.
Kern M, Fechtig T, Strub JR (1994). Influence of water storage and thermal cycling
on the fracture strength of all-porcelain, resin-bonded fixed partial dentures. J
Prosthet Dent 71(3):251-6.
Kern M, Thompson VP (1995). Bonding to glass infiltrated alumina ceramic:
adhesive methods and their durability. J Prosthet Dent 73(3):240-9.
Kern M, Strub JR (1998). Bonding to alumina ceramic in restorative dentistry: clinical
results over up to 5 years. J Dent 26(3):245-9.
Kern M, Strub JR, Lu XY (1999). Wear of composite resin veneering materials in a
dual-axis chewing simulator. J Oral Rehabil 26(5):372-8.
Kerschbaum T, Voss R (1981). Die praktische Bewährung von Krone und Inlay.
Dtsch Zahnarztl Z 36(4):243-9.
Kiliaridis S, Kjellberg H, Wenneberg B, Engström C (1993). The relationship
between maximal bite force, bite force indurance, and facial morphology during
growth. A cross-sectional study. Acta Odontol Scand 51(2):323-31.
King ML, Aboush YE (1999). Effect of adhesive resin cement on design of partial
veneer crowns. J Prosthet Dent 82(2):157-60.
Krämer N, Frankenberger R, Pelka M, Petschelt A (1999). IPS Empress inlays and
onlays after four years--a clinical study. J Dent 27(5):325-31.
Krejci I, Sparr D, Lutz F (1987). Dreischichtiges Lichthärteverfahren mit
herkömmlichen
Komposite-Kunststoffen
Quintessenz 38(7):1217-29.
für
Black-Klasse-II-Restaurationen.
77
Krejci I, Reich T, Lutz F, Albertoni M (1990). In-Vitro-Testverfahren zur Evaluation
dentaler Restaurationssysteme. 1 Computergesteuerter Kausimulator. Schweiz
Monatsschr Zahnmed 100(8):953-60.
Krejci I, Lutz F (1990). In-Vitro-Testverfahren zur Evaluation dentaler Restaurationssysteme. 3. Korrelation mit In-vivo-Resultaten. Schweiz Monatsschr Zahnmed
100(12):1445-9.
Krejci I (1992). Zahnfarbene Restaurationen Hanser: München.
Krejci I, Krejci D, Lutz F (1992). Clinical evaluation of a new pressed ceramic inlay
material over 1.5 years. Quintessence Int 23(1):181-86.
Krejci I, Lutz F, Reimer M, Heinzmann JL (1993). Wear of ceramic inlays, their
enamel antagonists, and luting cements. J Prosthet Dent 69(4):425-30.
Leempoel PJ, Van't Hof MA, de Haan AF (1989). Survival studies of dental
restorations: criteria, methods and analyses. J Oral Rehabil 16(4):387-94.
Lehmann KM, Hellwig E (1998). Einführung in die restaurative Zahnheilkunde. Ein
Lehrbuch für den propädeutischen Studienabschnitt , 8. überarb. Auflage, Urban und
Schwarzenberg, München.
Lehner C, Studer S, Brodbeck U, Schärer P (1998). Six-year clinical results of
leucite-reinforced glass ceramic inlays and onlays. Acta Med Dent Helv 3(2):137-46.
Lindberg NE, Lindberg E, Larsson G (1994). Psychologic factors in the etiology of
amalgam illness. Acta Odontol Scand 52(4):219-28.
Ludwig K, Joseph K (1994). Untersuchungen zur Bruchfestigkeit von IPS-EmpressKronen in Abhängigkeit von den Zemetiermodilitäten. Quintessenz Zahntech
20(2):247-56.
Magne P, Versluis A, Douglas WH (1999). Effect of luting composite shrinkage and
thermal loads on the stress distribution in porcelain laminate veneers. J Prosthet
Dent 81(3):335-44.
Malament KA, Grossman DG (1987). The cast glass-ceramic restoration. J Prosthet
Dent 57(6):674-83.
78
Malament KA (1988). Considerations in posterior glass-ceramic restorations. Int J
Periodontics Restorative Dent 8(4):32-49.
Manhart J, Chen HY, Neuerer P, Scheibenbogen-Fuchsbrunner A, Hickel R (2001).
Three-year clinical evaluation of composite and ceramic inlays. Am J Dent 14(2):959.
Mante FK, Brantley WA, Dhuru VB, Ziebert GJ (1993). Fracture toughness of high
alumina core dental ceramics: the effect of water and artificial saliva. Int J
Prosthodont 6(6):546-52.
Martin N, Jedynakiewicz NM (1999). Clinical performance of CEREC ceramic inlays:
a systematic review. Dent Mater 15(1):54-61.
Mehl A, Pfeiffer A, Kremers L, Hickel R (1998). Randständigkeit von Cerec-IIInlayrestaurationen bei ausgedehnten Kavitäten mit stark geschwächten Höckern.
DZZ 53(1):57-60.
Mesaros AJ, Jr., Evans DB, Schwartz RS (1994). Influence of a dentin bonding
agent on the fracture load of Dicor. Am J Dent 7(3):137-40.
Milleding P, Ortengren U, Karlsson S (1995). Ceramic inlay systems: some clinical
aspects. J Oral Rehabil 22(8):571-80.
Mitchell CA, Douglas WH, Cheng YS (1999). Fracture toughness of conventional,
resin-modified glass-ionomer and composite luting cements. Dent Mater 15(1):7-13.
Molin M, Karlsson S (1992). A clinical evaluation of the Optec inlay system. Acta
Odontol Scand 50(4):227-33.
Molin M, Karlsson S (1996). A 3-year clinical follow-up study of a ceramic (Optec)
inlay system. Acta Odontol Scand 54(3):145-9.
Molin MK, Karlsson SL (2000). A randomized 5-year clinical evaluation of 3 ceramic
inlay systems. Int J Prosthodont 13(3):194-200.
Mörmann WH (1982). Kompositinlay: Forschungsmodell mit Praxispotential?
Quintessenz 33(10):1891-901.
79
Mörmann W, Brandestini M (1989). The CEREC Computer Reconstruction-Inlays,
Onlays, and Veneers. Quintessence, Berlin
Mörmann W, Krejci I (1992). Computer-designed inlays after 5 years in situ: clinical
performance and scanning electron microscopic evaluation. Quintessence Int
23(2):109-15.
Mörmann WH, Bindl A (2000). The Cerec 3--a quantum leap for computer-aided
restorations: initial clinical results. Quintessence Int 31(10):699-712.
Moscovich H, Roeters FJ, Verdonschot N, de Kanter RJ, Creugers NH (1998). Effect
of composite basing on the resistance to bulk fracture of industrial porcelain inlays. J
Dent 26(2):183-9.
Mühlemann H (1951). Die physiologische Zahnbeweglichkeit. Schweiz Mschr
Zahnheilkund 93(2):1-67.
Neiva G, Yaman P, Dennison JB, Razzoog ME, Lang BR (1998). Resistance to
fracture of three all-ceramic systems. J Esthet Dent 10(2):60-6.
Ottl P, Piwowarczyk A, Lauer HC, Hegenbarth EA (2000). The Procera AllCeram
system. Int J Periodontics Restorative Dent 20(2):151-61.
Otto T (1995). [Cerec restorations. Cerec inlays and onlays: the clinical results and
experiences after 6 years of use in private practice]. Schweiz Monatsschr Zahnmed
105(8):1038-46.
Pallesen U, van Dijken JW (2000). An 8-year evaluation of sintered ceramic and
glass ceramic inlays processed by the Cerec CAD/CAM system. Eur J Oral Sci
108(3):239-46.
Peters MC, de Vree JH, Brekelmans WA (1993). Distributed crack analysis of
ceramic inlays. J Dent Res 72(11):1537-42.
Platt JA (1999). Resin cements: into the 21st century. Compend Contin Educ Dent
20(12):1173-6, 1178, 1180-2, 1184.
Presern
ZF,
Strub
röntgenologische
93(3):154-62.
JR
(1983).
Inlay
Nachuntersuchung.
versus
SSO
Onlay.
Schweiz
Eine
klinische
Monatsschr
und
Zahnheilkd
80
Pröbster L (1996). Klinische Erfahrung mit vollkeramischem Zahnersatz-Ein
Rückblick. In: Vollkeramik: Werkstoffkunde- Zahntechnik-Klinische Erfahrung.
Kappert HF editor. Quintessenz, Berlin, pp. 103-16.
Pröbster L (1997). Die Entwicklung der vollkeramischen Restauration- ein
historischer Abriß (I). Quintessenz 48(7):939-47.
Qualtrough AJ, Wilson NH, Smith GA (1990). Porcelain inlay: a historical view. Oper
Dent 15(2):61-70.
Reiss B, Walther W (1991). Überlebensanalyse und klinische Nachuntersuchungen
von zahnfarbenen Einlagefüllungen nach dem CEREC-Verfahren. Zwr 100(5):32932.
Reiss B, Walther W (1998). Ereignisanalyse und klinische Langzeitergebnisse mit
Cerec-Keramikinlays. Dtsch Zahnarztl Z 53(1):65-8.
Reiss B, Walther W (2000). Clinical long-term results and 10-year Kaplan-Meier
analysis of Cerec restorations. Int J Comput Dent 3(1):9-23.
Retief DH, Mandras RS, Russell CM, Denys FR (1993). Evaluation of the Syntac
bonding system. Am J Dent 6(1):17-21.
Ritter JE (1995a). Critique of test methods for lifetime predictions. Dent Mater
11(2):147-51.
Ritter JE (1995b). Predicting lifetimes of materials and material structures. Dent
Mater 11(2):142-6.
Ritter AV, Baratieri LN (1999). Ceramic restorations for posterior teeth: guidelines for
the clinician. J Esthet Dent 11(2):72-86.
Rosenblum MA, Schulman A (1997). A review of all-ceramic restorations. J Am Dent
Assoc 128):297-307.
Rosenstiel SF, Gupta PK, Van der Sluys RA, Zimmerman MH (1993). Strength of a
dental glass-ceramic after surface coating. Dent Mater 9(4):274-9.
Roulet JF (1994). Zahnfarbene Restaurationen als Amalgam-Alternativen. Dtsch
Zahnärztl Z 49(11):859-66.
81
Roulet JF, Soderholm KJ, Longmate J (1995). Effects of treatment and storage
conditions on ceramic/composite bond strength. J Dent Res 74(1):381-7.
Roulet JF (1997a). Benefits and disadvantages of tooth-coloured alternatives to
amalgam. J Dent 25(6):459-73.
Roulet JF (1997b). Longevity of glass ceramic inlays and amalgam--results up to 6
years. Clin Oral Investig 1(1):40-6.
Sakaguchi RL, Douglas WH, DeLong R, Pintado MR (1986). The wear of a posterior
composite in an artificial mouth: a clinical correlation. Dent Mater 2(6):235-40.
Sano H, Ciucchi B, Matthews WG, Pashley DH (1994). Tensile properties of
mineralized and demineralized human and bovine dentin. J Dent Res 73(6):1205-11.
Scheibenbogen A, Manhart J, Kunzelmann KH, Hickel R (1998). One-year clinical
evaluation of composite and ceramic inlays in posterior teeth. J Prosthet Dent
80(4):410-6.
Schwickerath H (1986). Dauerfestigkeit von Keramik. Dtsch Zahnarztl Z 41(2):26466.
Schwickerath H, Coca I (1987). Einzelkronen aus Glaskeramik. Phillip J 6(4):336-38.
Schwickerath H (1996). Werkstoffprüfung von Vollkeramiksystemen. In: Vollkeramik:
Wekstoffkunde
-
Zahntechnik
-
klinische
Erfahrhung.
Kappert
HF
editor.
Quintessenz, Berlin, pp. 87-102.
Seghi RR, Denry IL, Rosenstiel SF (1995). Relative fracture toughness and
hardness of new dental ceramics. J Prosthet Dent 74(2):145-50.
Seghi RR, Sorensen JA (1995). Relative flexural strength of six new ceramic
materials. Int J Prosthodont 8(3):239-46.
Siervo S, Bandettini B, Siervo P, Falleni A, Siervo R (1994). The CELAY system: a
comparison of the fit of direct and indirect fabrication techniques. Int J Prosthodont
7(5):434-39.
Sjögren G, Bergman M, Molin M, Bessing C (1992). A clinical examination of
ceramic (Cerec) inlays. Acta Odontol Scand 50(3):171-8.
82
Sjögren G, Molin M, van Dijken JW (1998). A 5-year clinical evaluation of ceramic
inlays (Cerec) cemented with a dual-cured or chemically cured resin composite
luting agent. Acta Odontol Scand 56(5):263-7.
Soderholm KJ (1981). Degradation of glass filler in experimental composites. J Dent
Res 60(11):1867-75.
Sparrius O, Grossman ES (1989). Marginal leakage of composite resin restorations
in combination with dentinal and enamel bonding agents. J Prosthet Dent 61(6):67884.
Stenberg R, Matsson L (1993). Clinical evaluation of glass ceramic inlays (Dicor).
Acta Odontol Scand 51(2):91-7.
Stoll R, Sieweke M, Pieper K, Stachniss V, Schulte A (1999). Longevity of cast gold
inlays and partial crowns--a retrospective study at a dental school clinic. Clin Oral
Investig 3(2):100-4.
Studer S, Lehner C, Brodbeck U, Scharer P (1996). Short-term results of IPSEmpress inlays and onlays. J Prosthodont 5(4):277-87.
Studer SP, Wettstein F, Lehner C, Zullo TG, Scharer P (2000). Long-term survival
estimates of cast gold inlays and onlays with their analysis of failures. J Oral Rehabil
27(6):461-72.
Sturdevant JR, Bayne SC, Heymann HO (1999). Margin gap size of ceramic inlays
using second-generation CAD/CAM equipment. J Esthet Dent 11(4):206-14.
Taleghani M, Leinfelder KF, Lane J (1987). Posterior porcelain bonded inlays.
Compendium 8(6):410, 412, 414-5.
The Academy of Prosthodontics (1999). The glossary of prosthodontic terms 7th
edition. J Prosthet Dent 81(1):39-110.
Thonemann B, Federlin M, Schmalz G, Hiller KA (1995). Resin-modified glass
ionomers for luting posterior ceramic restorations. Dent Mater 11(3):161-8.
83
Thonemann B, Federlin M, Schmalz G, Schams A (1997). Clinical evaluation of
heat-pressed glass-ceramic inlays in vivo: 2-year results. Clin Oral Investig 1(1):2734.
Thordrup M, Isidor F, Horsted-Bindslev P (1999). A 3-year study of inlays milled from
machinable ceramic blocks representing 2 different inlay systems. Quintessence Int
30(12):829-36.
Thordrup M, Isidor F, Horsted-Bindslev P (2001). A 5-year clinical study of indirect
and direct resin composite and ceramic inlays. Quintessence Int 32(3):199-205.
Tidehag P, Gunne J (1995). A 2-year clinical follow-up study of IPS Empress
ceramic inlays. Int J Prosthodont 8(5):456-60.
Touati B (1996). The evolution of aesthetic restorative materials for inlays and
onlays: a review. Pract Periodontics Aesthet Dent 8(7):657-66, 668.
Tsai YL, Petsche PE, Anusavice KJ, Yang MC (1998). Influence of glass-ceramic
thickness on Hertzian and bulk fracture mechanisms. Int J Prosthodont 11(1):27-32.
van Dijken JW, Hoglund-Aberg C, Olofsson AL (1998). Fired ceramic inlays: a 6year follow up. J Dent 26(3):219-25.
van Dijken JW, Sjostrom S (1998). Development of gingivitis around aged
restorations of resin-modified glass ionomer cement, polyacid-modified resin
composite (compomer) and resin composite. Clin Oral Investig 2(4):180-3.
van Dijken JW (1999). All-ceramic restorations: classification and clinical
evaluations. Compend Contin Educ Dent 20(12):1115-24, 1126, 1136.
van Dijken JW, Kieri C, Carlen M (1999). Longevity of extensive class II opensandwich restorations with a resin-modified glass-ionomer cement. J Dent Res
78(7):1319-25.
van Dijken JW (2000). Direct resin composite inlays/onlays: an 11 year follow-up. J
Dent 28(5):299-306.
van Dijken JW, Hasselrot L, Ormin A, Olofsson AL (2001). Restorations with
extensive dentin/enamel-bonded ceramic coverage. A 5-year follow-up. Eur J Oral
Sci 109(4):222-9.
84
Walther W, Reiss B, Toutenburg H (1994). Longitudinale Ereignisanalyse von
Cerec-Einlagefüllungen. Dtsch Zahnarztl Z 49:914-917.
Wassell RW, McCabe JF, Walls AW (1994a). A two-body frictional wear test. J Dent
Res 73(9):1546-53.
Wassell RW, McCabe JF, Walls AW (1994b). Wear characteristics in a two-body
wear test. Dent Mater 10(4):269-74.
White SN, Caputo AA, Li ZC, Zhao XY (1996). Modulus of rupture of the Procera AllCeramic System. J Esthet Dent 8(3):120-6.
Williamson RT, Kovarik RE, Mitchell RJ (1996). Effects of grinding, polishing, and
overglazing on the flexure strength of a high-leucite feldspathic porcelain. Int J
Prosthodont 9(1):30-7.
Wilson AD, McLean JW (1988). Glassionomerzement. Quintessenz, Berlin.
Wiskott HWA, Scherrer SS, Belser UC (2000). Ceramics: Elementary principles of
fracture and reinforcment. www.worlddent.com.
Zuellig-Singer R, Bryant RW (1998). Three-year evaluation of computer-machined
ceramic inlays: influence of luting agent. Quintessence Int 29(9):573-82.
85
13. Acknowledgments
I would like to express my deep thanks to Prof. Dr. J. R. Strub, Chair, Department of
Prosthodontics, Albert Ludwigs University, Freiburg, Germany for giving me the
opportunity to do research under his supervision, as well as for his revision of the
manuscript. I would also like to extend my gratitude to the Ministry of Higher
Education, Damascus, Syria for granting me a 3-year scholarship.
In addition, I would like to address my acknowledgments to the following persons ,
without whose help this thesis could not have been completed
Dr. C. F. J. Stappert, Department of Prosthodontics, Dental, School, Albert Ludwigs
University, Freiburg, Germany for the idea of this research project, his revision of the
research proposal and support during the whole study.
Dr. P. Hahn, Associate Professor, Department of operative Dentistry and
Periodontology , Albert Ludwigs University, Freiburg, Germany for her review of the
manuscript.
Company Ivoclar-Vivadent, Schaan, Liechtenstein for the fabrication of the test
samples.
Prof. Dr. H. F. Kappert, former Chair, Division of Dental Materials, Albert Ludwigs
University, Freiburg, Germany for his useful advise and help in carrying out the
fracture strength test.
Dr. S. Chitmongkolsuk for his support at the start of this research project and
guidance in operating the artificial oral environment.
Mr. T. Gerds, Institute of Medical Biometry and Medical Informatics, Albert-Ludwigs
University, Freiburg, Germany for doing the statistical analysis of the data.
I would add a special thank to my dear parents for their continuous moral and
financial support during all circumstances.
86
14. Curriculum vitae
Date of Birth:
March 31st, 1975
Place of Birth:
Damascus, Syria
Parents:
Mohammad Abdulhadi Att
Layla Zaki
Marital Status:
Single
Nationality:
Syrian
Education:
1989-1992
Secondary School, Damascus, Syria
1992
High school certificate by the special test arranged
by the Ministry of Education, Damascus, Syria
University:
1992-1997
Faculty of Dentistry, University of Techrin, Lattakia,
Syria
1997
Graduation from the Faculty of Dentistry (rated the
second among the best graduates for the year
1997
Further education: 1998
English language study at the American School,
Damascus, Syria
1998
TOEFL test in the American Language Center,
Damascus, Syria with a score of 607
1998-2000
Resident for specialization in the Department for
Oral & Maxillofacial Surgery, Teshreen Military
Hospital, Damascus, Syria
2000-2003
Postgraduate student, Department of
Prosthodontics, Albert Ludwigs University,
Freiburg, Germany, Program director:
Dr. R. Kohal, Associate Professor
2003-present Assistant Professor, Department of
Prosthodontics, Albert Ludwigs University,
Freiburg, Germany
Director: Prof. Dr. J. R. Strub