IN VITRO WEAR OF NINE CEMENTS AGAINST ENAMEL
By
MOHAMAD KYSON
JOHN O BURGESS, COMMITTEE CHAIR
JACK LEMONS
AMJAD JAVED
LANCE C. RAMP
A THESIS
Submitted to the graduate faculty of The University of Alabama at Birmingham, in partial
fulfillment of the requirements for the degree of Master of Science
BIRMINGHAM, ALABAMA
2013
Copyright by
MOHAMAD KYSON
2013
ii
IN VITRO WEAR OF NINE CEMENTS AGAINST ENAMEL
MOHAMAD KYSON
BIOMATERIALS
ABSTRACT
The objective of this study was to measure and compare in vitro wear resistance of nine
cements against human enamel cusps in glycerol media using UAB second generation wear
machine (hit and slide). Six cements were dual cured polymer-based cements; total-etch:
Variolink II (Ivoclar Vivadent), self-etch: Multilink Automix (Ivoclar Vivadent) and selfadhesives: Maxcem Elite (Kerr), RelyX Unicem 2 (3m ESPE), PANAVIA SA (Kuraray) and GCEM LinkAce (GC America). Three cements were water-based chemical cured cements; Zincphosphate: Harvard Cement (Harvard) and resin modified glass ionomers cements: RelyX
Luting Plus (3M ESPE) and GC FujiCEM 2 (GC America). Samples were scanned after wear
testing using a non-contact 3D profilometer (PROSCAN2000) to determine wear volume and
depth. 2-way ANOVA, separate 1-way ANOVA and Tukey/Kramer post-hoc tests (p≤0.05) for
the statistical significance.
iii
The only dual cured cement in this investigation that showed a statistical difference in the
wear as function of the curing modes was Maxcem Elite. Resin cements showed higher wear
resistance in this study than glass ionomer cements which showed higher wear resistance than
zinc phosphate cement (Harvard). There was a significant difference in two groups of the dual
cured cements of this study (G-CEM LinkAce, PANAVIA SA and RelyX Unicem 2) showed
higher wear resistance than (Maxcem Elite, Multilink Automix and Variolink II).
iv
DEDICATION
I lovingly dedicate this thesis to my great mother Dr. Najah Habeeb, who supported me
in every professional step in my life, for my dear grandmother for rasing me up and to my father
Nabieh Najim for the best childhood memories he gave me.
Also, this thesis is dedicated to my lovely wife Dr. Shayma Kyson for standing beside me
through thick & thin, I also dedicate it to our adorable sons Ammar & Zeyad who have been a
great source of motivation and inspiration.
Finally, this thesis is dedicated to my mentors Dr. John Burgess and Dr. Jack Lemons
whom I owe very much for all the guidance they showed me, the instructions they gave me and
the knowledge they shared with me.
v
ACKNOWLEDGEMENTS
My gratitude to the members of my dissertation committee, as previously mentioned Dr.
Lemons and Dr. Burgess, as well as Dr. Amjad Javed & Dr. Lance C. Ramp have generously
extended their time to help me professionally mature.
I am grateful to my senior Dr. Dave Kojic who became my best friend for the continuous
encouragement, for being an advice source for me professionally and socially and for the life
time memories we share.
vi
TABLE OF CONTENTS
Page
ABSTRACT ……………………………………………………………….………....…….....iii
DEDICATION …………………………………………………………….……………. ……v
ACKNOWLEDGEMENTS ……………………………………………….……………. ……vi
TABLES OF CONTENT ………………………………………………………..……... ……vii
LIST OF TABLES ……………………………………………………….……………………xi
LIST OF FIGURES …………………………………………………….……………..………x
INTRODUCTION …………………………………………………….………………………1
•
•
Literature Survey………………………………………….…………….................1
•
Objective………………………………………………….………………….........4
•
Hypotheses……………………………………………………...............................5
•
Specific Aims……………………………………………………...........................5
•
Data Analysis……………………………………………………...........................5
MATERIALS AND METHODS……………………………….…………………………6
•
Materials……………………………………………….……………………….....6
•
Specimen Preparation For Wear Testing……………….…………………………6
•
Premolar Preparation For The Stylus…………………..………………………….9
•
Wear Measurement…………………………………………………….................10
vii
•
RESULTS………………..……………………………………………………………..21
•
Data Presentation……………………………………………………………….21
•
Dual Cured Cements……………………………………………………………21
•
Curing Modes of Each Dual Curing Cement…………………………………...22
•
Cements Types……………………………………….…………………………22
•
DISCUSSION ………………………………………………………………………… 31
•
SUMMARY AND CONCLUSIONS…………………………………………………..32
•
LIMITATIONS………………………………………………………………………...34
•
SUGGESTIONS FOR FUTURE RESEARCH………………………………………..34
REFERENCES ……………………….……………………………..……….. …………...35
APPENDIX ………………………………………………………………………………..42
viii
LIST OF TABLES
Table
Page
•
Volume and depth wear data………………………………………………...23
•
Wear volume mean and standard deviation………………………….……...27
ix
LIST OF FIGURES
Figure
Page
1
Study Design………………………………………………………………….11
2
Specimen Molding, Light-curing & Storing………………………………….13
3
Specimen Embedding………………………………………………………....14
4
Specimen Polishing, Finishing & Cleaning……………………………….…..15
5
Premolar Grinding, Cusp Standardization & Polishing……………………….16
6
UAB Second Generation Wear Machine……………………………………...17
7
Specimen & Stylus in Wear Machine…………………………………………18
8
PROSCAN 2000………………………………………………………………19
9
PROSCAN Images at Baseline, After Wear Testing & Superimposition…….20
10
Wear Volume of Zinc-Phosphate, RMGIs & The Dual Cured Cements……...28
11
Wear Volume Magnitude For The Dual Cured Cements………………….......29
12
Wear Volume Magnitude For Both Curing Modes of The Dual Cements….....30
x
INTRODUCTION
Overview and Literature Survey
Dental cements are often classified on the basis of their components into water
and acid based systems such as zinc phosphate, zinc polyacrylate (polycarboxylate) and
glass ionomer. They contain metal oxide or silicate fillers embedded in a salt matrix.
Non-aqueous acid-based cements include zinc oxide eugenol and non-eugenol types.
These also contain metal oxide fillers embedded in a metallic salt matrix. The polymerbased systems include acrylate or methacrylate resin cements which has been sub
classified into self-etch, total-etch and the latest generation of self-adhesive resin cement
systems which contain silicate or other types of fillers in an organic resin matrix.
Cements can also be classified based on the type of their matrix; eg, phosphate (zinc
phosphate, silico phosphate), polycarboxylate (zinc polycarboxylate, glass ionomer
cement), phenolate (zinc oxide eugenol and ethoxybenzoic acid) and resins (polymeric)
[41].
1
Dental cements have been and are used to retain restorations to the prepared teeth,
to seal the marginal gap between the prosthesis and the finishing line on the tooth and
also, to interconnect (attach) any type prosthesis to the tooth structure or an implant
construct. It is also recognized that the cement surface exposed within the oral
environment may be subject to multiple changes over time and function. These include
wear, especially when it is used for inlays against enamel [1-4, 24]; resorption [5];
subsurface degradation [6]; marginal ditching [7]; and discoloration [8-10]. These
conditions including wear could make the tooth susceptible to caries [11], periodontal
disease [12] and altered prosthesis esthetics and these type changes could ultimately lead
to loss of the prosthesis [8-10, 13-16]. These situations are most significant if the cement
marginal gap region is larger and directly exposed to occlusion [43]. Despite of these
situations, loss of marginal integrity at the exposed cement region has not always been
related to the loss of clinical restorations [7, 8, 10, 13-15]. The wear of resin cements at
margins has been reported in some studies which showed that these did not directly
influence the survival rates of some indirect restorations [7]. In contrast, comprehensive
eight-year clinical evaluation of cemented ceramic inlays using scanning electron
microscope (SEM) analyses and 3D morphological measurements showed a relationship
to cement alterations and clinical outcome [28, 29]. Also, margins cracks of ceramic and
enamel reported from prospective clinical trials [13, 16] have been listed as the main
reasons for a decrease in marginal integrity.
2
Some studies used optical scanners [4, 29, 30] which allowed for more detailed
evaluations and interpretations of wear degradation and the processes occurring at
surfaces of dental materials subjected to wear.
Some recently introduced dental cements do not require pretreatment of the tooth
surface, hence this is proposed to reduce the technique sensitivity of placement
procedures. The resin cements are usually dual-cured systems including systems that can
be light-cured and/or self-cured [17]. Studies of these systems mainly, have considered
bond strength, marginal adaptation, microleakage, physico-mechanical properties and
adhesion [18, 23] while, the wear of dental cements have received minimal attention [36,
37]. This is especially important with the cements that have been recently introduced for
clinical applications.
Another aspect related to the wear of cements when contacted by enamel which
could be clinically important in the future is the possibility that the US Environmental
Protection Agency may further limit the use of amalgam restorations due to mercury
contamination related to concerns about disposal plus some issues about toxicity [25].
Alternatives to amalgam such as some polymeric dental composite systems have been
shown to exhibit shrinkage and marginal deterioration with time which could limit
longevity [26].
3
Also, some composite systems and techniques have demonstrated less than ideal
wear resistance, particularly along tooth to restoration regions of occlusion [32, 33],
difficulty in generating proximal contours and contacts [34] and some issues with
postoperative sensitivity [35]. Thus ceramic inlays especially chairside milled inlays that
are cemented into teeth are an important consideration for the future [27]. This focused
literature survey using showed that available data on the wear of cements are limited and
relatively inconsistent [31, 38] . Also, minimal emphasis has been given to the various
methods for curing the cements [39].
Objective
The central objective of this study was to evaluate the in vitro wear resistance of
selected cements. The assessment of wear for different types of the nine cements was
tested in vitro using human enamel cusps as an antagonist.
4
Hypotheses
1- The light cure mode of each dual cured resin cement has higher wear resistance
than its chemical cure mode.
2- Chemically cured dual cured resin cements wear resistance is comparable to each
other and have higher wear resistance than water-based controls.
Specific Aims
1. To compare the wear resistance of a variety of cements when tested against intact
human enamel cusps.
2. To evaluate the light cured versus the chemical cured modes of each dual cured
cement.
3. To compare the chemically cured modes of the dual cured resin cements with the
control cements.
Data Analysis
In consideration of the parametric data developed in this project plus council from
a biostatistician resulted in a joint decision to utilize ANOVA and Tukey/Kramer posthoc tests (a=0.05) for the statistical significance.
5
MATERIALS AND METHODS
Materials
The following nine cements were selected to compare relative properties of wear:
Self-adhesive resin cements; Maxcem Elite (Kerr), RelyX Unicem 2 (3M ESPE),
PANAVIA SA (Kuraray) and G-CEM LinkAce (GC America), self-etch resin cement;
Multilink Automix (Ivoclar Vivadent), total-etch resin cement; Variolink II (Ivoclar
Vivadent), resin modified glass ionomers cements; RelyX Luting Plus (3M ESPE), GC
FujiCEM 2 (GC America) and zinc-phosphate; Harvard Cement (Harvard). The details
about these nine cements and the machines/materials used for wear testing are provided
in Appendix 1.
Specimen preparation for wear testing
To prepare specimens, 3.5X magnification loupes and powder free gloves were
utilized throughout all of the procedures. A rectangular elastomeric impression material
mold (length, width and depth of 9, 7 and 4mm) was used to mold prepare and
standardize the size for the specimens. The overall study design is shown schematically
in (Fig. 1A, B). A mold was filled with the mixed cement and placed on a vibrator (low
speed) to minimize specimen porosity (Fig. 2A).
6
Eight specimens were made for each cement curing mode which included using
an incubator and an Elipar™ S10® curing light of circa 1200 mW/cm² illuminator (Fig.
2B). the usable wavelength range of the Elipar S10 LED curing light is 430 – 480 nm
with a center wavelength of 455 ± 10 nm. The spectrum of the Elipar S10 LED curing
light matched the absorption spectrum of the dual cured cements in this study.
Calibration of the S10 was done before each curing using a FieldMate®. The light
curing tip was placed directly on the sample with the operator wearing curing light
protective glasses (Zoom®) and using a curing light clean sleeve on the curing light tip.
Curing was done following the manufacturers’ instructions (Appendix 1). After curing
the top surface, the specimens were removed from the mold, the surface (air inhibited
layer) was removed with clean gauze, the sides and bottom surfaces of the rectangular
specimens were treated by light curing the same way as the top surface. The self cured
specimens were made in the dark inside an incubator. The specimens were individually
stored in sealed bags using moist napkins soaked with distilled water away from each
other at 37°C for 24 hours in an incubator (Fig. 2C).
The specimens were subsequently embedded in brass holders (d=15mm,
h=10mm) using a 1:2 ratio of liquid to powder acrylic, with 1mm of the sample
extending above the top of the wear machine brass holder (Figs. 3A-C).
7
The upper face of the specimen was positioned parallel to the rim of the brass
holder for polishing using 600 and 1200-grit SiC abrasive papers under copious tap
water. The specimen surfaces were finished with an alumina slurry and a cloth. The
method included four minutes for each sample, (one minute for each direction of the four
sides of the rectangular sample) for the 600 and 1200-grit papers and alumina slurry
finishing on a polishing cloth. Polishing and finishing was done on medium speed of the
rotational polishing device with light finger pressure.
New abrasive paper was used for each specimen and after one minute of the
polishing and finishing procedures, the specimens were rotated 90° clock-wise and placed
on a fresh inner concentric circle of the polishing paper and finishing cloth (Figs. 4A-C).
The final polishing direction along the abrasive papers for each sample was
oriented along the specimen width. This was done so that this polishing direction would
be perpendicular to the sliding path of the enamel antagonist within the wear machine.
Before using the alumina slurry polishing cloth, the cloth and supporting disc were
cleaned by hand washing in running water while held on the polishing stage during
rotation on high speed. The final polishing step was followed by rinsing with distilled
water for five seconds, and each specimen was sonicated in an ultrasonic machine (Fig.
4D) separately for five minutes using fresh distilled water for each specimen at a
temperature of 37°C.
8
Premolar preparation for the stylus
Intact extracted premolar teeth were selected without visible defects and the
enamel cusps were standardized for wear testing using Brasseler Sintered Diamond
S5030.11.050 bur, preparation was done without abrading the cusp tip (Fig. 5A). A new
bur was used for each cement curing mode group (n=8) and each bur was cleaned
ultrasonically in distilled water for two minutes after each use. Cusps were prepared
using a hand-piece set at 20,000 rpm for one minute each, with regular intervals of
dipping the cusp in distilled water for cleaning and to prevent the cusp tip alteration by
cutting or overheating (Fig. 5B).
The premolar teeth were subsequently reduced using a polisher-grinder with water
cooling from the root towards the standardized cusps, screws were embedded onto the
sectioned root side for mounting in the wear machine (Figs. 6 and 7) using acrylic. The
cusps were positioned so that the polished cusp tip was aligned parallel to the screw
center. The cusps were subsequently polished using pumice for one minute each with
slow-speed hand-piece and a rubber cup.
9
Wear Measurements
The second generation UAB wear machine (Fig. 6) (which includes a contact and
slide motion with fiberglass mounting cylinders to mimic the teeth movement within the
periodontium) was calibrated to a dead-load of 10N on each station. Load was applied to
the cement specimens through the enamel cusps. The testing media was a solution of
glycerol to water 1:3 (25% Glycerol) at a pH 6.3 and temperature of 24°C. The media
was renewed after each cement curing mode group (n=8), the wear machine was
programmed for 70 cycles/minute and 50,000 cycles.
After 50,000 cycles, the specimens were cleaned with dry paper towels, rinsed
with distilled water then subjected to light air drying. Specimens were examined visually
and scanned using a non-contact 3D surface profilometer and software (PROSCAN
2000®) (Fig. 8) of 0.1% accuracy to determine the wear depth and volume loss of each
cement specimen (Figs. 9A, B).
10
Water based
controls
Zinc-phosphate
RelyX Luting Plus
GC FujiCEM 2
8 chemical
cured
8 chemical
cured
8 chemical
cured
A
11
G-CEMLinkace
Panavia SA
RelyX Unicem 2
Dual Cured
Maxcem Elite
Multilink Automix
Variolink II
8 light
cured
8 chemical
cured
8 light
cured
8 chemical
cured
8 light
cured
8 chemical
cured
8 light
cured
8 chemical
cured
8 light
cured
8 chemical
cured
8 light
cured
8 chemical
cured
B
Fig. 1: schematics showing (A) Water base controls study design, (B) Dual cured
resin cements study design
12
A
B
C
Fig. 2: Images showing (A) molding, (B) light curing and (C) storing in incubator.
13
A
B
C
Fig. 3: Images showing embedding in UAB wear machine brass holder (A and B) and an
embedded sample (C).
14
A
B
C
D
Fig. 4: Images showing specimen (A) polishing, (B) finishing (C) polishing & finishing
direction and (D) ultrasonic cleaning.
15
A
B
C
Fig. 5: Images showing (A) grinding intact human premolar to the cusps (B) cusp
standardization and (C) cusp polishing.
16
Fig. 6: Image showing UAB wear, second generation machine.
17
Fig. 7: Image showing specimen mounted in the wear test machine for testing.
18
Fig. 8: Image showing the Proscan 2000 non-contact surface profilometer.
19
A
B
Fig. 9: Images of Proscan wear measurements showing (A) specimen surface
before wear cycles (upper) and after wear cycles (lower) and (B) superimposition the two
images to calculate wear volume and depth.
20
RESULTS
Data Presentation
The relative comparisons of the cement loss, measured by depth and volume
within the wear zone are summarized in (Table 1) and shown graphically in [Figs 11-13].
The volume and depth measurements presented in mm3 and µm respectively are listed for
each specimen and summarized as means with standard deviations (Table 1). The overall
data are summarized for the cements in (Table 2). The data shown in graphical format
[Figs. 11-13] presents comparisons between the systems as a function of material type
[Fig. 11] and mode of curing [Figs 12, 13].
Dual cured cements
The dual cured cements, Maxcem Elite showed the lowest wear resistance while
G-CEM LinkAce showed the highest wear resistance to machine induced wear against
enamel [Fig. 12]. A statistically significant difference (p<0.05) was found between the
dual cured cements (Multilink, Variolink II, Maxcem Elite) which showed less wear
resistance than (G-CEM LinkAce, PANAVIA SA, RelyX Unicem 2) [Fig. 12].
21
Curing modes of each dual cured cement
There was no significant difference (p>0.05) between the resin cements as a
function of curing mode of each cement except for Maxcem Elite which exhibited a
significant difference (p=0.01) when comparing the light cured and chemically cured
modes [Fig. 13].
Cements types
All the cements in this study showed a significant difference (p<0.05) when
compared to the control zinc phosphate [Fig. 10]. The dual cured resin cements also
showed a significant difference (p<0.05) when compared to the resin modified glass
ionomer chemical cured cements (FujiCEM 2 and RelyX Luting Plus) [Fig. 10].
22
Table 1: Volume and depth wear data
PANAVIA SA (Kuraray)
Light cured
G-CEM LinkAce (GC America)
Non-light cured
Light cured
Non-light cured
Volume
Depth
Volume
Depth
Volume
Depth
Volume
Depth
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
A
0.005
0.620
0.011
3.070
0.006
5.980
0.024
39.780
B
0.005
1.230
0.006
4.280
0.009
16.950
0.006
10.880
C
0.009
1.240
0.038
15.380
0.006
12.810
0.007
12.330
D
0.040
13.780
0.011
1.430
0.005
11.470
0.017
26.740
E
0.007
1.230
0.014
3.700
0.005
15.600
0.011
22.150
F
0.005
0.900
0.008
1.130
0.009
16.180
0.007
22.250
G
-
-
0.016
3.450
0.006
12.090
0.009
13.070
H
0.034
4.270
0.040
10.560
0.006
13.070
0.007
16.880
Mean
0.015
3.324
0.018
5.375
0.006
13.018
0.011
20.510
SD
0.015
4.770
0.013
4.979
0.001
3.483
0.006
9.591
23
RelyX Unicem 2 (3M ESPE)
Light cured
Variolink II (Ivoclar Vivadent)
Non-light cured
Light cured
Non-light cured
Volume
Depth
Volume
Depth
Volume
Depth
Volume
Depth
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
A
0.012
27.790
0.016
51.790
0.010
17.260
0.014
59.690
B
0.021
61.750
0.023
58.780
0.032
36.400
0.022
72.380
C
0.013
28.110
0.006
17.470
0.024
27.090
0.020
34.460
D
0.008
24.500
0.005
11.140
0.013
23.620
0.034
146.970
E
0.037
76.520
0.011
23.440
0.048
95.800
0.028
33.940
F
0.014
53.550
0.008
26.600
0.048
54.490
0.032
45.380
G
0.031
74.300
0.007
12.940
0.007
13.630
0.066
80.230
H
0.008
14.010
0.021
52.740
0.040
56.920
0.029
39.240
Mean
0.018
45.066
0.012
31.862
0.027
40.650
0.030
64.036
SD
0.010
24.400
0.007
19.459
0.016
27.430
0.015
37.743
24
Multilink (Ivoclar Vivadent)
Light cured
Maxcem Elite (Kerr)
Non-light cured
Light cured
Non-light cured
Volume
Depth
Volume
Depth
Volume
Depth
Volume
Depth
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
(mm3)
(µ)
A
0.048
62.500
0.065
106.340
0.038
73.900
0.073
122.390
B
0.029
47.780
0.041
79.250
0.019
56.320
0.059
99.060
C
0.038
61.340
-
-
0.058
102.190
0.043
58.720
D
0.043
61.010
0.050
75.140
0.073
94.850
0.075
129.170
E
0.020
45.210
0.048
110.650
0.034
72.480
0.045
59.450
F
0.020
44.560
0.026
63.270
0.017
29.310
0.089
160.550
G
0.019
52.330
0.035
87.340
0.027
37.840
-
-
H
0.062
82.700
0.021
70.010
0.063
86.550
0.109
108.090
Mean
0.034
57.178
0.040
84.571
0.041
70.305
0.070
105.347
SD
0.015
12.682
0.015
18.003
0.021
25.801
0.023
37.042
25
FujiCEM 2 (GC
RelyX Luting Plus
America)
(3M ESPE)
Self cured
Self cured
Zinc phosphate (Harvard)
Self cured
Volume (mm3)
Depth (µ)
380680
0.567
100.320
0.065
11.480
0.523
90.680
38.420
0.379
75.000
1.555
156.040
0.260
32.410
0.307
73.600
0.294
37.920
E
0.244
28.180
0.181
37.260
1.347
185.590
F
0.403
61.910
0.623
77.520
1.196
124.680
G
0.306
41.850
0.140
47.930
0.389
63.680
H
0.170
23.900
0.500
97.530
0.637
103.440
Mean
0.251
39.536
0.294
57.375
0.813
107.793
SD
0.078
13.539
0.194
28.136
0.479
47.601
Volume
Depth
Volume
Depth
(mm3)
(µ)
(mm3)
(µ)
A
0.235
56.980
0.160
B
0.154
32.640
C
0.238
D
26
Table 2: Wear volume mean and standard deviation
27
Fig. 10: Wear volume (mm3) of zinc-phosphate, self-cured RMGIs and both curing
modes of the dual cured dental cements
28
Fig. 11: Wear volume (mm3) magnitude for the dual cured cements
29
Fig. 12: Wear volume magnitude for both curing modes of the dual cured cements
30
DISCUSSION
Overall this study showed that zinc-phosphate cement was the least resistance to
wear within this simulation test, followed by the resin modified glass ionomers while the
resin cements had the highest resistance to wear which correlate with results in [31]. The
previous study of Kawai K, Isenberg BP, Leinfelder KF showed that the microfilled
cement exhibited less wear than hybrid cements. The smoother microfilled surface was
shown to provide a greater resistance to wear. The study results also showed a linear
relationship between horizontal gap and vertical cement dimensions due to wear loss. The
greater the interfacial gap, the greater the amount of wear [41].
Related to material structure and properties, dental cements polymerization is
started by light and/or by a chemical reaction of the initiator system. The setting reaction
is a radical dependent polymerization during which the single monomer molecules are
chemically cross-linked to form a three-dimensional polymer network. Simultaneously,
neutralization reactions take place, which are important for the long-term stability of the
set cement material. There is a linear correlation between the degree of conversion and
the plasticization of material [44], higher degree of conversion results in increased crosslinkage density of the polymeric matrix which is a major factor influencing the bulk
physical properties.
31
In general, the higher the degree of conversion, the greater the mechanical
strength [45]. The final degree of conversion depends on the chemical structure of the
cement and the polymerization conditions i.e., atmosphere, temperature, light intensity
and photo-initiator concentration [46]. Also, the biocompatibility of a cement has been
related to its degree of conversion and complaints from patients about sensitivity may be
due to incomplete polymerization of the cement [47, 48]. Thus, in general, physical and
mechanical properties have been shown to influence the wear of any material. In this
study, additional testing would be required to correlate structure versus wear property
relationships.
SUMMARY AND CONCLUSIONS
Samples processing of eight specimens for each curing mode of the nine cements
included using a mold on a vibrator, storing in the incubator for 24 hours to complete the
polymerization, mounting in the wear machine in brass holders using acrylic, polishing
on a rotational machine and ultrasonically cleaning in distilled water.
32
Intact human premolars were prepared by grinding to the cusps, processing the
cusp tips to standardized dimensions using a bur and polishing with pumice, mounting
with acrylic in the UAB second generation wear machine to act as antagonists using axial
screws, and testing in 25% glycerol media against the standardized dental cements
specimens for 50,000 cycles, with 10N dead loads and 75 cycles/minute.
A Proscan 2000 instrument was used after the wear testing to determine the wear
volume and depth. Two(2)-way ANOVA, separate 1-way ANOVA and Tukey/Kramer
post-hoc tests (a=0.05) was used for statistical analysis of the first for the two curing
modes of the dual cured resin cements and the second for the chemical cured modes of all
the cements in this study.
The only dual cured cement in this investigation that showed a statistical
difference (p=0.01) related to its curing mode was Maxcem Elite. Resin cements showed
higher wear resistance than glass ionomer cements which showed higher wear resistance
than zinc phosphate. There was a significant difference in two groups of the dual cured
cements and the zinc phosphate cement. Thus the investigation hypotheses were rejected
within the limitations of this project.
33
LIMITATIONS
Some limitations included a constant media (pH, viscosity, amount and
temperature) while the oral cavity is subjected to changes in temperature, changes in
saliva pH, viscosity and quantity of saliva. The machine produced a constant load and
direction while in vivo occlusal forces and movement varies for each patient. The media
in the machine was not circulated and filtered while during in vivo function there is saliva
circulation and clearance in oral cavity.
SUGGESTIONS FOR FUTURE RESEARCH
Some suggestions for future studies include the following. Conducting wear
testing on a machine that has the ability to circulate and filter the media to mimic salivary
flow during mastication in oral cavity could be a better simulation. Also, testing the
materials with standardized changes in temperature, pH, media, media viscosity and
media circulating speed would provide an opportunity to investigate these effects on the
wear resistance of the study cements.
34
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41
Appendix 1
Material
Manufacturer
Lot #
Expiry
Self Cured
Date
G-CEM
GC America
LinkAce
(Alsip, IL)
RelyX Unicem
3M ESPE (St.
2 Automix
Paul, MN)
Light
Cured
1205244
Not listed
4min
20sec
Box 466325
07-2013
20sec
6min
4min
10sec
Tube and
package
465917
Box,
09-2013
package and
tube 471886
Maxcem Elite
Kerr (Orange,
Box 4568232 10-2013
CA)
Tube
4579155
RelyX Luting
3M ESPE (St.
Box
08-2014
Plus
Paul, MN)
N442148
42
5min
Tube and
package
N436375
GC FujiCEM 2 GC America
(Alsip, IL)
Box and
12-2013
5min
06-2014
5min
Tube
1112141
PANAVIA SA
Kuraray
Box
America (New
0065AAA
York, NY)
Tube
0065AA
07-2014
Box
0067ABA
Tube
0067AB
Harvard
Harvard Dental
Powder Box
06-2014
1.5g : 1ml
ZincPhosphate
(Hoppegarten
and Bottle
90sec
Cement
Germany)
1111108
mixing
time
43
5sec
Liquid Box
04-2014
and Bottle
5min
1101111
setting
time after
mixing
Multilink
Ivoclar
R36511
09-2014
4min
30sec
Automix
Vivadent
Ivoclar
Catalyst
10-2014
1:1 ratio
10sec
Vivadent
Yellow
10sec
(Amherst, NY)
(210,A3)
mixing
High
time
(Amherst, NY)
Variolink II
Viscosity
R43895
Base Yellow
(210/A3)
Box R32649
Tube
R25428
44
3.5min
12-2013
08-2014
R34712
08-2014
Genie Heavy
Sultan
PVS
Healthcare
040925856
(Hackensack,
NJ)
Grinder
Wehmer
Corporation
(Lombard, IL)
Elipar™ S10
3M ESPE (St.
Paul, MN)
FieldMate
Coherent
(Santa Clara,
CA)
Cross Linked
(Chicago, IL)
Flash Acrylic
SiC abrasive
Mark V
papers and
Laboratory
45
04-2009
polishing cloth
(East Granby,
CT)
Rotational
Buhler (Lake
polishing
Bluff, IL)
device No:
233-0-1997
.05µ Gamma
Buhler (Lake
Alumina slurry
Bluff, IL)
No:40-6301080
Branson 1200
Branson
Ultrasonics (
Danbury, CT)
Glycerol
Acros Organics
(Fair Lawn,
NJ)
SensION pH
Hach Company
meter
(Loveland, Co)
Thermometer
Control
Company
46
(Friendswood,
TX)
PROSCAN
Scantron
2000
Industrial
Products Ltd.
(Taunton,
England)
NSK Z500
Brasseler
hand-piece and
(Savannah,
GA)
Sintered
Diamond
S5030.11.050
bur
47