SCIENTIFIC ARTICLE
Australian Dental Journal 2006;51:(2):162-169
Resin adhesion to caries-affected dentine after different
removal methods
V Sattabanasuk,* MF Burrow,† Y Shimada,‡ J Tagami,‡
Abstract
Background: Caries-affected dentine is the common
bonding substrate when treating a patient. At
present, there are many methods used for caries
removal. The aim of this study was to evaluate the
microtensile bond strength of two adhesives (Clearfil
Protect Bond and OptiBond Solo Plus Total-Etch) to
caries-affected dentine after three different caries
removal methods.
Methods: Extracted carious human third molars
were used and caries-affected dentine surfaces were
obtained from one of the three removal methods:
(i) round steel bur in a slow-speed handpiece;
(ii) Er:YAG laser; or (iii) 600-grit silicon carbide
abrasive paper. Each of the adhesives was used to
bond resin composite to the caries-affected dentine
according to the manufacturers’ instructions.
Hourglass-shaped specimens were prepared and
stressed in tension at 1mm/min. Data were analysed
using two-way analysis of variance and least
significant difference test.
Results: Clearfil Protect Bond showed significantly
lower bond strength than OptiBond Solo Plus TotalEtch after caries removal with round steel bur, but
the opposite was found for specimens treated with
silicon carbide abrasive paper. For laser-treated
dentine, no significant differences between the
adhesives were revealed.
Conclusions: Besides the differences in adhesives,
different caries removal methods seem to influence
resin adhesion to caries-affected dentine.
Key words: Bond strength, caries-affected dentine, smear
layer.
Abbreviations and acronyms: Er:YAG = erbiumdoped:yttrium-aluminium-garnet; LSD = least significant
difference; SEM = scanning electronic microscopic; SiC =
silicon carbide.
(Accepted for publication 8 July 2005.)
*Department of Conservative Dentistry and Prosthodontics,
Srinakharinwirot University, Bangkok, Thailand.
†School of Dental Science, The University of Melbourne, Victoria.
‡Cariology and Operative Dentistry, Tokyo Medical and Dental
University, Tokyo, Japan.
162
INTRODUCTION
The philosophy of caries removal and cavity
preparation has changed greatly in the last decade.
With the advent of effective adhesive systems and the
subsequent developments in minimal cavity design,
changes in the concepts of surgical removal of diseased
tooth now aim at conserving as much of the tooth as
possible.1 It is desirable that only the bacterialcontaminated, denatured, caries-infected dentine
should be completely removed, leaving the cariesaffected dentine which can be remineralized in a vital
tooth following restoration.1
The methods that are currently available to remove
carious dentine include mechanical rotary and
non-rotary techniques.2,3 Conventional techniques,
comprising rotary instrumentation and dental burs, are
routinely used in clinical practice and very useful for
removal of caries. Recently, the use of lasers for dental
applications as an alternative to rotary instrumentation
has been proposed. The erbium-doped:yttriumaluminium-garnet (Er:YAG) laser has been reported to
be a promising technique for dental treatment, including
surgical ablation of diseased tooth structure.4-7 Under
scanning electron microscopic observation, previous
studies have shown that these two caries removal
techniques resulted in different caries-affected dentine
surfaces. Laser-treated dentine surfaces exhibited patent
dentinal tubules without smear layer production,5,6
whereas a prominent smear layer with dentinal tubule
occlusion occurred after the use of a round steel bur.8
The differences in surface characteristics of dentine
after caries removal might be a factor that influences
the bonding of adhesive resins.
Several laboratory studies have been performed using
silicon carbide abrasive paper for preparing the cariesaffected dentine.9-11 Oliveira et al.12 demonstrated that a
dentine surface prepared using 600-grit silicon carbide
abrasive paper was covered with a relatively thin smear
layer, which was easily removed prior to the application
of bonding resin. The thin smear layer was suspected to
have influenced the resin bonding to caries-affected
dentine and contributed to a favourable outcome,
especially for the self-etch system.11 To investigate
whether the differences in the various caries removal
Australian Dental Journal 2006;51:2.
methods could influence the adhesion to caries-affected
dentine, microtensile bond strengths and bonded
interface structures of two adhesives, a self-etch system
and an etch-and-rinse system, were evaluated. The
hypotheses proposed were, firstly, adhesive resins bond
equally well to caries-affected dentine, irrespective of
the removal method. Secondly, there is no difference in
bond strengths between the adhesive resins bonded to
caries-affected dentine.
MATERIALS AND METHODS
Forty extracted human third molars with occlusal
carious lesions extending approximately half-way
between the enamel-dentine junction and pulp chamber
were collected and used within approximately six
months of extraction. The teeth were obtained from the
patients who required an extraction as a routine part of
their treatment. Tissue remnants were removed and the
teeth were stored at 4°C in saline solution containing a
few crystals of thymol until used.
Specimen preparation
The caries lesion was exposed by removing the
occlusal enamel and superficial dentine using a slowspeed diamond saw (Isomet; Buehler, Lake Bluff,
Illinois, USA) under water lubrication. The teeth were
randomly allocated to three groups according to the
three different caries removal methods. In the first
group, the carious tissue was mechanically removed
using a round carbon-steel bur (ISO #310 204 018;
Hager & Meisinger, Neuss, Germany) mounted in a
contra-angle slow-speed handpiece with air as the
coolant.13 For the laser-treated group, an Er:YAG laser
(Elfine 400; Osada Electric, Tokyo, Japan) was used
with water cooling. An output energy of 180mJ was
used to treat the caries lesion with a repetition pulse
rate of 2Hz. These parameters were reported to be safe
in a clinical study showing the risk of thermal damage
to the tooth was very low.7 The laser beam was
delivered perpendicularly to the dentine surface in a
non-contact irradiation mode. For the last group,
grinding was performed using wet 600-grit silicon
carbide (SiC) abrasive paper on a table-top polishing
machine (Ecomet 4; Buehler, Lake Bluff, Illinois, USA)
to remove the infected carious dentine.
Fig 1. Schematic illustration of specimen preparation procedures.
Carious tissue was excavated using one of the three
methods and guided by the combined criteria of visual
inspection and numerical values from a laser
fluorescence device (DIAGNOdent; KaVo Dental,
Biberach, Germany) until they decreased to
approximately 20.14,15 This resulted in an apparently
hard caries-affected dentine surface and slight
discolouration of the dentine observed in all specimens
(Fig 1). After preparation, the teeth were rinsed with
distilled water for 30 seconds. The exposed dentine
surfaces were bonded with one of the adhesives listed in
Table 1. Each of the adhesives was used according to
the manufacturers’ instructions. A block of resin
composite (Clearfil AP-X; Kuraray Medical, Okayama,
Table 1. Materials, manufacturers, batch numbers, system compositions and bonding procedures
Material
Batch number
Compositions
Procedures
Clearfil Protect Bond
(Kuraray Medical,
Okayama, Japan)
Primer: 00004A
MDP, MDPB, HEMA, hydrophilic
dimethacrylate, water
MDP, Bis-GMA, HEMA, hydrophobic
dimethacrylate, photoinitiator, silanated
colloidal silica, surface treated NaF
37.5% phosphoric acid, water, silica
thickener, dye colourant
Bis-GMA, GDM, GPDM, HEMA,
ethanol, barium glass, sodium
hexafluorosilicate
Apply 20s; air dry
OptiBond Solo Plus
Total-Etch
(Kerr, Orange,
California, USA)
Bond liquid: 00008A
Etchant: 204742
Bond liquid: 209467
Apply and air thin; light cure 10s
Etch 15s; rinse 15s; blot with damp lint-free
paper, leaving the surface visibly moist
Apply 15s with light brushing motion;
air thin; light cure 20s
Bis-GMA = bis-phenol A diglycidylmethacrylate; GDM = glycerol dimethacrylate; GPDM = glycerophosphate dimethacrylate; HEMA = 2-hydroxyethyl methacrylate; MDP = 10-methacryloyloxydecyl dihydrogen phosphate, MDPB = 12-methacryloyloxydodecylpyridinium bromide.
Australian Dental Journal 2006;51:2.
163
Table 2. Comparison of mean microtensile bond strengths±SD (MPa; n=10)
Removal method
Steel round bur
Er:YAG laser
600-grit SiC paper
Adhesive
Clearfil Protect Bond
OptiBond Solo Plus Total-Etch
12.2±3.1a,c
32.5±7.1a,c
35.4±9.7a,c
21.3±7.5b,c
26.6±9.4b,c
25.7±5.9b,c
Mean values identified with the same superscript letters are not statistically different (p>0.05).
Japan) was built up on the treated surface in three
1mm-in-thick increments, with each increment light
cured for 40 seconds. Light-curing was done using a
quartz-tungsten halogen curing unit (Candelux;
Morita, Tokyo, Japan) with a light output not less than
550mW/cm2. The teeth were marked so as to locate the
bonded caries-affected dentine site, so that when the
teeth were sectioned for specimen production for
microtensile bond test, cuts could be made to include
the lesion, and then stored in distilled water at 37°C for
24 hours (Fig 1).
Bond strength testing
After storage, the teeth were sliced into slabs,
approximately 0.7mm thick, using a slow-speed
diamond saw under water cooling. One to three slabs
containing bonded caries-affected dentine specimens
were obtained from each tooth depending on the size of
caries lesion. The slabs of bonded caries-affected
dentine were trimmed to form a gentle curve with the
narrowest portion located along the adhesive interface
using a cylindrical superfine-grit diamond bur (SF114:
ISO #158 504 013; Shofu Inc., Kyoto, Japan) in highspeed handpiece. The resultant hourglass-shaped
specimens had an average rectangular cross-sectional
area of 0.50±0.04mm2 at the bonded interface. Ten
specimens were obtained for each group. Specimens
were attached to the testing apparatus with a
cyanoacrylate glue (Zapit; DVA, Corona, California,
USA). A tensile stress was applied with a universal
testing machine (EZTest; Shimadzu Co., Kyoto, Japan)
at a crosshead speed of 1mm/min (Fig 1). The maximum
stress at failure was recorded and converted to MPa.
Scanning electron microscopic (SEM) evaluations
After bond strength testing, the fracture surfaces of
all specimens were sputter-coated with gold and
examined using a SEM (JSM-5310LV; JEOL, Tokyo,
Japan) to determine the mode of failure. The SEM
pictures were transferred to the computer, and the
surface areas of different modes of failure (adhesive
failure, cohesive failure in dentine, and cohesive failure
in resin) were identified and measured using image
analysing software (SemAfore; JEOL Skandinaviska,
Sollentuna, Sweden).
An additional six teeth were prepared for SEM
observations. The caries-affected dentine was prepared
as previously described. To observe the etching
characteristics of these dentine surfaces, the acidic
primer of Clearfil Protect Bond or phosphoric acid of
164
OptiBond Solo Plus Total-Etch was applied to the
surface as recommended by the manufacturer. After
each application time, the monomer components of the
acidic primer were removed by rinsing the specimens
with ethanol for five minutes and placed in distilled
water for a further five minutes,16 whereas the
phosphoric acid gel was flushed with water for 15
seconds. The specimens were fixed in 10 per cent
neutral buffered formalin for 24 hours and washed in
running water for 15 minutes, then dehydrated in
ascending concentrations of ethanol and water up to 90
per cent ethanol and placed in 100 per cent ethanol
three times, for 20 minutes each. The dehydrated
specimens were immersed in hexamethyldisilazane
solution for 30 minutes, placed on a filter paper inside
a covered glass vial, and dried at room temperature.17
The specimens were gold sputter-coated and observed
using SEM.
For the observation of resin-dentine interface, the
bonded teeth were prepared as for the bond strength
measurement. After overnight storage in 37°C distilled
water, a shallow groove was prepared using diamond
disc in a slow-speed handpiece under copious water
across the surface of resin composite and on the dentine
side over the area where the bonded caries-affected
dentine was located. The specimens were fixed and
dehydrated as described above, then fractured along
the prepared groove.18 The fractured specimens were
sputter-coated with gold and observed using SEM.
Statistical analysis
The mean and standard deviation of the tensile bond
strength were calculated for each group. The data were
analysed by two-way analysis of variance and least
significant difference (LSD) test at the 95 per cent level
of confidence. The chi-square test was used to analyse
the non-parametric failure mode data. All statistical
analyses were processed using the statistical software
system (SPSS 11.0 for Windows; SPSS Inc., Chicago,
Illinois, USA).
RESULTS
The results for the bond test are summarized in
Table 2. For Clearfil Protect Bond, the highest bond
strength was achieved after caries removal with 600-grit
SiC paper. This value was statistically higher than the
group bonded with OptiBond Solo Plus Total-Etch
using the same removal method (p=0.006), but not
different from that with laser-treated dentine bonded
with the same adhesive (p=0.386). The lowest value
Australian Dental Journal 2006;51:2.
Table 3. Results of failure modes as a percentage of the total bonding area (n=10)
Clearfil Protect Bond
Removal method
Steel round bur
Er:YAG laser
600-grit SiC paper
Adhesive failure
39
21
8
OptiBond Solo Plus Total-Etch
Cohesive failure
Dentine
Resin
32
29
49
29
50
43
Adhesive failure
16
22
10
Cohesive failure
Dentine
Resin
5
21
19
79
57
71
No statistically significant differences were observed among the groups (p>0.05).
was obtained after caries removal with a round steel
bur. Significant differences were determined both for
caries removal methods (p<0.001) and between the
adhesives (p=0.009). For OptiBond Solo Plus Total-Etch,
statistical analyses failed to show significant differences
between bond strengths derived from any of the caries
removal methods (p>0.05). Among the caries removal
methods, statistical similarity of bond strengths
between adhesive materials was noted only for the
laser-treated group (p=0.084).
Table 3 presents the failure mode patterns as a
percentage of the total bonding area. No statistically
significant differences were observed among the tested
groups (p>0.05). However, on closer inspection, there
was a slight decrease in the areas of adhesive failure for
OptiBond Solo Plus Total-Etch compared with Clearfil
Protect Bond after caries removal with a round steel bur.
SEM observations revealed that the acidic primer of
Clearfil Protect Bond could not effectively condition
the dentine surface after caries removal with the round
Fig 2. SEM photographs of specimens after caries removal with steel round bur. (A) Acidic primer treated dentine surface. There is still residual
smear layer on the dentine surface with dentinal tubules remaining occluded with smear plugs. (B) Resin-dentine interface created by Clearfil
Protect Bond. Poor adaptation to the underlying dentine with gap formation is observed along the bonded interface (pointers). No clearly
visible hybrid layer can be detected. (C) Phosphoric acid treated dentine surface. The smear layer on the dentine surface and smear plugs in the
dentinal tubules are partially removed. Exposed collagen fibril network can be noticed in some areas. (D) Resin-dentine interface created by
OptiBond Solo Plus Total-Etch. The fractured specimen shows the resin-infiltrated zone, approximately 5µm thick (arrows), with numerous
porosities being observed.
Australian Dental Journal 2006;51:2.
165
Fig 3. SEM photographs of specimens after caries removal with Er:YAG laser. (A) Acidic primer treated dentine surface. The surface is generally
free of smear layer, accompanied by open dentinal tubules. Micro-irregularities and micro-cracks are observed throughout the surface.
(B) Resin-dentine interface created by Clearfil Protect Bond. Good adaptation of the bonding resin to the underlying dentine is apparent. No
clear hybrid layer is observed. The bonding resin has penetrated into the microfissures (arrowheads). Mineral crystals in the dentinal tubules are
fixed with the infiltration of bonding resin (pointer). (C) Phosphoric acid treated dentine surface. Lack of smear layer with open dentinal
tubules is also observed. The intertubular dentine and peritubular dentine seem to be slightly etched with the phosphoric acid. (D) Resin-dentine
interface created by OptiBond Solo Plus Total-Etch. The bonding resin has adapted well to the conditioned dentine surface, and there is no
clearly distinguishable hybrid layer.
steel bur. A thicker smear layer remained on the dentine
surface and smear plugs in the dentinal tubules were
still clearly observed (Fig 2A). No clear hybrid layer
was detected in the fractured specimen (Fig 2B). In
contrast, phosphoric acid used on OptiBond Solo Plus
Total-Etch could better remove the smear layer and
plugs, but not completely (Fig 2C). The fractured
specimen exhibited a resin-infiltrated zone
approximately 5µm thick but the penetration of resin
was not complete. Numerous porosities could be seen
throughout the resin-infiltrated zone (Fig 2D). For
laser-treated specimens, after the application of both
acid conditioners, all the surfaces were free of smear
layer and the dentinal tubules were open. Peritubular
dentine was more conspicuous than intertubular
dentine. Micro-cracks were clearly observed throughout the surface (Figs 3A and 3C). The intertubular
dentine and peritubular dentine seemed to be more
etched with the use of phosphoric acid (Fig 3C). Both
166
adhesives showed good adaptation to the underlying
dentine. No distinguishable hybrid layers were
observed in the fractured specimens (Figs 3B and 3D).
For caries-affected dentine exposed using SiC paper, the
collagen fibril network of intertubular dentine was
clearly perceived after the application of both acidic
primer and phosphoric acid. The acidic primer of
Clearfil Protect Bond could effectively dissolve the
smear layer on the dentine surface, partially exposing
the collagen fibril network, but leaving residual
smear plugs within the dentinal tubules (Fig 4A). The
fractured specimen showed intimate contact between
the bonding resin and dentine, with approximately
1µm-thick of hybrid layer was discerned (Fig 4B). With
the use of phosphoric acid, the smear layer on
the dentine surface and smear plugs in the
dentinal tubules were completely removed (Fig 4C).
The thickness of the resin-infiltrated zone was
approximately 5µm (Fig 4D).
Australian Dental Journal 2006;51:2.
Fig 4. SEM photographs of specimens after caries removal with silicon carbide abrasive paper. (A) Acidic primer treated dentine surface. The
smear layer on the dentine surface is removed, but there are still remnants of smear plugs within the dentinal tubules. (B) Resin-dentine
interface created by Clearfil Protect Bond. The fractured specimen shows intimate contact between adhesive resin and dentine. The resininfiltrated zone is about 1µm thick (arrows). (C) Phosphoric acid treated dentine surface. Both smear layer and smear plugs are completely
removed, showing patent dentinal tubules with peritubular collagen fibril network and intertubular microporosities. (D) Resin-dentine interface
created by OptiBond Solo Plus Total-Etch. The resin-infiltrated zone is approximately 5µm thick (arrows). Minute porosities occur throughout
the resin-infiltrated zone. The lumen of dentinal tubule is occupied by mineral crystals that interfere with the penetration of bonding resin
(pointer).
DISCUSSION
Most laboratory bonding studies prepare the dentine
surfaces with a 600-grit SiC paper,9-11 whereas this
preparation technique could not be practical clinically.
However, the use of SiC paper creates a uniform surface
and smear layer that does not closely resemble those
created under clinical situations. As noted, a dentine
surface prepared with SiC paper is covered with a
relatively thin and loose smear layer.12 Therefore, resin
adhesion is unlikely to be affected by the presence of
this smear layer. In the present study, highest bond
strengths were achieved after caries removal with SiC
paper compared with the other methods. However, the
presence of acid-resistant mineral crystals in the tubules
of caries-affected dentine has been reported to prevent
the accomplishment of resin tag formation.9-11 The use
of an etch-and-rinse adhesive system or the additional
utilization of phosphoric acid prior to the application
of bonding resin was claimed to solve this problem by
Australian Dental Journal 2006;51:2.
effectively removing the mineral deposits in the
dentinal tubules.9-11 Surprisingly, the result of this study
demonstrated that, after caries removal with SiC paper,
the self-etch adhesive presented significantly higher
bond strengths than the etch-and-rinse adhesive. The
reason for this result is unclear, although it has been
stated that there is the possibility that there could be
some chemical bonding to the calcium at the tooth
surface when the self-etch adhesive is used.19 It would
appear that phosphoric acid was unable to completely
remove all mineral crystals precipitated in the dentinal
tubules, hence the formation of resin tags might still be
impeded or poorly formed and thus not helpful in the
resin adhesion. The 37.5 per cent phosphoric acid
supplied with OptiBond Solo Plus Total-Etch has been
demonstrated to produce one of the deepest levels of
dentine demineralization.20 The employment of this
aggressive conditioner might cause over-etching
because the caries-affected intertubular dentine already
167
has a reduced mineral content that may lead to
incomplete infiltration of the bonding resin.
In contrast to the caries removal with SiC paper,
caries-affected dentine exposed using the round steel
bur was covered with a rather dense and thick smear
layer, with dentinal tubules being occluded by dense
smear plugs.8 In this study, the SiC paper on the
polishing machine used a speed of 50rpm with water
lubrication but, during bur preparation, air was used
instead of water as the coolant in order to permit
adequate vision of the area being operated on.13
Therefore, heat generated and speed of the rotary
instrument may have caused the compaction of dentine
debris over the surface and into the dentinal tubules
that probably is not easily removed. The mild acidic
primer of Clearfil Protect Bond seemed too weak to
etch through this smear layer, hence there was little
penetration of resin beyond the smear layer into the
underlying dentine matrix to form a resin-infiltrated
zone, resulting in the low bond strength. The use of
phosphoric acid was better able to remove the smear
layer and smear plugs. Even though residual dentine
debris was observed, exposure of the collagen fibril
network was evident in some areas and was likely to
facilitate the infiltration of bonding resin. Higher bond
strengths and a decreased tendency of adhesive failure
after testing were observed for the specimens bonded
with OptiBond Solo Plus Total-Etch.
It has been accepted that a dentine surface treated
with Er:YAG laser is generally free of smear layer, thus
eliminating any hindrance to the adhesion.5,6 However,
the superficial layer of laser-treated dentine,
approximately 5µm thick, was transformed to a zone
where the collagen fibrils were completely melted
and/or vapourized.5,6 This feature has been claimed to
interfere with resin adhesion if the laser-treated dentine
surface was not conditioned prior to the application of
a bonding resin.6 The use of either acidic primer or
phosphoric acid seemed capable of removing this
surface laser-modified layer. Furthermore, regarding the
dentine surface topography after irradiation, the
Er:YAG laser increases the free surface energy and
surface roughness21 that may affect the degree of
mechanical anchorage, as the bonding resin could
infiltrate into the micro-irregularities in the lasertreated dentine. These micro-irregularities have been
reported to occur due to the thermomechanical
ablation process of the Er:YAG laser that causes the
micro-explosions in areas of high water concentrations
and on the hydrated part of hydroxyapatite.6 With
respect to SEM observations, the resin-infiltrated zones
were difficult to distinguish, which is in agreement with
previous studies.5,22 The extent of laser treatment has
also been reported to extend deeply into the subsurface
intertubular dentine in which the collagen fibrils were
most likely denatured by the heat generated.6 These
partially denatured collagen fibrils could not be easily
removed by etching agents and might affect the resin
infiltration.6 This provides one explanation as to why
168
the resin-infiltrated zone could not be observed in the
laser-treated specimens.
One limitation of this study was the diagnostic
methods used for caries detection that combined visual
inspection and measurements with a DIAGNOdent.
Even though the laser fluorescence device has been
shown to provide high validity for fissure caries
detection,14,15 application for the detection of residual
caries during excavation is still unclear.15 The use of
other methods to determine the extent of remaining
carious dentine may have provided greater validation
for this study. However, the application of a cariesdetecting liquid to laser-treated dentine requires some
caution. Laser irradiation results in some denaturing of
the superficial dentine that has been reported to stain
pink, even after all the caries-affected dentine has been
removed.5 This would probably lead to a false positive
diagnosis and, subsequently, to overtreatment and
overcutting of the dentine. Further studies evaluating
the extent of caries removal with Er:YAG laser by the
use of caries-detecting solution are needed.
Within the limitations of this laboratory study, both
null hypotheses were disproved. For the first hypothesis,
a similarity in bond strengths among three caries
removal methods was determined only for the cariesaffected dentine bonded with OptiBond Solo Plus
Total-Etch. Clearfil Protect Bond showed significantly
lower bond strength after caries removal with round
steel bur compared with other two removal methods.
For the second hypothesis, only the caries-affected
dentine exposed using Er:YAG laser showed
statistically similar bond strengths between the two
adhesives. OptiBond Solo Plus Total-Etch showed
significantly higher bond strengths than Clearfil Protect
Bond after caries was removed with the round steel bur.
However, the opposite was found for specimens treated
with SiC paper. It would seem that, besides the
differences in adhesives used, the differences in caries
removal methods could influence the bonding of resins.
The smear layer and smear plugs left following caries
removal methods might contribute to the success or
otherwise of resin adhesion to caries-affected dentine.
ACKNOWLEDGEMENT
This work was funded by a grant from the Centre of
Excellence Program for Frontier Research on
Molecular Destruction and Reconstruction of Tooth
and Bone at Tokyo Medical and Dental University.
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Address for correspondence/reprints:
Dr Vanthana Sattabanasuk
Department of Conservative Dentistry and
Prosthodontics
Faculty of Dentistry
Srinakharinwirot University
Sukhumvit 23, Wattana
Bangkok, Thailand
Email: mengvanthana@hotmail.com
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