Australian Journal of Basic and Applied Sciences, 6(3): 686-694, 2012

ISSN 1991-8178

Effect of Simulated Gastric Juice on Surface Characteristics of Direct Esthetic

Restorations
1
Dalia Yehia Ibrahim Zaki, 2Esmat Mahmoud Aly Hamzawy, 3Sahar Abd El Halim, 3Mohamed
Ahmad Amer
1
Department of Restorative and Dental Materials researches, National Research Centre, Cairo- Egypt.
2
Department of Glass, National Research Centre, Cairo- Egypt.
3
Misr University for Science and Technology, Department of Operative Dentistry, Cairo- Egypt.
4
Length and Precision Engineering Division, National Institute for Standards, Ministry of Scientific
Research.

Abstract: The aim of this study was to investigate the proper direct esthetic restorative materials to be
used for bulimia nervosa patients. Therefore the effect of simulated gastric juice on the microhardness
and surface roughness of five direct esthetic restorative materials was investigated. Simulated gastric
juice was prepared and adjusted to pH 3.8. Sixty specimens of each restorative material, including a
microhybrid composite resin, a nanofilled composite resin, a low shrinkage composite resin, a
conventional glass ionomer, and a nanofilled glass-ionomer restorations, were prepared and divided
into three groups (n=20). One group was immersed in distilled water (control), the second and third
groups were immersed in the simulated gastric juice for 6 hours and 12 hours respectively. Each group
was further subdivided into two groups (n=10), for surface topography characterization and for
microhardness evaluation. Energy dispersive X-ray microanalysis and scanning electron microscopic
analysis of selected samples were performed. Data were analyzed using 2-way analysis of variance and
Tukey’s post-hoc test. For all the tested materials, there was a statistically significant increase in mean
Ra and decrease in mean microhardness after immersion in simulated gastric juice compared with the
control groups. KetacTMN100 after immersion for 6 hrs and 12 hrs showed the statistically significantly
highest mean Ra values and lowest microhardness values, while FiltekTMZ350 showed the statistically
significantly lowest mean Ra values and highest microhardness values. It was concluded that
nanofilled composite resin was the most suitable material for restoration in patients suffering from
bulimia nervosa.

Key words: Bulimia nervosa; simulated gastric juice; microhybrid composite resin; nanofilled
composite resin; low shrinkage composite resin; conventional glass ionomer
restoration; nanofilled glass-ionomer restoration; Atomic force microscopic analysis;
Vickers microhardness; Energy dispersive X-ray microanalysis.

INTRODUCTION

Bulimia nervosa (BN) is an eating disorder characterized by episodic binge eating and the practice of
inappropriate purging behaviors such as self-induced vomiting, misuse of laxatives and diuretics, and excessive
exercise (Russo et al, 2008). BN together with anorexia nervosa is among the most serious diseases affecting
female teenagers and persons engaged in sports that emphasize thinness for performance or appearance (Russo,
2003 and Dynesen et al 2008). Bulimic behaviors have been reported to be prevalent in 10% to 20% of all
university women, and in 8% to 20% of high-school girls (Emans, 2000). A longitudinal survey of college
freshmen women demonstrated that the incidence of BN was 4.2 new cases per 100 women a year. Data on
large cohorts has revealed that the prevalence of bulimic behaviors that include vomiting ranges from 4.8% to
12.5% (Walter, 2002).
Persons with BN often tend to hide their disease and avoid professional help (Russo et al, 2008, Becker et
al, 1999 and Dynesen et al, 2008). Oral symptoms related to bulimia nervosa that have been described in case
reports, descriptive studies, and case-control studies; include enamel erosion, dental caries, dental pain,
increased levels of cariogenic bacteria, reduced saliva secretion, decreased salivary pH (Yager et al, 2005,
Spear, 2009, Philipp et al, 1991 and Touyz et al, 1993) . However, dental complications due to eroding effects
of maxillary anterior teeth and usually the maxillary first premolars which is known as perimolysis, are
objective signs of BN (Altshuler et al, 1990 and House et al, 1981).
According to Giovanni et al; BN patients are classified according to frequency of self induced vomiting into
three groups defined as minimum (twice a week = infrequent vomiting group), moderate (3–7/week= moderate

Corresponding Author: Dalia Yehia Ibrahim Ahmed Zaki, Department of Restorative and Dental Materials researches,
National Research Centre, Cairo- Egypt.
E-mail: daliasaniour@yahoo.com
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vomiting group), or severe (>7/week= heavy vomiting group). The average pH upon analysis of gastric contents
of bulimic patients is about 3.8 (Brady, 1985 and Bartlett & Coward, 2001).
The literature on dental treatment of bulimic patients is restricted to case reports of restoration of the
damaged surfaces with porcelain-laminated veneers, dentin-bonded crowns with minimal tooth preparation,
resin composite and complete–coverage restorations (Walter, 2002, Spreafico, 2010, Bonilla et al 2001,
Schunke & Schlee, 2006, Van Roekel, 2003, Broliato et al, 2008 and Reis et al 2009).
Nowadays, there are many modern composite resins and glass ionomer restorations developed for highly
esthetic procedures, where little preparation is required, and do not require laboratory collaboration.
Additionally, all functional, biological, and esthetic demands are successfully met in a very short period of time.
Limited studies have been conducted to investigate the proper direct esthetic restorative materials to be used
for BN patients. Therefore; the purpose of this study was to elucidate influences of simulated gastric juices on
surface characteristics of different direct esthetic restorative materials.

MATERIALS AND METHODS

The effect of simulated gastric juice, together with distilled water as a control on three types of composite
resin and two types of glass ionomer restorative materials, was investigated. The materials studied were
microhybrid composite resin, nanofilled composite resin, low shrinkage composite resin, conventional glass
ionomer, and nanofilled glass-ionomer restoration. The details of these materials are given in table 1.

Preparation of Simulated Gastric Juice:

For the preparation of simulated gastric juice, pepsin was suspended in sterile saline (0.85% NaCl, w/v) to a
concentration of 10 g/L. the pH was adjusted to 3.8 with sterile 1 M HCl using a pH meter (State
Pharmacopoeia Committee of the People’s Republic of China, 2005 ).

Study Design:
Sixty specimens of each restorative material were fabricated; 12 mm in diameter and 2 mm in thickness
using a split polytetrafluoroethylene matrix. Specimens were equally divided into three groups (n=20). One
group was immersed in distilled water (control); the second and third group was immersed in the simulated
gastric juice for 6 hours and 12 hours respectively. Each group was fatherly subdivided into two groups (n=10),
for surface topography characterization and for microhardness evaluation. The immersion time is the equivalent
of 2 and 4 years exposure to gastric juice respectively, with vomiting frequency = 7/weak representing the
moderate or heavy vomiting group (Abbate-Daga et al, 2005). The minimal estimated contact time of gastric
juice with restorations = 30 seconds (Table 2). Immersion was done at 37°C in polyethylene containers, and the
prepared gastric juice was changed regularly every one hour.

Specimens Preparation:
Specimens were fabricated according to the manufacturers’ instructions. The molds were positioned on a
transparent plastic matrix strip lying on a glass plate. The molds were then slightly overfilled with the material,
covered with a plastic matrix strip and pressed flat with a microscopic glass slide to extrude the excess material
and to provide a smooth and flat surface. Specimens of the three types of composite resins and KetacTM N100
restorative materials were light-cured through the glass plate using a halogen LCU (Ultralux; Dabi Atlante SA).
Curing time was 40 seconds (20 s over the glass plate and 20 s without the glass plate).
For the Ketac Fil Plus specimens, the material was mixed in accordance with the manufacturer’s direction,
prepared as previously described, and left undisturbed for 8 min. Following removal of the plastic matrix strip,
the surface of Ketac Fil Plus specimens were coated with a protective varnish (Ketac Glaze, 3M ESPE AG,
Seefeld, Germany) recommended by the manufacturer. The cured specimens were removed then stored in
distilled water at 37 °C for 24hours to ensure complete polymerization. After storage, all the specimens were
polished by the same operator using medium, fine, and superfine discs (Sof-Lex, 3M ESPE, MN, USA) rotating
in one direction. The polished specimens were cleaned in distilled water in an ultrasonic cleaner for 1 min to
remove any debris, and then specimens were blotted dry with tissue paper before immersion and examination.

Surface Topography Characterization:

Atomic force microscopic (AFM) observation and the average surface roughness (Ra) of the control and
treated surfaces were performed using AFM (Autoprobe CP-II, Veeco, CA, USA). The microscope was
operated in the contact mode, using a gold-coated silicone nitride sharpened cantilever tip (Microlever,Veeco)
with a spring constant of 0.05 N/m. Three dimensional images (25 µm x 25 µm) of the surface at three
randomly selected places per specimen were obtained. The topography and the average surface roughness (Ra)
of the scanned areas were qualitatively and quantitatively evaluated, using image processing and data analysis
software V 2.1.15.

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Table 1: Materials used in this study

Product Material type Main composition Shade LOT Manufacturer
Tetric Ceram Micro-hybrid Bis-GMA, UDMA, TEGDMA . A2 K14247 Ivoclar Vivadent.,
composite resin Inorganic fillers: Barium glass, Schaan,
ytterbium trifluoride, Ba-Al- Liechtenstein
fluorosilicate glass, SiO2 and
spheroid mixed oxide
Filtek TM Z350 Nanocomposite resin Combination of aggregated A3.5 N144092 3M ESPE, MN,
zirconia/silica cluster filler, bis- USA
GMA, UDMA, TEGDMA and bis-
EMA
Filtek TM P90 Low shrink posterior Silorane-based hydrophobic resin A2 N139697 3M ESPE, St.
restorative matrix, camphorquinone, fine Paul, MN, USA
quartz filler, yttrium fluoride.
Conventional glass- Aluminium–calcium–lanthanum A3 351620 3M ESPE AG,
Ketac Fil Plus ionomer cement fluorosilicate glass, polycarboxylic Seefeld, Germany
acid
KetacTM N100 Nanofilled glass - Resinous Paste: A3 AM7AN 3M ESPE, St.
ionomer restorative Fluoroaluminosilicate glass, silane Paul, MN, USA
treated silica and zirconia
nanofillers
Methacrylate and dimethacrylate
resins, Photoinitiators
- Aqueous paste:
silane treated zirconia silica
nanoclusters, silane treated silica
nanofiller,
Hydroxyethylmethacrylate

Table 2: Mode of gastric juice treatments used in this study.

Duration of Estimated time for gastric juice contact with restorations Regurgitation Total immersion time
disease / Regurgitation frequency
2 years 30 seconds 7/weak 6 hours
4 years 12 hours

Microhardness Measurements:
For the microhardness measurements, a Vickers microhardness tester with microscopic lens (HMV-2,
Shimadzu Corp., Kyoto, Japan) was used, with a 100 gram load and 30-s dwell time at room temperature
(26°C). Five microhardness measurements were obtained on the top surface of each specimen and the mean
VHN was measured.

Microstructure and Microanalysis:

Scanning electron microscope (SEM) attached with Energy-dispersive X-ray spectroscopy (EDX) unit
(Quanta FEG 250, FEICO. Holland) was used to examine the surface microstructure and provide chemical
microanalysis, where elements with relative values expressed in weight percentage was determined. The
prepared selected specimens from Ketac Fil Plus restoration and Tetric Ceram restoration were examined before
and after immersion in simulated gastric juice (for 6 and 12 hours).

Statistical Analysis:
The collected data were tabulated and statistically analyzed. Data were presented as mean and standard
deviation (SD) which is a measure of variation between values. Regression model using Two-way Analysis of
Variance (ANOVA) was used in testing significance for the effect of material, time and their interactions on Ra
and microhardness. Tukey’s post-hoc test was used for pair-wise comparison between the means when ANOVA
test is significant. The significance level was set at P ≤ 0.05. Statistical analysis was performed with PASW
Statistics 18.0 (Predictive Analytics SoftWare) for Windows.

Results:

Surface Roughness:

For all tested materials, there was a statistically significant increase in mean Ra values after 6 hrs
immersion time (P ≤ 0.05). Then a statistically significant decrease occurred in glassionomer types, and increase
in composite restorations, after 12 hours immersion time. But comparing the mean Ra after 12 hours with
control (Table 3), there was a statistically significant increase in Ra (P ≤ 0.05). Data in table (4) indicate that no
significant difference in the mean Ra values between Filtek TM Z350 after 6 hrs and 12 hrs immersion times and
that of the control groups of Filtek TM P90 and Tetric Ceram specimens (P ≤ 0.05). Data also indicate that no
statistically significant difference between FiltekTM P90 after immersion for 6 hrs and that of Tetric Ceram

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specimens after 6 and 12 hrs immersion times (P ≤ 0.05). KetacTM N100 after immersion for 6 hrs and 12 hrs
showed the statistically significantly highest mean Ra values, while Filtek TM Z350 control specimens showed
the statistically significantly lowest mean Ra values (P ≤ 0.05). The 3D AFM images (Fig.1) showed the
increase in micro-noses after 6 and 12 hrs immersion times, which was detected as smoothness in FiltekTM P90
and Tetric Ceram.

Table 3: Comparison between mean (SD) surface roughness (Ra) (nm) with different immersion times in simulated gastric juice.
Control 6 hours 12 hours P-value
Mean (SD) Mean (SD) Mean (SD)
c a b
28.3 (17.9) 85.6 (38.6) 45.5 (23.2) <0.001*
*: Significant at P ≤ 0.05, Means with different letters are statistically significantly different according to Tukey’s test

Table 4: Comparison between mean (SD) surface roughness (Ra) (nm) of the five restorative materials; before and after immersion in
simulated gastric juice for different immersion times.
Material Time Mean (SD) Rank P-value
Ketac Fil Plus Control 82.3 (0.1) D <0.001*
6 hours 153.2 (0.2) B
12 hours 76.1 (0.02) D
KetacTM N100 Control 21.9 (0.04) F
6 hours 223.5 (0.3) A
12 hours 92.9 (0.02) C
Filtek TM Z350 Control 10.2 (0.02) H
6 hours 13.4 (0.03) G
12 hours 13.2 (0.3) G
TM
Filtek P90 Control 12.2 (0.02) G
6 hours 18.1 (0.002) F
12 hours 25.8 (0.03) E
Tetric Ceram Control 14.5 (0.04) G
6 hours 20.0 (0.02) F
12 hours 19.6 (0.02) F
*: Significant at P ≤ 0.05, Means with different letters are statistically significantly different according to Tukey’s test

Fig. 1: AFM 3-D images of the tested materials, (a) the control groups, (b) after immersion for 6 hrs, and (c)
after immersion for 12 hrs in simulated gastric juice.

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Microhardness:
For all the tested materials, there was a statistically significant decrease in mean microhardness after 6
hours, and then a statistically significant increase occurred in glass ionomer types and decrease in composite
restorations, after 12 hours immersion time (P ≤ 0.05). But comparing the mean microhardness after 12 hours
with the control groups (Table 5), there was a statistically significant decrease in microhardness (P ≤ 0.05).
Comparing the mean microhardness after immersion for 6 hrs (Table 6); indicate that FiltekTMZ350 had the
statistically significantly highest mean microhardness, while KetacTM N100 and Tetric Ceram showed the
statistically significantly lowest mean microhardness with no statistically significant difference between the two
types (P ≤ 0.05). After 12 hrs immersion in the simulated gastric juice; Filtek TM Z350 showed the statistically
significant highest mean microhardness values, while Tetric Ceram provides the statistically significantly lowest
mean microhardness values (P ≤ 0.05).

Table 5: Comparison between mean (SD) Vickers hardness number (VHN) with different immersion times in simulated gastric juice.
Control 6 hours 12 hours P-value
Mean (SD) Mean SD Mean SD
123.5 a (32.3) 52.5 c (18.3) 61.1 b (16) <0.001*
*: Significant at P ≤ 0.05, Means with different letters are statistically significantly different according to Tukey’s test

Table 6: Comparison between mean (SD) Vickers hardness number (VHN) of the five restorative materials; before and after immersion in
simulated gastric juice for different immersion times.
Material Time Mean Rank P-value
SD
Ketac Fil Plus Control 73 (0.01) F <0.001*
6 hours 43.6 (0.04) J
12 hours 76 (0.03) F
KetacTM N100 Control 161 (0.9) A
6 hours 36.4 (0.06) K
12 hours 51.3 (0.2) I
Filtek TM Z350 Control 148.8 (0.5) B
6 hours 82.8 (0.3) E
12 hours 81.8 (0.1) E
Filtek TM P90 Control 104.3 (0.9) D
6 hours 62.8 (0.1) G
12 hours 56.5 (0.1) H
Tetric Ceram Control 130.3 (1.2) C
6 hours 37.2 (0.2) K
12 hours 39.7 (0.2) K
*: Significant at P ≤ 0.05, Means with different letters are statistically significantly different according to Tukey’s test.

Microstructure and Microanalysis:

Results from EDX spectroscopy microanalysis of Ketac Fil Plus (Table 7), revealed the presence of
elements such as C, O, F, Na, Al, Si, La, and Sr. A marked decrease in all elements specially Al and Si; and a
marked increase in La and Sr was detected after 6 hrs immersion time. Regarding the 12 hrs immersion
specimens; the reverse effect with detected where a marked increase in all elements especially Al and Si; and a
marked decrease in La and Sr was detected. Representative SEM photomicrograph of Ketac Fil Plus, revealed
observable differences in the specimen's surface characteristics; before and after immersion (Fig. 2a,b&c).
Results from EDX spectroscopy microanalysis of Tetric Ceram (Table 8), revealed the presence of elements
such as C, O, F, Al, Si, Ca, Ba, Yb, and Ce. A decrease in Al, Ca, and Ba, accompanied by O and F, and an
increase in C, Si and Yb elements was detected after 6 and 12 hours immersion time compared to the control
group. Representative SEM micrographs of Tetric Ceram showed differences in the inorganic fillers, shape and
size, together with decrease in filler content after immersion (Fig. 3a, b&c).

Table 7: Energy dispersive X-ray micro analysis of Ketac Fil Plus with relative values expressed in weight percentages.
C O F Na Al Si La Rb Sr
Control 13.36 10.55 6.17 1.71 16.09 19.70 8.50 - 23.92
6 hrs 8.85 7.37 1.24 0.94 3.44 3.02 13.35 2.23 59.56
12 hrs 13.02 13.13 2.22 1.28 17.03 19.94 10.27 - 22.76

Table 8: Energy dispersive X-ray micro analysis of Tetric ceram with relative values expressed in weight percentages.
C O F Al Si Ca Ba Yb Ce
Control 6.19 18.37 2.52 5.56 29.62 0.90 19.30 17.54 0.00
6 hrs 6.85 15.6 2.11 5.00 30.31 0.70 18.93 20.38 0.11
12 hrs 7.70 17.24 1.99 5.49 29.54 0.61 19.30 18.13 0.00

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Fig. 2: SEM of Ketac Fil Plus specimens, (a) the control specimens (b) after immersion for 6 hrs, and (c) after
immersion for 12 hrs in simulated gastric juice (X 1000).

Fig. 3: SEM of Tetric ceram specimens, (a) the control specimens (b) after immersion for 6 hrs, and (c) after
immersion for 12 hrs in simulated gastric juice (X 20 000).

Discussion:
The materials studied represent recent and conventional types of glassionomer and composite restorative
materials for comparison and determination of the most suitable restorative material type to be used for dental
treatment of (BN) patients. The pH of the prepared gastric juice was 3.8; which is the average pH upon analysis
of gastric contents of bulimic patients (Brady, 1958 and Bartlett & Coward, 2001). In order to keep the H+ ion
concentration at the cement surface as constant as possible, the solution was regularly changed every one hour.
The results showed that for the tested glassionomer types, there was a significant increase in roughness and
decrease in microhardness after 6 hrs immersion time; representing 2 years exposure to gastric juice.
Interestingly, there was a significant decrease in roughness and increase in microhardness after 12 hrs
immersion time; representing 4 years exposure to gastric juice.
Results also showed significant differences in roughness and microhardness between different types of the
examined materials. The two glassionomer types showed a significant increase in surface micro-roughness
compared to that of the three composite resin types; where the nanofilled glass ionomer type (KetacTM N100)
had the highest roughness values, and the nanocomposite resin type (Filtek TM Z350) showed lowest roughness
values after treatment. On the other hand the microhybrid type (Tetric Ceram) and nanofilled glass ionomer type
(KetacTM N100) showed the lowest microhardness values after treatment.
EDX spectroscopy microanalysis for selected specimens of Ketac Fil Plus and Tetric Ceram were
performed to detect the elemental changes in specimens' surface. Since all the tested materials showed the same
pattern of results, these two materials, being the simplest and unmodified forms, were selected.
Glass ionomer cements are a group of materials based on the acid/base reaction between poly (alkenoic)
acid and an ion-leachable silicate glass, mainly aluminium–calcium or strontium–lanthanum fluorosilicate glass
(Kovarik et al, 2005). The set cement has a two phase composite structure: unreacted glass particles embedded
in the matrix gel which contains polycarboxylate and fluoride complexes. During setting considerable amounts
of metal cations (eg. Ca 2+ or A1 3+ ) are extracted from the glass particles into the matrix to cross-link the
polycarboxylic-acid molecules in the cement matrix.
Previous study by Fukazawa et al, 1987; suggests that during immersion in acidic solutions, the solution
penetrates the cement from the surface and the matrix gel swells. Hydrogen ions (H+) diffuse into the cement
and were replaced with metal cations. According to the concentration gradient, the free metal cations would
diffuse through the cement outward. As soon they reached the interface between the cement and the solution,
they are released into the solution. The extraction of metal cations causes an increase in non-bridging oxygen in
the network of the glass near its surface. The surface of the glass particles would become rich in the silanol
group, and simultaneous attack by H ions and F- ions would dissolve the Si-O-Si glass network further.
Therefore, a complete dissolution of the glass particles and many pores near the surface of the cement takes
place.

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These findings are in agreement with the results obtained by EDX in the present study, where a marked
decrease in wt% of Al, Si and other elements; was detected after immersion for 6 hrs, and was evident as an
increase in surface micro-roughness and a decrease in microhardness. The destructed matrix; which could be
clearly seen in the SEM photograph; (Fig. 2b), after 6hrs immersion time, exposes the underlying fresh layer of
the specimens; where higher concentrations of Al, Si, F and other elements were present. Furthermore; the
maturation of the matrix with increasing aging time makes diffusion of the species from acidic medium difficult
and the elution of Al, F, and Si could decrease. These findings are in agreement with results obtained from EDX
microanalysis in the present study; where the wt% of Al, Si, F and other elements were increased after 12 hours
immersion time, and was evident as a decrease in roughness and an increase in microhardness.
Solubility of dental resin based composite materials, depend on several factors including, chemistry of the
monomer resins, the extent of polymerization of the polymer matrix, filler particle size, shape, and distribution
and the interfacial properties between the filler and resin matrix (Kovarik et al, 2005). In this study; two
aromatic and aliphatic dimethacrylates based composite resins and one was based on a new compound material,
silorane (Bis-3,4-Epoxycyclohexylethyl-Phenyl-Methylsilane3,4-Epoxycyclohexyl cyclopolymethylsiloxane )
was selected.
The two methacrylate based composite types tested in this study had the same polymer matrix composition;
however, their inorganic compositions were different. Therefore, the differences in surface roughness and
microhardness among the methacrylate based composites could be explained by the size, shape, and amount of
filler particles present in the compositions of the materials (Table 1).
The decrease in microhardness and the increase in surface roughness after immersion in simulated gastric
juice could be explained by the acid attacking the resin matrix, causing the softening of bisphenol-A-glycidyl
methacrylate (Bis- GMA) which could be caused by leaching of the diluent agents such as triethylene glycol
dimethacrylate (TEGDMA) (Asmussen, 1984 ).
Additionally a hydrolytic breakdown of the bond between silane and the filler particles could result in filler-
matrix debonding (Yua et al, 2009). Also the previous studies indicated that the quality of this interface
influences the extent to which the composite material is affected by solvents, where a poor, nonbonded interface
may provide a low energy pathway for solvent molecules (Kalachandra, 1989).
Furthermore the presence of fillers in a polymer network can greatly affect solvent uptake and dissolution.
Studies indicated that composites containing radiopaque glasses, such as Ba glass, Sr, Yb and La have been
shown to undergo greater dissolution than silica and quartz containing resin composites (Asaka et al, 2004 and
Ferracane, 2006). This may explain the significant decrease in microhardness and increase in roughness in Tetric
Ceram and FiltekTM P90 compared to FiltekTM Z350 composite types, where Ba glass, Ba-Al-fluorosilicate
glass, Ytterbium trifluoride are part of their filler content. The hydrolytic degradation of the fillers may alter the
microstructure of the composite bulk through the formation of pores. These findings are clearly seen in SEM
(Fig.3) and are in agreement with results of other studies (Yesilyurt et al 2009, Asmussen, 1984, Yua et al 2009
and Kalachandra, 1989).
FiltekTMP90 is classified as a microhybrid composite, and the presence of the cyclosiloxane backbone
imparted hydrophobicity, therefore decreasing solvent sorption (Yesilyurt et al, 2009). However; results of this
study indicated a significant increase in roughness and decrease in microhardness after immersion. Such finding
suggests that, for composite restorations, the main effect of the acidic gastric juice is on the inorganic fillers
more than on the organic matrix. This finding is in agreement with results obtained from EDX microanalysis for
Tetric Ceram, where the increase in C wt% after immersion revealed an increase in the organic matrix content
relative to the other leached inorganic elements.
The small amounts of TEGDMA as mentioned by the manufacturer, the small filler particle size, and the
absence of Ba glass, Sr, Yb and La may explain the significant resistance of Filtek TM Z350 compared to the
other tested composite types.
On the other hand, KetacTM N100 is based on the acrylic and itaconic acid copolymers necessary for the
glass-ionomer reaction with fluoroaluminosilicate (FAS) glass and water. A blend of resin monomers, BisGMA,
TEGDMA, PEGDMA and HEMA which polymerize via the free radical addition upon curing are present.
Fluoroaluminosilicate glass, silane treated silica and zirconia nanofillers, are also parts of their composition.
Therefore the combined effect of the acidic gastric juice on glassionomer cement and composite resin could be
clearly manifested as a significant increase in roughness and decrease in microhardness values of nanofilled
glass ionomer restorative material (KetacTM N100) compared to the other tested materials.
The presence of saliva and different types of acidic or alkaline foods in the oral cavity together with gastric
juice could affect results of the present study clinically. The effect of these factors is recommended in future
research.

Conclusions:
Within the limitations of this in vitro study, it may be concluded that surface microhardness and roughness
of all tested materials were affected by the simulated gastric juice. On the other hand, the tested composite

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restorations were more resistant to the acidic gastric juice, than both types of glass ionomer cement. Filtek TM
Z350 type showed the least roughness and microhardness changes among the three composite materials, while
KetacTM N100 was the most affected type. For clinical decision-making, Filtek TM Z350 is the most suitable
material for restorations in patients suffering from BN.

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