Statement of Problem: Composite reins have recently become popular for posterior teeth restorations.Gap formation and subsequent microleakage are of the complications resulting from such restorations.One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light cure and self cure) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected.Purpose: The aim of this in vitro study was to evaluate the effects of self- cure and light- cure composite resins in sandwich technique on the bond strength of light cure glass ionomer and dentin.Materials and Methods: 40 extracted human premolars were selected and divided into four groups:Group 1: Light cure glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light cure glass ionomer plus a mass of self cure composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light cure glass ionomer plus light cure composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light cure glass ionomer with 37% phosphoric acid etching followed by two separate layers of light cure composite resin of 1mm thickness were placed.SEM was used to determine gap size at GI- dentin and GI- composite interfaces. The findings were analyzed by ANOVA and t-student tests.Results: Groups 1 and 2 showed no gap at GI-dentin interface and also cracks were not observed in all these specimens. In group 3, there was gap between light cure GI and light cure composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups 1 and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2.Conclusion: Base on this study, the application of self-cure composite resin on light cure GI showed no gap and crack formation on GI-dentin and GI-composite interfaces and GI itself. However, light cure composite resins and glass ionomer etching aggregated crack and gap formation.

Polymerization shrinkage of light cure composite resins causes many complications in conservative and esthetic restorations. The objective of this in-vitro study was to evaluate the polymerization shrinkage, degree of conversion and the amount of filler in IDM and tetric ceram composites. Ten disks shaped, uncured specimens (8mm×1.547mm) of each composite were placed on glass slide in the center of the metal attached to it. Then specimens were light cured for 60s from underneath. After 30 minutes, the thickness of specimens, using a micrometer and the percent of the polymerization shrinkage of each sample were measured. Statistical analysis was carried out by t-test (P<0.05). Also the degree of conversion of specimens was evaluated with FTIR and the mineral filler content was measured by burning in electric oven. Polymerization shrinkage in IDM and tetric ceram was not significantly different. Degree of conversion and mineral filler content in tetric ceram was greater than that of IDM. It is assumed that the low degree of conversion in IDM is due to its chemical composition and filler content. Also, the similarity in linear polymerization shrinkage between IDM and tetric ceram may be caused by the low degree of conversion in IDM.

Background and Aim: Microleakage has been always a major concern in restorative dentistry. The curing contraction of composites still presents a problem with controlling microleakage and postoperative sensitivity. The aim of this study was to investigate the effect of flowable and dual-cure resin composite liners on gingival microleakage of packable resin composite restorations.Materials and Methods: Sixty class II cavities with cervical margins 1 mm below the CEJ were prepared in 30 extracted human molars. The teeth were randomly divided into five groups of 12 each. In control group, each tooth was restored incrementally with Tetric Ceram composite without applying any liner. In the second and forth groups, flowable materials-Tetric Flow and dual-cure composite resin cement Relay X ARC were placed respectively as a 1-mm thick gingival increment and cured before the resin composite restoration, whereas, in the third and fifth groups liners were cured with the first increment of packable composite.The restored teeth were stored for one week in distilled water at 37oC, and thermocycled between 5oC and 55oC, sealed with nail varnish except the tooth – composite interface in cervical restoration margins and immersed in 2% basic fuchsin for 24 hours. Dye penetration was evaluated using a stereomicroscope with 28x magnification. The data were analyzed by Kruskal-Wallis and Mann-Whitney U-tests with p<0.05 as the level of significance.Results: The results of this study indicated that there were significant statistical differences between controlcured flowable liner, control-flowable liner without separately curing, control-cured dual cure composite resin cement groups.However there were no significant differences between dual-cure composite resin cement without separately curing and control, cured flowable liner and cured dual cure composite resin cement, flowable liner without separately curing and dual cure composite resin cement without separately curing groups.Conclusion: The results of this study indicated that none of techniques could thoroughly eliminate microleakage in gingival floor, however the effect of flowable or a dual-cure liner on reducing the gingival microleakage was found to be statistically significant in tested restorative material.

Background and purpose: In orthodontic brackets, unlike restorative materials or porcelain, the shear bond strength of the adhesives used is important because the oblique forces from food or objects or the tension of the adhesive food affect the brackets. This study aimed at measuring and comparing shear bond strength and adhesive remnant index of light cure composite, no mix (self-cure) composite, and no bond composite (GC Orthoconnect). Materials and methods: A total of 27 non-carious and sound human premolar teeth were used. The samples were divided into three groups, including light cure composite, self-cure composite, and no bond composite (GC Orthoconnect). After bonding and thermocycling process, the metal brackets (American Orthodontics) were then debonded using universal testing machine. Adhesive remnant index (ARI) score was assessed. Results: The highest and lowest SBS mean values were seen in self-cure group (18. 0402±, 5. 71665) and light cure group (7. 7890±, 3. 98995), respectively. There were significant differences in SBS values between all groups except between the no bond group and the self-cure group (P= 0. 18, P>0. 05). The highest ARI scores were 0 in the self-cure group and 3 in the no bond group and the light cure group. Conclusion: The no bond composite provided acceptable overall shear bond strength and compared to light cure composite showed higher shear bond strength and lower bond failure.

Background and Aim: Nonmetallic tooth- colored posts adhere to canal walls by dentin bonding agents and resin cements. Better retention and proper distribution of stress result from enough and proper bonding. The purpose of this study was to evaluate bond strength of D.T. Light - post with two different resin cements (selfcure & dual-cure) and to investigate the effect of irrigating solutions applied in root canal on bond strength of the resin cements and D.T.Light- post to root canal wall.Materials and Methods: In this experimental study 40 single root teeth (maxillary canine & central) were selected and stored in 0.1% thymol solution for one week and transferred to distilled water. The teeth were decoronated 2mm above CEJ. The canal space was mechanically enlarged using k-files (up to # 70). The teeth were randomly divided into two groups. The first group was irrigated with 2.6% NaOCl, and the second was irrigated with normal saline. After drying, the teeth were filled with gutta percha cones using lateral condensing method. After two weeks the post space was prepared and D.T.Light- post was inserted in each subgroup using self or dual-cure cements according to manufacturer's instructions. After thermocycling, the apical part was cut 1cm below CEJ. The remained length was divided into 9 equal sequential sections. Each section was submitted to shear push-out test in universal testing machine. Statistical analysis of the bond strength data was performed using ANOVA and post hoc tests with p<0.05 as the level of significance. All failed specimens were examined under stereomicroscope. Degrees of conversion (DC) of the cements were determined by FTIR.Results: Significant difference in bond strength values were found among sites (P=0.001) and cements (P=0.03). With increasing in depth, bond strength decreased. The mean bond strength value in dual-cure resin cement was higher than self-cure cement. The irrigating solutions caused no significant difference in bond strength (P=0.46). DC% had significant difference in various depths.Conclusion: According to the results of this investigation, bond strength of dual-cure cement is higher than self-cure one in D.T Light- post because of post's translucency. 2.6% sodium hypochlorite does not affect the bond strength.

Aim: The aim of this study was to compare the etching effect of porcelain with Hydrofluoric acid (HF) one shear bond strength using one coat bond and self cure composite.Methods & Materials: The study was conducted experimentally using observation as its technique. 40 porcelain cubes were prepared and assigned into 4 groups. Group I specimens were treated with 35% phosphoric acid.Subsequently one coat bond was applied to bond the bracket, group II specimens were made fresh with fine diamond bur, treated with a 35% phosphoric acid and one coat bond was applied to bond the bracket, group III specimens were treated with a 20% hydroflouric acid (HF) and Nomix composite bond was applied to bond the bracket, group IV specimens were treated with a 40% HF acid and the same procedure in the group III was followed. The Instron machine was used at a crosshead speed of 0.5 mm/min to test the shear bond strength.Result: The shear strength was 2.47±1.8Mpa for group I, 5.64±2.6Mpa for group II, 3.28±1.8Mpa for group III and 3.03±2.6 for group IV. The overall difference between the four groups was statistically significant (P<0.05). Conclusion: The use of fine diamond bur and 35% phosphoric acid for Etching and use of one coat bond can achieve a successful bond between either use only phosphoric acid or 20% HF acid-Etched with No mix composite and 40% HF acid etched with No mix composite.

Background and Aim: Oral candidiasis is the most common opportunistic infection of the oral mucosa with Candida spp. Candida species form a biofilm in patients who need orthodontics with removable plaque, and this structure can lead to Candidemia. It is important to find effective plant compounds, which have fewerside effects and are natural, to prevent biofilm formation. The aim of the present study was to determine the effect of adding Thymus vulgaris and Cinnamomum verum essential oils to self- cure acrylic blocks on Candida albicans colonization. Methods: In this experimental study, the antifungal activity of essential oils of Thymus vulgaris, Cinnamomum verum and nystatin against of Candida albicans ATCC10231 was evaluated in order to determine MIC according to CLSI-M27S4 guidelines. Powder and monomer were poured into tablet molds to make self-cure acrylic plaques. A total of 144 self- cure acrylic plaques were divided into 24 groups of 6 in petri dish. Three groups contained powder and monomer, three groups contained nystatin drug, and 18 groups contained different concentrations of essential oils of Thymus vulgaris and Cinnamomum verum. Then, the samples were incubated in artificial saliva enriched, with Candida albicans at 37°C and the effects of essential oils of Thymus vulgaris and Cinnamomum verum on the binding of Candida albicans were reported by the cfu/ml count method. Statistical analysis of data was done using Stata-15 software. ANOVA and Tukey's test were used to confirm the results. Results: The evaluating the sensitivity of Candida albicans ATCC10231 to essential oils of Thymus vulgaris, Cinnamomum verum and Nystatin were obtained as MIC= 120µg/ml, MIC= 340µg/ml and MIC= 1µg/ml, respectively. The attachment of yeast cells to self- cure acrylic blocks for Cinnamomum verum essential oil was significant in MIC= 340 µg/ml (p= 0.02), MIC= 680 µg/ml (p= 0.01) and nystatin 1 µg/ml (p= 0.00) compared to the negative control group. However, this amount was not statistically significant for Thymus vulgaris essential oil        (p= 0.14). Conclusion: Adding essential oil of Cinnamomum verum to acrylic resin prosthesis can be effective in controlling the proliferation of Candida albicans on the surface of the prosthesis. However, its effects on the physical properties of acrylic resin dentures need further studies.

Discoloration of composite resins is considered to be a major factor in esthetic restoration failures. The aim of this study was to evaluate color stability of IDM composite (both light and self cure samples namely IL and IS), and to compare it with a self-cure composite (Degufill named DS) and a light cure ormocer composite (Definite, called DL in the Report). 60 disk shaped samples of each composite were prepared, according to ISO-7491. The samples were divided into 3 groups and aged as follows: A- (Control) 7 days in dark 37 c chamber B- Foil covered and kept in 100% humidity, and 370 c in xenotest chamber for 24 hours, then transferred to a dark 370 c chamber for 6 more days.C- Kept in 370 c, 100% humidity under the emission of xenon lamp of xenotest chamber for 24 hours, and then transferred to 370 c dark chamber for 6 more days.The lightness and chromaticity values of samples were measured both before and after aging using a spectrophotometer (Data Flash). The total color changes as well as changes in lightness and chromaticity values were measured in the CIE L * a * b * scale, and analyzed. Color change was recorded to be significant in all samples after aging. The maximum change belonged to IL, which was significantly different from DL and DS. It seems, in order to have a durable esthetic restoration using IDM, more scientific and professional consideration is needed in the production process.

Objectives: The present study aimed to evaluate the bond strength of heat-cure denture base resin to newly designed Iranian artificial acrylic teeth. Materials and Methods: In this in-vitro experimental study, shear bond strengths of Ivoclar acrylic, Apple composite, and B-Star nanocomposite teeth to heat-cure acrylic denture base resin were compared. A total of 18 samples were selected from each group of teeth. The samples were attached to heat-cure resin according to ISO 10477 standard. For the assessment of bond strength, the samples were placed in a universal testing machine and were subjected to shear forces at a speed of 1 mm/minute to record the fracture load. Descriptive statistics, including frequency, mean, and standard deviation, were calculated using SPSS 20 software. Two-way analysis of variance was used to compare the shear bond strength of the groups with and without monomers and the studied artificial teeth. Results: The mean shear bond strengths of Ivoclar acrylic teeth were 392. 22± 23. 76 MPa and 337. 11± 32. 18 MPa with and without adding monomers to the tooth surface, respectively. The mean shear bond strengths were 250. 44± 29. 84 MPa and 238. 33± 27. 28 MPa (without monomers) and 438. 33± 24. 16 MPa and 311. 56± 32. 78 MPa (with monomers) for Apple composite and B-Star nanocomposite artificial teeth, respectively. Conclusion: The greatest shear bond strength was attributed to Ivoclar acrylic teeth followed by Apple composite and B-Star nanocomposite artificial teeth. Addition of monomers to the tooth surface significantly strengthened the shear bonding of acrylic base resin to the teeth.

Background and Aim: The present study aimed at determination of the fatigue resistance and failure mode of cuspreplacing onlays in endodontically treated premolars using indirect composite resin restorations. Materials and Method: In this experimental study, 84 human premolars were randomly divided into 7 groups of 12. These groups were prepared as follows: Intact teeth used in groupl as control, the second group covers the endodontically treated teeth, restored with indirect onlays using Z-250 composite resin, the next two groups (i.e. 3,4) were similar to the second group, but subjected to 1 and 2 million fatigue load cycles, respectively. Groups 5, 6, 7 were similar to groups 2, 3, 4, respectively, however, in these groups Tetric Ceram used as the restorative material. All specimens were loaded using a Universal Testing Machine until fracture occurred and the mode of failure observed with naked eye. Kruskal-Wallis and Chi-Square tests were used to analyze the data (a=.05). Results: All specimens withstood the masticating simulation. The mean fracture strength for groups 1 to 7 were: 1276.92, 1269.05, 1217.80, 1188.13, 1228.97, 1127.86, 1105.58, respectively. No statistically significant differences were found between the groups in fracture strength and failure mode. There was no statistically significant difference between two types of resin composite (P=0.203) and load cycles (P=0.298) after zero, 4 and 8 years aging. Conclusion: Within the limitation of this study, restored premolars with indirect composite onlays show fatigue resistance equal to natural tooth up to 8 years after restoration. Furthermore, no statistically significant differences were found between 4 and 8 years of load cycles. Tetric Ceram Z-250 restoration agent showed no effect on the tooth fracture resistance with the most observed fractures to be occur under CEJ with no capability to be restored.