Comparative Effect of two Types of Surface Treatments on Shear Bond Strength of New Composite to Old Composite.

STATEMENT OF THE PROBLEM: Composite restoration failures may occur because of different factors. In these situations, the repair of a composite restoration has many advantages over replacement such as saving time, lower cost, and lower risk of excessive removal of sound tooth structure and subsequent pulp exposure. PURPOSE: The purpose of this in vitro study was to evaluate the effects of two surface treatments on shear bond strength (SBS) of new composite to old composite. MATERIALS AND METHOD: In this in vitro study, 60 composite discs were fabricated using a plexiglass mold measuring 4 mm in thickness and 7 mm in diameter, and were randomly divided into three groups (n=20). In group 1, the bonding procedure was done with no modification. After roughening of one surface in all remaining samples, chloroform (CHCl3) was applied on the surface of samples in group 2 and phosphoric acid 35% was applied on the surface of the samples in group 3. PermaSeal was then applied in all samples and new composites were bonded to the surface. The samples were stored in distilled water for one week and were then subjected to 500 thermal cycles and shear bond strength between two layers of composite and mode of failures were evaluated. RESULTS: The lowest and the highest SBS values of repair composite to old composite were noted in groups 3 and 1, respectively and this difference was statistically significant (p< 0.05).The difference between groups 1 and 2 was not significantly different (p= 0.197). The mode of failure was mixed in all samples of groups 2 and 3 and cohesive in group 1. CONCLUSION: After grinding, the surface treatment with phosphoric acid did not increase the SBS of new composite to old composite, while chloroform increased the SBS almost to the level of the baseline in control group.

In Vitro Comparative Evaluation of Newly Produced Desensitizer, Chlorhexidine and Gluma on Bond Strength and Bond Longevity of Composite to Dentin.

STATEMENT OF THE PROBLEM:  Etching process on dentin can activate matrix metalloproteinase (MMP) which hydrolyze organic matrix of demineralized dentin. Gluma and chlorhexidine could inhibit the activation of MMP. PURPOSE:  The aim of the study was to evaluate the effect of a new desensitizing material consisting of Gluma and chlorhexidine together on the shear bond strength and bond durability of composite restorations. MATERIALS AND METHOD: One hundred and twenty caries-free extracted premolars were sectioned horizontally from one third of the coronal crown to expose flat dentin surface and randomly divided into 4 groups. In the control group, no surface treatment was used. In the first group chlorhexidine (CHX) 2%, in the second group, new material (NM) and in third group Gluma desensitizer (GD) was applied after etching and before bonding(total-etch bonding system). After the bonding process, the composite was placed on the surface of the samples using a cylindrical mold. Then, the shear bond strengths of half of the specimens were measured after 24 hours and the other half after 6 months of storage in distilled water and thermocycling. The failure types of specimens were evaluated with a stereomicroscope. Data were analyzed using One-way Anova and Tukey's Post Hoc tests in SPSS software. RESULTS:   After 6 months, the bond strength decreased in all groups and differences were statistically significant (p= 0.002).The highest shear bond strength was observed after 6 months in the NM group and the GD group with no statistically significant difference. The 24-hour bond strengths were not significant between groups. Mix failure had the highest rate in all groups. CONCLUSION:  It can be concluded that the effect of combination of chlorhexidine and Gluma on maintaining the integrity and strength of bond over time is similar to Gluma compound alone and they have better effect than chlorhexidine.

The effect of composite resin preheating on marginal adaptation of class II restorations.

BACKGROUND: One of the problems with a high filler content composite resins is gap formation at restorative material-tooth interface. The present study investigated the effect of preheating composite resins on the formation of marginal gap in Cl II restorations. MATERIAL AND METHODS: In this in vitro study Sixty Cl II cavities were prepared on the mesial and distal surfaces of 30 extracted premolar teeth. The gingival floor of cavities was placed 1 m below the CEJ. The samples were randomly allocated to 4 groups for restoration placement: group 1, Filtek P60 composite resin at room temperature; group 2, Filtek P60 composite resin at 68°C; group 3, X-tra fil composite resin at room temperature; and group 4, X-tra fil composite resin at 68°C. After a thermocycling procedure, the teeth were sectioned longitudinally in a buccolingual direction. Then the marginal gaps of the samples were measured at proximal and gingival margins under a scanning electron microscope at ×2000 magnification in µm. The data were analyzed with SPSS 21, using one-way ANOVA, post hoc Tukey tests and paired t-test (α=0.05). RESULTS: Groups 2 and 4 exhibited significantly lower marginal gaps, compared to groups 1 and 3, at both enamel (P<0.0001 and P=0.001, respectively) and dentinal walls (P<0.0001). In all the groups, there was significantly less marginal gaps at composite-enamel wall compared to composite-dentin wall interfaces (P<0.0001). There was no significant difference between groups 1 and 3 and groups 2 and 4 in enamel walls (p= 0.96, p= 0.99 respectively) and dentinal walls (p= 0.85, p=0.98 respectively). CONCLUSIONS: Preheating resulted in a decrease in marginal gaps in both composite resins. The effect of composite resin type on marginal adaptation was the same. Key words:Composite resin, dental marginal adaptation, preheating.

The effect of preheating of composite resin on its color stability after immersion in tea and coffee solutions: An in-vitro study.

BACKGROUND: One of the concerns in using composite resins is color change. The aim of this study was to investigate the effect of preheating on color stability of composite resins when immersed in coffee and tea. MATERIAL AND METHODS: This experimental study included 60 composite disks. The samples were divided into 2 groups, one group prepared at room temperature and the other prepared at 68 °C. After curing, the samples were placed in 37 °C distilled water for 24 hours. The color of the samples was measured (t0) using spectrophotometer according to CIE-L*a*b* system. The samples of each group were then divided into 3 subgroups and respectively immersed in distillated water, coffee and tea for 30 days and the final color (t1) was measured. The difference between the measured colors was calculated (∆E) and the results were analyzed using version 21.0 of SPSS software, Paired t-test, ANOVA, Tukey's test, and Dunnett t-test. RESULTS: The preheated composites showed significantly lower staining in the coffee solution than the room temperature composites (p<0.0001). In contrast, no statistically significant difference was observed for the tea solution (p =0.317). The staining of the preheated composites in distillated water was higher than those in the room temperature, however, the difference was not significant (p =0.99). CONCLUSIONS: Within the limits of this study, preheating was effective to improve color stability of composite resin after long time immersion in coffee solution. Key words:Composite resin, color stability, preheating.

Effect of Light-Curing Unit Type and Bulk-Fill Composite Resins with Different Photoinitiators on Marginal Gaps of Class II Restorations

Abstract Objective: To evaluate the effect of two types of light-curing units (second and third generations) and two types of bulk-fill composite resins with different photoinitiators - Tetric N-Ceram Bulk Fill (TNCB) and Xtra Fil (XTF) on gap formation at the gingival margins of Cl II restorations. Material and Methods: Fifty-six standard Cl II cavities were prepared on the mesial and distal surfaces of premolar teeth, with the gingival margin of the cavities 1 mm apical to the CEJ. The samples were randomly assigned to two groups based on the composite resin type and two subgroups based on the light-curing unit type and restored. After 5000 rounds of thermocycling, gingival margin gap in each sample was measured in µm under an electron microscope at ×2000 magnification. Data were analyzed by two-way ANOVA and Tukey tests (α=0.05). Results: Marginal gaps of TNCB composite resin were significantly smaller than those of XTF composite resin (p<0.001). There were no significant differences between the two light-curing units in each group (p=0.887 with XTF and p=0.999 with TNCB). Conclusion: The gaps at gingival margins of Cl II cavities with TNCB bulk-fill composite were smaller than XTF composite resin. Both composite resins can be cured with both the second- and third-generation LEDs (AU).

Dermatomyositis Leading to Necrotizing Vasculitis: A Perfect Response to Applied Therapy.

Dermatomyositis is an idiopathic inflammatory myopathy that cause skin and muscle complications. The ethiology is not understood well yet. Released cytokines including interferon and interleukins are suggested to make inflammatory responses in the skin or muscle. Muscle weakness and skin lesions including heliotrope rash, shawl sign and Gottron's papules are the most common symptoms. A biopsy (muscle or skin) is always the most reliable method for diagnosis. Corticosteroids in association with immunosuppressive agents are used as standard treatment. The patient was a 30 years old woman who got involved with dermatomyositis for 10 years. She has been under therapy with Methotrexate, Prednisolon and Azathioprine until she came to us suffering from progressive skin lesions. Experiments and examinations were normal except the lesions and detected lipoatrophy. Because of immune cells infiltration and observations necrotizing vasculitis was diagnosed. After three month of high dose prednisolon and intravenous cyclophosphamide therapy the lesions vanished remarkable. True and immediate diagnosis gives physicians the chance not only to assess the best treatment but have adequate time to apply the procedure. However shortening the therapy and diminishing morbidity of the disease need more investigations and efforts.

A Comparative Evaluation of Microleakage of Two Low-Shrinkage Composites with a Conventional Resin Composite: an In Vitro Assessment.

STATEMENT OF THE PROBLEM: Polymerization shrinkage stress in composite restorations may lead to microleakage. Clinical methods such as using low-shrinkage composites have been suggested to overcome this problem; however, there are controversies about their efficiency in decreasing the microleakage. PURPOSE: This in vitro study was conducted to compare the microleakage of two low-shrinkage resin composites with a conventional one. MATERIALS AND METHOD: Fifty class V cavities of 2.5×3×2 mm (depth× length× width) were prepared in the buccal surfaces of intact bovine incisor teeth with the incisal margin on the enamel and gingival margin on the cementum. The teeth were randomly divided into 5 groups. In group 1, Clearfil APX (conventional) with SE Bond was used in 2 layers (Kuraray; Japan). In group 2, GC Kalore (low -shrinkage) with GC UniFil Bond was applied in one layer (GC Company). In group 3, the material of group 2 was applied in two layers. In group 4, FiltekP90 (low -shrinkage) with P90 System adhesive was applied in one layer (3M ESPE). In group 5, the materials of group 4 were applied in two layers. The samples were thermocycled and immersed in 0.5% fuchsin solution for 24h. The restorations were sectioned in buccolingual direction. Then they were evaluated for microleakage by using a stereomicroscope and scored as 0, 1, 2, and 3 and then Kruskal-Wallis test was used (p< 0.05). RESULTS: The groups were not significantly different regarding the microleakage in the coronal and cervical margins (p< 0.423 and p< 0.212, respectively); however, the Filtek P90 yielded the best results. In all groups, except group 5 (p= 0.018), the cervical margins had greater microleakage than the coronal margins. CONCLUSION: The results suggested that low-shrinkage resin composites may not reduce the marginal microleakage. The proper use of conventional resin composites may offer comparable clinical results.

Translucency and masking ability of various composite resins at different thicknesses.

STATEMENT OF THE PROBLEM: Optical properties of the composite resins, concerning their translucency and thickness, are affected by discolored tooth structure or inherent darkness of the oral cavity. PURPOSE: This study aimed to compare the translucency parameter (TP) of five different composite resins in different thicknesses and to evaluate their masking ability in black backgrounds. MATERIALS AND METHOD: Five brands of composite resins; Gradia (GC) and Crystalline (Confi-dental) in opaque A2 (OA2), Vit-l-escence (Ultradent) in opaque snow (OS), Herculite XRV (Kerr) and Opallis (FGM) in dentin A2 (DA2) shades were selected to enroll the study. Color coordinates of each composite were determined at 0.5, 1, and 1.5 mm thicknesses on a white backing, the backing of material itself and a black backing were calculated by using a spectrophotometer to evaluate the translucency parameter (TP) of the study materials. The masking ability was also calculated from the specimens on the material itself and on black backing. The values under 2 were estimated as imperceptible. One-way ANOVA, T-test and Tukey HSD were employed for statistical analysis. RESULTS: The masking ability values, recorded for the 1.5 mm-thick specimens, were in the range of imperceptible except for the Herculite. There was no difference in TP values of the materials at 1.5 mm thickness. Opaque snow shade of Vit-l-escence and opaque A2 shade of Gradia showed lower TP values in comparison with the other 1 and 0.5 mm-thick materials and this difference was statistically significant (p< 0.05). CONCLUSION: In relatively thin thicknesses (≤1mm), these opaque/dentin shade composite resins could not mask the black background color.

Effect of different decontamination procedures from a saliva-contaminated cured bonding system (Single Bond).

BACKGROUND: A few studies have investigated the effect of saliva contamination of cured or uncured adhesive systems. The aim of this study was to compare the effect of different decontamination methods on the shear bond strength of composite to enamel and dentin using an adhesive contaminated after light activation. MATERIALS AND METHODS: In this in vitro experimental study, 80 extracted sound human teeth, 40 premolars and 40 central incisors were selected for dentin and enamel specimen preparation. Within each of the two test groups, the teeth were randomly subdivided into five groups. The materials used consisted of single bond (3M) and Z250 (3M). Except group 1 (Control), in Groups 2-5, cured adhesive was contaminated with saliva (20 s). Decontaminating procedures were rinsing, blot-drying, rebonding (Group 2), rinsing, air-drying, rebonding (Group 3), etching, rinsing, blot-drying, rebonding (Group 4) and etching, rinsing, blot-drying (Group 5). Then, composite resin was inserted on the treated surfaces and cured. The results were subjected to one-way ANOVA and Tukey honestly significant difference (HSD) tests. RESULTS: Group 5 (etching, rinsing, blot drying) resulted in significantly lower bond strength to both enamel and dentin surfaces in comparison with the other groups (P < 0.05). CONCLUSION: When the adhesive was re-applied, all decontamination methods in this study seemed sufficient to decrease the adverse effect of saliva.