Objectives: The polymerization shrinkage of methacrylate-based composites is among the most important causes of failure of composite restorations. The manufacturers claim that bulk-fill composites have a lower polymerization shrinkage than conventional composites. This study aimed to assess the polymerization shrinkage of five bulk-fill composites in comparison with a conventional composite. Materials and Methods: In this in-vitro experimental study, composite discs (n=30) were fabricated using everX Posterior (EXP), Filtek Bulk-Fill Posterior (FBP), SonicFill 2 (SF2), Tetric N-Ceram Bulk-Fill (TNB), X-tra fil (XF), and Filtek Z250 conventional composite at the center of a metal ring bonded to a microscope slide and were covered with a coverslip. This assembly was transferred to a linear variable differential transformer (LVDT). Light-curing (1200 mW/cm2) was performed from underneath the slide for 30 seconds. The deflecting disc method and LVDT were used to assess the dimensional changes of the samples (indicative of polymerization shrinkage) at 1, 30, 60, and 1800 seconds following the onset of light irradiation. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s test. Results: The groups were significantly different regarding polymerization shrinkage (P<0.002). The polymerization shrinkage of the tested composites following the onset of light irradiation ranged from 0.19 to 3.03. EXP showed a significantly higher polymerization shrinkage than other composites at 30, 60, and 1800 seconds after light irradiation, while XF showed the lowest polymerization shrinkage at the aforementioned time points. Conclusions: The tested bulk-fill composites had a polymerization shrinkage similar to that of the conventional composite.

Introduction: Bleaching process can affect surface roughness of enamel, which is a vital factor in esthetic and resistance of tooth. The aim of this study was to compare surface roughness of enamel in teeth bleached using Diode and Neodymium-Doped Yttrium Aluminium Garnet (Nd: YAG) lasers with those bleached using conventional method. Methods: In this study, 75 anterior human teeth from upper and lower jaws (These teeth extracted because of periodontal disease) were randomly divided into 5 groups. Group 1: Laser white gel (Biolase, USA) with 45% hydrogen peroxide concentration and GaAlAs Diode laser (CHEESE TM , GIGAA, China), group 2: Heydent gel (JW, Germany) with 30% Hydrogen peroxide concentration and Diode laser, group 3: Laser white gel and Nd:YAG laser (FIDELIS TM , Fotona, Slovenia), group 4: Heydent gel and Nd:YAG laser and group 5: The Iranian gel Kimia (Iran) with 35% hydrogen peroxide concentration were used. Surface roughness of the samples was measured using the Surface Roughness Tester system (TR 200 Time Group, Germany) before and after bleaching. In each group, one sample was randomly selected for SEM analysis. Results:The results showed that the mean surface roughness of the teeth before and after bleaching had a significant difference in all the study groups. It was indicated that after bleaching, the mean surface roughness had increased in all the study groups. The highest surface roughness was seen in the conventional bleaching group and the lowest surface roughness was reported in group 3 (laser white gel + diode laser), in which the average surface roughness increased by only 0.1 µm. Conclusion: It was concluded that using the Laser white gel and the diode laser for bleaching resulted in the least surface roughness compared to conventional method.

Objectives: Toothpastes and mouthwashes contain ingredients that may be toxic for oral mucosal tissues. This study aimed to assess the cytotoxicity of the ingredients of commonly used toothpastes and mouthwashes. Materials and Methods: This experimental study was performed on 16 toothpastes and four mouthwashes widely available in the Iranian market. First, the concentration of six main ingredients of these products, namely sodium fluoride (NaF), sodium lauryl sulfate, cocamidopropyl betaine, zinc lactate, paraben, and sodium benzoate, was determined. The methyl thiazolyl tetrazolium (MTT) assay was used to assess the cytotoxicity of these materials for human gingival fibroblasts (HGFs). The MTT assay was performed at 1, 15, and 30 minutes following exposure to five concentrations of each material in triplicate (according to the concentrations obtained in the isolation step). Data were analyzed using three-way analysis of variance (ANOVA). Results: The difference in the cytotoxicity of the materials was statistically significant (P<0.001). Cytotoxicity was time- and concentration-dependent; by an increase in the concentration of the materials, their cytotoxicity increased over time. The cytotoxicity of sodium lauryl sulfate and cocamidopropyl betaine was >90%. The cytotoxicity of NaF varied from 25% to 70%, and the cytotoxicity of all concentrations of zinc lactate and sodium benzoate was <50% for HGFs. Conclusion: To decrease the cytotoxic effects of toothpastes, sodium lauryl sulfate and cocamidopropyl betaine should be replaced with safer detergents, and the concentration of fluoride should be decreased to 400 parts per million (ppm). Alternatively, fluoride may be replaced with other antibacterial and cariostatic agents.

Background:Tooth restoration immediately after bleaching is challenging due to the potential problems in achieving adequate bond strength.Objective: The aim of this study was to evaluate the effect of surface treatment with ER:YAG, ND:YAG, CO2 lasers and 10% sodium ascorbate solution on immediate microtensile bond strength of composite resin to recently bleached enamel.Materials & Methods: Ninety sound molar teeth were randomly divided into three main groups (n:30) : NB (without bleaching), HB (bleached with 38% carbamide peroxide) and OB (bleached with Heydent bleaching gel assisted by diode laser). Each group was divided into five subgroups (n:6) : Si (without surface treatment), Er (Er:YAG laser), CO2 (CO2 laser), Nd (Nd:YAG laser) and As (Immersion in 10% sodium ascorbate solution). The bonding system was then applied and composite build-ups were constructed. The teeth were sectioned by low speed saw to obtain enamel- resin sticks and submitted to microtensile bond testing. Statistical analyses were done using two- way ANOVA, Tukey and Tamhane tests.Results:µTBS of bleached teeth irradiated with ND:YAG laser was not significantly different from NB-Nd group. Microtensile bond strength of OB-Er group was higher than NB-Er and HB-Er groups. The mean µTBS of HB-CO2 group was higher than NB-CO2 group; the average µTBS of HB-As and OB-As groups was also higher than NB-As group. Conclusion:Use of Nd:YAG, CO2 lasers and 10% sodium ascorbate solution could improve the bond strength in home-bleached specimens. Application of ND:YAG laser on nonbleached specimens and Er:YAG laser on office-bleached specimens led to the highest µTBS in comparison to other surface treatments in each main group.

No abstract