BackgroundRepair of composite restorations is a conservative method that can increase the longevity and durability of restorations while preserving the tooth structure. Achieving a suitable bond between the old and new composite is difficult. To overcome this problem, some methods have been recommended to increase the repair bond strength of composite.This study aimed to assess the effect of aging by thermocycling (5,000 and 10,000 cycles) and mechanical surface treatments (Er,Cr:YSGG laser and bur) on repair shear bond strength of composite resin.Material and MethodsTotally, 120 composite blocks measuring 6x4x4 mm were fabricated of Filtek Z250 composite and were randomly divided into three groups (n=40) based on initial aging protocol: (a) no aging: storage in distilled water at 37°C for 24 hours, (b) 5,000 thermal cycles, (c) 10,000 thermal cycles. Each group was then randomly divided into two subgroups (n=20) based on mechanical surface treatment (laser and bur). The laser and bur-prepared surfaces were silanized and Adper Single Bond 2 was then applied. The repair composite was bonded to surfaces. Half of the samples in each subgroup (n=10) were subjected to 5,000 thermal cycles to assess durability of bond. The remaining half were stored in distilled water at 37°C for 24 hours and all samples were then subjected to shear bond strength testing in a universal testing machine with a crosshead speed of 1mm/min. Data (in megapascals) were subjected to one-way ANOVA and Tukey’s test (P=0.05). Mode of failure was determined under a stereomicroscope.ResultsBur preparation significantly improved the bond strength compared to laser (P<0.001). Aging by 10,000 thermal cycles significantly decreased the repair bond strength of composite (P<0.001). No significant difference was noted in this regard between distilled water and 5,000 thermal cycles groups (P=0.699). Primary bond strength and bond strength after 5,000 thermal cycles in the same subgroups were not significantly different either (P=0.342).ConclusionsAging by 10,000 thermal cycles significantly decreases the repair bond strength of composite and surface preparation by bur provides a higher bond strength compared to laser. Key words:Thermocycling, Composite, Repair, Laser.

Surface preparation of aged composite by bur and application of universal adhesive can improve the repair bond strength of composite. Application of silane (without adhesive) in the process of repair cannot provide adequately high repair bond strength.

Objectives This study aimed to assess the effect of an optical whitening toothpaste on color stability of microhybrid, nanofilled, and microfilled composite resins and resin-modified glass ionomer (RMGI) cement in comparison of two other toothpastes. Materials and Methods In this experimental study, disc-shaped composite samples were fabricated. The samples were then polished using silicon carbide papers. Twenty-seven samples of each material were fabricated and subjected to colorimetry using a spectrophotometer. Each group of material was then divided into three subgroups for the application of conventional whitening and whitening containing blue covarine toothpastes. One operator brushed the samples with an electric soft toothbrush with circular motion twice a day, each time for 30 seconds. Colorimetry was performed at 0, 1, 7, 30, and 90 days. Statistical Analysis Two-way analysis of variance (ANOVA), one-way ANOVA, and Tukey’s honestly significant difference (HSD) test were used for statistical analysis. Results The interaction effect of type of restorative material and time on ∆E was not significant at baseline or 1 day (p > 0.05). The effect of type of toothpaste on ∆E was not significant at baseline or 1 day (p = 0.78) but the effect of type of material was significant (p < 0.05). The toothpastes had significantly different effects on ∆E of Z250 at all time points (p < 0.05) except for ∆E0–30 (p = 0.106). The toothpastes had significantly different effects on ∆E of Z350 and Gradia at all time points (p < 0.05). The same was true for RMGI except for ∆E0–7 (p = 0.43) and ∆E0–90 (p = 0.52). The majority of color changes caused by toothpastes were not clinically perceivable (∆E < 3.3), except for ∆E0–90 by the whitening toothpaste (∆E = 9), ∆E0–90 by the conventional toothpaste for Z350 (∆E = 3.9), and ∆E0–1 by the whitening toothpaste for RMGI (∆E = 3.7). Conclusion The color change of all composite samples was not clinically perceivable (<3.3) at all time points, which shows that the tested toothpastes do not cause a significant change in color of composite materials.

BackgroundThe aim of this study was to evaluate the effect of diode laser irradiation and bleaching materials on the dentinal tubule diameter after laser bleaching.Material and MethodsThe dentin discs of 40 extracted third molar were used in this experiment. Each disc surface was divided into two halves by grooving. Half of samples were laser bleached at different wavelengths with two different concentrations of hydrogen peroxide. Other half of each disc with no laser bleaching remained as a negative control. Dentin discs were assigned randomly into four groups (n=10) with following hydrogen peroxide and diode laser wavelength specifications; Group 1 (30% - 810 nm), group 2 (30% - 980 nm), group 3 (46% - 810 nm) and group 4 (46% - 980 nm). All specimens were sent for scanning electron microscopic (SEM) analysis in order to measure tubular diameter in laser treated and control halves. Data were analyzed by ANOVA and Tukey test (p<0.05).ResultsA significant reduction in dentin tubule diameter was observed in groups 1, 2 and 4. There was no significant difference between groups 1 and 2 and between groups 3 and 4 after bleaching.ConclusionsThe SEM results showed that diode laser was able to reduce dentin tubule diameter and its effect on dentin was dependent on chemical action of bleaching material. Key words:Laser, diode, dentin, tubule, diameter.

Background. The success of composite resin restorations depends to a great extent on their color stability. However, discoloration is still a problem in composite resin restorations. Objectives. The aim of the study was to evaluate the effect of different staining solutions on the color stability of composite resins. Material and methods. A total of 96 composite disks, 2 mm in height and 8 mm in diameter, were fabricated of 3 commercially available composite resins. The samples were divided into 4 groups of 8 and were immersed in 4 staining solutions: coffee, tea, soda, and artificial saliva. The color parameters of the samples were measured and recorded before as well as 2, 4 and 8 weeks after immersion by spectrophotometry, using the CIELAB color space. A color change (ΔE) ≤3.3 was considered the acceptable threshold for visual perception. The results were analyzed using the one-way analysis of variance (ANOVA) and Tukey's post hoc test (p < 0.05). Results. All the composite resins in the study showed discoloration in all the staining solutions. The ΔE of Vertise TM Flow was the highest in the tea solution. The lowest ΔE occurred in the Filtek TM Z250 composite in artificial saliva. Conclusions. This in vitro study showed that the color stability of tooth-colored restorations can be influenced by dietary habits.