Background:In order to compensate the adverse consequences of bleaching agents, the use of fluoride-containing remineralizing agents has been suggested by many researchers. The aim of this study was to compare the effect of applying two remineralizing materials on bleached enamel hardness and in comparison to natural saliva.Materials and Methods:In this experimental study, 30 enamel samples of sound human permanent molars were prepared for this study. Microhardness (MH) of all specimens was measured and 35% hydrogen peroxide was applied 3 times to the specimens. After completion of the bleaching process, MH of samples was measured and then enamel specimens were divided into three groups each of 10, specimens of groups 1 and 2 were subjected to daily application of hydroxyl apatite (Remin Pro) and casein phosphopeptide amorphous calcium phosphate fluoride (CPP-ACPF) (MI Paste Plus) pastes, respectively, for 15 days. In group 3, the specimens were stored in the operators' natural saliva at room temperature in this period of time. Final MH of all groups was measured. The data were analyzed using repeated measures ANOVA (α = 0.05).Results:The hardness significantly decreased in all groups following bleaching. Application of either Remin Pro, CPP-ACPF or natural saliva increased the hardness significantly. The hardness of the three test groups after 15 days were statistically similar to each other.Conclusion:The hardness of enamel increases eventually after exposure to either MI Paste Plus, Remin Pro or natural saliva.

Background and Aim: Changing the color of resin luting cements could affect the aesthetic appearance of thin porcelain veneer. The aim of this in vitro study was to evaluate the effect of artificially accelerated aging on color stability of light-cured resin cement and flowable composite as a luting agent through the porcelain veneer. Materials and Methods: This experimental study was carried out on 4 groups each contained 5 specimens with the dimension of 8 mm in diameter and 1 mm thickness. In group 1 and 2 five disks of resin cements and flowable composite were prepared, respectively. In group 3 and 4, the luting agent (1mm thickness) were bonded to feldspathic ceramic discs (1mm thickness). The color parameters of the samples in CIE Lab system were measured by spectrophotometer before and after artificially accelerated aging. The results were statistically analyzed by Two-way ANOVA and t-test. Results: The highest color change was observed in Z350 flowable composite that showed a statistically significant difference with other groups (P<0.001). Differences between veneered groups were not significant (P=0.04). Color changes in groups 3 and 4 which covered with porcelain laminate were statistically lower than uncovered groups and the differences were significant (P<0.001). Conclusion: Accelerated aging process could influence clinically unacceptable changes in the color of luting agents (E3.3). However, porcelain laminate with 1 mm thickness could cover the color changes of luting agent.

Objectives: This study aimed to assess the effect of tea on color stability of enamel lesions treated with resin infiltrant (RI). Materials and Methods: This in vitro, experimental study evaluated 30 extracted human third molars with no caries, cracks, or enamel defects. Enamel-dentin samples measuring 5 x 5 x 3 mm were prepared from the buccal surfaces of the teeth by a microtome. The samples were divided into three groups of 10 namely sound enamel, demineralized enamel, and demineralized enamel plus RI. White spot lesions (WSLs) were artificially created by immersing the samples in hydroxyethyl cellulose demineralizing gel with a pH of 4.5 for 4 days. Next, Icon RI was applied on the samples in group 3. The baseline color of the samples was measured using a spectrophotometer. They were immersed in tea solution 3 times a day, each time for 15 min, for a period of 2 weeks and then underwent colorimetry again. Data were analyzed using one-way ANOVA. Results: The maximum color change (∆E) was noted in demineralized enamel plus RI group (38.59±6.13) with significant differences with sound enamel (20.00±2.94) and demineralized enamel (25.27±7.47) groups (P<0.05). The difference between the latter two groups was not significant (P>0.05). Conclusion: Within the limitations of this in vitro study, the results showed that tea solution caused clinically unacceptable color change in all groups. However, the color stability of WSLs treated with RI was significantly lower than other groups following immersion in tea solution.

Background and Aim: Recurrent caries and low bond strength are the main causes of composite restorations failure. This study sought to assess the effect of chlorhexidine (CHX) on micro-shear bond strength (MSBS) to dentin of a fourth generation adhesive system and a universal bonding agent after aging. Materials and Methods: This in vitro study used 32 extracted third molars and 3-5mm thick dentin slices were cut out of each tooth. Specimens were randomly divided into 8 groups. After etching, Scotchbond fourth generation bonding agent or Single Bond universal adhesive was applied on dentin surfaces and Z250 composite cylinders were bonded to the surfaces. In groups B, D, F and H, CHX was applied for 1 minute after etching and prior to the application of bonding agent. The MSBS was measured after 24 hours and four months of water storage at 37C using a micro-tensile tester. The collected data were analyzed using three-way ANOVA. Results: The Scotchbond yielded significantly higher MSBS than the universal adhesive at 24 hours and four months (P<0.001). Application of CHX significantly increased the MSBS of both adhesives to dentin at 24 hours and four months (P<0.001). The bond strength decreased over the time irrespective of the type of bonding system (P<0.001). Conclusion: The MSBS of Scotchbond fourth generation bonding agent was generally higher than that of Single Bond universal adhesive. The MSBS of both adhesives decreased over time, however, the application of CHX decelerated the deterioration rate.