Journal of Dental Medicine

Background and Aims: The bleaching agents can lead to color and translucency changes in composite resins. Due to the increasing use of the nano composites and the silorane-based composites, this study aimed at examining the color and translucency changes of these restorations after bleaching agents.
Materials and Methods: In this experimental - laboratory study, 198 composite discs were divided into three groups of 66 specimens using three types of composite: the microhybrid composite Z250, the nanohybrid composite Z350 and the silorane-based composite P90. After acid etching, half of the specimens in each group were covered by a resin rebounding agent. Then, the color and translucency assessment was done by reflectance spectrophotometer, using CIE LAB system. Each group was divided into three subgroups of bleaching agents: the 40% hydrogen peroxide and 20% carbamide peroxide bleaching agents and the control group. After applying bleaching agents, the final color and translucency changes were assessed. Data were analyzed using Mann Whitney and Kruskal Wallis tests.
Results: The effect of composite and bleaching agent type and bonding agent were significant (P<0.001). The color changes in the microhybrid composite were higher than nanohybrid and silorane-based composites (P<0.001) (∆E>3.3). Also, the color changes by 20% carbamide peroxide were higher than that of hydrogen peroxide and control groups (P<0.001). The results of translucency changes were generally consistent with color-change measurements (∆E>3.3).
Conclusion: According to the present study, the most color changes appeared in the microhybrid composite and by 20% carbamide peroxide bleaching agent. Rebound samples were generally less affected by bleaching agents. The least color and translucency changes were related to nanohybrid composites.

Background and Aims: Today, academic stress and subsequent test anxiety is one of the most important problems for the last year of high school students. In addition to systemic effects, stress can affect the level of oral health by disrupting oral health behaviors. The aim of this study was to investigate the relationship between stress and variables related to oral health in the final year of high school students prior to University entrance exam.
Materials and Methods: In this descriptive-analytical study, the level of stress and variables related to oral health in 180 students of the final year of high school in Tehran, in three time periods during the academic year 2018-2019, were measured by a questionnaire and one clinical examination. Data were analyzed by Friedman, Bonferroni and Generalized Estimating Equations using SPSS software.
Results: As the exam approaches, some variables related to the oral health, such as toothbrush usage pattern, daily sleep, fast food frequency, and sweet snack consumption, changed (P<0.05). Daily sleep changes were significantly associated with the stress changes (P=0.022). According to the results of the Repeated Measures Analysis, significant changes were observed between the average score of the "Cognitive Error" aspect of three times (P<0.001). Also, according to the results of the Bonferroni Test, significant changes related to the difference in the average score of "cognitive error" 6 months and 3 months before the entrance exam (P<0.001), 6 months and 1 month before the entrance exam (P<0.001), and 3 months and 1 month before the entrance exam (P<0.001) were observed. In all three cases, as the time of the entrance exam approaches, the score of "cognitive error" had decreased significantly. Considering that the lower score in this index indicates a higher level of test anxiety, the closer we get to the entrance exam, the higher the level of test anxiety in the "cognitive error" dimension
Conclusion: The academic stress of the national university entrance exam can affect some oral health variables such as daily sleep, however, it is not related to other variables.