The comparative evaluation of effects of sodium ascorbate, alcohol and calcium hydroxide applications on bond strength of the composite resin to dentin in devital bleaching applied teeth

One of the most important goals of today's dentistry is to regain the natural aesthetics of the patient. The common expectation of many patients who apply to the dentist is to have better smile. Therefore, for patients, the color of the tooth is as important as the aesthetics of teeth. Whitening treatment has an increasing popular trend in recent years because of easy application, conservative intervention and being able to provide aesthetics painlessly to the patient. In many studies researching the bonding strenght of bleaching treatment applied dentin surfaces to composite resin, it is reported that there is a significant decrease in bond strength of the enamel after the bleaching application. This is because of the existence of residual oxygen layer formed after bleaching treatment. It is found that removing the residual oxygen layer increases the bonding values between the tooth and the composite. Using antioxidant agents in bleaching treatment applied teeth neutralizes free oxygen radicals and eliminates their negative biological effects. This purpose of this in-vitro study is to find out the effects of using sodium ascorbate, alcohol and calcium hydroxide as buffering agent on bond strength of teeth which have applied nonvital bleaching. Material and Method: In our study, 80 human upper central teeth were used. From the palatinal surface of the teeth endodontic access cavity was prepared and the root part of the teeth was cut out from its apex 2-3 mm of mine cement assembly. Nonvital whitening application with sodium perborate was made to all teeth. After the inital whitening, 4 different experimental groups were created by using sodium ascorbate, alcohol, application of calcium hydroxide and control group to the access cavity. After that, all groups were restored with bond and composite resin and 1x1 mm samples were obtained from 4 experimental groups by using minitom cutting device. These samples subjected to stress tests in the microtensile device and datas obtained by this method are compared in terms of strength of composite-dentin bonding. Results: Datas obtained in this study were statistically analyzed. While investigating differences between groups Kruskal Wallis-H test was used because of the fact that variables are far from the normal distribution. In case of significant differences in the Kruskal Wallis-H test, Post-Hoc multiple comparison test is used to find out groups having significant differences. While investigating the states of the variables coming from the normal distribution, Shapiro-Wilk's test was used due to the number of units. There is a statistically significant difference between groups in terms of bond strength values (p<0,05). Bond strength value of the group of sodium ascorbate is significantly higher than the calcium hydroxide and control groups (p<0,05). Despite of the fact that bond strength value of the sodium ascorbate group is higher than the alcohol group, no statistical difference is detected (p>0,05). Bond strength value of the alcohol group is higher than the calcium hydroxide group, but there is not a meaningful statistical difference (p>0,05). Bond strength value of the alcohol group is higher than the control group, but there is also not a meaningful statistical difference (p>0,05). Bond strength value of the group of calcium hydroxide and control groups are close to the each other and there is not a significant difference (p>0,05). Conclusion: Sodium ascorbate can be used to increase composite resin-dentin bond strength after nonvital bleaching. We conclude that the effect on the strength of bond of alcohol and calcium hydroxide applications is need to be investigated in more sample groups.