Investigation of the whitening efficiencies of different office type whitening techniques and the changes caused on the envelope surface

Aim: The aim of this in-vitro study is to evaluate the whitening efficacy of 5 different office bleaching methods and the changes in enamel morphology after bleaching. Materials and Methods: In this study, 75 human molar teeth are used. The teeth are divided in half in the mesiodistal direction and a total of 150 enamel samples are obtained. The obtained samples are divided into 3 main groups to evaluate the whitening efficacy, surface roughness and enamel surface hardness, and each group is composed of 50 samples. Then, each main group was divided into 5 separate subgroups (n=10) containing 5 varied bleaching techniques. Before the bleaching process, color measurement with spectrophotometer, surface roughness with profilometer and microhardness measurement with Vicker's test device are performed. After that, different bleaching procedures are applied to the 5 subgroups formed as follows; Group I: Bleaching was applied only with 40% Hydrogen Peroxide (20 min). Group II: Activation process was applied with 40% Hydrogen Peroxide and LED light source (20 min). (20 min). Group III: Activation process was applied with 40% Hydrogen Peroxide and Diode laser (2 minutes in 20 minutes in total with 7W-940 nm diode laser). Group IV: Bleaching with ozone gas is carried out (20 minutes). Group V: 40% Hydrogen peroxide and ozone gas are used in combination (20 minutes H2O2 and 2 minutes ozone gas). Furthermore, post-bleaching measurements are made under the same conditions. Statistical evaluation of the data attained as a result of the experiments is obtained using the SPSS 25.0 package program. Significance level is adopted as p<0.05. One-Way ANOVA is made use of to compare the data showing normality, and the Kruskal wallis H test is implemented to compare the independent groups that do not display normal distribution. Post-hoc Tukey and H tests are selected for multiple comparisons between groups. Results: As a result of the statistical evaluation, it was determined that significant bleaching occurred in all groups (p<0.05). However, there was no significant difference in whitening efficiency between the groups (p>0.05). Based on the mean values, the lowest activity is detected in group 3, and the highest activity is revealed in group 1. Vickers hardness value and surface roughness decreased significantly in all groups after bleaching (p˂0.05). In the comparison between the groups, there was no significant difference in terms of hardness and roughness levels (p˃0.05). Conclusion: In the light of the findings obtained from our study, we suggest that ozone can be used as an alternative bleaching agent to hydrogen peroxide. In addition, it is discovered that the use of light activation is not necessary to increase the whitening effectiveness. Finally, we believe that enamel surface morphology may be affected after office bleaching methods, therefore, various precautions should be taken before and after bleaching.