Effects of different bleaching application time on tooth color and mineral alteration

The aim of this study was to evaluate the color and mineral changes caused by the bleaching agent applications at different durations on the enamel surface. 60 caries-free lower central teeth extracted for periodontal reasons were standardized for enamel and dentin thickness after cone-beam computed tomography (CBCT) measurements in terms of mineral (n=24) and color change (n=36). All teeth were divided into 3 groups according to different bleaching durations for color (n = 12) and mineral change (n = 8) measurements. The samples for mineral change were examined with the scanning electron microscopy-energy scattering X-ray (SEM-EDX, Jeol Inc., Tokyo, Japan) device before and 2 weeks after the application. For color change, the measurement of the samples was performed with spectrophotometer device (VITA EasyShade 4.0, Zahnfabrik, Bad Sackingen, Germany). Opalescence Boost PF 40% (Ultradent Products, Inc., South Jordan, Utah, USA) was applied for 20 minutes (min) in Group 1, 40 minutes in Group 2 and 60 minutes in Group 3. In order to determine the efficacy of bleaching, color measurements were repeated at 24 hours, 7 and 14 days after the application. In the intragroup comparison, Friedmann and Wilcoxon tests were used for non-normally distributions, while repeated variance analysis and paired t test were used for normally distributions in dependent variables. In the intergroup comparison, ANOVA and LSD tests were used for normally distributions, while Kruskal-Wallis and Dunn tests were used for non-normally distributions in independent variables. p <0.05 was considered significant. In the study, statistically significant difference was observed between all groups in terms of color change (p < 0.05). In terms of mineral change, there was a statistically significant difference between phosphate (P), magnesium (Mg) and sodium (Na) elements in all groups (p < 0.05), but there was no significant difference for calcium (Ca) mineral (p > 0.05). Effective whitening was achieved in all study groups. When the results are evaluated as versatile in terms of bleaching effectiveness and mineral change, the most ideal bleaching duration was determined as 40 minutes (Group 2).