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

•Bleaching application is a conservative method applied to colored teeth.•Bleaching agents can cause damage enamel tissue after application.•OH– which is degradation product of bleaching gels, assigns efficacy of application. The effects of HP-based products upon dental enamel are inconclusive. The purpose of this study was to evaluate the colour and mineral changes caused by the bleaching agent applications at different durations on the enamel surface. 60 caries-free lower central incisor 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 colour change (n = 36). All teeth were divided into 3 groups according to different bleaching durations for colour (n = 12) and mineral change (n = 8) measurements. The samples for mineral change were examined with the -energy scattering X-ray (EDX, JSM-6390 LV, Jeol Inc., Japan) device before and 2 weeks after the application. For colour change, the measurement of the samples was performed with spectrophotometer device (VITA EasyShade 4.0, Germany). Opalescence Boost PF 40% (Ultradent Products, USA) was applied for 20 min (min) in Group 1, 40 min in Group 2 and 60 min in Group 3. In order to determine the efficacy of bleaching, colour measurements were repeated at 24 h, 7 and 14 days after the application. In the intragroup comparison, Friedman 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 colour change at different measurement times (p < 0.05). The highest ΔE00 values were observed in Group 3 (ΔE003 = 8.37 ± 2.15); the lowest value was observed in Group 1 (ΔE001 = 4.74 ± 1.26). Ca values were similar increase among all groups (p > 0.05). The highest Ca values were observed in Group 3 (69.91 ± 5.34); the lowest value was observed in Group 2 (66.08 ± 1.50). P values were similar increase among all groups (p > 0.05). The lowest P values were observed in Group 3 (26.54 ± 5.92); the highest value was observed in Group 2 (29.86 ± 2.26). Effective whitening was ach