ABSTRACT
AIM: This in vitro study assessed the effects of in-office bleaching with gels (35% hydrogen peroxide [HP] or 37% cabamide peroxide [CP]) and two activation sources (violet radiation [LED] or nonthermal atmospheric plasma [NTAP]) on the mineral content of bovine enamel. MATERIAL AND METHODS: Dental blocks (nâ¯=â¯90) were assessed for initial microhardness before random distribution into nine groups: LED, LEDâ¯+â¯HP, LEDâ¯+â¯CP, NTAP, NTAPâ¯+â¯HP, NTAPâ¯+â¯CP, HP, CP and control (without treatment). Specimens were subjected to bleaching (2 clinical sessions, 7 days apart) using LED [20x/session, 1-min/each, 30â¯s apart] or NTAP [1x/session, 10â¯min]. µRaman determined contents of phosphate (PO43) and carbonate (CO32). Micro-energy dispersive X-ray fluorescence (µEDXRF) and spectrophotometry of enamel microbiopsy evaluated the calcium to phosphorous ratios (Ca/P). Two-way ANOVA and Tukey tests analyzed µRAMAN and µEDXRF results. Spectrophotometry results were analyzed using Kruskal-Wallis and Dunn tests. Pearson correlation tested µEDXRF and spectrophotometry results (αâ¯=â¯5%). RESULTS: NTAP and NTAPâ¯+â¯HP exhibited greater PO43- content than LED, LEDâ¯+â¯HP and control (pâ¯<â¯0.05). No statistical differences were detected between CO32- among groups. While µEDXRF evaluation demonstrated that NTAP and LED did not alter Ca/P ratio of enamel (pâ¯>â¯0.05), spectrophotometry showed that Ca/P reduced for LEDâ¯+â¯HP (pâ¯<â¯0.05). No correlation was found between µEDXRF and enamel microbiopsy spectrophotometry (pâ¯>â¯0.05). CONCLUSIONS: Activation sources did not adversely impact enamel's phosphate and carbonate concentrations after specimens' exposure to bleaching gels (either HP or CP). Visible light radiation emitted by a LED source was shown to adversely impact specimens' Ca/P ratios when treated with HP-containing bleaching gels.