TMR and micro-Raman studies on enamel bleaching with remineralization treatment

Objectives: The aim of this study was to examine influences of remineralizing solution on the enamel surface properties and expect the effects of saliva against long-period bleaching. Methods: Bovine enamel specimens with 2 x 3mm windows were divided into following groups. As a control group, enamel specimens were immersed into a remineralizing solution simulating saliva (1.5mM CaCl2, 0.9mM KH2PO4, 130mM KCl, 20mM Hepes, pH 6.5) for 12 weeks. As experimental group (I), HiLiteTM was applied on the window once a week according to the manufacturer's instructions and was repeated for 12 weeks. During this period, the specimens were immersed in deionized water. As experimental group (II), HiLite™ was applied in the same way as the control group, however the remineralizing solution was used for immersing. After the experimental period, mineral profiles and integrated mineral loss (IML) were measured by transversal microradiography (TMR). Simultaneously, nano-indentation testing was performed across the lesion into the underlying sound enamel. Furthermore, to determine modifications of the molecules in the enamel structure, Raman microspectrometry was performed. The IML was analyzed statistically using ANOVA and Games-Howell test at p<0.05 (n=6). Results: The distinct sub-surface lesion was observed in the experimental group (I), however any lesion was not observed in the experimental group (II) and the control group. The IML indicated similar values during these groups (p>0.05). Also, the cross-sectional nano-hardness profiles of the control and the experimental group (II) were resembles. However, the Raman spectrum of the group (II) indicated the phosphate peak of surface of the lesions more intensively compared with the control. Conclusions: These results indicate that remineralization solution simulating saliva contributes not only recovering the mineral loss from enamel during the long-period bleaching with 35% H2O2 but also stabilizing of enamel crystals nearby the surface by exchanging the constituent elements.