Bleaching Systems: a Scanning Electron Microscopic and Micro Analytic Study

Objectives: The purpose of this in vitro study was to evaluate the simulated long term effects of five different bleaching agents on human enamel. Methods: Fifteen freshly extracted human teeth preserved in saline with 0.1% Thymol were randomly divided into five equal treated groups: Group I (Opalescence X-Boost^®), Group II (Opalescence^® 20%), Group III (Rembrandt^® 35%), Group IV (Whitestrips blend-a-med) and Group V (Bleach and Smile). Each group included one impacted tooth. The teeth were covered with wax except for a 5x5 mm window of buccal enamel. The bleaching agents were applied for 96h. Every 6h the bleaching agents were removed and the teeth were cleaned by toothbrush and paste. Surface micromorphology assessments by SEM and microanalysis of the elements (Ca, P, C) were performed and compared to the results of the unbleached regions of the same tooth. Results: Microanalysis: There was no statistical difference between bleached and unbleached regions referring to the amount of Ca, P and C. However, the wt% of C in nearly all bleached regions has decreased. Scanning electron microscopic analysis: A statistical difference between the increased prism core diameter and the number of open cores of bleached areas compared to normal enamel was observed for in-office bleaching agents of Groups I and III. Groups II, IV and V did not exhibit surface changes. Conclusion: It is hypothesized that the organic enamel layer (pellicle and cuticle) and the Ca-PO₄ layer (not corresponding to hydroxyapatite) were dissolved after exposure to simulated long term application of high percentage agents. Consequently, the cores of the prisms and the diameter increases without disintegrating the periphery of the prisms.