Confocal Laser Scanning Microscopy of Bleached Enamel and Dentin

Tooth whitening treatments in the United States include OTC strips. Objectives: This study compared subsurface and surface ultrastructure of human enamel and dentin exposed to a cycle of chronic bleaching with hydrogen peroxide bleaching strips (designed for daily application) in vitro. Methods: Enamel and dentin blocks were sectioned from extracted teeth and mounted in Durabase acrylic with 12 µm alumina polish (for a smear layer) on dentin and gamma alumina (0.30 µm alumina) on enamel. Teeth were bleached with 6.0 % hydrogen peroxide bleaching strips 4x/day for a total of 720 treatment cycles with Crest Whitestrips® Daily MulticareTM bleaching strips. Bleach and a non-bleach control groups received bid cycled treatment with Crest® Regular dentifrice as a 25% paste/water slurry for 5 minutes/day and between treatments specimens were stored in pooled human saliva. A third group of specimens was saved as a non-treated control. Following cycling, specimens from all three groups were selected for surface analysis or cross sectioned with a diamond saw for transverse evaluation of tooth ultrastructural changes. CLSM measures were carried out using a Leica TCS SP2 confocal laser scanning microscope with a He/Ne laser in reflection mode. Results: CLSM technique provides non-destructive in-depth imaging by recording series of consecutive images in tissues, which enables three dimensional visualizations of bleached dentin and enamel. CLSM observations revealed no etching or wear processes on enamel or dentin surfaces undergoing bleach treatments. Subsurface ultrastructure visualized below surfaces and on sectioned specimens revealed normal enamel prismatic and dentin tubular ultrastructure. Conclusions: The treatment regimen simulated over two years exposure to day-strips bleaching. CLSM analysis including histomorphological assessments of surface and subsurface enamel and dentin show that chronic bleaching with a day-strip did not influence tooth structure.