Effects of tooth-whitening gels on enamel and dentin ultrastructure--a confocal laser scanning microscopy pilot study

Confocal laser scanning microscopy (CLSM) in reflection mode provides a useful means for nondestructive microscopic examination of the ultrastructural characteristics of hard tissues, including enamel and dentin. In this study, CLSM was used to examine the effects of in vitro bleaching on enamel and dentin. The crowns of extracted human third molars were sectioned below the occlusal fissure, revealing subsurface dentin and the outer surface ring of enamel. Specimens were polished with 1,200-grit alumina followed by fine polish lapidary film, and cut into four equal sections per tooth, allowing each tooth to serve as internal control. Sections were mounted in acrylate for handling and were bleached for 0, 15, and 30 hours in 0.25 g of commercial Opalescence whitening gel (10% carbamide peroxide), the 5.3% hydrogen peroxide gel used in Crest Whitestrips, or 5% HClO4 solution. Blank glycerin served as a control treatment. In vitro whitening was confirmed by colorimeter readings of delta b and delta L with a PR 650 spectrophotometer/colorimeter. Treated teeth were examined with CLSM comparing enamel surface, dentoenamel junction (DEJ), and dentin at approximately 5 microns subsurface to the polished surfaces under an oil immersion objective. A single sample from each treatment (30-hour whitening) was also examined by environmental variable pressure scanning electron microscopy (VP-SEM). Internal comparison of glycerin (no whitening) controls (0-, 15-, and 30-hour exposures) revealed reproducible ultrastructure, facilitating treatment comparisons. Whitened teeth revealed no significant micromorphological changes associated with the whitening process in subsurface enamel, DEJ, and dentin areas. The direct treatment of cross sections permitted simple access of all areas to whitening gel, thereby eliminating the possibility of diffusion limitation of the gel in producing artifacts. VP-SEM observations similarly showed no significant changes in the surfaces after treatment.