Changes in dental enamel crystals by bleaching

Abstract

In recent years, enamel bleaching has been widely conducted clinically. Bleaching involves degrading pigments that are organic substances, and has been thought to have no effect on inorganic substances. However, no study has examined in detail how the enamel changes by bleaching. In the present study, the effects of two commercial bleaching agents; Hi-Lite (Hi-L) and Nite White Excel (NWE), on enamel were investigated by observations with contact microradiography (CMR), scanning electron microscopy (SEM), micro X ray diffractometer (XRD) and high-resolution transmission electron microscopy (HR-TEM), focusing on the effects on enamel crystals. CMR showed no change in degree of mineralization after bleaching with Hi-L or NWE as compared with the control. On SEM, gaps along the prism sheath and cracks between crystals were observed on the enamel surface of Hi-L-bleached and NWE-bleached enamel. XRD demonstrated no remarkable differences in crystal composition and crystallinity after bleaching by both agents as compared with the control. On HR-TEM, crystal growth findings were observed in some regions of Hi-L-bleached enamel, while crystal demineralization findings were observed in NWE-bleached enamel. All the above changes were limited to the very superficial layer of enamel in all the samples. © 2008 The Hard Tissue Biology Network Printed in Japan, All rights reserved.