Tooth Surface Observation after Bleaching by Optical Coherence Tomography

Abstract

 Purpose: To observe the tooth structure after bleaching by using experimental swept-source optical coherence tomography (SS-OCT, Yoshida Dental).
 Methods: This study was approved by the Showa University Institutional Review Board (Approval number 2011-035). Fourteen extracted intact human incisors were used. Commercial in-office bleaching gel containing 35% hydrogen peroxide (Shofu Hi-Lite, Shofu) was applied to the labial enamel surface according to the manufacturer's instructions. The bleaching gel was applied to the surface for 3 min once a week for 4 weeks, and the 4-week bleaching regimen was repeated three times. Before and after bleaching, the tooth structure was observed by SS-OCT, which constructs images by ultrahigh-speed scanning of the converted wavelength of a near-infrared laser and allows rapid noninvasive construction of tomographic images of teeth.
 Results: In the SS-OCT images, light reflection from the enamel surface became strong after bleaching. The light reflection intensity deep in the tooth tended to be lower than that at the enamel surface. The light reflection intensity in the SS-OCT images of the control before and after storage in water at 37℃ either decreased or remained the same. The tooth appeared whiter after bleaching to the naked eye. The value of luminosity (L^*) increased, and the values of color parameters (a^* and b^*) decreased. Significant differences in the color difference (ΔE^*ab) before and after bleaching were found by Student's t-test (p＜0.05).
 Conclusion: The light reflection intensity in the SS-OCT images increased for the enamel surface bleached with 35% hydrogen peroxide, indicating that small structural changes may occur that are not visible by SEM. SS-OCT can be used to provide patients with information in a clinical setting and may be a promising new tool for tooth bleaching.