Swept-source Optical Coherence Tomography Evaluation of Tooth Interior after Bleaching

Purpose: The demand for tooth bleaching for teeth whitening purposes has been increasing in recent years. However, the effects of the penetration of bleaching agents into the dentin have not yet been well studied. Swept-source optical coherence tomography (SS-OCT) enables the observation of tomographic images of hard tissues in a noninvasive manner. The present study employed SS-OCT to observe the state of the inner region of the dentin before and after tooth bleaching. Furthermore, imaging information was converted into numerical data to compare SS-OCT findings with micro-Raman spectroscopy findings, thereby assessing the diffusion dynamics of hydrogen peroxide within the dentin. Methods: Twenty extracted teeth were used with the approval of the Ethics Committee of Showa University Medical Association (approval number 2014-039). Specimens were divided into four groups and subjected to various numbers of bleaching sessions: once (Group 1), 3 times (Group 2), 6 times (Group 3), or 9 times (Group 4). Color measurement was performed and the dentin of each tooth was observed by SS-OCT before and after bleaching with Shofu Hi-Lite, a common bleaching agent. The area across the enamel and the dentin were examined after bleaching by micro-Raman spectroscopy using the specific wavelength for hydrogen peroxide. Results: Examination of L*a*b* values before and after bleaching confirmed a bleaching effect on all specimens. The ΔE*ab values increased alongside the number of bleaching sessions. Comparison of graphs of absolute numbers obtained from SS-OCT images before and after bleaching showed that after bleaching, the intensity of light reflection increased at the enamel surface but decreased around the dentin-enamel junction (DEJ). Statistical analysis of numerical data generated from SS-OCT images revealed significant changes in the enamel surface and the DEJ before and after bleaching (Student’s t-test, p