Evaluation of the Effect of Bleaching and Relapse after Treatment Using Non-contact Type Dental Spectrophotometer

Abstract

Purpose: We evaluated the color changes resulting from office bleaching and color variations over time using a non-contact type dental spectrophotometer. Methods: This study was performed at the Oro-facial Plastic Medical Center, Fukuoka Dental College, Medical and Dental Hospital with permission of the Institutional Review Board by the Fukuoka Dental College. After obtaining informed consent, 63 patients were examined. The teeth were bleached using a bleaching system with hydrogen peroxide (Beyond Whitening System, Beyond Dental & Health, USA) during three applications and photo-activation according to the manufacturer's instructions. After 14 days, the bleaching was done again. The tooth color was measured three times: before treatment, after office bleaching, and one month thereafter using a non-contact type dental spectrophotometer Crystaleye (CE100-DC, Olympus). The tooth color was quantified according to the CIEL*a*b* 1976 criteria (Commission Internationale de l'Eclairage, 1976). The labial surface of the tooth was divided into three areas, the "cervical", "body" and "incisal" areas. Any differences in the color of each part were statistically analyzed in comparison to the findings before treatment. The effect of office bleaching was evaluated based on the area that showed the color having the greatest statistical difference from that before treatment. The color analysis was done before treatment, after office bleaching, and one month thereafter. The obtained data were statistically analyzed by one-way ANOVA and Bonferroni's post-hoc test. Results: The color of every part of the tooth was analyzed at baseline. The body area showed a significantly different color compared to that seen in the cervical or incisal part. Therefore, the effect of office bleaching was evaluated based on the color. After office bleaching, L* was significantly higher, and a* and b* were significantly lower, in comparison to the baseline values. One month later, a* was not significantly different from that at the other time points. However, L* of most parts decreased except for the upper canines and lower lateral incisors, while b* of all parts increased in comparison to that seen after bleaching. Hence, a relapse was observed one month after office bleaching. Conclusion: Tooth color changes due to office bleaching were evaluated using a non-contact type dental spectrophotometer. Our findings suggest that the effect of office bleaching was observed objectively. However, one month thereafter, the result differed according to each tooth area and site, and the spectrophotometer findings suggested that the color change had occurred at one month after bleaching.