The role of enamel thickness and refractive index on human tooth colour

Objectives: To investigate the role of enamel thickness and refractive index (n) on tooth colour. Methods: The colour and enamel thickness of fifteen extracted human central incisors were determined according to CIELab colour scale using spectrophotometer (Crystaleye) and swept-source optical coherence tomography (SS-OCT), respectively. Subsequently, labial enamel was trimmed by approximately 100 mm, and the colour and remaining enamel thickness were investigated again. This cycle was repeated until dentin appeared. Enamel blocks were prepared from the same teeth and their n were obtained using SS-OCT. Multiple regression analysis was performed to reveal any effects of enamel thickness and n on colour difference (Delta E-00) and differences in colour parameters with CIELCh and CIELab colour scales. Results: Multiple regression analysis revealed that enamel thickness (p = 0.02) and n of enamel (p < 0.001) were statistically significant predictors of DE00 after complete enamel trimming. The n was also a significant predictor of Delta E-00 (p = 0.01). Enamel thickness and n were not statistically significant predictors of Delta L', Delta C', Delta a* and Delta b*. Conclusions: Enamel affected tooth colour, in which n was a statistically significant predictor for tooth colour change. Clinical significance: Understanding the role of enamel in tooth colour could contribute to development of aesthetic restorative materials that mimic the colour of natural tooth with minimal reduction of the existing enamel. (C) 2016 Elsevier Ltd. All rights reserved.