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

Rena Oguro; Masatoshi Nakajima; Naoko Seki; Alireza Sadr; Junji Tagami; Yasunori Sumi

doi:10.1016/j.jdent.2016.05.010

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

J Dent. 2016 Aug:51:36-44. doi: 10.1016/j.jdent.2016.05.010. Epub 2016 Jun 2.

Authors

Rena Oguro¹, Masatoshi Nakajima², Naoko Seki³, Alireza Sadr⁴, Junji Tagami⁵, Yasunori Sumi⁶

Affiliations

¹ Cariology and Operative Dentistry, Oral Restitution Department, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
² Cariology and Operative Dentistry, Oral Restitution Department, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan. Electronic address: nakajima.ope@tmd.ac.jp.
³ Dental Education Development Section, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan. Electronic address: nseki.edev@tmd.ac.jp.
⁴ Biomimetics Biomaterials Biophotonics & Technology Laboratory, Department of Restorative Dentistry, University of Washington School of Dentistry, 1959 NE Pacific St. Box 357456, Seattle, WA, 98195-7456, USA.
⁵ Cariology and Operative Dentistry, Oral Restitution Department, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan; Global Center of Excellence (GCOE) Program; International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
⁶ National Center for Geriatrics and Gerontology, Department for Advanced Dental Research, Center of Advanced Medicine for Dental and Oral Diseases, 36-3, Gengo, Morioka, Obu, Aichi, 474-8511, Japan.

PMID: 27265619
DOI: 10.1016/j.jdent.2016.05.010

Abstract

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 100μm, 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 (ΔE00) 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 ΔE00 after complete enamel trimming. The n was also a significant predictor of ΔH' (p=0.01). Enamel thickness and n were not statistically significant predictors of ΔL', ΔC', Δa* and Δb*.

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.

Keywords: Enamel; Enamel thickness; Refractive index; Tooth colour.

MeSH terms

Color
Dental Enamel*
Dentin
Humans
Refractometry
Tooth