The role of enamel thickness and refractive index on human tooth colour.
To investigate the role of enamel thickness and refractive index (n) on tooth colour.



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.



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*.



Enamel affected tooth colour, in which n was a statistically significant predictor for tooth colour change.



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.
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.
Rena
R
Oguro
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.
Masatoshi
M
Nakajima
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.
Naoko
N
Seki
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.
Alireza
A
Sadr
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.
Junji
J
Tagami
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.
Yasunori
Y
Sumi
D003116:Color; D003743:Dental Enamel; D003804:Dentin; D006801:Humans; D012031:Refractometry; D014070:Tooth
Enamel; Enamel thickness; Refractive index; Tooth colour