Variation in the Color of Japanese Teeth and Structural Changes in Enamel Rod Sheath Associated with Age

Abstract

This study was intended to clarify the changes in the color of teeth and enamel rod sheath with age. A total of 14 first premolars taken from patients between the ages of 10-70 years old were used in this study. Photographs of the buccal surface of teeth were taken and the tone was converted into color system marked as L*, a* and b* using image processing software. Thick sections of 1.5 mm traversing the tooth axis were prepared and the enamel translucency and color of enamel and dentin were determined in the same manner. Correlation analysis was carried out between the clinical color of the buccal surface and age, enamel color and age, dentin color and age and translucency and age. The sections were embedded in resin and the polished cross section was observed a backscattered electron image with SEM. The observation sites were the following: outer of the enamel, middle layer and deep layer (near the dentin-enamel junction). The structure of the enamel rod sheath was the focus of observation. The area and width of enamel rod sheath were measured from SEM images. Correlation analysis between color, area of enamel rod sheath and age were carried out with these data. Results showed that color of enamel and dentin became darker with age; the color of the entire buccal surface became dark reddish and yellowish but it was not due to increased permeability of enamel. The enamel rod sheath was clear in teeth of young people but it showed a rapid decrease with age. From the results, the crystal gap and enamel rod sheath suppress the reflection of the color of underlying dentin with the tendency of scattering the light from the outer layer to the deeper layer in teeth of young patients. However with increasing age, the crystal gap and enamel rod sheath decrease thereby strongly reflecting the color of dentin resulting to a darker color. Thus, microstructural changes in enamel affect the color of the tooth.