The role of enamel crystallography on tooth shade

Tooth shade is influenced by a combination of extrinsic-stains that are adsorbed to the enamel surface and by its intrinsic-shade resulting from the interaction of light with tooth structures. This study was designed to investigate how the variations in enamel ultrastructure may affect tooth optical properties.

One-hundred extracted teeth were collected from adult patients attending McGill-Undergraduate Dental Clinics. Shade-spectrophotometry, FTIR and XRD were used to assess tooth shade, enamel chemical composition and crystallography. The data obtained was analysed for Pearson correlation analysis and multiple linear regression analysis. The statistical significance was set at P < 0.05.

Tooth shade parameters varied dramatically within the studied population. Pearson correlation analysis demonstrated that tooth hue was associated with enamel hydroxyapatite (HA) crystal size (R = -0.358; B = -0.866; P = 0.007), tooth chroma was associated with enamel HA carbonization (R = -0.419; B = -99.06; P = 0.005), and tooth lightness was associated with both enamel HA crystal size (R = -0.313; B = -1.052; P = 0.019) and the degree of HA carbonization (R = -0.265; B=-57.95; P = 0.033). Multiple linear regression analysis demonstrated that the size of enamel HA crystals and the relative content of mineral carbonate were the most important predictors for tooth shade lightness (P = 0.018) and chroma (P=0.008), respectively. In contrast, enamel organic content had no correlation with tooth shade.

In the present study we have revealed that the tooth shade is regulated by the size of their HA enamel crystals. On the other hand, variation in the degree of enamel HA carbonization can also affect the tooth shade. These findings are of great relevance in dentistry since it provides better understanding of tooth aesthetics.