The Role of Enamel Crystallography on Tooth Shade

Objective: Tooth shade is influenced by a combination of extrinsic-stains that 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 and chemical composition may affect tooth optical properties.

Method: 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 (lightness, chroma and hue), enamel chemical composition and crystallography. The data obtained was analyzed for correlation, and statistical significance was set at P<0.05.

Result: Tooth shade parameters varied dramatically within the studied population. Tooth hue was influenced by enamel hydroxyapatite (HA) crystal size (R=-0.358; B=-0.866; P=0.007), tooth chroma was influenced by enamel HA carbonization (R=-0.419; B=-99.06; P=0.005), and tooth lightness was influenced by 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). In contrast, enamel organic content had no significant effect on tooth shade.

Conclusion: In the present study we have revealed that the tooth shade is regulated by the size and the lattice parameters 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 esthetics that could be translated into new possible tooth whitening treatments and restorations with superior esthetics.