Variations in Mechanical Properties of Enamel in Different Tooth Classes

Objectives: Variations in the hardness (H) and modulus (E) of human second molar enamel were previously reported to decrease by over 50% on moving from the occlusal surface to the dentin-enamel junction (DEJ) (Cuy, et al., 2002). The aim of this study is to expand this earlier effort and determine variations in mechanical properties for different teeth of the same class as well as different tooth classes. Methods: Maxillary first (M1), second (M2), and third (M3) molars were tested using nanoindentation techniques starting at the occlusal surface and proceeding to the DEJ in traverses at 3 locations in the crown: buccal, lingual, and intercuspal. Additionally, the H and E of maxillary central incisor (CI) enamel was mapped across a cross-section and compared to variations in molar properties. Results: Preliminary results have shown that M2s have a significant decrease in H and E from the occlusal surface to the DEJ (>50%) while M1 and M3 are more uniform throughout their thicknesses with decreases <20%. More specifically, M2s are harder and stiffer at the occlusal surface but softer and more compliant near the DEJ than M1s/M3s. M1s/M3s show similar properties through their thicknesses, but locally M1 varies more than M3. CIs display gradual changes in H and E throughout the thickness with decreases of 25% from the incisal surface to the DEJ. Ongoing studies of chemistry and microstructure are being conducted to determine the source of mechanical property variations. Conclusion: Mechanical properties of enamel vary by position within a tooth, within a tooth class, and between tooth classes. The results strongly suggest that enamel cannot be described with a single set of properties, which in turn may have a significant impact on dental restorative practices. NIH 5F30DE014130