Micro-mechanical characterisation of the properties of primary tooth dentine.

Objectives: Understanding the mechanical properties of dentine is of importance as adhesive restorative materials mainly achieve their bonding to the tooth structure through dentine. The current study measures the hardness and modulus of elasticity of primary molar dentine using an Ultra-Micro-Indentation System (UMIS), which allows the dentine to remain hydrated and thus is assumed to be closer to the in vivo conditions.

Methods: Eight sound primary molar teeth were axially sectioned, embedded in resin and fine polished. Two linear arrays of indentations were done on coronal dentine, from the pulp wall to dentino-enamel junction (DEJ) parallel to the tubule direction under a force load of 25mN.

Results: The mean hardness and elastic modulus of the dentine nearest the pulp wall was 0.52+/-0.24 and 11.59+/-3.95GPa, respectively, which was significantly lower than those of dentine in the middle area, which was 0.85+/-0.19 and 17.06+/-3.09GPa, respectively, and the dentine nearest DEJ, which was 0.91+/-0.15 and 16.33+/-3.83GPa, respectively. There is a statistically significant linear correlation between the hardness and modulus of elasticity.

Conclusions: The hardness and modulus of elasticity of dentine decreases with decreasing distance from the pulp. This is of importance to clinicians because an extension of cavity preparation towards the pulp may lead to less mechanical support for a restoration.