Mechanical and Physical Properties of Dentine in Hypomineralised/Hypoplastic Permanent Molars

Objectives: Isolated enamel defects are commonly seen in first permanent molar teeth and can be caused by developmental or genetic insults. It is speculated that the same insult that upsets the ameloblast function can also damage the odontoblasts. Anecdotal clinical evidence suggests that the dentine of affected teeth is softer or of an 'unusual' consistency in comparison to unaffected teeth. The aim of this study was to determine the mechanical properties and conduct scanning electron microscopy (SEM) investigations of the dentine of hypomineralised/hypoplastic first permanent molars. Methods: Seven such molars and two control teeth (first premolars) were embedded, sectioned and finely polished. Using an Ultra-Micro-Indentation System (UMIS) two arrays of indentations were completed in the dentine from the pulp to the amelo-dentinal junction directly under the hypomineralised enamel. From these indentations the hardness and modulus of elasticity of the dentine were computed. A single control and affected sample were investigated with the SEM. Results: The average hardness for control teeth for the inner and outer region of dentine was 0.65 +/- 0.10 GPa, and 0.69 +/- 0.09 GPa respectively whereas for the dentine of affected teeth the average hardness was 0.71+/- 0.10 GPa and 0.57 +/- 0.08 GPa respectively for the same regions. The average modulus of elasticity for the control teeth for the inner and outer region of dentine were 17.22 +/- 3.19 GPa and 18.43 +/- 1.97 GPa respectively, whereas the average modulus of elasticity of the dentine from the hypomineralised teeth was 18.29 +/- 1.20 GPa and 14.00 +/- 1.58 GPa for the same regions. Conclusion: This study showed that there was no significant difference in the mechanical and microscopic properties of the dentine beneath the hypomineralised enamel.