Mechanical properties of the dentinoenamel junction: AFM studies of nanohardness, elastic modulus, and fracture

Abstract

The dentinoenamel junction (DEJ) is a complex and poorly defined structure that unites the brittle overlying enamel with the dentin that forms the bulk of the tooth. In addition, this structure appears to confer excellent toughness and crack deflecting properties to the tooth, and has drawn considerable interest as a biomimetic model of a structure uniting dissimilar materials. This work sought to characterize the nanomechanical properties in the region of the DEJ using modified AFM based nanoindentation to determine nanohardness and elastic modulus. Lines of indentations traversing the DEJ were made at 1-2 microm intervals from the dentin to enamel along three directions on polished sagittal sections from three third molars. Nanohardness and elastic modulus rose steadily across the DEJ from bulk dentin to enamel. DEJ width was estimated by local polynomial regression fits for each sample and location of the mechanical property curves for the data gradient from enamel to dentin, and gave a mean value of 11.8 microm, which did not vary significantly with intratooth location or among teeth. Nanoindentation was also used to initiate cracks in the DEJ region. In agreement with prior work, it was difficult to initiate cracks that traversed the DEJ, or to produce cracks in the dentin. The fracture toughness values for enamel of 0.6-0.9 MPa . m(1/2) were in good agreement with recent microindentation fracture results. Our results suggest that the DEJ displays a gradient in structure and that nanoindenation methods show promise for further understanding its structure and function.

Understanding Nano-Anatomy of Healthy and Carious Human Teeth: a Prerequisite for Nanodentistry

“…The complex structure of human teeth [28][29][30][31][32] facilitates the preservation of hardness and wear resistance over many millions of masticatory cycles. Besides the microscopic structure, investigations of the nanostructure have been performed, mainly with local probe techniques including atomic force microscopy (AFM) and scanning electron microscopy (SEM) [22,[33][34][35][36]. Due to the reduced field of view, however, only restricted parts of the tooth of interest can be examined.…”

Effect of sterilization by gamma radiation on nano-mechanical properties of teeth

“…If carious teeth are used, higher radiation doses may be necessary and might cause alterations in material structure and properties. Nano-indentation has become a common technique for the determination of local mechanical properties of structural features in biological hard tissues [12][13][14]. Hence, while investigations of the mechanical properties (hardness, surface morphology and bond strength) on a micro-scale showed no effect of radiation doses up to 25 kGy [15][16][17][18], the effect on the mechanical properties on a nano-scale needed to be investigated.…”

Bracket bond strength and cariostatic potential of an experimental resin adhesive system containing Portland cement

“…21 In contrast, recent advances in the nanoindentation test have allowed the analysis of nanoscale mechanical properties. 22 In addition, the elastic modulus for this very small volume of material can be obtained mathematically from a load-displacement curve. The results of the cross-sectional nanoindentation a ARI indicates Adhesive Remnant Index; PC, Portland cement.…”