Abstract
In clinical dentistry, since fracture is a major cause of tooth loss, better understanding of mechanical properties of teeth structures is important. Dentin, the major hard tissue of teeth, has similar composition to bone. In this study, we investigated the mechanical properties of human dentin not only in terms of mineral density but also using structural and quality parameters as recently accepted in evaluating bone strength. Aged crown and root dentin (age ≥ 40) exhibited significantly lower flexural strength and toughness than young dentin (age < 40). Aged dentin, in which the dentinal tubules were occluded with calcified material, recorded the highest mineral density; but showed significantly lower flexural strength than young dentin. Dentin with strong alignment of the c-axis in hydroxyapatite exhibited high fracture strength, possibly because the aligned apatite along the collagen fibrils may reinforce the intertubular dentin. Aged dentin, showing a high advanced glycation end-products (AGEs) level in its collagen, recorded low flexural strength. We first comprehensively identified significant factors, which affected the inferior mechanical properties of aged dentin. The low mechanical strength of aged dentin is caused by the high mineral density resulting from occlusion of dentinal tubules and accumulation of AGEs in dentin collagen.
Highlights
IntroductionOrientation[18,19,20,21,22]. Dentin with tubules orientated perpendicular to the long axis and short axis of beam-shaped specimens had significantly higher flexural and tensile strength than dentin with tubules orientated parallel to their long axis
In the case of dentin, structural parameters could include the number of dentinal tubules and the degree of occluded tubule lumens; quality parameters would include mineral density, apatite orientation and advanced glycation end-products (AGEs) content
The variance inflation factor indices of both quality and structural parameters were below 1.5 (Table 1), indicating that the analysis was not affected by the multicollinearity
Summary
Orientation[18,19,20,21,22]. Dentin with tubules orientated perpendicular to the long axis and short axis of beam-shaped specimens had significantly higher flexural and tensile strength than dentin with tubules orientated parallel to their long axis. Further investigations into the mechanical properties of dentin showed that dentinal tubule density on the enamel side (11,000–30,000 tubules/mm2) was significantly lower than on the pulp side (50,000– 70,000 tubules/mm2), and that the flexural and tensile strength of dentin on the enamel side was significantly higher than on the pulp side[18,19]. To understand bone mechanical function properly, bone strength has been evaluated in terms of both structural and quality parameters[30]. Structural parameters include microstructures such as cancellous bone trabeculae and the porosity of cortical bone, while quality parameters include mineralization, mineral orientation, collagen cross-links, and microcracks. Because dentin shares most of these parameters with bone, evaluating the mechanical strength of dentin by such structural and quality parameters seemed reasonable. In the case of dentin, structural parameters could include the number of dentinal tubules and the degree of occluded tubule lumens; quality parameters would include mineral density, apatite orientation and AGE content. The purpose of this study was to investigate the mechanical strength of human dentin in terms of structural and quality parameters, and to identify the factors most influential in regulating its mechanical strength
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