Comprehensive analyses of how tubule occlusion and advanced glycation end-products diminish strength of aged dentin

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.

A paradigm shift for bone quality in dentistry: A literature review

“…Interestingly, this correlation was also seen in tooth dentin [85]. Thus, the BAp c-axis orientation is a potent parameter for bone quality and may be useful in evaluating and predicting mechanical properties of various types and conditions of biological hard tissues.…”

“…The relationships between BAp/collagen orientation and other bone quality parameters introduced in this review -collagen chemistry and osteocytes -are now becoming clarified. A negative relationship between the amount of AGE cross-links and the degree of BAp orientation is also suggested [85]. Moreover, synchronous alteration of anisotropic features in osteocyte network and BAp/collagen arrangement was reported [83,84,153,154].…”

The mechanical properties of human dentin for 3-D finite element modeling – numerical and analytical evaluation

“…27 As mentioned above, the decrease in the volumetric fraction and diameter of the tubules induces the increase of the shear modulus (G) and Young's modulus values. Considering the data obtained with the use of the analytical homogenization procedure, we could state that within the same layer of dentin an increase of the tubules' diameter (i.e.…”

“…27 At the same time, the ageing of the dentin, with the obturation of the tubules, resulting from higher mineralization, could diminish the flexural strength. Panfilov et al showed higher tensile strength of mature rather than teenage dentin (549.5 ± 26.9 MPa vs 445.2 ± 30.9 MPa, respectively).…”

The Tooth

“…In a recent multi-variable analysis of the reduction in flexure strength of dentin with age, Shinno et al, [75] reported that the changes were correlated with increasing Advanced Glycation End (AGE) product content, and increasing mineral density. AGEs are intra- and interfibrillar nonenzymatic crosslinks that develop through glycation [76].…”