Age-Related Deterioration of Human Dentin

Objectives: In Japan, maintenance of residual teeth in elderly people is becoming an important issue. Hence, efforts have been made to reveal aging effects on various oral tissues but the reports on teeth are limited. In this study, we focused on dentin, and analyzed parameters describing both organic and inorganic components, using human teeth extracted from donors of wide age range.
Methods: Human molars and premolars (n=30), freshly extracted for orthodontic or periodontal treatments, were used. The tooth samples were embedded and sectioned longitudinally into slices, parallel to the lingual-buccal surface, using a slow speed water-cooled diamond saw. 2D mapping evaluation of L*a*b* color coordinates, nano-indentation analysis, X-ray scattering analysis and collagen modification analysis were carried out respectively. In addition, human molars and premolars (n=3) were glycated by ribose in vitro and analyzed by the above-described methods.
Results: 2D gradients in each parameter (from pulp chamber to the outer side or from crown to root) were observed in lingual-buccal cross-section of dentin. Physical property evaluation revealed that b* (yellowish tint) and Young’s modulus increased upon aging significantly. Moreover, there was an aging-related decrease of hydroxyapatite particles’ aspect ratio as well as an increase of collagen pentosidine (a surrogate marker of Advanced Glycation End Products (AGEs)). Additionally, in vitro experiments revealed that the AGEs accumulation in dentin contributes to the increased b* and increased Young’s modulus.
Conclusions: Our study revealed that human dentin changes with age in aesthetic and mechanical properties, resulting in more yellow and brittle old dentin. In addition, the observation of extracted teeth combined with in vitro studies highlight the role of AGEs in aging-related tooth property alterations.