Structure, chemical composition and mechanical properties of human and rat cementum and its interface with root dentin

This work seeks to establish comparisons of the physical properties of rat and human cementum, root dentin and their interface, including the cementum–dentin junction (CDJ), as a basis for future studies of the entire periodontal complex using rats as animal models. In this study the structure, site-specific chemical composition and mechanical properties of cementum and its interface with root dentin taken from 9- to 12-month-old rats were compared to the physiologically equivalent 40- to 55-year-old human age group using qualitative and quantitative characterization techniques, including histology, atomic force microscopy (AFM), micro-X-ray computed tomography, Raman microspectroscopy and AFM-based nanoindentation. Based on results from this study, cementum taken from the apical third of the respective species can be represented as a woven fabric with radially and circumferentially oriented collagen fibers. In both species the attachment of cementum to root dentin is defined by a stiffness-graded interface (CDJ/cementum–dentin interface). However, it was concluded that cementum and the cementum–dentin interface from a 9- to 12-month-old rat could be more mineralized, resulting in noticeably decreased collagen fiber hydration and significantly higher modulus values under wet conditions for cementum and CDJ (Erat-cementum = 12.7 ± 2.6 GPa; Erat-CDJ = 11.6 ± 3.2 GPa) compared to a 40- to 55-year-old human (Ehuman-cementum = 3.73 ± 1.8 GPa; Ehuman-CDJ = 1.5 ± 0.7 GPa). The resulting data illustrated that the extensions of observations made from animal models to humans should be justified with substantial and equivalent comparison of data across age ranges (life spans) of mammalian species.