Adaptive properties of human cementum and cementum dentin junction with age.

Abstract

The objective of this study was to evaluate age related changes in physical (structure/mechanical properties) and chemical (elemental/inorganic mineral content) properties of cementum layers interfacing dentin. Human mandibular molars (N=43) were collected and sorted by age (younger=19-39, middle=40-60, older=61-81 years). The structures of primary and secondary cementum (PC, SC) types were evaluated using light and atomic force microscopy (AFM) techniques. Chemical composition of cementum layers were characterized through gravimetric analysis by estimating ash weight and concentrations of Ca, Mn, and Zn trace elements in the analytes through inductively coupled plasma mass spectroscopy. The hardness of PC and SC was determined using microindentation and site-specific reduced elastic modulus properties were determined using nanoindentation techniques. PC contained fibrous 1-3 µm wide hygroscopic radial PDL-inserts. SC illustrated PC-like structure adjacent to a multilayered architecture composing of regions that contained mineral dominant lamellae. The width of the cementum dentin junction (CDJ) decreased as measured from the cementum enamel junction (CEJ) to the tooth apex (49-21 µm), and significantly decreased with age (44-23 µm; p<0.05). The inorganic ratio defined as the ratio of post-burn to pre-burn weight increased with age within primary cementum (PC) and secondary cementum (SC). Cementum showed an increase in hardness with age (PC (0.40-0.46 GPa), SC (0.37-0.43 GPa)), while dentin showed a decreasing trend (coronal dentin (0.70-0.72 GPa); apical dentin (0.63-0.73 GPa)). The observed physicochemical changes are indicative of increased mineralization of cementum and CDJ over time. Changes in tissue properties of teeth can alter overall tooth biomechanics and in turn the entire bone-tooth complex including the periodontal ligament. This study provides baseline information about the changes in physicochemical properties of cementum with age, which can be identified as adaptive in nature.