Properties of Primary and Secondary Healthy Human Cementum

Introduction: Primary cementum (PC) anchors the tooth to alveolar bone by periodontal ligament extensions from cervical to the apical third of the root. Secondary cementum (SC) occurs from apical third to apex and mechanistically it is thought to be an occlusal load absorber. PC and SC are integrated with root dentin via cementum dentin junction (CDJ). Hypothesis: The inherent characteristics of PC and SC are significantly different within and across age groups. Methods: 150-200 µm thick ground sections were prepared from 500 µm thick longitudinal mid-sections from 9 molars, 3 from each age group (19-39, 40-59, 60-80 yrs) and von Kossa stained. One-half of each remaining tooth was embedded and polished to 1µm finish to evaluate microhardness. The other half was stained with picrosirius red to study the collagen fiber localization and orientation within respective cementums. Results: PC illustrated wide-radial collagen fibers. SC illustrated a woven-fabric-like structure with wide-circumferential and narrow-radial collagen fibers. Ground sections across age groups illustrated radially-oriented hypomineralized collagen fibers forming a wider CDJ coronally with a decrease in width apically. On average the width of the CDJ decreased with an increase in age: 44 ± 9 µm, 25 ± 5 µm, 23 ± 3 µm. Significant increases (t-test, P < 0.05) in PC and SC hardness values were found with age; PC: (0.38 ± 0.1 GPa, 0.41 ± 0.1 GPa, 0.45 ± 0.1 GPa); SC: (0.32 ± 0.1 GPa, 0.36 ± 0.1 GPa, 0.44 ± 0.1 GPa). Significant differences between PC and SC hardness values for the younger and middle age groups were observed. Conclusions: Age affected both the structure and properties of cementum and CDJ. Co-relating the properties within and across age groups elucidates the function of extracellular matrices of PC, SC and CDJ responsible for sustaining the cyclic masticatory loads. Support: NIH/1K99DE018212