Abstract
Functional loads on an organ induce tissue adaptations by converting mechanical energy into chemical energy at a cell-level. The transducing capacity of cells alters physico-chemical properties of tissues, developing a positive feedback commonly recognized as the form-function relationship. In this study, organ and tissue adaptations were mapped in the bone-tooth complex by identifying and correlating biomolecular expressions to physico-chemical properties in rats from 1.5 to 15 months. However, future research using hard and soft chow over relevant age groups would decouple the function related effects from aging affects. Progressive curvature in the distal root with increased root resorption was observed using micro X-ray computed tomography. Resorption was correlated to the increased activity of multinucleated osteoclasts on the distal side of the molars until 6 months using tartrate resistant acid phosphatase (TRAP). Interestingly, mononucleated TRAP positive cells within PDL vasculature were observed in older rats. Higher levels of glycosaminoglycans were identified at PDL-bone and PDL-cementum entheses using alcian blue stain. Decreasing biochemical gradients from coronal to apical zones, specifically biomolecules that can induce osteogenic (biglycan) and fibrogenic (fibromodulin, decorin) phenotypes, and PDL-specific negative regulator of mineralization (asporin) were observed using immunohistochemistry. Heterogeneous distribution of Ca and P in alveolar bone, and relatively lower contents at the entheses, were observed using energy dispersive X-ray analysis. No correlation between age and microhardness of alveolar bone (0.7±0.1 to 0.9±0.2 GPa) and cementum (0.6±0.1 to 0.8±0.3 GPa) was observed using a microindenter. However, hardness of cementum and alveolar bone at any given age were significantly different (P<0.05). These observations should be taken into account as baseline parameters, during development (1.5 to 4 months), growth (4 to 10 months), followed by a senescent phase (10 to 15 months), from which deviations due to experimentally induced perturbations can be effectively investigated.
Highlights
The change in morphology or form of an organ throughout development, growth, and senescent phases of an organism, is mediated by genetic and epigenetic factors [1,2,3,4,5]
Occlusal Wear and Morphology of the Root Light micrographs complemented by micro x-ray computed tomography (MicroXCT) volumetric reconstructions (Fig. 1 and Fig. S2) illustrated structural changes in molars as rats aged
Morphology changes with age were confirmed by an increase in the size of the mandible (Fig. S1) [60] and dentition [61,62], but more interestingly by the mesial curving of the roots caused primarily by secondary cementum apposition (Fig. 1)
Summary
The change in morphology or form of an organ throughout development, growth, and senescent phases of an organism, is mediated by genetic and epigenetic factors [1,2,3,4,5]. The inherited genetic influences dominate morphogenesis in prefunction, which become basal to the epigenetic factors (for e.g. functional loads) that mediate organ adaptation over a prolonged time [5]. Prolonged time alters form-function behavior due to load-related changes at an organ level and strain-related events at a cellular level. Physico-chemical changes include mineral formation or resorption, changes in elemental composition, and mechanical resistance of extracellular matrices of tissues. These processes occur in several adjoining tissues of the load bearing joint and play a key role in maintaining its functional efficiency
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