Effects of estrogen deficiency and its therapeutic agents on mechanical stability of teeth

Objectives: Postmenopausal estrogen deficiency gives rise to osteoporosis that is characterized by loss of bone mineral density (BMD). Parathyroid hormone (PTH) and bisphosphonate have been widely used as anabolic and anti-catabolic agents to treat osteoporosis, respectively. The objective of this study was to examine whether BMD and mechanical stability of jaw bone under masticatory loadings are altered by the estrogen deficiency and its therapeutic agents.
Methods: Following approval of IACUC, thirty 4-month female rats were obtained. Sham surgery was performed for 6 rats. The rest of rats were ovariectomized and assigned 6 rats to each non-treatment (OVX), PTH, a bisphosphonate (alendronate (ALN)), and PTH+ALN treatments groups. Mandibles were dissected and scanned using cone beam computerized tomography (CBCT) to measure BMD. The rat molar was compressed by static loading up to 7N and dynamic mechanical analysis (DMA) using a non-invasive compressive cyclic loading (-5±4N at 1 to 3 Hz). Static stiffness (K) was measured during loading and static energy dissipation (Hyst) was assessed using difference of areas under load-displacement curves during loading and unloading. Dynamic stiffness (K*) was measured during the cyclic loading of DMA. Multivariate analysis of variance was performed to compare the BMD, K, Hyst, and K* between the treatment groups (significant, p<0.05).
Results: The BMD was not significantly different between the sham and other treatment groups (p>0.167). The sham group had higher K, Hyst and K* than OVX, OVX and PTH, and PTH groups, respectively (p<0.032) but no difference with ALN and PTH+ALN groups (p>0.081).
Conclusions: The current results suggest that the estrogen deficiency decreases static occlusal mechanical stability of teeth in jaw bone, which is not detected by the traditional BMD based diagnosis of osteoporosis. The bisphosphonate likely prevented the estrogen deficiency dependent alteration of jaw bone more effectively than PTH.