Estrogen deficiency increases bone remodeling. Increased remodeling activity yields bone tissue with a higher percentage of immature/newly formed bone, ultimately leading to increased variability of mineralization. Due to the functional demands of mastication, alveolar bone is inherently a highly remodeled region of bone tissue. Does estrogen deficiency affect alveolar bone’s remodeling and subsequent mineralization?
Objectives: Using a rat model of ED, the objectives of this study were 1) to assess regional variation of mineralization in the mandible, and 2) to assess the effects of estrogen deficiency on the magnitude of regional variation.
Methods: Ovariectomized (OVX, n=10) and sham surgery (Sham, n=10) rat mandible sections were scanned by micro-computed tomography (micro-CT) with a voxel resolution of 20 micrometers. The images of each section were manipulated using imaging software to isolate a portion of alveolar bone (AB) within 200 micrometers of root surface and a control bone (CB) region 200 micrometers removed from all internal and external mandibular bone borders. CT attenuation values were maintained and gray level voxel values were reported in Hounsfield Units (HU). Histograms were generated to analyze gray level frequency distribution. HU parameters analyzed were Mean, Standard Deviation (SD), Coefficient of Variation (COV) (to normalize SD) and percentile values (5th = Low5, and 95th =High5). Paired t-tests were used to assess regional variation of mineralization between AB and CB for all specimens. The magnitude of regional variation (how different AB and CB were from each other) was compared for all parameters between OVX and Sham groups by expressing the difference of AB from CB, as a percentage of CB. The treatment groups were compared using ANOVA.
Results: AB and CB were significantly different (p<0.001) in all parameters measured within all subjects confirming significant regional variation, independent of estrogen deficiency. Comparisons between Sham and OVX groups for the percentage difference of AB resulted in percentage differences moderately different for SD (p<0.073) and significantly different for COV (p<0.039) and Low5 (p<0.019). The percentage difference of Mean and High5 were not significantly different (p>0.093) between Sham and OVX groups.
Conclusions: An increase in variability (COV and Low5) of mineralization represents a relative increase in bone remodeling. Higher variability of mineralization observed in AB of OVX group indicates that estrogen deficiency amplifies the active bone remodeling of AB already present due to mastication.