Evidence of Bone Remodeling in the Rabbit Jaw

Objective: The purpose of this study was to obtain quantitative data on the levels of osteonal bone remodeling in the rabbit jaw bone.

Method: To study intracortical bone remodeling, four, 7 months old female New Zealand rabbits, were given a pair of calcein (5mg/kg) bone labels seven days apart. After sacrifice, bone specimens were obtained from the maxilla, mandible and tibia, embedded in methyl methacrylate and sectioned. Two sections containing the entire tooth and surrounding bone were obtained bilaterally from the maxilla and mandible and two cross sections were obtained from the mid-section of the tibia for a total of 6 sections/animal.  Standard histomorphometric analyses were used to determine the bone volume/total volume (BV/TV, %), mineral apposition rate (MAR, µm/d), mineral surface/bone surface (MS/BS, %), and bone formation rate (BFR, %/yr =MAR X MS/BS), BFR being the main outcome variable of interest. Comparisons were made between the bone sites using multiple Mann-Whitney-Wilcoxon tests controlling for animal using the Cochran-Mantel-Haenszel chi square test. All p-values were adjusted using the step-down Bonferroni method of Holm.

Result: The mean (SD) for BFR (%/yr) of the bones sites were as follows: maxilla 2.40 (2.05), mandible 1.79 (1.95), tibia 1.02 (1.32), combined maxilla and mandible 2.11 (1.96). The BFR between the sites was not significantly different (p>0.05). However, the mean (SD) for BV/TV was significantly different (p<0.01) between each bone site, being lowest in the maxilla 93.49 (2.95) and highest in the tibia 99.50 (0.64).

Conclusion: Relatively low levels of intracortical bone remodeling exist in the rabbit jaw bone. Although few labeled osteons were present, unlabeled osteons with reversal lines were identified in all three skeletal sites. This data helps us to understand the range of bone turnover in rabbit jaws allowing for comparison with rodent and larger animal models.