Bone Remodeling and Strain Variation Following Altered Mandibular Condyle Loading in Retired Breeder Rabbits

Abstract

Several investigators have demonstrated modeling of the mandibular condyle foil following a change in load. A recent study evaluated the effect of age on the ability of the condyle to adapt to such a change. The present study explored the early changes in the mandibular condyles of retired breeder rabbits following an alteration in load, and attempted to quantify this load. Twelve female retired breeder New Zealand white rabbits were divided into four equal groups. Under general anesthesia strain gauges were placed on the lateral inferior body of the mandible bilaterally in two of the groups. Two days post-surgery acrylic splints were placed on the anterior teeth (resulting in a posterior open bite) of one the strain gauge groups and one group that did not receive strain gauges. The splints were maintained for 26 days. A control group received neither strain gauges nor splints. Intravital bone labels were administered to all groups to allow for histomorphometric analysis of condylar modeling and remodeling. In addition, principal strain measurements were recorded pre- and post-splint placement. The histomorphometric findings revealed a significant (p<.03) decrease in the subcondylar space of animals that received splints. Splinted animals also showed a significant increase in labeled surface area (p<.02) and in volume percent label (p<.05) of the trabeculae in the condylar neck region. In addition, surgical placement of the strain gauges significantly (p<.05) decreased the labeling of the periosteal surface in the neck region. The strain gauges proved functional in most rabbits for only a few days and registered large variations and no discernible differences in average maximum microstrain, and average change in microstrain. It was concluded from these results that an incisal prematurity (causing a posterior openbite), 26 days in duration, caused an increase functional load on the condyle. This load resulted in an increase in trabecular label and decrease in porosity of the subchondral plate. The decreased subcondylar space is possibly an indication of stiffening in this region. A stiffening of this nature has been suggested in previous studies to be a precursor to osteoarthritic degeneration.