Condylar Bone Mineral Density Differences in Anterior-Posterior and Superior-Inferior Directions

Objective: To examine the changes in bone mineral density (BMD) in the mandibular condyles of splinted versus non-splinted pigs in the anterior-posterior (A-P) and superior-inferior (S-I) directions.

Method: Twelve dried mandibular condyles from 9-month-old miniature pigs were obtained from a previous experiment where two-thirds wore chrome-cobalt  intra-oral splints for two months.  Subchondral bone scans (GE eXplore Locus Small animal MicroCT Scanner) of each condyle were reconstructed with 0.1mm voxel size and converted to three-dimensional images.  An iso-surface of the entire condyle was created (MicroView) to determine the relative medial-lateral (M-L) axis.  A-P direction was defined as normal to both the M-L and S-I axes.  Origin of the resulting coordinate system was centered between the M-L poles creating an axis 4 mm deep to the central portion of the condylar articular surface.  Regions of interest (ROI) 2 mm^3 were collected every 2 mm along A-P and S-I axes.  Examiners were blinded to splinted/non-splinted grouping.  T-tests and one-way ANOVAs were used for data analysis.

Result: No significance difference between splinted and non-splinted groups was observed along either axis.  Pooling all specimens in the A-P direction, the most posterior ROI was significantly less dense (400mg/cm^3±148) than all but one ROI (most anterior) and the densest ROI, on average, was the origin (647±110mg/cm^3).  Along the S-I axis, the non-splinted group was significantly less dense near the condylar surface than below the origin.  High variability was seen in the splinted group along the S-I axis.

Conclusion: Two months of splinting did not produce any significant change in condylar subchondral BMD. Variations in BMD along the A-P and S-I axes are consistent with theoretical loading pattern of a pig mandibular condyle during function.