Purpose:

The full physiologic impact of UMDO on the CM remains uncertain. The aim of this study was to determine the degree of structural change in the CM after UMDO utilizing metrics of bone mineralization. Our hypothesis was that the biomechanical stimulus of UMDO would cause a compensatory increase bone volume and bone mineral density in the CM. Our goal is to better understand the risks and benefits of UMDO to the CM.

Methods:

Unilateral osteotomies were created behind the third molar after external fixators were placed on male Sprague Dawley rat mandibles. The UMDO group (n=26) was distracted to 5.1mm after 4days latency at 0.3mm Q12hrs. The 2mm fracture group (n=12) was distracted to create a 2mm defect eight hours after surgery. The reduced fracture group (n=10) was left undisturbed. (The two fracture groups were included as controls.) Animals were euthanized after 28days consolidation. Unoperated controls (UC, n = 18) and the CM of all surgical groups underwent ex-vivo Micro-CT scanning. Three independent reviewers measured Bone Mineral Density (BMD), Bone Volume Fraction (BVF) and Volumetric Bone Mineral Density (vBMD = BMD/BVF), utilizing Microview version 2.2. and validated region of interest templates. Statistical analyses were considered significant if p≤0.05.

Results:

We found significantly higher BMD and BVF in the CM of all groups when compared to UC's. However, we also found significantly lower vBMD in the CM of all groups when compared to UC's. There were no statistically significant differences of this effect when the CM's of the surgical groups were compared to each other.

Conclusions:

Quantitative outcome analysis of CM’s demonstrated a statistically significant increase in BMD and BVF in the CM's when compared to the UC group indicating an overall increase in the amount of mineralized bone. However, further analysis utilizing vBMD, an algorithm calculated in our lab to determine bony structural properties, demonstrated findings consistent with an overall lower quality of the involved bone. These changes are uniform across all surgical groups, indicating that the osteotomy, rather than the distraction , may be the agent triggering the observed structural changes. These exciting findings have prompted further research focused on determining if the observed changes in bone mineral density are due to loco-regional alterations in dynamic loading or to humeral responses to injury And to determine the clinical implications for the care of the CM after surgery or trauma.