Alteration in volumetric bone mineralization density gradation patterns in mandibular distraction osteogenesis following radiation therapy.

BACKGROUND

The use of mandibular distraction osteogenesis for tissue replacement after oncologic resection or for deformations secondary to radiotherapy could have immense therapeutic ramifications. Radiotherapy, however, drastically impairs bone healing, potentially precluding the use of mandibular distraction osteogenesis as a durable reconstructive option. The authors have previously demonstrated significantly decreased mechanical and histologic metrics of the mandibular distraction osteogenesis regenerate after 36 Gy. The authors' goal is to now investigate the effect of these same radiation dosages on bone densitometrics using micro-computed tomographic scanning.

METHODS

Six Sprague-Dawley rats received 36-Gy fractionated radiotherapy sessions to the left mandible; six received none. All animals had external fixators placed, creation of osteotomies, distraction, and consolidation. Mandibles were scanned with micro-computed tomographic scanning. Volumetric density and microdensitometric measurements were analyzed.

RESULTS

There was a significant difference in volumetric bone mineralization patterns in irradiated animals. Bone volume fraction and bone mineral density, however, demonstrated no significant differences.

CONCLUSIONS

The authors discovered a significant increase of low mineralized, immature bone and a significant decrease of highly mineralized, mature bone in the irradiated regenerate. These findings corroborate the authors' hypothesis that radiation induces a diminution in cell function, impairing optimal bone regeneration. Overall densitometrics, however, were unchanged according to micro-computed tomographic measurements, despite documented significant changes in biomechanical and histologic metrics. An optimal radiation dose must now be sought that demonstrates a higher degree of reproducible degradation, but not irreversible destruction, in all three outcomes. Such an approach will allow formulation of therapeutic interventions designed to enhance mandibular distraction osteogenesis so that it may be used as a viable reconstructive option.