Qualitative assesement of newly formed bone after distraction osteogenesis of mandible in patients with facial asymmetry using 3 dimensional computed tomography.

Introduction: Distraction osteogenesis is a surgical technique of new bone formation between the osteotomized bone segments with the help of gradual incremental traction. As distraction osteogenesis is slow biologic process, soft tissue changes gradually follow the new bone formation. Mandibular distraction is one of the accepted modalities to treat the triad of TMJ ankylosis, obstructive sleep apnoea & micrognathia and also for facial asymmetry cases like hemifacial microsomia, mandibular hypoplasia etc. After the distraction osteogenesis, some relapse has been noticed in patients. Therefore, this study was conducted to assess the quality of the newly formed bone after distraction osteogenesis of mandible using 3 dimensional computed tomography (3DCT Scan) to evaluate its relation with relapse if any.

Objectives: 1) To objectively analyse the quality of bone formed after mandibular distraction osteogenesis.2) To observe the site & architecture of newly formed bone after distraction is complete.

Material And Methods: Total 5 patients of facial asymmetry reported to the Department of Oral and Maxillofacial Surgery were enrolled. Distraction osteogenesis of mandible was carried out in all the patients. Radiographic analysis (CT Scan) was done after 1 year of surgery for further planning and management of deformity. The non-distracted site was considered as a control side and it was compared with newly formed bone at distraction site. The standard & universally accepted radio density measuring Hounsfield Unit (HU) in 3DCT scan was calculated in axial,coronal, sagittal sections from distraction site and it was compared with non-distraction site, as Hounsfield unit is considered as a standard tool for measuring the bone density to evaluate the quality as well as quantity of newly formed bone.

Results: The total mean Hounsfield Unit of distracted site of all three sections was 359.8 HU and non-distracted site was 545.2 HU. Statistical analysis was carried out using students paired test and p value was obtained which was <0.01 suggestive of statistically significant difference between the quality of bone in distracted site and non-distracted site.

Conclusion: The findings of our study concluded that the quality of bone formed after distraction osteogenesis was satisfactory but it was less mineralized with less dense trabecular pattern compared to non-distracted bone region of mandible which leads to some relapse. Therefore it was advisable to reinforce the distracted bone segment by cutting the activation arm of distractor itself or mini plate or reconstruction plate to prevent relapse.