Implant-based three-dimensional superimposition of the growing mandible in a rabbit model.

BACKGROUND: The reliable assessment of craniofacial morphological changes during growth requires invariant regions for image registration. As these regions have not yet been identified in three dimensions, intra-osseous implants are required as fiducial markers for the reliable assessment of three-dimensional (3D) mandibular growth changes. The objective of this study was to develop an animal model for the assessment of the 3D morphological changes of the mandible during growth, using implants as fiducial markers. MATERIALS AND METHODS: Titanium implants were placed in the body of the mandible of six New Zealand White rabbits. Cone beam computed tomography (CBCT) scans were taken 1-week following implant placement and after an additional 8-weeks of growth. Segmentations of CBCT images were exported into custom-made scripts, implant centroids were identified, implant stability during growth calculated, and the segmented mandibles were registered on the implant centroids. RESULTS: The buccal cortical bone of the body of the mandible was stable during growth and suitable for fiducial marker placement. Bilateral implants resulted in more accurate rigid registration of the growing rabbit mandible than only unilateral implants. 3D mandibular growth changes were visualised by means of semi-transparencies. CONCLUSIONS: This animal model appears to be feasible for the assessment of the 3D morphological changes occurring during mandibular growth. To the best of our knowledge this is the first time that the implant superimposition method has been combined with 3D imaging to accurately reveal mandibular growth changes.

A nine-year review of orthognathic surgery at the University of Otago.

OBJECTIVE: To describe the demographic characteristics of patients undergoing orthognathic surgery at the University of Otago over a nine-year period. METHODS: The case notes of patients who underwent orthognathic surgery procedures at the University of Otago from 2001 to 2009 were reviewed retrospectively. This was augmented with a brief literature review of surgical considerations and complications in orthognathic surgery among older patients. RESULTS: The 92 patients included in the study were aged 15 to 56 years. The mean patient age increased over the nine-year observation period, from 22.1 years (sd, 9.4) during 2001-2003, 25.0 years (sd, 12.7) during 2004-2006, to 27.7 years (sd, 11.4) during 2007-2009. Most patients were from New Zealand European or European backgrounds, with only 5.5% identifying as Maori, and 3.3% as Asian. A female preponderance was observed (with a female:male ratio of 1.6:1). Complications were encountered with 24 patients (26.1%). Ten patients had long-term (lasting for one year or more) sensory nerve disturbance; all of those had undergone a mandibular bilateral sagittal split osteotomy (BSSO) procedure (they comprised 12.7% of all BSSO patients treated); half of those patients were over 35 years old, and four were over 40 years old. CONCLUSIONS: There has been an increase in the proportion of older patients undergoing orthognathic surgery at the University of Otago. Observations from this case series support findings from other studies demonstrating a higher rate of sensory nerve disturbance among older BSSO patients.