Retrospective study on mandible morphology towards improving implant design

[摘要] ENGLISH ABSTRACT: Pre-surgery planning is crucial to the success of orthognathic surgery. Withthe advancement in 3D imaging modalities, modern methods in predictinga pathological mandible's ideal geometry have improved. As a result, thedesign of patient-specific implants has become more commonplace. Before this,standard sized implants were inevitably used. Despite these enhanced virtualreconstruction techniques, limitations in these methods still exist. The mosteffective approach during virtual reconstruction is to replace the pathologicalarea with the unaffected region on the opposite half of the mandible. Thismirroring method becomes futile in scenarios where the disturbance overlapsthe mandibular midline. Therefore, the aim of this study was to develop avirtual mandibular reconstruction technique for the purpose of aiding surgeonsduring implant design, whilst accounting for this limitation. It was proposedthat this could be achieved by performing a retrospective investigation on thepopulation's mandibular structure and developing prediction models based onstatistical methods.Two prediction models were formulated: a sparse prediction model (SPM)and a statistical shape model (SSM). The SPM offers a prediction of importantunknown mandibular measurements when receiving the values of knownmeasurements as an input, whilst the SSM provides an estimate for the fullmandibular geometry after receiving mandibular coordinates as an input. Theeffectiveness of these techniques was tested by predicting missing anatomicalfeatures on subjects not part of the dataset used to create the models. The tests took place for two scenarios: the first being for when the plane of symmetryis available and the second for when it's not. For the first scenarioof testing, the mirroring method was also implemented, where the resultingaccuracy served as the baseline.For both testing scenarios, the SSM clearly outperformed the SPM. Thus,there is no clear benefit in using the SPM over the SSM for virtual reconstructionscenarios. For the first scenario of testing, the SSM compared similarlyto the mirroring method, where no significant difference was found betweentheir respective accuracies (p<0.05). The difference between these two methodslies in their restriction of use. Whilst the mirroring method is constrainedto situations such as the first scenario, the SSM has no such restriction. Forthe second scenario, the SSM produced estimations with accuracies similar tothe first scenario, thus producing consistent accuracies in geometry predictionregardless of the area being reconstructed. It was therefore concluded that aSSM of the mandible presents itself as a modular virtual reconstruction techniquethat successfully accounts for the limitations found in current methods.

[发布机构] Stellenbosch University