Abstract
Introduction: In the everyday clinic, it is not unusual to come across cases diagnosed with skeletal mandibular prognathism displaying problems in the upper and lower jaw widths along with anteroposterior discrepancies. Conventionally, model analysis and lateral cephalometric analysis have been used in determining anteroposterior jaw placements when planning orthognathic surgery. However, in cases such as skeletal crossbite where improvement of the upper and lower jaw width and molar axis become necessary, it is difficult to interpret deep cranial structures using conventional frontal cephalograms, and there is no clear guideline for determining whether the problem lies in the maxillary or the mandibular arch width, or how the molar axis should be improved. Thus, this study used CBCT images of patients who underwent orthognathic surgery for correcting skeletal mandibular prognathism that displayed few signs of relapse with good stability of jaw position with more than 2 years’ retention to analyze pre- and post-treatment changes and the relationships among muscle direction, inter-molar width, and molar axis.
Materials and Methods: Twenty-one patients （6 adult men and 15 adult women with an average age of 20 years and 7 months） diagnosed with skeletal mandibular prognathism were subject to investigation. Frontal section CBCT images at first visit and after 2 years of retention were used to investigate the correlations between inter-molar width, molar axis, and inclination angles of the jaw-closing muscles following surgical mandibular setback.
Results and Conclusion: Investigation of cases with good stability after orthognathic treatment revealed a positive correlation between the inclination angles of the jaw-closing muscles and molar axis, and a positive correlation between jaw width and inter-molar width, which could be used as an index in diagnosis and treatment planning.
