Investigation of midfacial and mandibular morphology: Strain tensor analysis

Abstract

The method of strain tensor (ST) analysis efficiently demonstrates the morphological differences in skeletal jaw growth and provides more information for orthodontic diagnosis and orthopedic therapy of jaw disharmonies. The purpose of this study was to investigate midfacial and mandibular size and shape differences in a sample of normal Class I molar occlusion and Class III malocclusion. Fifty Chinese boys aged 10–12 years, each occlusal group of 25 subjects, have been selected. The results indicated that statistically significant differences in midfacial and mandibular configurations between Class I occlusion and Class III malocclusion occurred at P< 0.01 levels. The mandibular corpus of Class III malocclusion was larger than that of Class I occlusion and the extension direction of growth tensors was chiefly manifested along the long axis of general mandibular morphology. In contrast, the midfacial size of Class III malocclusion was smaller than that of Class I occlusion and a horizontal reduction was observed at the posterior midface. Shape differences in the midface and mandible manifested for the two occlusal types. The present investigation with a new geometric morphometrics (ST analysis) provides more information and better understanding of the midfacial and mandibular morphology and growth pattern in Class III growing children.