Morphometric Study Of The Mandible And Cranial Base Shape Of The Subjects With Class Ⅰ Skeletal Pattern In The Different Verticle Facial Types.

Objective:The purpose of this study was to investigate the differences of the mandible and cranial base shapes of the subjects with class I skeletal pattern in the different verticle facial types by geometric morphometrics.Method:(1)The pretreatment lateral cephalograps of 90 skeletal class I patients (30 hypodivergent, 30 hyperdivergent, 30 normodivergent)were selected randomly. All cephalographs were scanned, and eight homologous mandibular landmarks were identified and digitized . Average mandibular geometries were generated by means of Procrustes analysis. Thin-plate spline analysis and EDMA was then applied to mandibular configurations to determine local form differences between the three divergent classes.(2) 13 homologous landmarks of cranial base were identified and digitized on the scanned lateral cephalograps of the high-angle and low-angle patients. Average geometries of cranial base were generated by means of Procrustes analysis. Thin-plate spline analysis was then applied to cranial base configurations to determine local form differenc in the two vertical facial types.Result:(1)With increase of the MP-SN angle, as shown below, the mandblur shape had some changes: gonion angle and the distance of Id-Pg increased, the ramus height reduced, the chin rotated downward and backward, Ar point relative to Co point moved farward. (2) The high-angle patients had the characteristics of the cranial base as follow:â‘ the anterial and posterior cranial bases of the high-angle patients circled S point opposite direction revolving,cranial base angle decreased significantly;â‘¡Horizontal and vertical expansion occured in the sphenoida region. The low-angle characteristics of the cranial base is just opposite with high-angle's.Conclusion:(1)The geometric morphometry, as a good effective morphometric method of investigating the differences of shapes , could provide more accurate differences of shapes of the mandible and cranial base in the three divergent classes after we had remowed any effects due to translation,rotation,and scale.(2)The shapes of mandibular and cranial base was different in the three divergent classes,which contributed to develop the different verticle facial type.