Thin-plate spline analysis of mandibular growth

The analysis of mandibular growth changes around the pubertal spurt in huma ns has several important implications for the diagnosis and orthopedic corr ection of skeletal disharmonies. The purpose of this study was to evaluate mandibular shape and size growth changes around the pubertal spurt in a lon gitudinal sample of subjects with normal occlusion by means of an appropria te morphometric technique (thin-plate spline analysis). Ten mandibular land marks were identified on lateral cephalograms of 29 subjects at 6 different developmental phases. The 6 phases corresponded to 6 different maturationa l stages in cervical vertebrae during accelerative and decelerative phases of the pubertal growth curve of the mandible. Differences in shape between average mandibular configurations at the 6 developmental stages were visual ized by means of thin-plate spline analysis and subjected to permutation te st. Centroid size was used as the measure of the geometric size of each man dibular specimen. Differences in size at the 6 developmental phases were te sted statistically. The results of graphical analysis indicated a statistic ally significant change in mandibular shape only for the growth interval fr om stage 3 to stage 4 in cervical vertebral maturation. Significant increas es in centroid size were found at all developmental phases, with evidence o f a prepubertal minimum and of a pubertal maximum. The existence of a puber tal peak in human mandibular growth, therefore, is confirmed by thin-plate spline analysis. Significant morphological changes in the mandible during t he growth interval from stage 3 to stage 4 in cervical vertebral maturation may be described as an upward-forward direction of condylar growth determi ning an overall "shrinkage" of the mandibular configuration along the measu rement of total mandibular length. This biological mechanism is particularl y efficient in compensating for major increments in mandibular size at the adolescent spurt.