Ted Rothstein

Presented in partial fulfillment for the Ph.D. degree, Graduate School of Arts and Sciences, University of Pennsylvania, 1971

The purpose of this study was to describe and analyze the craniofacial and dentofacial skeletal characteristics associated with Angle’s Class II, Division 1 dental malocclusion – clinically characterized by (1) an apparent posterior position of the mandibular first permanent molars and (2) protruding maxillary central incisors.

The material examined included 613 lateral head radiographs comprising two series: (1) 278 films of children presenting "normal" occlusion and (2) 335 films of children presenting Class II, Division 1 malocclusion. Each series was subdivided into six samples – three male and three female; skeletal ages 10, 12, 14 (± 6 months) as assessed by hand-wrist radiographs -- representing children ages ranging from 8.5 to 15.5 years. The material was drawn from the files of the Philadelphia Center for research in Child Growth.

Radiographic skeletal contours were traced and marked off in accordance with a standardized computer method for the semi-direct measurement and analysis of radiographs of the head devised by G. F. Walker at the University of Pennsylvania. An optical scanner/IBM key punch converts the 177 cephalometric and derived anatomic end points of each tracing into Cartesian coordinate computer retrievable data, constituting a "mathematical model," or computer-drawn plot, of the skull.

Fifty-two linear, angular and coordinate variable measurements were computed to evaluate the size, form, positional and proportional characteristics of the skull, its components and their relationship to one another. Ten radiographs from each sample were prepared again, and measurements were computed a second time to determine the extent of measurement error. A multiple, independent, universal statistical analysis was used to evaluate mean differences between the series. Findings were verified by superimposition of computer-drawn plots of the mean skull configuration of the two series. A composite growth series was constructed for selected reference points from the cross-sectional mean data. this permitted a graphic comparison of the magnitude and direction of the mean growth changes in the two series.

The six study comparisons indicated that in Philadelphia children the morphologic basis of Class II, Division 1 malocclusion is consistent with a forward (mesial) position of the maxillary dentition, the skeletal associations of which most frequently included (1) a larger A-P cranial length attended by an increased frontal bone thickness at the level of the sinus, a more obtuse cranial base angle, and a larger anterior cranial base length; (2) a larger maxilla and a forward-positioned orbitomalar complex; (3) an inclined palate (inferiorly positioned at its posterior limit or superiorly positioned at its anterior limit or both), the anterior moiety of which was noticeably larger. The mandible was most often within the range of normal for size, form and positional characteristics as was the position of the mandibular first permanent molar. The mandibular incisor-alveolar segment, however, was superiorly positioned. The magnitude and direction of growth of representative dental and upper, middle and lower facial skeletal end points suggest that growth is more intense and directed more horizontally forward than vertically downward: in females noticeably from 10-12, decidedly from 12-14; in males noticeably between 12 and 14. The direction of mandibular movement closely mimicked that observed in the cranial base.