Evaluating the mandible with cone-beam computed tomography

Introduction: The purpose of this research was to examine methods for assessing the shape and growth of the mandible 3 dimensionally. Furthermore, 1 method was defined and applied. Methods: Thirty mandibles were assessed. An average or mean shape was determined, and the mandibles were ranked quantitatively, by using the root mean square (RMS), according to their variation from the mean. The rankings ranged from mandibles that were small, short, and narrow at the minus-RMS end, to large, tall, and broad at the plus-RMS end. A second analysis provided a method to superimpose a mandible over the average mandible and determine the differences from the average-derived mandible by using a spectrum of colors to indicate changes in a region. Results: Variations in the mandible were greatest in the condylar heads, coronoid tips, canine-incisor dentoalveolar segment, and chin point. Conclusions: The visual images of the 30 segmented mandibles suggest that a new method of classification needs to be developed that extends the original 2-dimensional lateral evaluation to a total 3-dimensional view that provides new relationships, such as the direction of the condylar heads to the ramus and the ratio of the intergonial angle length to the intercondylar head length to define the narrowness of a mandible. (Am J Orthod Dentofacial Orthop 2010;137:S58-70)