Mandibular condyles and rami are asymmetric structures

The purpose of this study was to determine the degree of bony asymmetry between the right (R) and left (L) mandibular condyles and rami. On 25 dry skulls, condylar height, breadth and length, as well as ramus height and breadth were assessed. On each skull the average of the three measurements on the right and left sides, respectively, were calculated with the corresponding reference points being redetermined for each measurement. The raw absolute differences magnitude of R - L as well as the relative absolute differences magnitude of R - L/R + L were computed. The relative absolute differences showed that asymmetries were of similar magnitude (between 1.20% and 2.58%) for all variables except for condylar height (11.06%). After taking three additional measurements with reference points chosen only once, the intra-individual measurement error, consisting of reproducibility of the reference points and accuracy in measuring the distance between the chosen points, was assessed with the help of a statistical variance component technique. Estimates of the 95% range of the absolute differences were computed. Between 60% and 88% of the measured differences were outside the predicted 95% range, thus much too large to be explained by random measurement error; hence, they were due to real individual asymmetries. We concluded that asymmetries of mandibular condyles and rami are part of the biologic variation of humans. It still remains unclear, however, when such asymmetries should be considered "unphysiological."