Factors influencing the development of molar occlusion: a longitudinal study

Longitudinal records, in the form of study casts, of 35 Class I cases were examined for factors associated with changes of sagittal molar relationship during childhood. These were studied at two phases: between the deciduous and mixed dentitions, and between the mixed and permanent dentitions. During the first of these periods, there was a small, but general move to a less post-normal occlusion, although some cases were found to show a slight reverse trend. In the second period, the permanent molar relationship became less post-normal, but this was reflected only weakly in that of the canines. Throughout development, asymmetry of occlusal relation became more marked with age, an unexplained bias towards less post-normal occlusion on the left side developing in the second phase. The amount of change in this period was related to variations of deciduous molar size, especially that of the upper second molar.