Trends of dental arc variation in a young adult male population and their meaning in the concept of occlusion.

To describe the variation of shape and size of dental arcs the method of principal components was applied. 27 measurements of every dental cast made from 50 young adult males with good occlusion were made, and the following parameters were calculated: 7 widths, 5 left chords, 5 right chords, 5 sagittal lengths (calculated as orthogonal to corresponding width) and 5 angles. Different sets of features were analyzed for both arcs together and for each arc separately. Three independent analyses by the method of principal components show a good description of the main trend of dental arc shape and size variation and a difference between the growth and variation of frontal and distal parts of the arcs. They also describe the variations of occlusion. The trends of dental arc variation ascertained help us to understand the nature of malocclusions and the causes of their preservation in evolution.