The dimensions of the roots of the human permanent dentition as a guide to the selection of optimal orthodontic forces.

BACKGROUND The dimensions of the roots of the teeth are important in the assessment of orthodontic anchorage and to estimate the forces to be used during orthodontic tooth movement. AIMS To investigate the relations between the lengths, widths and projected areas of the roots of the permanent teeth. METHODS Intact, extracted human permanent teeth were photographed and the lengths, widths and projected areas of selected surfaces measured. Descriptive statistics and associations between selected linear dimensions and root areas were calculated. RESULTS The data showed significant kurtosis and skewness. Neither exponential nor polynomial transformations improved the goodness of fit, and there was no a priori reason to use other than linear regression. When the lengths of all teeth were multiplied by the respective widths of the mesial, distal and lingual surfaces, the correlations between the product of length and width and area improved in 28 out of 30 surfaces. In the lower arch the correlation coefficients ranged from r = .343 (mesial surface first premolar) to r = .845 (mesial surface of the canine). The correlations in the upper arch ranged from r = .201 (mesial surface of the second molar) to r = .847 (mesial surface lateral incisor). CONCLUSIONS For clinical purposes, root length may be an acceptable indicator of root area. Low correlations were attributed to variations in root shape.