The aim of this investigation was to examine the accuracy of Moyers probability tables and the Tanaka and Johnston prediction equations in predicting the size of unerupted canines and premolars of the maxillary and mandibular quadrants in an Iranian population and to derive a standard formula for it.
Methods: Out of a sample of 280 subjects, 50 (25 males and 25 females) were selected by specific inclusion criteria. An electronic digital caliper was used to read the nearest 0.01 mm. The teeth measurements derived were compared with those predicted from Tanaka Johnston equations and Moyers probability tables and then standard regression were developed.
Results: Tanaka and Johnston regression equations overestimate the mesiodistal width of permanent canines and premolars. There were no statistically significant differences between actual mesiodistal width of canines and premolars and the predicted width from Moyers charts at 65% for the lower and upper arches in male subjects and for the lower arch in females but none of the probabilities has good accuracy for the upper arch in females. For the newly developed regression equations, the correlation coefficients between the sum of the mandibular incisors and the sum of the canine and premolars were 0.709 (for lower) and 0.539 (for upper) in subjects.
Conclusions: Tanaka and Johnston overestimate the actual size for Iranian teeth widths. Moyers method can be used at 65% probability level for male subjects and at the 75% and 85% level for upper arch and the 50% and 65% level for lower arch in female subjects.