Aim: Tanaka and Johnston have offered a very simple method for estimating mesio-distal witdh of unerupted canines and premolars; But it seems that these estimations are not appropriate for Iranian population. In this investigation we've tried to offer a new formula to estimate the width of unerupted teeth in Iranians.
Material and method: In this study we measured the size of premolars and canins on 400 dental casts and did a regression analysis to find any correlation between the size of these teeth and four lower incisors.
Results: We found that using Tanaka and Johnston analysis in Iranian children, unerupted teeth estimated wider than actual size.This study showed that there was a strong correlation between the width of lower incisors and unerupted canine and premolars of both jaws in Iranian population.
Conclusion: As we found Tanaka and Johnson's formula will estimate canines and premolars wider and a new formula is offered for Iranian population.