COMPARISON OF 2 NONRADIOGRAPHIC METHODS OF PREDICTING PERMANENT TOOTHSIZE IN THE MIXED DENTITION

The determination of the tooth size-arch length discrepancy in the mix ed dentition requires an accurate prediction of the mesiodistal widths of the unerupted permanent teeth. Three approaches have been used to estimate the mesiodistal crown widths of unerupted canines and premola rs: (1) measurements from erupted teeth, (2) measurements from radiogr aphs, and (3) a combination of measurements from erupted teeth and fro m radiographs of unerupted teeth. The purpose of this study was to com pare two mixed dentition prediction methods that do not require the us e of periapical radiographs of the unerupted permanent teeth. The two methods compared were the Tanaka/Johnston and the Boston University Pr ediction approaches. Records on 33 male and 22 female subjects who wer e participants in the Iowa Longitudinal Growth Study were used in the present study, The findings indicated that on the average the Tanaka/J ohnston approach slightly overestimated the tooth size of the unerupte d teeth ((x) over bar = 1.1 +/- 0.9 mm). On the other hand, the Boston University approach slightly underestimated the tooth size of the une rupted teeth ((x) over bar = -0.1 +/- 1.2 mm). The findings further in dicated that there were statistically significant correlations between the predicted and actual tooth size. In general the r values were hig her for the Tanaka/Johnston method than with the Boston University app roach. The error involved in the use of the predicted equations was ex pressed as the standard error of the estimate. The present findings in dicated that the standard error of the estimate for Tanaka/Johnston pr ediction equations ranged between 0.67 and 0.92 mm and the correspondi ng values for the Boston University equations ranged between 0.92 and 1.02 mm. Depending on the stage or dental development, i.e., which dec iduous and permanent teeth are present, the Tanaka/Johnston approach c an be used when the four mandibular incisors have completely erupted, whereas the Boston University approach can be used when all the decidu ous canines and first molars are still present.