Comparison of two methods of unerupted teeth size of determination (Tanaka and Johnstone, Moyers) during 2004

The purpose of this study was to compare two methods of unerupted teeth size determination (Tanaka and Johnstone and Moyers) in patients referred to Shaheed Beheshti University Dental School. Methods & Materials: The study was descriptive and its technique was observation and questionnaire. The study included dental casts of patients referred to orthodontic department of Shahid Beheshti University of Medical Sciences which met the requirements of the study. 117 pairs of models were studied after analyzing existing 1500 pairs. The mesiodistal width of canine, first and second premolar and also four lower incisors were measured by digital caliper with precision of 0.01 mm in both maxilla and mandible. The overall width of teeth was predicted using the formulas and compared with their true size. The statistical analysis included paired t test, student t test and linear regression. The study showed that both methods of Tanaka and Johnstone and Moyers in 50%, 65% and 75% overestimated the true size of canine and premolars in both maxilla and mandible while Moyers method in 25% underestimated their real size in females. At both maxilla and mandible of studied females, significant differences existed between real and predicted sizes. The linear regression showed a formula of "y=0.65x+6.1" and "y=0.62x +7.2" in mandible and maxilla. In males, both methods of Tanaka and Johnstone and Moyers in 65% and 75% overestimated the true size of canine and premolars in both maxilla and mandible while Moyers methods in 25% and 50% underestimated the real sizes. Significant differences existed between real and predicted sizes in all methods with the exception of Moyers in 50%, so that, Moyers method in 50% had been estimated the sizes with high accuracy. The linear regression showed a formula of "y=0.58x+7.98" and "y=0.64x+7.2" in mandible and maxilla respectively. Except for Moyers method at 50% that predicted the size of canine and premolars with higher accuracy in males, the other formulas could not predict the real size of unerupted teeth. As there was no significant differences between true and predicted teeth sizes, the application of the suggested formulas are suggested for Iranian people.