Objetive:

Determine the accuracy of Tanaka-Johnston and Moyers indexes through the initial analysis of study models with permanent teeth of Chilean patients of the Graduate School Orthodontics of University Andres Bello in Santiago.

Materials and Methods:

100 pairs of models were selected by convenience as the inclusion and exclusion criteria established, corresponding to 50 female and 50 male. Direct measurement was performed with a manual caliper gauge by two examiners previously calibrated. The sum of permanent mandibular incisors and sum of segments canine-premolar were measured. The accuracy of each of the present methods and statistical differences were determined.

Results:

In females, the prediction of width of unerupted canines and premolars is more accurate on maxilla with Moyers 65% and mandible with Moyers 50%. For males, Moyers 75% on maxilla and Moyers 65% in mandible are more accurate. Tanaka-Johnston method although only presented statistically significant differences in mandible of female gender (p <0.05), is less accurate tending to overestimate actual values in women as in men underestimated.

Conclusion:

Moyers method is more accurate in predicting space required in Chilean patients, the confidence level varies according to gender and jaw. Differences are explained by sexual dimorphism and ethnic variations from the source population of prediction methods.