Comparison of space analysis performed on plaster vs. digital dental casts applying Tanaka and Johnston's equation

OBJECTIVE: The purpose of this study was to compare dental size measurements, their reproducibility and the application of Tanaka and Johnston regression equation in predicting the size of canines and premolars on plaster and digital dental casts. METHODS: Thirty plaster casts were scanned and digitized. Mesiodistal measurements of the teeth were then performed with a digital caliper on the plaster and digital casts using O3d software system (Widialabs ).The sum of the sizes of the lower incisors was used to obtain predictive values of the sizes of the premolars and canines using the regression equation, and these values were compared with the actual sizes of the teeth. The data were statistically analyzed by applying to the results Pearson's correlation test, Dahlberg's formula, paired t-test and analysis of variance (p<0.05). RESULTS: Excellent intraexaminer agreement was observed in the measurements performed on both dental casts. No random error was present in the measurements obtained with the caliper and systematic error (bias) was more frequent in the digital casts. Space prediction obtained by applying the regression equation was greater than the sum of the canines and premolars on the plaster and digital casts. CONCLUSIONS: Despite an adequate reproducibility of the measurements performed on both casts, most measurements on the digital casts were higher than those on the plaster casts. The predicted space was overestimated in both models and significantly higher in the digital casts. OBJETIVO: comparar medidas de tamanhos dentários, suas reprodutibilidades e a aplica o da equa o de regress o de Tanaka e Johnston na predi o do tamanho dos caninos e pré-molares em modelos de gesso e digital. MéTODOS: trinta modelos de gesso foram escaneados para obten o dos modelos digitais. As medidas do comprimento mesiodistal dos dentes foram obtidas com paquímetro digital nos modelos de gesso e nos modelos digitais utilizando o software O3d (Widialabs). A somatória do tamanho dos incisivos inferiores foi utilizada para obter os valores de predi o do tamanho dos pré-molares e caninos utilizando equa o de regress o, e esses valores foram comparados ao tamanho real dos dentes. Os dados foram analisados estatisticamente, aplicando-se aos resultados o teste de correla o de Pearson, a fórmula de Dahlberg, o teste t pareado e a análise de variancia (p < 0,05). RESULTADOS: excelente concordancia intraexaminador foi observada nas medidas realizadas em ambos os modelos. O erro aleatório n o esteve presente nas medidas obtidas com paquímetro, e o erro sistemático