Accuracy of Moyers' probability chart in a group of Thai subjects

The objective of this study is to investigate the accuracy of Moyers' probability chart in predicting canine and premolar sizes from the sum of lower incisors in a group of Thai subjects. The fifty models of orthodontic patient, Faculty of dentistry, Mahidol University with no loss of tooth material mesio-distally, fully erupted permanent teeth, no mesial or distal restoration and normal tooth morphology were selected. The results of this study show that the under-estimation less than or equal to 2 mm. is 32 casts on upper (64%) and 28 casts on lower (56%) and the over estimation greater than 2 mm. is 16 casts on upper (32%) and 18 casts on lower (36%). In comparison of 14 models which have the same value of sum of lower incisors, there is a significant (alpha = 0.05) difference between the combined canine and premolar size of this study and Moyers' probability chart.