A New Method To Predict The Required Dental-arch Perimeter And An Establishment Of A Software For Space Analysis In Mixed Dentition

Prediction of tooth size-arch length discrepancy in mixed-dentition patients is an important aspect for orthodontic diagnosis. With the erupting of the first molar in the maxilla and mandible, the length and width of anterior maxilla or mandible arch is approaching its maximum. When the canines and premolars are having been erupting, the discrepancies will be obvious. And prediction of discrepancies requires an accurate mesiodistal width-prediction of unerupted canines and premolars.Up to now, there are three methods to determine the mesiodistal widths of unerupted canines and premolars. 1)Analyses based on linear regression equations: Moyers regression scheme and Tanaka-Johnston prediction equation have achieved widespread clinical acceptance because of its simplicity and ease of application. Since then, several simple linear regression equations have been proposed for populations of different ethnic origins.2)Analyses based on measurements of the unerupted teeth on radiographs: De Paula et al introduced a technique using a 458 cephalometric radiographs. Although the correlation of this method is high, the accuracy depends in large part on the technique with which radiographs are taken, the quality of radiographs and the position of teeth in the crypts. 3) Analyses based on a combination of linear regression equations and measurements on radiographs. However, the selection of the combination of predicting teeth is yet limited and the results are still not accurate. We need a more comprehensive selection for the predictors.255 dental study casts (112 male and 143 female without a history of orthodontic treatment) were selected from the Orthodontic Department of Stomatology of the Forth Military Medical University. The new regression equations were established on a sample consisting of 100 female and 80 male patients. The methods of Moyers, Tanaka-Johnston equations and the new equation were tested on another 32 males and 43 females. The combination of permanent upper and lower central incisors and upper first molars was selected as the best predictor for the unerupted canine and premolars in this sample, and the correlation coefficients between the variables were 0.753 for maxillary teeth and 0.834 for the mandibular teeth. The P value was less than 0.001 respectively for male and female. The correlation coefficients had significantly statistical difference. Equations predicting summation of mesiodistal crown-widths of upper and lower unerupted canine and premolars in male and female were established respectively. The male: Y=0.64X+6.89(upper), Y=0.79X+2.45(lower). The female: Y=0.64X+6.86(upper), Y=0.72X+3.90(lower). (Y represents the summation of the mesiodistal crown-widths of unerupted canine and premolars on one buccal side, X represents half of the summation of the mesiodistal crown-widths of upper and lower central incisors and upper first molars:11,21,16,26,31,41 )Basing on the new prediction equations and the Bolton rates and the Pont index for Chinese, we have established a software"ToothDiagnosis1.0",which can help us make a diagnosis assistantly in clinical practice.