Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances.

Major effort is put into the design of brackets to accomplish an optimal completion of orthodontic treatment with respect to 1st, 2nd, and 3rd order corrections. Because such brackets are standardized, the intraindividual variation of the teeth is not taken into consideration. The influence of vertical bracket displacement on 1st and 3rd order corrections was studied on the plaster models, including all teeth from central incisors to first molars, of 28 young persons. The facial contours were evaluated at the mesial, central, and the distal aspect of the bracket. The contours were calculated with the formula of a parabola, and the fit was found sufficient. Intertooth variation was extreme, the biggest curvature was found among the first mandibular molars. The variation was also marked between corresponding teeth. It can be concluded that the intraindividual variation in tooth morphology is larger than the variation between the different types of preadjusted appliances. Thus, if the straight wire approach should be followed, the bracket would have to be custom made. All the calculations were made with the precondition that full size wires were used. If this is not the case, the discussion concerning individual prescription is only of limited importance.