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 co mpletion of orthodontic treatment with respect to 1st, 2nd, and 3rd order c orrections. Because such brackets are standardized, the intraindividual var iation of the teeth is not taken into consideration. The influence of verti cal bracket displacement on 1st and 3rd order corrections was studied on th e plaster models, including all teeth from central incisors to first molars , or 28 young persons. The facial contours were evaluated at the mesial, ce ntral, and the distal aspect or the bracket. The contours were calculated w ith the formula of a parabola, and the fit was found sufficient. Intertooth variation was extreme, the biggest curvature was found among the first man dibular 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 app liances. Thus, if the straight wire approach should be followed, the bracke t would have to be custom made. All the calculations were made with the pre condition that full size wires were used. If this is not the case, the disc ussion concerning individual prescription is only of limited importance.