The relationship of arch length to alterations in dental arch width

An accurate method is presented for forecasting alterations in arch length related to various width increases in each dental arch. It is based on comb ined beta and hyperbolic cosine functions which express the expanded dental arches with correlation coefficients of r = 0.98, between measured data an d representations of the dental arch. When the midpalatal suture is expande d, canine width and molar width alterations are not equal because the line of action of the expanding force is anterior to the center of resistance of the dentomaxillary complex. Therefore, canine to molar width ratio alterat ions of 1:1, 1.25:1, and 1.5:1 are examined, and simple linear functions ar e presented for purposes of predicting changes in arch length.