Changes in the Relative Position of Teeth in the Construction of Denture Bases

During the construction of denture bases the original position of the teeth is often changed, resulting in a modification of the previously established occlusion. Some of the variables associated with the dimensional changes which occur in dentures have been studied by Atiyyah, ' Steck,2 Grunewald, Paffenbarger, and Dickson.3 However, a number of factors remain to be investigated, while others warrant further study. It was the purpose of this research to investigate the influence of certain factors as they influ-ence tooth relationships and to attempt to define more clearly the exact role played by each of the following entities: (1) the distortion of the wax and base plate during storage on the model; (2) the setting expansion of the investing stone; (3) the type of resin used for construction of denture base; (4) the molding process and polymerization procedure employed; (5) the influence of the finishing and polishing procedure. MATERIALS AND METHODS Very briefly, the procedure consisted of constructing upper and lower dentures by a variety of techniques, incorporating the pertinent variables and determining the amount of change induced in the relative position of the teeth both by the individual factors and through the interaction of the various factors. Acrylic teeth were used in all dentures. Stainless-steel reference points were inserted in the central incisors, first bicuspids, and first molars (Fig. 1). By measuring the distance between these points with a comparator microscope-the accuracy of which was 0.005 mm.-it was possible to determine the amount of change occurring in various areas of the same denture. Seven individual measurements were taken on each denture (Fig. 2). They were: Distance 1: bimolar-between the tips of the mesial-buccal cusps. Distance 2: bi-bicuspid-between the tips of the buccal cusps of the first bicuspids. Distance 3: bi-incisor-between the mid-points of the incisal edge of central incisors. Distance 4