Comparison of the Dimensional Accuracy of Injection‐Molded Denture Base Materials to that of Conventional Pressure‐Pack Acrylic Resin

Purpose : This study compared the linear dimensional changes of 3 injection‐molded denture base materials to that of conventionally processed polymethylmethacrylate (PMMA) resin. Materials and Methods : An impression of an aluminum maxillary edentulous arch was made with a condensation silicone impression material (Denture Elasticon) to fabricate a gypsum master cast that was replicated as a silicone mold. A maxillary complete denture with acrylic teeth was waxed to full contour on the master cast and replicated to make 40 wax dentures. ERA attachments cast in metal (Rexillium) with indices milled into the centers were waxed into 3 positions in each denture for recording dimensional measurements of the wax denture. Ten dentures were allocated to each of 4 groups; Group 1 was processed using conventionally processed PMMA (Microlon), Group 2 used injection‐molded PMMA (SR‐lvocap), Group 3 employed injection‐molded nylon (Valplast), and Group 4 used injection‐molded styrene (Northern). All processed specimens were stored at room temperature (25°C, ambient humidity) for 1 week (while still on the master cast) before anteroposterior and cross‐arch measurements were made using the ERA reference points with a digital caliper. After separation from the master cast and following water storage at 37°C for 7 days additional measurements were made. Results : An analysis of the results showed that the effect of processing was not the same for the 3 dimensions studied, regardless of which dimension was considered ( p < 0.0001). The pattern of dimensional changes associated with the material type was not the same between the wax and processing stages as it was for the change between the processing and decasting stages ( p < 0.0001). Conclusions : Processing the denture base materials produced unequal deformation in different dimensions (anterior‐posterior and cross‐arch). Each material tested also responded differently to the processing stages.