Effect of processing method on the dimensional accuracy and water sorptionof acrylic resin dentures

Statement of problem. Acrylic resin complete dentures exhibit certain unavo idable dimensional changes. Processing shrinkage and expansion due to water uptake are 2 important aspects influencing dimensional accuracy. Purpose. This study investigated linear dimensional changes and water sorpt ion of dentures processed by dry and wet heat with different rates of cooli ng. Methods. Fine crosses marked on tinfoil inserts were placed at the incisive papilla and tuberosity regions of edentulous maxillary casts and incorpora ted into the dentures during polymerization by 3 processing techniques. A t raveling microscope was used to measure the distances between the reference points to determine dimensional changes. Water uptake and content were det ermined by the mass changes of the dentures with an electronic balance. Dat a of linear dimensional change and water sorption were: analyzed by multiva riate analysis of variance and analysis of variance, respectively. Bonferro ni simultaneous confidence intervals (95%) were applied for multiple compar ison. Results. Dry heat-processed and water bath-processed acrylic resin dentures did not exhibit significant differences in shrinkage (0.42% to 0.58%) at w ater saturation. Amounts of water sorption of dentures processed by dry and wet heat (0.50 and 0.48 mass%, respectively) were not significantly differ ent, and their associated expansion did not entirely compensate for the pro cessing shrinkage. The initial water content of dry heat-processed dentures (1.77 mass%) was unexpectedly slightly higher than that of wet heat-proces sed dentures (1.68 mass%). The rate at which the dentures cooled did not af fect their initial water content and subsequent water uptake. Conclusions. Water uptake of dry and wet heat-processed acrylic resin dentu res after deflasking was in both cases low, and the dentures did not reveal significant differences in shrinkage at water saturation. Air oven-process ed and water bath-processed acrylic resin dentures show similar dimensional shrinkage at water saturation.