Processing factors affecting the clarity of a rapid-curing clear acrylic resin

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

STATEMENT OF PROBLEM

Acrylic resin complete dentures exhibit certain unavoidable 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 sorption of dentures processed by dry and wet heat with different rates of cooling.

METHODS

Fine crosses marked on tinfoil inserts were placed at the incisive papilla and tuberosity regions of edentulous maxillary casts and incorporated into the dentures during polymerization by 3 processing techniques. A traveling microscope was used to measure the distances between the reference points to determine dimensional changes. Water uptake and content were determined by the mass changes of the dentures with an electronic balance. Data of linear dimensional change and water sorption were analyzed by multivariate analysis of variance and analysis of variance, respectively. Bonferroni simultaneous confidence intervals (95%) were applied for multiple comparison.

RESULTS

Dry heat-processed and water bath-processed acrylic resin dentures did not exhibit significant differences in shrinkage (0.42% to 0.58%) at water saturation. Amounts of water sorption of dentures processed by dry and wet heat (0.50 and 0.48 mass%, respectively) were not significantly different, and their associated expansion did not entirely compensate for the processing shrinkage. The initial water content of dry heat-processed dentures (1.77 mass%) was unexpectedly slightly higher than that of wet heat-processed dentures (1.68 mass%). The rate at which the dentures cooled did not affect their initial water content and subsequent water uptake.

CONCLUSIONS

Water uptake of dry and wet heat-processed acrylic resin dentures after deflasking was in both cases low, and the dentures did not reveal significant differences in shrinkage at water saturation. Air oven-processed and water bath-processed acrylic resin dentures show similar dimensional shrinkage at water saturation.

Denture base resins: comparison study of color stability

Several denture base resins have been recently introduced that provide easier or faster processing. Although these materials have adequate strength properties, the color stability is also of interest. This study evaluated the color stability of five denture base acrylic resins and one denture base repair resin. The samples were subjected to conditions of accelerated aging to test color stability. Five samples of each material were processed and aged for 100 and 300 hours. The color stability was quantitatively measured using the Minolta Chroma Meter II. Color measurements were made before weathering and at 100 and 300 hours the color difference delta E was calculated for all samples. At 300 hours the color change of the materials was significantly different at p less than 0.01. It was found that: (1) the color of Lucitone Hy-pro and Acron was least affected by conditions of accelerated aging; (2) Triad, Accelar 20, and Perm demonstrated noticeable color changes; and (3) Compak-20 had an appreciable color change and was the least color-stable of the materials tested.