Abstract
The aim of this study was to evaluate the dimensional changes of denture bases made from different resins after different storage periods. For this purpose, 25 sets of plaster models/resin bases were prepared using 4 acrylic resins submitted to two types of polymerization: 1--QC-20 submitted to polymerization by microwave energy; 2--QC-20 submitted to polymerization by water hot bath; 3--Vipi Cril submitted to polymerization by water hot bath; 4--Vipi Wave submitted to polymerization by microwave energy; and 5--Onda Cryl submitted to polymerization by microwave energy. After polymerization, the specimens were sectioned for accuracy readings using a comparison microscope. Readings were taken at 3 points: the crests of the right (A) and left (B) ridges, and the median region of the palate, in 4 different periods. The data obtained were submitted to two-way ANOVA and Tukey's test at 5% significance level. The greatest distortions were found in the posterior palatal region of the base (M), with statistically significant difference (p<0.05) for the studied resins. All acrylic resins presented dimensional changes and the storage period influenced these alterations.
Highlights
The magnitude of the acrylic resin dimensional changes may be influenced by several factors, such as polymerization techniques, in which the internal stresses are produced by different coefficients of thermal expansion of gypsum and acrylic resin (1), and the base thickness, which may vary at different sites inside the flask (2,3), altering the denture base adaptation and stability (4)
The hypothesis of this study that different commercial types of acrylic resin and different periods of water storage can change the adaptation of the denture base was confirmed
The greatest dimensional change (0.3109 mm) between the resin base and the plaster cast occurred in the median region of the palate (M)
Summary
Dimensional changes in denture bases result from monomer shrinkage during polymerization and stresses released when the flask cools. Shrinkage due to the polymerization reaction is not uniform, being more accentuated in the posterior region of the palate, and it is difficult to compensate after processing. Distortion results from cooling and removal of the base from the plaster model, both causing the release of stresses induced during processing (5). Acrylic resin is the most commonly used material in artificial dental construction, it is subject to polymerization shrinkage and distortion. The shrinkage resulting from the polymerization reaction is not uniform, being more evident on the palate of the maxillary denture and is be poorly compensated after resin base processing (3). The distortion resulting from flask cooling and stone cast deflasking induces stresses released during the base procedure (6)
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