Estimation of the linear dimensional changes of autoclave cured acrylic resin with multiple palatal depths and investment materials

Abstract

Background: Dimensional changes of acrylic denture bases after polymerization results in need for furtheradjustments or even ends with technical failure of the finished dentures. The purpose of this study was to estimate thelinear dimensional changes for different palatal depths when using multiple investment materials and polymerizationtechniques.Materials and methods: Ninety upper complete denture bases were constructed for this study. They were dividedinto two main groups according to the polymerization methods: conventional water bath and experimentalautoclave (short and long cycles). Each main group was further subdivided into three subgroups according to thepalatal depth (shallow, medium and deep). Furthermore, for each palatal depth; complete denture bases wereinvested either with dental stone or laboratory silicone. For each upper complete denture, measurements of lineardimensional changes were done by fixation of metallic screws on the tissue surface of the denture base. Thedistances were measured by using travelling microscope with an accuracy of 0.001 %. The data were statisticallyanalyzed using three way analysis of variance (ANOVA) for three variables, which were (palatal depth, investmentsand polymerization techniques), LSD test and student T test for comparisons between groups.Results: There were significant improvements in the dimensional accuracy of denture bases cured with autoclavecompared with water bath. Also, silicone investments were a successful alternative to stone, study data shows thatshort autoclave processing with silicone reduces the magnitude of the linear dimensional changes. On the otherhand, long autoclave processing and stone investments were better than silicone in reducing dimensional changes.Conclusion: The findings of this study indicates that the use of autoclave processing in acrylic curing is a promisingalternative to the conventional water bath and leads to better dimensional stability for the finished dentures in alloral configurations and palatal depths. Also, Silicone is more preferable than stone, although it's not as stronginvesting materials when compared with stone