Comparison of the Dimensional Stability of Splinting Material with Different Polymerization Times

Abstract

Purpose: The purpose of this study was to evaluate the effects of polymerization time and sectioning on the dimensional changes of auto-polymerizing acrylic resin used in splinting impression copings and the resulting fit of the prosthesis. Materials and Methods: Open-tray impression copings were connected to a master cast containing 5 external-hex implants. Auto-polymerizing acrylic resin was allowed to polymerize in a heavy-body polyvinyl siloxane matrix according to 3 different time groups (8 minutes (8MN), 1 hour (1HR), and 24 hours (24HR)), with 20 sets of splinted impression copings per time group. Each time group was further divided into non- sectioned (NS) and sectioned (S) groups (10 samples per group). A total of 60 gypsum bases were fabricated from implant analogs connected to the impression copings. A milled titanium bar fabricated from the master cast was used to verify the fit of the bar to the implant analogs. The casts were viewed using loupes (2.5x magnification) and a microscope (12.8x magnification) to visually detect any gap. The gap sizes were evaluated with a measuring gauge with pre-determined thickness in microns (μm). Results: Of the 30 casts tested in the sectioned groups (8MN-S, 1HR-S, and 24HR-S), all of the casts displayed clinical fit when evaluated with magnification loupes and a dental explorer. From this evaluation, only the 8MN-S group showed statistical significant difference (p < 0.05) when compared to its non-sectioned counterpart (8MN- NS). When evaluated with a microscope, no significant differences were found between the different time groups or sectioned samples. The microscope was able to detect gaps that were not detectable with magnification loupes and a dental explorer. Conclusion: Overall, difference in polymerization time and sectioning did not have an effect on the accuracy of fit. Sectioning for the 8-minute time group did show an improvement in the fit when compared to the non-sectioned samples. Although clinical fit appeared to be present, it did not always indicate the presence of absolute fit.