Verification for Implant Supported Dental Prostheses: Evaluation of Gap Distance and Polymerization Time

Objective: To determine whether the width and orientation of luted autopolymerizing resin at a specified inter-implant distance and time to polymerization affects accuracy in the verification of implant location for a simulated implant supported fixed dental prosthesis. Methods: A master model was fabricated using two Astra-Tech implant replicas spaced 17mm apart and embedded in Fuji Rock. Open-tray implant impression copings were attach to the replicas and torqued to 10Ncm. A prefabricated GC pattern resin cylinder with the dimensions of 16mm length and 5mm diameter was attached to the copings using the Nealon technique. Eighty specimens were fabricated in total. Ten specimens for each of the following sample groups were tested: polymerization for 17min for a 1mm, 3mm, and 5mm vertical gap distance, 1mm horizontal gap distance, 1mm 45 degree diagonal gap distance; and 3, 10 and 17 minute polymerization time for a 3mm vertical gap distance. Measurements were made using a Nikon optical projector microscope (accurate to 1μm) at 4 points from one coping to the second, before and after subjecting the samples to the test variable. Post-luting measurements were compared to the initial baseline measurements to determine the amount of polymerization shrinkage observed in the sample group. Results: Luting orientation of a 1mm gap distance and polymerization time of a 3mm vertical gap distance did not yield a statistically significant difference when comparing the pre- and post-test variable values. A trend towards increasing shrinkage, and total error of the system was observed as the vertical gap distance increased. Overall change of 10μm was observed for a 1mm vertical gap distance, 12-22μm for a 3mm vertical gap distance, and 18-27μm for a 5mm vertical gap distance. Conclusions: A larger gap distance between the impression copings for fresh autopolymerizing material to bridge will result in more shrinkage, distortion and introduce more error into the system. The luting orientation of a 1mm gap distance and polymerization time of 3, 10, and 17 minutes for a 3mm vertical gap distance did not significantly affect the accuracy of the assembly. The manufacturer recommendation for use of autoploymerizing resin is suitable for accuracy in the clinical and laboratory settings.