Accuracy of implant casts generated with splinted and non-splinted impression techniques for edentulous patients: an optical scanning study

Background: The accuracy of implant casts generated with various impression techniques was mainly investigated in vitro resulting in limited clinical data. Purpose: (1) To compare the three-dimensional (3-D) accuracy of splinted and non-splinted impression techniques to the control casts (verification jigs) that had been used for actual patient treatment; and (2) to determine the maximum level of clinically undetectable misfit. The null hypothesis was that there would be no significant difference in the accuracy of casts generated with different impression techniques. Materials and methods: The implant casts used for the prosthetic rehabilitation of 12 edentulous jaws with CAD/CAM zirconia, implant-fixed complete dental prosthesis (IFCDP) were included in this study. Intraoral acrylic jigs were used to fabricate index casts. Splinted and non-splinted, open-tray techniques were used to generate two casts. Optical scanning acquisition of the x-coordinates, y-coordinates and z-coordinates of the implant positions for each individual cast was performed. The best fit algorithm was used with computer software to superimpose the scanning datasets. Group I (n=12) included casts from the splinted impression technique vs. acrylic jig casts, and group II (n=12) included casts from non-splinted technique vs. jig casts. Results: The paired t-test and Wilcoxon's signed ranks test were used to compare the 3-D discrepancies within and between groups I (splinted vs. jig) and II (non-splinted vs. jig), respectively. Significant difference was found at the x-axis, y-axis and 3-D between groups I and II (P<0.05), but not in the vertical z-axis (P>0.05). Within subject, global 3-D discrepancies between groups I and II were significantly different (P<0.05), corroborated by in vivo observations of clinical fit. Implant position in the arch affected the 3-D accuracy of casts for both anterior and posterior implants (P<0.05). Conclusion: The splinted technique generated more accurate master casts than the non-splinted technique for one-piece IFCDPs in edentulous jaws and the null hypothesis was rejected. These clinical implications demonstrate improved accuracy of splinted impression techniques compared with the non-splinted technique. For the external connection, the implant system used in this study, a 3-D misfit ranging from 59 to 72 mu m, may be considered the maximum discrepancy resulting in an acceptable clinical fit with one-piece IFCDPs.