Verification jig for implant-supported prostheses: A comparison of standard impressions with verification jigs made of different materials

Statement of problem. Implant verification jigs are routinely used during the fabrication of implant-supported prostheses. The dimensional accuracy of these jigs is unknown. Purpose. The purposes of this study were to (1) compare the dimensional accuracy of verification jigs with that of conventional impression procedures and (2) measure the dimensional accuracy of 3 resin materials used to fabricate verification jigs. Material and methods. Thirty verification jigs and 20 impressions were made of 3 externally hexed Steri-Oss implants in a master stone base according to the following groups (n = 10 per group): (Group 1) jig: GC pattern resin; (Group 2) Jig: Duralay resin; (Group 3) Jig: Triad gel resin; (Group 4) Impression: closed-tray impression copings; and (Group 5) Impression: open-tray impression copings. A stone base was fabricated for each experimental jig and impression. Master stone base and experimental stone bases were measured with the following methods: X and Y coordinates of each implant center were obtained with a traveling microscope by averaging the X and Y coordinates of the implant external hex corners. The origins of the coordinates during measurement of each base were arbitrary. Distances between implant center points were calculated by use of the Pythagorean theorem. Vertical measurements (Z-plane) were obtained with a digital caliper at the 2 terminal-implant locations. Interimplant distances and vertical measurements were subtracted from those of the master base, and the resultant distortion values were analyzed with analysis of variance and Tukey Studentized range tests. Statistical significance was set at P<.05. Results. Verification jigs were not significantly more accurate than standard impression procedures. Open-tray impressions showed a significantly greater vertical distortion (Z-R location: 262 +/- 158 mum; P=.0001; Z-L location 333 +/- 189; P=.0001) compared with the other groups. Triad gel jigs showed a significantly greater distortion in one interimplant distance (C-L) than closed-tray impressions (P=.04), whereas Duralay jigs exhibited significant greater distortion than closed-tray and open-tray impressions in the interimplant distance R-C (P=.006). Although not significantly different from other groups, the closed-tray group showed the lowest mean distortion values in all measurements. Conclusion. Within the limitations of this study, the accuracy provided by verification jigs was not significantly superior to standard impression procedures. The results suggest that jig fabrication does not improve the dimensional accuracy of stone casts. Open-tray impressions showed a significantly greater inaccuracy in the vertical plane.