Accuracy of Impression and Pouring Techniques for an Implant-Supported Prosthesis

Purpose: The purpose of this in vitro study was to compare the dimensional accuracy of a stone index and of 3 impression techniques (tapered impression copings, squared impression copings, and squared impression copings splinted with acrylic resin) associated with 3 pouring techniques (conventional, pouring using latex tubes fitted onto analogs, and pouring after joining the analogs with acrylic resin) for implant-supported prostheses. Materials and Methods: A mandibular brass cast with 4 stainless steel implant-abutment analogs, a framework, and 2 aluminum custom trays were fabricated. Polyether impression material was used for all impressions. Ten groups were formed (a control group and 9 test groups formed by combining each pouring technique and impression technique). Five casts were made per group for a total of 50 casts and 200 gap values (1 gap value for each implant-abutment analog). Results: The mean gap value with the index technique was 27.07µm. With the conventional pouring technique, the mean gap values were 116.97 µm for the tapered group, 57.84 µm for the squared group, and 73.17 µm for the squared splinted group. With pouring using latex tubes, the mean gap values were 65.69 µm for the tapered group, 38.03 µm for the squared group, and 82.47 µm for the squared splinted group. With pouring after joining the analogs with acrylic resin, the mean gap values were 141.12 µm for the tapered group, 74.19 µm for the squared group, and 104.67 µm for the squared splinted group. No significant difference was detected among Index, square/latex techniques, and master cast (P >.05). Conclusions: The most accurate impression technique utilized squared copings. The most accurate pouring technique for making the impression with tapered or squared copings utilized latex tubes. The pouring did not influence the accuracy of the stone casts when using splinted squared impression copings. Either the index technique or the use of squared coping combined with the latex-tube pouring technique are preferred methods for making implant-supported fixed restorations with dimensional accuracy. Keywords: dental implantation, dental impression technique, dental models