Passivity of complete arch implant-supported fixed dental prostheses fabricated using a scan gauge system and...

Intraoral scanning of an edentulous full arch with implants is subject to scanning errors. These errors may lead to a misfit of the final implant-supported restoration if a verification procedure is not employed. The purpose of this in vitro study was to compare the passivity of fit of metal frameworks on full arch multi-unit abutments (MUAs) fabricated using different intraoral impressions of full arch dental implants.

Maxillary and mandibular master casts were fabricated with Type IV gypsum with MUAs located 0.5 mm subgingivally. The maxillary cast consisted of two straight MUA anterior analogs and two distally angulated MUA posterior analogs. The mandibular cast consisted of six MUA straight analogs. Digital scans of the maxillary and mandibular master casts were completed by one operator with a Trios 4 intraoral scanner (3Shape). One set of scans was completed with scan gauges and the other with scan bodies. Screw-retained metal bars were fabricated from each of the four scans. In addition, two bars were fabricated with intentional misfit to serve as a negative control. All bars were milled with the same bar design dimensions. Twelve evaluators were asked to evaluate the bars and to provide a yes or no answer to three questions related to bar fit on the casts. A Fisher's Exact test was used to analyze the data.

Twelve evaluators completed a clinical assessment of each bar. In the maxilla, a significant number of prosthodontists considered the bar fabricated using the Nexus technology more accurate than the bar fabricated using conventional scan bodies (p < 0.001). Ten out of twelve (83.33%, p < 0.05) of evaluators reported that the maxillary Nexus bar passed the one screw test and had a clinically acceptable fit. Only 8.33% of evaluators felt that the bars fabricated from the conventional scan bodies had a passive fit and were clinically acceptable. In the mandible, a majority (75%, p < 0.05) of evaluators responded that the Nexus bars had a clinically acceptable fit, whereas none of the conventional scan body bars did. Only 16.66% of evaluators determined the conventional scan body bars to have a passive fit, while 58.33% (p = 0.089) determined that the Nexus bars did have a passive fit. All the evaluators deemed the bars fabricated with intentional misfit clinically unacceptable.

Over 75% of the evaluators reported that both the maxillary and mandibular bars fabricated utilizing the Nexus scan gauge system achieved a clinically acceptable result. Future studies are needed that expand on more objective findings.