Accuracy Evaluation of Full-arch Implant Impressions Using Different Workflows: A Prospective Study

The aims of this clinical study are: 1) to compare the accuracy of conventional versus digital impression techniques for implant impressions; 2) to assess the passive fit of the prosthesis constructed from the most accurate impression.

Study design The ethical approval will be obtained from the research ethics board. Thirty edentulous patients who received 4 - 6 implant and indicated for implant-supported fixed prosthesis will be invited. All participants will require to read and sign the informed consent form before initiation of the treatment. The impression procedures will be performed by one experienced prosthodontist. The prostheses will be evaluated by an independent prosthodontist.

Sample size calculation The sample size is calculated based on the tests for paired means. With α= 0.05, β= 0.2, mean of distance deviation, IOS= 17 μm, and standard deviation= 34 μm, a sample size of 25 is necessary, which would have the power of 90% to detect the difference. Therefore, a total of 25 patients will be invited to participate in this clinical study. This sample size is more than previous studies evaluating IOS and SPG workflows (15 - 17 patients). However, it has been reported that the dropout rate in clinical studies is 20%. For this reason, a total of 30 patients will be invited to compensate for the anticipated loss of patients.

Treatment procedure Conventional impression Abutment-level impression copings will hand tightened onto the abutments and splinted with autopolymerizing acrylic resin (Pattern Resin; GC), and allowed to polymerize. A custom open-tray splinted impressions will be made with a polyether material (Impregum Penta Soft; 3M ESPE). After 5 minutes, the impression copings will be unscrewed from the implants, and the impression will be removed. Type IV dental stone (dentostone 220; dentona AG) will be poured into the impression to generate a definitive cast. The models will be digitalized with a high-resolution laboratory scanner (E4; 3Shape A/S) with an accuracy of 4 mm to obtain the 3D data of the models in standard tessellation language (STL) format.

Digital impressions After tightening the scan bodies (CARES® RC Mono Scan body, Straumann, Basel, Switzerland), the intraoral scanner will be used according to the manufacturer's recommendations. Three scanners will be used since they have different ways of obtaining 3D images and working principles. The technology of Trios scanner (TRIOS 4, 3Shape A/S) depends on confocal microscopy, ultrafast optical scanning and auto-correction; Cerec Primescan (Dentsply Sirona) depends on optical triangulation and confocal microscopy; Medit i700 (Medit, Seoul, Korea) depends on 3D in-motion video technology, 3D full-color streaming capture and advance algorithm to stitch images. The scanning path will begin with the occlusal surfaces, then turned to the palatal or lingual surfaces, and lastly to the buccal surfaces of the scan bodies. Then, removing the scan body with a trim tool from the occlusal view and exporting the STL file.