[Accuracy of photogrammetry and conventional impression techniques for complete-arch implant rehabilitation: an in vitro comparative study]

Objective: To compare the accuracy of photogrammetry and conventional impression techniques for complete-arch implant rehabilitation. Methods: An edentulous maxillary stone cast containing 8 screw-retained implant abutment replicas was derived from a 74-year-old male patient who visited the Department of Dental Implant Center, Capital Medical University School of Stomatology in September 2019. The stone cast was copied through the open-tray splinted impression, and the copied cast was used as the master cast for this study. The abutment-level impressions of master cast were made by photogrammetry (PG) and the conventional impression technique (CNV) by one attending doctor. Group PG: after which scan bodies were connected to each implant replica, a photogrammetry system was used to obtain digital impressions of the master cast (n=10); Group CNV: conventional open-tray splinted impression technique was performed to fabricate conventional definitive casts (n=10). After connecting the scan bodies onto each implant replicas, the master cast and the 10 definitive casts from group CNV were digitized with a laboratory reference scanner. All data of group PG, group CNV and mater cast were saved as ".stl" files. For all test scans and reference scan, the three-dimensional information of scan bodies were converted to implant abutment replicas using a computer aided design software (Exocad). The data of the group PG and the group CNV were respectively registered with the reference data (trueness analysis) and pairwise within group (precision analysis) for accuracy evaluation in a three-dimensional analysis software (Geomagic Control X). Results: The trueness and precision of group PG [(17.33±0.34) and (2.50±0.79) μm ] were significantly statistically better than those of group CNV [(24.30±4.16) and (26.12±4.54) μm] respectively (t=-5.29 and -34.35, P<0.001). Conclusions: For complete-arch implant abutment-level impression, photogrammetry produces significantly better accuracy than conventional impression technique.

[Application of digital technique aided occlusal rehabilitation in implant-supported fixed prosthesis of fully edentulous patients]

Objective: To evaluate the clinical outcomes of digital technique-aided occlusal rehabilitation based on implant-supported fixed prostheses (ISFP), and to provide some information for clinical application of digital technique. Methods: Retrospectively reviewed the cases which had used neuromuscular system and condylar movement tracing device to reconstruct occlusion in one or double jaw fully edentulous ISFP from January, 2013 to January, 2020. A total of 6 eligible patients were enrolled in the present study with 56 implants and 8 ISFP, including 4 male patients and 2 female patients, aged from 43 to 74 years. The clinical outcomes were evaluated in four aspects, including implant survival rate, implants success rate, marginal bone loss and the occurrence of prosthesis complications. Results: The follow-up time was (4.0±2.2) years (1-7 years). The implant survival rate was 100% (56/56) and the implant success rate was 98% (55/56), with an average missal and distal marginal bone loss of (0.04±0.11) mm/year. Veneer chipping occurred at incisal edge of 2 adjacent incisors in only one prosthesis 3 years after rehabilitation. Conclusions: Combination of digital techniques of neuromuscular system and condylar movement tracing device to assist occlusal rehabilitation based on ISFP showed a high implant success rate. The complication seldom happened. Long and stable occlusion has been observed. The clinical outcomes were favorable.