[A multi-view stereo vision methodology for digital soft-tissue impressions in fixed implant rehabilitation of edentulous patients]

To explore the methodology and feasibility of reconstructing soft tissue morphology for fixed implant rehabilitation in edentulous patients using multi-view stereo vision technology, and to conduct a preliminary evaluation of the method's in vitro accuracy.

A pair of edentulous resin models were designed and printed, with 6 implant analogs placed in the maxilla and 4 in the mandible. The experimental group (n=10) utilized a self-developed photogrammetric quad-camera system and the automated reconstruction software RealityScan 2.0.1. Self-developed scan bodies were attached to the analogs, and the handheld camera system was used to capture images of the models in vitro. The images were imported into the software to reconstruct the 3D models, and the data were exported as ".stl" files. The control group (n=10) used an intraoral scanner. Scan caps were attached to the analogs, and the models were scanned to generate ".stl" data. Reference data were obtained by scanning the maxillary and mandibular resin models once each with a desktop scanner (EX-PRO). All data were imported into Geomagic Wrap 2021. The root mean square (RMS) was calculated by comparing the 3D morphology of the experimental and control group data against the reference data to represent the magnitude of the 3D morphological deviation and evaluate accuracy. The evaluation was conducted in 4 specific regions: the alveolar ridge, peri-implant soft tissue, buccal, and lingual areas.

In the maxilla, the RMS of the experimental group was significantly higher than the control group in the alveolar ridge [(124.89±21.30) μm vs. (53.90±8.93) μm, P < 0.001], peri-implant soft tissue [(157.74±19.13) μm vs. (67.03±3.94) μm, P < 0.001], and lingual areas [(146.01±33.87) μm vs. (46.20±11.19) μm, P < 0.001]. The RMS in the buccal area was lower for the experimental group than the control group [(50.56±8.34) μm vs. (53.83±12.66) μm], but the difference was not statistically significant (P=0.571). In the mandible, the RMS of the experimental group was significantly higher than the control group in the alveolar ridge [(254.04±88.42) μm vs. (58.28±38.96) μm, P < 0.001], peri-implant soft tissue [(165.18±21.30) μm vs. (70.48±28.20) μm, P < 0.001], and lingual areas [(421.75±59.51) μm vs. (54.59±36.77) μm, P < 0.001]. When comparing the buccal and lingual sides, the lingual RMS was significantly higher than the buccal RMS for the experimental group in both the maxilla (P < 0.001) and mandible (P < 0.001). For the control group, the maxillary lingual RMS was significantly lower than the buccal RMS (P < 0.05), while the mandibular lingual RMS was higher than the buccal, but the difference was not statistically significant (P=0.378).

The self-developed quad-camera system, combined with multi-view stereo vision reconstruction software, can successfully record the 3D morphology of soft tissue. This study provides a research foundation for the development of extraoral photogrammetric devices capable of simultaneously determining the spatial positions of multiple implant units and acquiring soft tissue morphology.