Positional accuracy of intraoral scan alignment to a facial scan using structured light scanning and trial denture base with occlusal rim markers in patients with complete maxillary edentulism

Statement of problem: Creating precise 3D virtual head models for patients with complete maxillary edentulism remains challenging owing to the lack of natural landmarks and limitations of current image-matching technologies. Purpose: The purpose of this study was to evaluate the positional accuracy of intraoral scan alignment to structured light-based facial scans using varying sizes and positions of occlusal rim markers under maxillary edentulous conditions. Material and methods: Radiopaque artificial markers of 3 sizes (2, 4, and 6 mm) were made and attached to the maxillary occlusal rim of a completely edentulous patient at different positions (midline-canine [MC], midline [M], canine [C]). Facial scans were obtained of the patient by using a structured light facial scanner under 9 experimental conditions (size-location: 2MC, 2M, 2C, 4 MC, 4M, 4C, 6MC, 6M, and 6C; 5 scans under each condition). Intraoral scans were aligned to the facial scans using stepwise images matching the occlusal rim scan casts. The alignment accuracy was evaluated by comparing the intraoral scan with a reference position established using cone beam computed tomography data. Measured variables included anterior and posterior linear deviations and angular deviation of the arch plane. Statistical analysis was conducted using the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni correction (α=.05). Results: The 4-mm and 6-mm marker groups exhibited significantly lower deviation in image registration than the groups without markers and those with 2-mm markers (P<.001). Regarding the marker position, the midline-canine group exhibited the lowest deviation value, followed by the midline and canine groups. Markers positioned in the midline exhibited less deformation compared with those in the canine region. Conclusions: Occlusal rim markers can be used to align intraoral and facial scans in patients with complete maxillary edentulism when structured light face scanning is included. Markers with a clearly recognizable size in facial scans are less prone to deformation in the facial midline area.