[Esthetic analysis of upper lip morphology variation after the cross-arch fixed restoration of maxillary implant-supported prostheses via radiographic methods].

Objective: To measure and analyze upper lip morphology variation before and after the cross-arch fixed restoration of the maxillary implant-supported prostheses using cone- beam CT (CBCT) to provide an esthetic objective reference for maxillary edentulous patients. Methods: There were 32 maxillary edentulous patients selected in the Department of Dental Implantology, The Affiliated Stomatological Hospital of Nanjing Medical University from January 2010 to December 2023. The CBCT data of patients with maxillary full-arch implant-supported fixed prostheses were retrospectively collected before implantation (T0), at the time of radio-guide insertion (T1), and after final repair (T2). The length and thickness of the upper lip were measured and analyzed at each time point, and the correlation between the upper lip contour data and facial esthetic parameters was analyzed. Results: After the final prosthodontic treatment, the length of the upper lip was significantly increased from (21.72±2.84) mm to (24.98±2.93) mm (t=-8.13, P<0.001) compared with that before implant treatment. The widths of the middle and vermilion of the upper lip (Sm-Hm/Ls-UP), were reduced from (13.24±1.41), (12.81±1.67) mm to (11.36±1.67), (10.21±1.69) mm, with significant differences (t=7.79, P<0001; t=9.37, P<0.001). The lower face height (Sn-Gn) was increased from (54.52±4.95) mm to (58.70±4.42) mm, with significant differences (t=-11.05, P<0.001). However, the nasolabial angle reduced significantly from 95.35°± 7.70°to 90.53°±7.28°(t=7.68, P<0.001). The width of the middle of the upper lip with a radiation guide was (10.94±1.24) mm, and it increased significantly compared with that after the final prosthesis treatment (t=-0.76, P<0.05). The proportion of straight upper lip profiles accounted for 59% (19/32), and the proportion of concave upper lip profiles accounted for 41% (13/32) after the final prosthesis treatment. In addition, the results of correlation analysis showed that the nasolabial angle variation was weak and negatively correlated with residual bone height (r=-0.37, P=0.490). Conclusions: After the treatment of the maxillary full-arch implant-supported fixed prosthesis, the length of the upper lip increases, and the thickness of the upper lip becomes significantly thin. The maxillary full-arch implant-supported fixed prostheses support upper lips to improve the patients' side appearances.