Long-term radiographic marginal bone changes and implant survival in tooth agenesis versus non-agenesis sites: a retrospective cohort study of 710 implants

Abstract Purpose Tooth agenesis is associated with reduced alveolar ridge dimensions and altered local anatomy, potentially affecting implant long-term outcomes. This study compared marginal bone loss (MBL), implant survival, and implant success between implants placed in agenesis and non-agenesis sites. Methods This retrospective cohort study included 316 patients with 710 implants placed between 2000 and 2010. Implants in tooth agenesis sites (TA group, n = 284) were compared with implants in normally developed alveolar bone (control group, n = 426). Mesial and distal MBL were assessed radiographically at short-term (1–<3 years), mid-term (3–<8 years), and long-term (≥ 8 years) follow-up. Survival was evaluated using Kaplan–Meier analysis, and success was assessed according to the Albrektsson, Buser, and Misch criteria. Results Bone augmentation was required less frequently in the TA group than in controls (34.5% vs. 43.0%; p = 0.028). MBL increased over time in both groups, without significant between-group differences at any follow-up interval. Implant survival was comparable between groups (TA: 96.1%; control: 93.9%; p = 0.604). Success rates were similar according to the Buser and Misch criteria, whereas the Albrektsson criteria indicated lower radiographic success in the TA group. Combined internal and external augmentation was associated with significantly lower survival than either procedure alone ( p = 0.003). Conclusions Implants placed in tooth agenesis sites showed long-term bone stability and survival comparable to controls. These findings suggest that local anatomical conditions and reconstructive complexity may influence long-term implant prognosis more strongly than tooth agenesis itself.