The Long-Term Impact of Single Implant-Supported Crowns on Adjacent Natural Teeth: A Retrospective Longitudinal Study.

OBJECTIVE: To evaluate the long-term impact of single implant-supported crowns on the health status of adjacent natural teeth. METHODS: Clinical and radiographic data from 456 subjects with single implants were analyzed. Complication rates (caries, new restorations, tooth loss) of adjacent teeth were compared against three intra-patient control groups (other quadrants) using data at restoration delivery as the baseline. Multivariate models assessed risk over short-term (1-5 years) and long-term (5-15 years) periods. RESULTS: Mean follow-ups were 3.88 ± 1.75 years for the short-term (n = 456) and 8.90 ± 2.10 years for the long-term (n = 180) cohorts. Adjacent teeth showed significantly higher overall complication rates compared to all control groups in both the short-term (8.0% vs. 2.2%-2.7%; ORs: 2.92-3.65) and long-term follow-ups (15.0% vs. 6.4%-7.8%; ORs: 2.16-2.57). A clear positional dichotomy emerged: mesial teeth showed pronounced short-term caries susceptibility, while distal teeth drove a short-term risk of tooth loss. Restoration needs remained consistently elevated. Bone-level implants (short-term OR: 0.44; long-term OR: 0.38), narrow-diameter implants (OR: 0.23), and pre-existing orthodontic alignment (OR: 0.20) were associated with a lower incidence of complications, whereas patient-level factors such as bruxism (OR: 5.78) and male gender (OR: 10.88) correlated with increased complication rates. CONCLUSION: Single implant-supported restorations significantly elevate the incidence of caries, new restorations, and tooth loss in adjacent teeth relative to controls. While adjacent tooth loss is predominantly an acute short-term risk localized to distal teeth, susceptibility to carious lesions and restorative interventions represents a persistent, long-term morbidity.