Survival and Risk Factors of Implants Placed in Sites of Previous Failures-A Nationwide Retrospective Cohort Study

To assess the survival rates of dental implants placed in previously failed sites and identify systemic, site-specific and implant-related factors associated with implant loss.

This study included all dental implants (177,410 implants in 59,238 patients) placed between 2014 and 2023 within a nationwide dental network. Implant sequence (first, second, third or subsequent placement at the same site) was identified. Implant survival was assessed using Kaplan-Meier analysis and log-rank test. The Andersen-Gill extension of the Cox proportional hazards model was used in a multivariable analysis to identify independent predictors of failure. Separate Andersen-Gill Cox models were fitted for early and late failures.

Overall implant survival was 97.5% after a mean follow-up of 4.61 ± 2.72 years. Survival declined progressively with repeated placement, from 97.6% (169,990/174,187) for first implants to 92.2% (2748/2980) for second implants and 88.5% (215/243) for third or subsequent implants (p < 0.001). The hazard of failure was 4.6 times higher for second implants (HR 4.60; 95% CI, 3.98-5.32; p < 0.001) and 5.7 times higher for third or later implants (HR 5.71; 95% CI, 3.68-8.87; p < 0.001), compared to the first implants. Independent predictors of failure included smoking, male sex, penicillin allergy, narrow diameter and maxillary placement. The association between implant sequence and failure differed by time after implantation. The hazard of early failure was 6.80 times higher for second implants (95% CI, 5.78-8.00; p < 0.001) and 9.27 times higher for third or later implants (95% CI, 5.57-15.45; p < 0.001), compared to the first implants. The hazard of late failure was 1.93 times higher for second implants (HR 1.93; 95% CI, 1.40-2.65; p < 0.001) and 2.63 times higher for third or later implants (HR 2.63; 95% CI, 1.24-5.58; p = 0.011), compared to the first implants.

Reimplantation showed relatively favourable survival; however, failure risk increased with each successive implant placed at the same site, particularly early failures. Additionally, smoking, male sex, penicillin allergy, short and narrow implants and maxillary location were independent predictors of failure.