Predicting clustered dental implant survival using frailty methods

The purpose of this study was to predict future implant survival using information on risk factors and on the survival status of an individual's existing implant( s). We considered a retrospective cohort study with 677 individuals having 2349 implants placed. We proposed to predict the survival probabilities using the Cox proportional hazards frailty model, with three important risk factors: smoking status, timing of placement, and implant staging. For a non-smoking individual with 2 implants placed, an immediate implant and in one stage, the marginal probability that 1 implant would survive 12 months was 85.8% ( 95% CI: 77%, 91.7%), and the predicted joint probability of surviving for 12 months was 75.1% ( 95% CI: 62.1%, 84.7%). If 1 implant was placed earlier and had survived for 12 months, then the second implant had an 87.5% ( 95% CI: 80.3%, 92.4%) chance of surviving 12 months. Such conditional and joint predictions can assist in clinical decision-making for individuals.