BACKGROUND/AIMS: Ankylosis and subsequent tooth loss is a serious complication following tooth avulsion and replantation. The aim of the study was to evaluate the risk of ankylosis of human teeth replanted after various periods of dry storage prior to replantation. The material originates from a previously reported clinical study of 400 replanted teeth. METHODS: Initial treatment, clinical and radiological examination and follow-up were conducted according to a standardized protocol. PDL was not removed. Follow-up periods ranged from 0.2 to 20 years (mean 5.1 years). The risk of ankylosis was analysed using the Cox regression model including stage of root development, length of dry time and age > 20 years. RESULTS: The risk of ankylosis significantly increased with increasing length of dry time (hazard ratio: 1.22, P = .002) and was significantly higher for teeth with mature root development than for teeth with immature root development (hazard ratio: 2.1 P < .0001). The estimated risks of ankylosis after 900 days for teeth with immature root development were: dry time < 20 minutes: 33.9% (95% confidence interval (CI): 25.4-42.7), dry time 20-40 minutes: 49.6% (95% CI: 37.5-64.8), dry time 40-60 minutes: 54.4% (95% CI: 37.1-71.3) and dry time > 60 minutes: 60.0% (95% CI: 45.0-75.8). The risks for teeth with mature root development were: dry time < 20 minutes: 59.4% (95% CI: 51.6-66.5), dry time 20-40 minutes: 78.3% (95% CI: 69.5-86.2), dry time 40-60 minutes: 81.9% (95% CI: 67.2-92.4) and dry time > 60 minutes: 86.4% (95% CI: 79.7; 92.9). CONCLUSION: The risk of ankylosis rose with increasing length of dry time. However, some teeth may heal without ankylosis even after 60 minutes of dry time. Immature teeth have a lower risk of developing ankylosis. Replantation should therefore always be considered for avulsed teeth.