45-YEAR TOOTH SURVIVAL PROBABILITIES AMONG MEN IN OSLO, NORWAY

Changes in tooth survival probabilities over a person's lifetime have remained largely unexplored. The goal of this study was to evaluate ch anges in the 45-year tooth survival probabilities in a cohort of 565 N orwegian males who were examined in 1969 as young adults, and followed up into mid-life (examination years and sample sizes (n): 1971 (n = 3 81), 1973 (n = 292), 1975 (n = 245), 1981 (n = 228), 1988 (n = 202), a nd 1995 (n = 223). The results indicated that the tooth survival proba bilities varied considerably both (i) among teeth within individuals, and (ii) over time. The 45-year survival probabilities for the 28 teet h fell into the following ranges: larger than 95% for incisors and cus pids; between 84% and 92% for premolars; and between 59% and 96% for m olars. Over the first 4 post-eruptive decades, the tooth mortality ris ks (excluding orthodontic extractions) were: Ist decade, 2.0% (from 1. 7 to 2.4%); 2nd decade, 0.2% (from 0.1 to 0.4%); 3rd decade, 0.6% (fro m 0.4 to 0.8%); and 4th decade, 1.1% (from 0.8 to 1.5%). The tooth mor tality risks in the 2nd, 3rd, and 4th decades were probably somewhat u nderestimated (due to dropout bias), suggesting that the true underlyi ng tooth mortality hazard function may have been V-shaped. The conclus ions were that the tooth mortality hazard during the first 4 post-erup tive decades was bathtub-shaped and that it varied considerably among teeth within individuals.