A method of estimating tooth life expectancy.

One of the most important outcome measures for dental services is the increase in tooth life expectancy which is brought about by the interventions provided. Thus, a convenient and accurate index of tooth survival is critical both to clinical decision making and to more general assessments of public dental health policies. This paper describes a simple method of approximating tooth life expectancy (TLE). The method is based on the assumption that tooth survival follows a simple declining exponential function. Assuming a constant mortality rate, TLE is the integral of the survival function, expressed as S(t) = e-mu t, where t is time and mu the constant mortality rate. Using 3-year tooth-specific mortality rates for 491 subjects aged 50 years or more, tooth-specific life expectancies for the population as a whole where found to range from 27 years for upper canines to 71 years for lower incisors. Individuals with a mean periodontal attachment loss greater than 4 mm and people on low incomes had significantly lower tooth life expectancies than their periodontally fit and more wealthy counterparts. This technique can be used to obtain disease-specific or intervention-specific tooth life expectancies. Thus, gains in TLE for individuals with different oral, social and behavioural characteristics can be calculated. The declining exponential approximation of tooth life expectancy has the potential to become a powerful tool in the evaluation of dental services and treatments.