Objective: To develop and test a scale for measuring expectancy of retaining teeth for life and to compare the estimates when using a global item with those obtained with a multi-item scale of measurement.
Material and methods: The design of the study was cross-sectional selected and random sample surveys using a self-administered questionnaire or interview. There were two groups of patients and a national sample aged 16-79 years (n=1274); response rate 64%. The main results pertain to dentate subjects in a global group (n=615) and in a scale group (n=609). The outcome measure was expectancy of retaining natural teeth for life. Results. When using the global item, 92% (95% CL 89.8, 94.1) of the respondents believed they would definitely or possibly retain their natural teeth for life, significantly higher than the 81% (95% CL 77.6, 84.0) obtained with the 4-item conditional scale. Cronbach's alpha was 0.89 for the 4-item scale and the test-retest reliability moderate (kappa = 0.51; 0.77 for +/-1). The adults' belief in retaining teeth for life was significantly associated with having a live-in partner (p = 0.009) when the global question was the dependent variable; and sex (p = 0.000) and education (p = 0.004) when the 4-item scale was the dependent variable. Explained variance was 3.8% and 4.5%, respectively. Conclusions. The internal reliability of the 4-item scale was high. A significantly lower proportion of people reported belief in retaining natural teeth for life when employing the 4-item conditional scale than when the unconditional global question was used.