This paper attempts to identify characteristics of a longitudinal clinical study's "dropout" population (1974-1996) of patients using overdentures. This study included 395 subjects. Dropouts were identified as persons who did not respond to letters or telephone calls after participating in the study for up to 2 years, could not be located, or did not wish to return to the study. Participants (N=273) and Dropouts (N=84) were compared by evaluating a series of factors: sociodemographic, medical, health, and some oral health behaviors. The population was divided into two very similar cohorts for analysis based on years of recruitment: Group I (1974-1984) and Group II (1985-1993). Significant differences were found between them, including vision problems and risk of oral soft tissue problems related to medical diagnosis. Dropouts were significantly younger than Participants, had fewer hearing and vision problems, tended to brush their teeth more often and were more likely to use daily topical fluoride in their overdentures. The differences between the Dropouts and the Participants may be that younger persons are more mobile and have fewer vision and hearing problems, but this does not help predict their commitment to a study. Health behaviors such as brushing overdenture abutments or fluoride use may be more predictable but are harder to assess until persons have been study participants for some time.
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