Why is there heterogeneity in the effect of dental checkups? Assessing cohort effect

To evaluate age as a potential effect modifier of the relation between frequency of dental check-up and oral health.

Data from a Brazilian oral health survey carried out in 2002-2003 was obtained for three age groups: 15-19-year-old (n=16411); 35-44-year-old (n=13269); and 65-74-year-old (n=5 300). Individuals were examined by dentists and followed to an interview. Self-reported time since last dental visit was measured as 'less than 1 year'; 'from 1 to 2 years'; '3 or more years' or 'never'. Outcomes modelled with negative binomial regression were DMFT index and DT, MT and FT.

Visiting the dentist more recently was associated with fewer teeth with untreated dental caries (DT) and more teeth with fillings (FT) across all age groups. Among the 15-19-year-old, the longer the time since last visit the lower the DMFT and MT. On the other hand, among the 35-44 and the 65-74-year-old the longer the time since last dental visit the higher the DMFT and MT, though this trend reverted in the 'never visited' group.

Age modified the effect of dental visits on DMFT and MT. In younger cohorts, the low frequency of dental check-up among those with good oral health may reflect the fact that these young people do not feel they need to go to the dentist very often, while in older cohorts, the current low frequency of dental check-up associated with bad oral health may be a reflection of a lifetime of high disease incidence coupled with access barriers. Questions regarding the time and frequency of dental visits may capture different dimensions of utilization of dental services, and so pooled estimates are not appropriate. Our results may help explaining contrasting results in previously published studies.