Limitations
A potential limitation is that the results were based on self-reported data, and the use of more objective measures of data would help to improve the accuracy with which oral health behaviours are measured. In addition, because of the study setting, leaflets were also distributed to the e-learning group. It is possible that the oral health care effects of the leaflets may have influenced the results, but our difference-in-difference study design was intended to account for the shared effect of these leaflets in both groups, so this is unlikely to be a significant limitation. Another potential limitation is that the sample was recruited only from volunteer organizations in Japan; in addition, the study participants were mostly female, which may have affected the representativeness of the target population.