Sir, despite the increasingly high prevalence of depression and depressive disorders, there has been a lack of well-conducted observational studies that have examined the associations between depression and adverse dental outcomes. Some of the published studies to date have found associations while others have not. Two studies that observed positive associations are described below. The first, a multivariable analysis of adult patients in India, detected an association between depression and periodontitis, and the authors concluded that depression can be considered an important risk factor for the development of periodontal diseases.1 The second, a study using self-reported data among patients from a randomised trial at two cancer centres in the US, concluded that depression was associated with non-adherence to therapeutic oral medications in patients with oral cancer.2

While the aforementioned studies have various limitations including cross-sectional designs that limit our ability to make statements of causality between depression and adverse dental outcomes, they provide initial insights into the associations and the need for further study of them. There are various plausible biological and behavioural pathways by which depression can lead to a worsening of dental outcomes including an increased prevalence of periodontal disease and dental caries.

Our purpose is to draw attention to an understudied area of research. In two recent analyses of the Nationwide Emergency Department Sample we identified associations between the presence of depression and an increased likelihood of hospital admission among older male patients with prostate cancer (in press) and among patients with head and neck cancer (under review). We hypothesised in both analyses that depression would be associated with worsening overall health, as indicated by the need for hospital admission vs. discharge after controlling for possible confounding variables including demographic, hospital and clinical characteristics. Our analyses add to other studies that show associations between depression and worsening health, including oral health. There is a clear need for well-designed prospective studies that examine if depression can lead to an increased incidence of adverse dental outcomes including dental caries and periodontal disease.