Abbas Kharal, MD, MPH, and Richa Sharma, MD, MPH
This is a well-designed study exploring the relationship of dental disease, a prevalent and modifiable condition, and the incidence of ischemic stroke. The authors sought to investigate whether an association was present between the two conditions given significant prior retrospective studies suggesting a correlation.
The study population is the ARIC (Atherosclerosis Risk in Communities) cohort who also had a dental examination during the fourth visit, resulting in a total of 6,736 patients. Utilization of regular dental visits was assessed by self-report. The degree of periodontal disease was determined by classifying each patient by aggregating data on the tooth level involving 7 dental parameters. The diagnosis of ischemic stroke and stroke subtype from visit 4 onwards was documented as the outcome of interest. Covariates that were accounted for included demographic data and history of vascular risk factors. Education level was used as a proxy for economic status of the participants as data about income level and insuredness were not included. Hazard ratios were obtained to assess the risk of incident stroke based on degree of dental disease and usage of dental care. Compared to those with dental health, participants with any dental disease, as categorized by periodontal profile class, had a higher risk of incident ischemic stroke, both in unadjusted and adjusted regressions (see Figure below). There was a trend towards increase in stroke risk with each periodontal profile class severity increment, suggesting a possible dose response. Furthermore, the increased hazard of ischemic stroke was noted only in patients with cardioembolic and thrombotic strokes, not lacunar strokes. The authors have also implicated that this association may be biologically plausible since periodontal disease induces systemic inflammation, which may lead to atherosclerosis and atrial fibrillation. Another possibility is that these patients may be transiently bacteremic and the burden of endocarditis was not assessed.
The greatest barrier to access to dental care in the United States is resource limitation. Thus, it is possible that poor dental care may be a marker of lower economic status, which may be associated with ischemic stroke risk due to medication nonadherence, lack of access to healthcare for measures such as cancer screening, accident/trauma risk, and stress in general. Thus, it is critical to control for economic status, which does not always correlate with educational level. If there is truly a causative relationship between dental health and ischemic stroke, then perhaps these results may provide an impetus for widely increasing access to dental care given the morbidity, mortality, and cost of ischemic stroke care in the acute and chronic setting.
Although this study is a great effort in assessing the risk of periodontal disease and its association with incident ischemic stroke by using a subclassification of periodontal profiles of varying severity, the observational nature of the study and confounding by selection bias is of high concern. In general, it is understandable that those with a higher socioeconomic status, hence better medical insurance plans, and those with higher education are perhaps the ones who visit the dentist more often. On the contrary, those with poor socioeconomic status, lower education and multiple vascular risk factors may plausibly not pay a visit to their dentist as often. Not surprisingly, this was exactly the case in this study, where those with poor dental hygiene were also the patients with lower education and higher vascular risk factors, including higher prevalence of hypertension, diabetes, obesity and cigarette smokers. These factors have been independently linked with an increased risk of ischemic stroke. Both in the crude and adjusted analysis, for example, those with dental profiles of PPC C, PPC-F & PPC G had the highest rates of stroke; however, these were also the patients with the highest prevalence of diabetes, hypertension, higher BMI’s and had a significantly higher percentage of black patients compared to others. This perhaps may be why the rate of stroke is higher in these groups compared to those in PPC D & E. This could imply that although there may be an association between periodontal disease and stroke, it was possibly amplified significantly by the fact that patients with dental disease also had more poorly controlled vascular risk factors. Also, other racial factors, such as socioeconomic status, type of insurance and access to dental care, were not accounted for.
Additionally, the authors state that ischemic stroke occurred more in patients with periodontal disease possibly due to increased systemic inflammation; however, this does not explain why lower rates of lacunar strokes were seen compared to thromboembolic and cardioembolic strokes. This may, in fact, be due to variability in the risk factor profiles of these patients and other unaccounted factors, such as a single periodontal disease assessment, antiplatelet or anticoagulant drug use, and the presence of cardiac arrhythmias and other prothrombotic states that were not accounted for in this observational study.
Identifying periodontal disease as an independent risk factor for stroke indeed has great implications from a stroke reduction perspective; however, further research in the form of a randomized controlled clinical trial is needed to make any strong association between the two. Particularly, an RCT that can balance racial, socioeconomic, educational and vascular risk factor profiles across both arms in order to better understand the true association of poor dental hygiene alone on incident stroke risk. The effect of treating periodontal disease on recurrent vascular ischemic events is being studied in the PREMIERS Trial (Periodontal Treatment to Eliminate Minority Inequality and Rural Disparities in Stroke) and appears promising in providing more information about the true association between periodontal care and ischemic stroke risk.