Using data from the 2011–2014 NHANES, our study results showed that well over half (58%) of US adults with diabetes had periodontitis, a figure much higher than the 42% prevalence of periodontitis in the general population of US adults, also reported from previous NHANES research (15). Notably, we found the practice of preventive oral self-care behaviors (i.e. flossing and utilization of preventive dental services) was associated with better periodontal health in adults with diabetes. However, flossing but not obtaining of preventive dental visits was associated with reduced risk for poor glycemic control, adjusting for other factors. Overall, our results support the importance of preventive dental care especially routine flossing for periodontal health and glycemic control among people with diabetes.
Our findings are somewhat consistent with the work of Cepeda and colleagues, showing that among US adults (with or without diabetes), flossers are 23% less likely to have periodontitis than non-flossers (16). However, we found a 39% reduced likelihood for periodontitis among the diabetes population that flossed regularly, indicating that adults with diabetes may experience even greater benefits than their non-diabetic peers in terms of periodontal health through practicing regular flossing.
Due to the scarcity of high-quality oral self-care intervention studies, especially flossing trials among people with diabetes, it is not clear whether oral self-care interventions, such as flossing, may benefit glycemic control among people with diabetes. Nevertheless, a number of studies have shown that non-surgical periodontal treatment, such as scaling and tooth planing, reduces glycemic levels among people with diabetes, the reductions in HbA1c ranging from 0.27–1.03% (17). The hypothesized underlying mechanism is that periodontal treatment reduces the local periodontium inflammation as well as systemic inflammation, measured by pro-inflammatory biomarkers. This decrease in systemic inflammatory burden contributes to reduced insulin resistance among people with diabetes (18, 19). In a randomized controlled trial among people with type 2 diabetes, O’Connell and colleagues reported non-surgical periodontal treatment reduced HbA1c by 0.9%, and also found the intervention reduced serum levels of inflammatory biomarkers such as interleukins (IL-6, IL-12), and granulocyte colony-stimulating factor (20). Due to our cross-sectional design and the lack of biomarker measures in NHANES 2011–2014, we were not able to evaluate whether the relationship between flossing and glycemic control potentially is related to a reduction of systemic inflammatory burden. A recent pathway analysis using NHANES 2009–2010 data provided limited evidence to support this hypothesis (21). Luo and colleagues reported flossing mitigates the effect of poor oral health on systemic inflammation as measured by C-reactive protein (21). As others have observed, even very minor changes in HbA1c can have a major impact on clinical outcomes in diabetes (12). Additionally, a large observational study reported that a 1-point (1%) reduction in the HbA1c level reduces risk by 12% for stroke, 21% for deaths related to diabetes, 14% for myocardial infarction, 19% for cataract extraction, and 43% for amputation (22). In the present study, we found after adjusting for potential confounders, flossing was associated with 0.3% reduction in HbA1c. Although the magnitude is modest, this warrants further investigation using an experimental approach as it could be clinically meaningful in glycemic control among people with diabetes.
Periodontal disease is considered the sixth complication of diabetes mellitus (23). Although it may not be considered as directly life-threatening as other diabetic complications, it influences glycemic control and systemic inflammation among people with diabetes. Therefore, the American Diabetes Association (ADA) recommends people with diabetes brush twice a day, floss once a day, and visit dentists twice a year (24). However, despite the importance of brushing and flossing on periodontal disease prevention and management, people with diabetes are less likely to obtain preventive dental service and practice flossing than their counterparts without diabetes (25). Moreover, there are missed opportunities for educating patients with diabetes about the proper technique of tooth brushing and flossing. A previous study of diabetes self-management education programs recognized by the ADA showed only about 10% of diabetes self-management curricula included in their survey have included the demonstration of proper tooth brushing/flossing techniques, and almost none of these programs had their clients demonstrate the recommended tooth brushing/flossing technique (26). Substantial efforts are needed to improve diabetes self-management related to oral health care.
Obtaining preventive dental care and practicing effective toothbrushing and flossing are key oral health self-management behaviors and are particularly important for the population with diabetes. Understanding the nuance in the determinants and outcomes of different oral self-care behaviors is important to inform the design of oral self-care interventions and policy making. For example, we reported previously that having health insurance (as a proxy for dental insurance) is only associated with obtaining preventive dental visits but not with the practice of regular flossing (27), indicating that merely increasing dental insurance coverage may not resolve the issue of inadequate oral hygiene among people with diabetes. In this study, we found although both obtaining preventive dental visits and flossing are associated with lower risk for periodontitis among the diabetic population, only flossing was associated with reduced HbA1c after controlling for confounders. It is plausible that regular flossing works continuously against the daily accumulation of dental biofilm (28), which provides the source for local inflammation. Our results support the idea that obtaining regular preventive dental services cannot take the place of regular flossing for the maintenance of oral health; both are important components of diabetes self-management.
Since the outbreak of coronavirus disease 2019 (COVID-19), aerosol-generating dental procedures including periodontal treatment have been limited, and non-aerosol-generating-preventive dental care is currently recommended (29). Also, the numbers of people obtaining regular dental care has declined during the pandemic with most dental practices in the US seeing only patients with dental emergencies during lockdowns (30). As a result of the pandemic, it has become even more imperative that people with diabetes practice optimal oral self-care at home.
We recognize there are caveats of the study due to the limitations of the data. As with all cross-sectional studies, we cannot confirm the directionality or temporality of the associations that were found in this study. Secondly, we restricted our definition of oral self-care to flossing because NHANES does not have brushing frequencies in adults. Thus, we cannot determine the role tooth brushing may play in oral care and periodontitis prevention and glycemic control. Of note, we used the term, “flossing”, in reference to the question, “using dental floss or any other device”, which is a conventional approach in previous analyses using NHANES (16, 21). Lastly, key measures such as diabetes diagnosis, flossing, and the use of preventive dental visits were based on self-report and are susceptible to recall or reporting bias.
In summary, we found flossing is associated with lower likelihood of periodontitis and better glycemic control among US adults with diabetes. This study highlights the importance of promoting preventive oral self-care as an integral part of diabetes self-management. However, further longitudinal or experimental studies are warranted in order to advance oral health in persons with diabetes.