A Scoping Review of the Relation Between Toothbrushing and Diabetes Knowledge, Glycemic Control, and Oral Health Outcomes in People With Type 2 Diabetes

The informationist (K.K.O.) searched MEDLINE via PubMed and CINHAL Complete. The search strategy, shown in the Supplementary Appendix, contained a combination of controlled vocabulary terms and key words associated with type 2 diabetes and home oral care. No filters or database supplied limits were used.

Studies involving adults with type 2 diabetes, an assessment of home toothbrushing activity, diabetes knowledge, some measure of glycemia, and measures of oral health were included in the analysis. We excluded studies exclusively involving individuals who had other forms of diabetes or in which the data on people with type 2 diabetes were not presented separately from those of subjects with other forms of diabetes. We also excluded studies evaluating the impact of professional dental treatment on glycemia in individuals with type 2 diabetes.

We included all studies that had assessments of both home toothbrushing activity and glycemic control and/or diabetes knowledge. These included survey-based investigations looking for associations, as well as studies with an interventional component designed to improve home oral care.

Using systematic review software (DistillerSR), one of us (R.D.L.) screened citation titles and abstracts for eligibility and then screened in full text the references initially selected. Data were independently extracted in duplicate (by R.D.L. and J.K.B.) and included the following characteristics of the study design: inclusion/exclusion criteria, number of participants, experimental design, baseline participant characteristics (e.g., sex and age), intervention(s), and reported outcomes.

Of the 148 unique citations returned from the literature database searches, 11 studies were identified that met the inclusion criteria of exploring the relation between toothbrushing activity and glycemic control and/or diabetes knowledge in people with type 2 diabetes (19–29). Figure 1 illustrates the screening process according to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines (30). These seven observational and four interventional studies were published between 1999 and 2021 with experimental approaches that included the use of survey questionnaires (20,23,28,29), chart review (25), both chart review and survey questionnaires (24), longitudinal follow-up (22), or interventional designs (19,21,26,27). The studies were conducted in a variety of international settings that included China (28,29), Japan (22,25,26), Korea (23), Saudi Arabia (19), Thailand (27), Turkey (20,21), and the United States (24). Although one study included a breakdown of participant race and/or ethnicity (24), participant race and/or ethnicity were either not reported or might be surmised from the location of recruitment. Study design, participant demographics, primary intervention, and measures reported are presented in Table 1.

The oral health and glycemic outcomes measured, the direction of associations observed, and/or observed changes in the studies are summarized in Table 1.

Six of the seven observational studies included an assessment of diabetes prevalence, diabetes-related knowledge, or glycemia (20,22,23,25,28,29). The observational study by Kanjirath et al. (24) reported only on measures of oral health.

From the observational studies that included people both with and without type 2 diabetes, individuals with type 2 diabetes more often reported rare or never as their toothbrushing frequency compared with those who did not have type 2 diabetes (P <0.001) (24,29). With respect to type 2 diabetes prevalence, Kuwabara et al. (25) found a significant association between low frequency of toothbrushing and diabetes prevalence (odds ratio [OR] 2.03, 95% CI 1.29–3.21), and Furuta et al. (22) found that the adjusted prevalence rate ratio (PRR) of brushing less than one time daily (i.e., less than the recommended twice daily [14]) was 1.62 (95% CI 0.91–2.88). Zhuang et al. (29) did not find a significant association between self-reported brushing frequency and type 2 diabetes (hazard ratio 0.94, 95% CI 0.86–1.03).

Survey studies explored the relationships between toothbrushing frequency and glucose levels using self-reported A1C (20), measured A1C (28), 2-hour postprandial plasma glucose (PG) (28), and fasting blood glucose (FBG) (28). Cinar et al. (20) found those reporting more frequent toothbrushing were more likely to be able to report their A1C (OR 10.5, 95% CI 1.01–103). The study by Su et al. (28), using a model adjusted for multiple potential confounding factors, found that, among urban residents, the lowest reported frequency of toothbrushing (rarely/never) was associated with a 0.26% (95% CI 0.04–0.47%) higher A1C (P = 0.02), and brushing once daily was associated with a 0.12% (95% CI 0.03–0.22%) high A1C (P <0.01) compared with those brushing at least twice daily. Smaller differences were seen for rural residents in whom A1C for those with a reported brushing frequency of rarely/never was 0.20% (95% CI 0.09–0.31%) higher (P <0.01) and A1C was 0.09% (95% CI 0.00–0.18%) higher for those reporting brushing once daily compared with those brushing at least twice daily (P = 0.04). Similarly, compared with people who reported brushing at least twice daily, these investigators found a statistically significant higher FPG in urban and rural populations, with 9 mg/dL (95% CI 1.8–16.2 mg/dL) (P = 0.02) and 1.7 mg/dL (95% CI 2.52–8.64 mg/dL) (P <0.01) for urban residents brushing rarely/never and once daily, respectively, and 4.7 mg/dL (95% CI 0.9–8.6 mg/dL) (P = 0.02) and 3.42 mg/dL (95% CI 0.18–6.48 mg/dL) (P = 0.03) for rural residents brushing rarely/never and once daily, respectively. No statistically significant differences in 2-hour postprandial PG levels were observed for either group of residents with different toothbrushing frequencies. In the study by Furuta et al. (22), people who reported brushing their teeth only once daily and not at night had a higher PRR for hyperglycemia as assessed by FPG, with a PRR of 1.3 (95%CI 1.02–1.66) compared with those brushing at night (PRR of 1).

A variety of oral health–related outcomes were reported in the cross-sectional and longitudinal observational studies. Poorer oral health status was reflected as more bleeding on probing (BOP), more gingival crevicular fluid (GCF), greater periodontal pocket depth (PPD), larger build-up of calculus, more tooth decay, and increased risk of periodontal disease. Among the observational studies, five of the seven included at least one oral health–related assessment (20,22–24,29), whereas two had none (25,28).

Cinar et al. (20) found a strong positive correlation (R = 0.82, P <0.01) between toothbrushing self-efficacy and frequency. Hong et al. (23) found a significant difference in the prevalence of periodontitis in individuals with type 2 diabetes (18.7%) compared with those who did not have diabetes (9.0%) (P <0.001), although, among people with type 2 diabetes, there was not a statistically significant associated between toothbrushing frequency and risk of periodontitis. Kanjirath et al. (24) used probing depths of <4 mm as their cutoff for healthy periodontal tissue and found that only 60.29% of those who did not report brushing regularly had healthy periodontal tissue compared with 81.57% of those who did report brushing regularly (P = 0.04). In addition, 31.66% of those who did not brush regularly were found clinically to have decayed teeth compared with only 15.01% of those who brushed regularly (P = 0.03).

The study by Furuta et al. (22) found no associations between brushing at night and any of the oral health–related parameters evaluated for individuals who reported brushing twice daily. However, for those brushing only once daily, not brushing at night was associated with poorer outcomes for four of the six oral health–related parameters evaluated. Those not brushing at night compared with those who did brush at night had a higher percentage of sites with BOP (23.9 ± 22.5 vs. 20.4 ± 21.9%, P = 0.005), greater clinical attachment level (CAL) (2.61 ± 0.73 vs. 2.44 ± 0.65 mm, P <0.001), deeper PPD (2.32 ± 0.52 vs. 2.16 ± 0.43 mm, P <0.001), and more calculus (0.58 ± 0.53 vs. 0.47 ± 0.45%, P = 0.003) but no significant difference in the amount of dental plaque debris index or number of teeth.

In four interventional studies (19,21,26,27), in addition to providing study participants with toothbrushes, the researchers examined whether provision of oral health education or coaching among people with type 2 diabetes had meaningful impact on glycemic management, physical activity, quality of life, and diabetes knowledge. Three of the four included measures of oral health (19,21,26), whereas the fourth, by Saengtipbovorn and Taneepanichskul (27), only had self-report of oral hygiene behaviors. Notable differences among the studies were populations studied, instructional approaches used, study durations, and outcome measures reported.

Three of the four interventional studies included systemic measures only. Two of the interventional studies (19,21) reported statistically significant improvements in glycemic status after provision of oral health education or coaching, whereas the third (26) did not. After providing oral hygiene instruction and toothbrushes to study participants, Almas et al. (19) observed that FBG decreased from 193.85 ± 32.47 to 187.15 ± 32.28 mg/dL (P = 0.002) and from 233.55 ± 21.53 to 212.95 ± 16.71 mg/dL (P <0.001) in those with early or moderate periodontal disease and advanced periodontal disease, respectively. Cinar and Schou (21) observed statistically significant (P ≤0.01) decreases in A1C for individuals receiving health coaching, with A1C levels dropping from 7.7 ± 1.8 to 7.1 ± 1.5%, from 7.4 ± 1.5 to 7.0 ± 1.3%, and from 7.3 ± 1.2 to 6.8 ± 1.0% for those with low, moderate, and high toothbrushing self-efficacy (TBSE), respectively. They also observed a statistically significant (P = 0.02) decrease in A1C for those at the lowest TBSE level in the health education group (from 7.9 ± 1.5 to 7.7 ± 1.4%). However, the intervention by Nishihara et al. (26) resulted in no statistically significant change in A1C.

In comparing outcomes after health coaching or health education, Cinar and Schou (21) also found that those in the health coaching group engaged in significantly more physical activity (P = 0.001) and had better quality of life as assessed using the abbreviated World Health Organization Quality of Life instrument (P = 0.003). Although Saengtipbovorn and Taneepanichskul (27) included no direct measures of glycemia, they did find that, compared with usual care diabetes education, receipt of combined diabetes and dental care education resulted in significantly greater improvement in diabetes knowledge and attitude (P = 0.001) and engagement in exercise (P = 0.016). Although the intervention by Nishihara et al. (26) resulted in no statistically significant change in A1C, they did report a significant decrease in mean level of tumor necrosis factor-α (TNF-α) in the intervention group, from 1.4 ± 0.7 to 1.2 ± 0.5 ng/mL (P = 0.03).

All four of the interventional studies included oral health–related outcomes (19,21,26,27). Although the invention by Almas et al. (19) was a brief (7 days), they observed statistically significant improvement in GCF in both the cohort with early or moderate periodontitis and the cohort with advanced periodontitis, in which levels decreased from 0.399 ± 5.02 to 0.362 ± 4.47 µL (P <0.001) and from 0.547 ± 5.28 to 0.504 ± 4.56 µL) (P <0.001), respectively. They also reported that the mean plaque score in the cohort with advanced periodontitis went from 94.3 to 41.85% after the intervention (P <0.001). Saengtipbovorn and Taneepanichskul (27) included no clinical measures of oral health but found that provision of combined diabetes and dental care education resulted in statistically significant (P <0.001) greater improvements in oral health knowledge and attitude, reported as mean ± SD differences at 6 months of 0.94 ± 0.19 and 3.17 ± 0.52, respectively, and in self-reported use of dental floss of 48 versus 11% (P <0.001), but they saw no differences in toothbrushing or having had a dental treatment in the past 6 months compared with the usual diabetes care education group. The educational intervention promoting optimal behavior for improvement of diabetes and periodontal disease by Nishihara et al. (26) had mixed results, with no significant differences observed for change in PPD but a significant group-by-time interaction (P = 0.007) for decreases in BOP of 12.5% and 0.4% observed in the intervention and control groups, respectively. In addition, there was a 3.1-point improvement in toothbrushing score in the intervention group compared with a 0.8-point decline in the control group (P = 0.001). Cinar and Schou (21) found statistically significant improvements in CAL (P ≤0.004) in both the health coaching and health education groups at all levels of TBSE.

The results of this systematic scoping review suggest that interventions that are successful at improving toothbrushing engagement in people with type 2 diabetes have potential to improve their oral health and glycemic control. More limited data from this study support the idea that oral health coaching, as opposed to more passive oral health education, may be the more successful approach for achieving improved toothbrushing engagement. Taken together, given that the American Diabetes Association’s 2023 Standards of Care guidelines (31) are silent on toothbrushing (spelled as either one or two words), we suggest there is room to improve consideration about oral hygiene as a component of self-care behavior for people with type 2 diabetes.

The 2022 update of the Cochrane review of periodontitis treatment and glycemic control in people with diabetes analyzed 30 studies and reported evidence of moderate certainty that professional treatment of people with diabetes for periodontitis reduced A1C by 0.43% (95% CI 0.28–0.59%) (5). The authors did not report on any elements of home oral hygiene. This scoping review of associations among type 2 diabetes, toothbrushing, oral health, and glycemic outcomes contributes findings of interest to the field of diabetes self-management education and care.

A commonality among the observational studies included here was the finding that lower frequency of toothbrushing was associated with both poorer glycemic control and poorer oral health in people with type 2 diabetes. One interpretation is that there is overlap between populations who are not engaged in optimum home oral care and those not engaged in optimum diabetes self-management. An alternative is the testable hypothesis that increasing toothbrushing frequency has the potential to improve glycemic control and oral health outcomes in people with type 2 diabetes. The interventional studies included in this review examined a variety of approaches for doing just that (i.e., increasing toothbrushing frequency). Although these studies (19,21,26,27) varied in their experimental designs, were all relatively small in scale, and might not be generalizable to more diverse populations, each found measurable improvement in some aspect of glycemic control, measure of systemic health, and/or engagement in what are classically considered diabetes self-management behaviors. The outcomes observed are at least suggestive that engagement in toothbrushing is an area of self-care amenable to improvement. Although improved interdental cleaning is typically thought of as the behavior change associated with periodontal disease improvement, it is worth noting that improvements seen with enhanced interdental cleaning are always made in the context of a routine toothbrushing habit (32). Whether the proportion of people with the suboptimal toothbrushing frequency observed in the populations studied is generalizable more broadly needs to be determined.

These data may suggest that improvement in toothbrushing frequency, or at least having people exposed to strategies designed to increase their engagement in home oral hygiene, has potential to result in meaningful improvement in health outcomes among people with type 2 diabetes. The potential to improve glycemic control might be mediated via some pathway associated with oral hygiene activities, actual improvements in oral health, or perhaps the success with one behavior change (i.e., toothbrushing) serving as positive reinforcement that results in engagement with other health-related behavior changes, or it could be mediated by some combination of all three.

Although a dental exam is mentioned in the diabetes self-management and support curriculum (33), how it and its natural extension—home oral care—are assessed in practice have not been studied. We suggest that home oral care could be presented in a positive framing as something that is not strictly a diabetes-related issue and/or something to be judged on, but rather as an opportunity for positive reinforcement about an aspect of self-care. Furthermore, we suggest that consideration of toothbrushing be incorporated into guidelines of national organizations that are stakeholders in the care of individuals with type 2 diabetes, and we advocate additional research to identify effective strategies for improving home oral hygiene engagement through self-care management education among adults with type 2 diabetes.

Although oral health outcomes may not be included along with cardiovascular disease, neuropathy, nephropathy, and retinopathy as common conditions associated with type 2 diabetes, oral health may hold a potentially unique place among diabetes comorbidities. The presence of gingivitis and periodontal disease can be visually evaluated by people with diabetes and clinicians. In addition, the impact of toothbrushing engagement can be monitored at home and in clinic visits. Adhering to twice-daily toothbrushing, like any behavior change, may be challenging, although potentially less so than other lifestyle changes associated with diabetes self-management. Given that optimal engagement in toothbrushing is applicable to all people and not just those with diabetes, toothbrushing is likely less laden with the emotional and psychological burden of diabetes-related health behaviors. Thus, success with improved toothbrushing may have the potential to serve as an influence or nudge toward additional diabetes-related self-care activities.

Although this is a systematic and comprehensive review of the available literature, there are several important limitations of this work. The lack of consistent measures of glycemia and oral health outcomes meant that we were unable to conduct a meta-analysis and so have no effect size estimate. Although some of the survey studies included large numbers of participants, many had relatively small sample sizes. There was a great geographic variability in study setting, which can be viewed as a strength suggesting general applicability of the results but also could mean that some of the specific findings might not be generalizable to other populations. Finally, reliance on self-report of toothbrushing may not accurately reflect actual toothbrushing engagement.

This scoping review of toothbrushing, oral health, and glycemic control in people with type 2 diabetes suggests that toothbrushing engagement leads to improved oral health and glycemic control. Further study is needed to better document the efficacy of this approach. In addition, there are many touch points in the delivery of medical and dental care that could be used as opportunities to reinforce messaging and coaching about the importance of home oral hygiene, although further research into this is also needed.

A commonality among governmental agencies (e.g., the Centers for Disease Control and Prevention and the National Institutes of Health) and stakeholder organizations (e.g., the American Dental Hygienist Association, American Dental Association, Association of Diabetes Care and Education Specialists, American Diabetes Association, and National Association of Community Health Workers) positions them to implement recommendations to improve oral health outcomes for people with diabetes. They could all engage in efforts to recognize oral health as a component of overall health and well-being of people with type 2 diabetes.

The authors thank Drs. Leslie Kolb and Marcelo Araujo for their interest in and encouragement of the exploration of this topic and Drs. Cameron Estrich and Heba Hussein for their valuable feedback on an early draft of the manuscript.

No potential conflicts of interest relevant to this article were reported.

R.D.L. and K.K.O. developed the search strategy. R.D.L. and J.K.B. compiled the data. R.D.L., J.K.B., and M.F.M. wrote the manuscript. R.D.L. is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.