Discussion
The findings of this study suggest a significant reduction of around −€12 in the quarterly diabetes-related healthcare costs per person following periodontal treatment in individuals with assumed diabetes. Furthermore, the findings indicate that more advanced periodontitis treatment may result in higher benefits, the benefits are mainly attributable to non-medication-related healthcare costs, and that different patient groups may benefit differently from periodontal treatment.
The findings presented in this study are in line with two previous claims data studies showing reductions in (diabetes-related) healthcare costs for patients with diabetes after receiving periodontal treatment,15 16 although our results show smaller reductions. This may be explained because of differences in study design or context. The study by Nasseh et al15 focused on patients with newly diagnosed diabetes, and the reported diabetes healthcare costs were much higher than observed in the current study. The study by Jeffcoat et al16 defined periodontal treatment as receiving more than three periodontal treatments compared with three or less periodontal treatments as the control group. Both studies, however, suggest lower diabetes-related healthcare costs after periodontal treatment in patients with diabetes. This was confirmed by a recent cost-effectiveness study showing that providing periodontal treatment to patients with type 2 diabetes would be cost saving.12
Besides the overall finding that periodontal treatment reduces overall diabetes-related healthcare costs, these findings suggest that individuals receiving advanced periodontal treatment benefit more than individuals receiving intermediate periodontal treatment. The dose-response relation between periodontitis and diabetes may play a role here.22 Possibly people receiving advanced periodontal treatment have more severe periodontitis and may benefit more from this treatment. More severe periodontitis may have a greater impact on diabetes status as well.
The overall reduction of diabetes-related costs through periodontal treatment seems to be largely attributable to patients receiving insulin but not to patients receiving metformin or other oral blood glucose-lowering drugs. It should be noted that the costs of metformin became lower in 2017 and 2018, which partly explains the lower diabetes costs overall in these years. According to Dutch type 2 diabetes guidelines, insulin is the third and final step in pharmacotherapy after metformin and sulfonylurea derivatives.20 It may be that the effect of periodontal treatment is dependent on diabetes severity, that is patients with more severe diabetes (who receive insulin medication) benefit more from periodontal treatment compared with those with less severe diabetes (who receive metformin or other oral blood glucose-lowering drugs). However, it should be mentioned that the diabetes medication groups were based on medication reimbursement claims in 2012. Patients can switch from medication regime, which was not controlled for in this study. The observed effect of periodontal treatment resulting in increased diabetes-related costs for patients receiving metformin or other oral blood glucose-lowering drugs may reflect adaptations in the diabetes management regime.
Besides lowering HbA1c levels and financial benefits of periodontal treatment in individuals with diabetes,5 7 8 periodontal treatment could also have additional benefits. Severe periodontitis is linked to a higher risk of diabetes complications,23 and it might be hypothesized that treatment of periodontitis and improving the periodontal status may lead to a lower risk of these complications. A retrospective study in Taiwan found lower rates of cardiovascular disease among individuals with diabetes and advanced periodontal treatment compared with those with non-advanced periodontal treatment.24 In addition, periodontal treatment in patients with diabetes has been associated with improved quality of life and higher diabetes treatment satisfaction.25 26 Periodontal treatment in individuals with diabetes may therefore be beneficial on multiple outcomes.
The findings of this study support the integration of medical and dental healthcare, especially in patients with diabetes. The Dutch guidelines for type 2 diabetes already suggest short oral health checks during the yearly diabetes visit and recommends to advice patients with diabetes to see the dentist twice a year.20 The current findings contribute to the evidence for these statements and might even suggest to raise more awareness for periodontitis as the sixth complication of diabetes. Vice versa, the dentist could play an important role by assessing diabetes risk in high-risk patients such as those with periodontitis. Easy screening tools for diabetes exist, such as the Finnish Diabetes Risk Score,27 and could be included in standard patient evaluations.28 Possibly, the development and advancement of electronic decision support systems might provide unique and novel opportunities for integrated management of patients with diabetes and periodontitis.29
The present study has some strong features to be mentioned. First, it used a large database including all insured individuals at one of the largest health insurers in the Netherlands. In total, almost 1 million individuals were included in the original sample, which is almost 6% of the total Dutch inhabitants. Then, we included all individuals with assumed diabetes in 2012, giving us a sample of over 40 000 individuals with a follow-up period of 7 years. For these 7 years, extensive data were available regarding the number of claims and the reimbursements for periodontitis-related and diabetes-related healthcare costs. We were able to perform fixed effect models, which corrected for confounding variables and accounted for the longitudinal data.21
Despite the extensiveness of the data, the nature of the data was claims data. As such, we had no information on the outcome of clinical measures, oral hygiene or quality of life. However, claims data is usually very well recorded, and therefore the influence of information bias often observed for retrospective studies is limited. Additionally, we had limited access to descriptive variables due to privacy regulations. By using fixed effects models, we adjusted for unobserved heterogeneity to the maximum extent possible with the data at hand. Furthermore, because dental care is not part of the social health insurance package for adults, dental care utilization is only reimbursed and registered via the health insurers for individuals who have opted for additional private dental coverage. Therefore, our initial sample of 1 million individuals included only individuals with additional dental coverage. While this may have affected the external validity of our study through selection bias (ie, generalizability for the general Dutch population) to some extent, our data source still warrants internal validity for a study sample which represents about 1 million individuals. The generalizability of the findings to other countries however, can be seen as limited. Diabetes-related healthcare costs may differ substantially between countries, although earlier studies in the USA found higher financial benefits after periodontal treatment in patients with diabetes.15 16
In addition, the dental coverage has a maximum reimbursement ceiling per year. The maximum depends on the type of dental coverage and ranges from €250 to €1250 per year. People exceeding this boundary must pay the additional costs out-of-pocket. Therefore, this study may underestimate the claims for periodontitis. However, individuals who received periodontal treatment once were included in the treatment group always thereafter. As such, we did not distinguish between individuals with just a few periodontal treatments compared with those with many periodontal treatments, and presumably more severe periodontitis. Instead, we distinguished between intermediate and advanced periodontal treatment. Since the clinical status of the individuals included in this study is unknown, it was uncertain whether people included in the non-treated group experienced periodontitis. It can be assumed that a large proportion did not have periodontitis and would likely not benefit from cost savings due to periodontal treatment. Therefore, our findings may be considered to provide lower bound estimates of actual effect sizes.
To overcome some of the limitations present in the current study, a longitudinal, observational study may be performed to assess the long-term effects of periodontal treatment in patients with diabetes. In this case, different outcomes should be assessed, including clinical, financial as well as patient-reported outcomes. This could confirm the results of the current and previous studies regarding the different outcomes as a result of periodontal treatment. Furthermore, such a study would allow for assessment of this association in different severities of periodontitis as well as differences in HbA1c levels. This would provide more information about the actual relationship between periodontitis and diabetes. Possibly, this information could justify insurance coverage for periodontal treatment for individuals with diabetes, as well as investments in adequate training for physicians and dentists on integration and coordination of healthcare.
In summary, periodontal treatment in individuals with assumed diabetes may potentially reduce diabetes-related healthcare costs, in addition to improving HbA1c levels. These findings underscore the potential importance of periodontal treatment in individuals with diabetes. They may support initiatives to promote additional attention to the periodontal status of individuals with diabetes and to raise more awareness for the benefits of periodontal treatment. Future research is needed to assess the exact financial benefits of adequate periodontal treatment in patients with diabetes.