Introduction
Root caries are common dental problems that primarily affect the root surfaces of teeth, especially in elderly individuals who have gingival recession and exposed root surfaces [
1]. The prevalence of root caries varies across studies. According to the latest national survey in China, it has been reported that approximately 60% of adults over the age of 65 have experienced root caries [
2]. In addition to the higher incidence of exposed root surfaces due to gingival recession, the condition is exaggerated in elderly persons due to factors such as age-related changes in saliva production, diminished oral hygiene practices, and the presence of systematic medical conditions that may impact overall immunity [
3]. Root caries can have significant adverse effects on the oral health of elderly individuals. As the tooth roots become demineralized and decayed, individuals may experience symptoms, such as tooth sensitivity, pain, and chewing difficulty. Root caries can eventually lead to pulp inflammation, infection, and potential tooth loss, which significantly affect an individual’s overall well-being, nutrition, and quality of life [
4].
Fluoride therapy plays a key role in caries prevention and has been proven to be effective in preventing root caries in elderly persons [
5], acting by reducing the solubility of dental tissue, enhancing remineralization, and inhibiting cariogenic bacteria [
6]. Fluoride therapy can be delivered through various methods, such as high fluoride concentration toothpaste, mouth rinse, varnish, or gel. All of them are easy to perform and noninvasive, which is favorable for elderly individuals.
When it comes to addressing root caries that have already developed, restoration is the most common treatment for root caries. However, restorations may fail and require retreatment as well as additional costs. Moreover, pulp-affected cases need further endodontic treatment, and crown restoration is suggested afterward, which is very expensive. In severe cases, there is no choice but to extract root caries-affected teeth. Those teeth are prone to fracture during the extraction and may require extra efforts or more experienced dentists to accomplish, which means higher cost and, most unfavorably, the loss of natural teeth. On the other hand, preventive methods, such as fluoride therapy, are more affordable for a single application than treatment for root caries, which seems to be a more cost-effective alternative, but they need to be performed repeatedly, and over time, the cumulative costs may become significant.
Studies on the cost-effectiveness of caries prevention mostly target children, while few specifically target adults and especially elderly persons [
7]. Therefore, the present study aimed to evaluate the cost-effectiveness of a fluoride varnish application program in preventing root caries among elderly persons compared with no specific intervention in the context of Chinese public healthcare. The analysis was performed by establishing a Markov simulation model of root caries in a hypothetical scenario. The results would provide a scientific basis for decision makers aiming to optimize healthcare resource allocation.
Discussion
The present study focused on evaluating the cost-effectiveness of a fluoride treatment program in preventing root caries among elderly persons, a topic that has been overlooked for a long time. A healthcare system perspective was chosen in the study because it fit the public-private payer mixed system of China healthcare, of which certain healthcare service items are covered by the public healthcare insurance while the rest needs to be paid by the patients or their various commercial healthcare insurances. The results indicated that fluoride treatment, or regular 5% sodium fluoride varnish application more specifically, was a cost-effective strategy with an ICER below the WTP threshold of ¥214 in most scenarios (70.5% of the simulated cases). But the advantage was to a limited extent as the ICER of base case (¥160.35) was barely below the threshold.
It is a common approach to set 1–3 times gross domestic product (GDP) per capita as the ICER threshold to evaluate the cost effectiveness of an intervention [
24,
25]. However, since our study did not use quality adjusted life year (QALY) or disability-adjusted life year (DALY) as the health outcome, GDP per capita was probably not a proper threshold in our case. A WTP of ¥214 was set as the threshold of the cost-effectiveness analysis, which represented the cost for a filling of root caries tooth in Chinese public healthcare system (the same as the cost of direct restoration of base case value). The cost of restoration of a root caries tooth not only involved the ¥120 “Complex filling-composite resin” item, but also items like “Refinement and finishing” and other examination before treatment, which were indispensable steps of a restoration treatment and should be added to the total cost (Table
2). However, as there is an absence of appropriately elicited or generally accepted WTP threshold for oral health-specific outcomes [
26], it is suggested that decision makers should interpret the results with caution.
As shown in the one-way sensitivity analysis, the risk ratio of root caries in the fluoride treatment group had the greatest impact on the result. Currently, few studies have evaluated the preventive effect of fluoride varnish on root caries [
12,
27]. More similar clinical research in the future and summarizing of the results may provide more reliable data as the parameter to alleviate uncertainty.
There were a few possible reasons that the intervention was not dominant over the control. One of the most significant reasons was that the transition probabilities of a root caries tooth to restoration or extraction were relatively low, which indicated that most of teeth with root caries would remain untreated into the next cycle. The low rate of treatment limited the expense caused by the disease and further made the preventive intervention fail to achieve a superior economic result. The transition probabilities of treatment accord with the low root caries filling rate (3.4%) [
2] in the national oral health survey in China. This is probably because root caries tends to be neglected by patients unless they become serious enough to have symptoms, such as excessive pain or facture at the cervical part, which usually have a poor prognosis. If the public continues to improve dental health awareness in the future, as national surveys have demonstrated [
2,
28], more root caries will be treated at an earlier stage, resulting in an increased cost of the treatment over time, but which can make the intervention more cost-effective.
In addition to 5% NaF varnish, 38% silver diamine fluoride (SDF) solution and 1.23% acidulated phosphate fluoride (APF) gel are also fluoride agents that have proven effective in preventing root caries in elderly individuals [
5]. Not only is 38% SDF solution a preferable option for root caries prevention, but it is also considered able to arrest root caries [
29,
30] However, no 38% SDF solution product was approved for use in mainland China at the time of the study. Moreover, it may stain tooth tissue and cause aesthetic issue [
31]. Therefore, we chose 5% NaF varnish as the agent for fluoride treatment. The situation in which root caries being arrested after fluoride treatment was not considered in the model due to the lack of evidence of the root caries-arresting effect of 5% NaF varnish [
5,
32], although the possible arresting effect, if it exists, would lead to a better effectiveness and lower cost in the intervention group and a more favorable overall result.
Only one previous study on the cost-effectiveness of root caries prevention was identified [
33]. A similar result (€29.15 per root caries-free tooth year with varnish four times yearly) that root caries prevention was more effective but also more costly in most cases was acquired, despite the difference in preventive agents. In comparison with the previous study, ours adopted a relatively more complex and realistic model, which managed to demonstrate more possible outcomes and associated treatments other than direct restorations immediately at the same cycle. Our model involved the possibility that root caries teeth remaining untreated instead of always treated, which would greatly reduce the costs caused by root caries and potentially result a less cost-effective conclusion of the intervention but closer to reality. On the other hand, further treatment options other than direct restorations might increase the costs and lead to a opposite change to the result. Collectively, our model was expected to produce a relatively more accurate estimation and improve the significance of the results.
There were several limitations in the study. First, the sources of transition probabilities did not have similar scenarios or populations. We tried to gather data on older Chinese adults in recent years. However, limited longitudinal or cohort studies on root caries and related sequelae, let alone multiple studies on certain populations, were found; such studies would have helped us estimate the transition probabilities. Thus, some of the data were based on foreign studies of non-Chinese citizens, conducted decades ago, or were compromised in quality. A real world preliminary longitudinal study to provide data for the analysis, such as what was performed by some other cost-effectiveness analysis studies [
34,
35], is a possible solution to improve this drawback. Second, although we choose composite resin for direct restoration in base cases because it is a more common choice for dentists in China, the transition probability of restoration failure is from research on resin-modified glass-ionomer. Sensitivity analysis including the cost of direct restoration and possibility of restoration failure was performed to account for it. Third, although our model was relatively closer to real life cases, simplification was still present due to the great complexity of real-world disease progression. For example, filled root caries can still experience secondary caries, pulp infection or extraction, ultimately, and a crowned tooth may fail and need to bond again or be extracted if fractured. Moreover, the model omitted the process of replacing extracted teeth. However, all of these factors would increase the cost incurred due to root caries and make the intervention more cost-effective to some degree. Finally, all costs were estimated based on the public health system because it is the mainstream approach for dental care in China, but patients can still access private providers [
36], which results in more freedom in pricing and are difficult to summarize. Sensitivity analysis on all cost parameters was performed to address the problem.
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