This systematic review aimed to assess clinical findings from the past eight years on the effectiveness of different agents to prevent and treat root caries in older adults. For that, randomized clinical trials, published from 2011 to 2018 (July), with population over 50 years old, were taken into consideration. Different diagnose methods for dental caries activity were applied at baseline and follow-up examinations. Only half of the selected studies [8–10, 12, 13] were performed to evaluate the agents’ effect specifically on root surfaces caries. The other half [11, 14–17] took root caries as an inclusion factor, with results related to dental caries in older adults in general.
Different methods were used to diagnose and determine the activity of caries lesions at baseline and after follow-up. The standard visual-tactile method was performed by four studies [9, 11–13]. In this method, the visual examination of the tooth surface aims to identify lesion’s color, contour and presence of cavitation, and the tactile examination is performed, with the aid of a probe, to determine if the affected tissue is hard, leathery or soft. A blunt probe, with light force, can easily penetrate an active carious lesion. In contrast, the surface of arrested lesions are hard and smooth . The greatest limitation of this diagnose method is that it can only be useful when the lesion is at an advanced stage, even though inter-examiner reliability has been reported as good to excellent in clinical trials .
The second most used method to evaluate caries activity was the ICDAS scoring system, performed by 3 of the selected studies [14, 16, 17]. This method was created in order to standardize caries diagnose method and allow the detect and assess carious lesions in enamel or dentine, coronal and root surfaces, including non-cavitated lesions – which is one of the limitations of other systems . This seems to be a complete method, since the detection of caries in an early stage (non-cavitaded stage) is important for prevention. However, none of the selected studies, that used ICDAS or ICDAS II as a diagnose method, had enough results regarding root surfaces lesions assessment.
Electric caries monitoring assessment (ECM) was used by two studies [9, 10]. ECM is considered a complementary method, and measures the electrical resistance of a site on a tooth during controlled drying, where a sound dentin has higher resistance to electricity [9, 26]. This method allows monitoring the alterations in lesions over time, i.e. monitoring the process of de- or remineralization of the tooth surface, which can be useful (along with a visual-tactile examination), to evaluate the efficacy of preventive or arresting agents that can provide dentin remineralization .
Other 3 scoring methods were performed. The first one was proposed by Ekstrand et al. , which is a well standard visual-tactile assessment, specific for root caries lesions. This method was used by one of the selected studies  and had a good reproducibility level. For the second study , a scoring method described previously , identifies coronal caries lesions in 3 stages (non-cavitated, cavitated in enamel only, and cavitated involving enamel and dentin). This classification was extended for root surfaces, with 2 stages of lesions: non-cavitated and cavitated. However, the authors were not able to provide sufficient results regarding root caries lesions, due to the lack of exposed root surfaces (7%). The method, described by Pitts and Fyffe , uses radiographs as a complement examination of subjects, which was not used by Papas et al. . Perhaps, the use of radiograph images could have helped the authors to identify lesions that were still non-cavitated and/or in hard-to-see locations, like under interproximal contact.
SDF presented the best results in arresting and preventing root caries lesions in patients over 65 years old [12, 13]. The combination of silver and fluorides have the ability to halt caries progression and prevent new caries to develop. SDF has antibacterial properties, remineralization effect on inorganic tooth tissues and can inhibit the degradation of the organic matrix. The amount of fluoride present on 38% SDF solution is 44,800 ppm of fluoride, for that reason, the promotion of remineralization of hydroxyapatite in enamel and dentine can be higher when compared to all other fluoride-based agents . Zhang et al.  results show that the control group (placebo solution) developed over a third more new root caries (1.33) when compared to the group that received annual application of 38% SDF (1.00). In addition, the combination of 38% SDF application with biannual oral hygiene education (OHE) provided significantly less number of new caries (0.70). In terms of arresting caries, the benefits of SDF over placebo is also significant, and the addition of OHE promoted the arrest of 18% more active root caries (0.33) than the SDF intervention alone (0.28). Therefore, it is clear the importance and beneficial impact of OHE as a supporting method on the prevention and treatment of caries among elderly. The results of Li et al.  corroborates with the previous research  in terms of high effectiveness of 38% SDF in arresting root caries, achieving over 90% of lesions arrested. The major side effect of this product is the dark pigmentation of lesion spot after application caused by silver ions. The application of KI immediately after SDF application could prevent this effect by precipitating silver ions. However, according to the same study , KI does not reduce blackening of the arrested caries. The use of 38% SDF seems to be a great option for treating root caries in elderly population, especially due to its ease of application and high effectiveness after only one single use. However, the anti-esthetic effect could dissatisfy some patients.
The substitution of a regular toothpaste for daily brushing with a toothpaste that can prevent or treat primary root caries can be a viable and easy treatment method, since brushing teeth daily is a routine for all patients. Hu et al.  and Souza et al.  evaluated the benefits of a dentifrice containing 1.5% arginine and 1450ppm F in a calcium-base, to manage primary root caries in adults. Their findings suggest that the 6 months use of this arginine-containing dentifrice is able to increase hardness of root surface (61.7%  and 70.5% ) when compared to the use of dentifrices with fluoride only (56.0%  and 58.1% ) or without arginine and fluoride (18.2% ). The authors attribute the beneficial effect of the non-fluoridated toothpaste (negative control) is by simple plaque control. The inclusion of fluoride (positive control) improves the remineralization effect, due to this well known ability of fluoride. The effect of arginine is related to its capability to modulate plaque metabolism, helping to control acid-producing organisms and reduce pathogenicity [9, 30]. In addition, this arginine-containing dentifrice has an insoluble calcium ratio, which acts as a reservoir of free calcium ions, enhancing the remineralization process .
The amount of fluoride in a product composition is an important factor for its effectiveness. The property that fluoride has to control caries development is effective for patients with low risk. However, low concentrations of fluoride might not be enough to decrease caries susceptibility in high-risk patients, like elderly patients (especially those living in community-based residences) . The fluoride concentration in saliva to permit the formation of calcium fluoride needs to be over 100ppm. Throughout brushing, concentration of fluoride in saliva is around 110 for low-fluoride toothpaste, and 650 for 5000ppm toothpaste. Thus, the high-fluoride toothpaste has a greater advantage on this matter, maintaining a higher concentration of fluoride in oral environment than low-fluoride toothpastes, which allows more formation of calcium fluoride to promote remineralization. Ekstrand et al.  and Srinivasan et al. , when both compared the efficacy of 5000ppm F toothpaste with low-fluoride toothpastes, found that its use is significantly more effective in arresting coronal and root caries. Particularly for root caries, the preventive effect of the low-fluoride toothpaste was over 2x lower (2.55) than the high fluoride (1.05). In terms of the capability to arrest primary root caries, the daily use of 5000ppm F was 3 times more effective than the low-fluoride toothpaste.
The use of fluoride varnish, chlorhexidine varnish and xylitol were the least effective of the agents found in this review. In Xin et al.  clinical trial, the quarterly application of a fluoride varnish provided dental caries prevention ratio of 32,5%, when compared to a placebo application. However, the differences were not statistically significant. The authors attribute this result to a Type II error; where the number of patients recruited were less than estimated, and they do not have enough data to refute or accept their hypothesis. Another limitation of this study could be the selected population (patients with Sjögren’s Syndrome). These patients have reduced salivary flow rate that leads to changes in the saliva’s composition, reducing its protective effect.
Prevention by chlorhexidine varnish was also not significant. In the selected study , this finding may be due to the previously reported  inefficiency of CHX in preventing dental caries, to the difficulty in diagnosing caries in the early stages and to the fact that all patients had several procedures done in the dental appointments (restorations at baseline and during the trial, rubber cup prophylaxis, prophy cleaning). Only 7% of the population had root surfaces exposed and the results of this trial represented primarily coronal data. Although their outcomes were not enough to confirm, the authors suggest that CHX varnish might have prevention effect for root caries in very high-risk populations.
Two trials [16, 17] evaluated the potential preventive effect of xylitol lozenges for adults. These studies were related (different sites, same research group – Xylitol for Adults Caries Trial - X-ACT) and did not achieved significant findings to prescribe the supplementation with 1g xylitol for caries prevention. The tooth-surface-specific trial  showed no significant effect of xylitol, after 33 months, for smooth-surfaces (p = 0.100), occlusal-surfaces (p = 0.408) and proximal-surfaces (p = 0.159). However, patients of the experimental group developed 40% less root caries than those in the placebo group per year (p < 0.001). Which means that more research is required to verify the specific effect of xylitol supplementation for root caries prevention.
For the two non-randomized trials included in this review, there is a need for standardization and details in the methods used. The main concerns regarding Wyatt et al.  follow-up study are the absence of a control group, the specifications of the agent used (fluoride concentration and composition of the toothpaste), and the number of patients. These parameters are important to provide validity to the results presented. For example, the statistical significance of the results could be different or not significant if the number of patients were higher. This error is shown in this paper by the high standard deviation value. The lack of control group makes impossible to assess if the use of fluoride toothpaste is in fact effective for this high-risk population or if they should use a better agent to prevent caries. Despite these limitations, the follow-up period of 2 years is enough to show the effect of the toothpaste tested. However, the absence of pertinent details does not allow the authors to provide a reliable conclusion if the use of fluoride toothpaste is effective in reducing the progression or reversal of root caries lesions in elderly after 2 years.
The main limitations of Katsura et al.  trial are related to the sample size and its characteristics. The number of patients that concluded the study is small and varies between groups, which could affect the significance of the results. The difference of 10 years (mean age) among the experimental and control groups could also influence the outcome. Regardless of these limitations, this seems to be a well-conducted trial. Their promising results can encourage new research to assess the efficacy of CPP-ACP with sodium fluoride to prevent root caries in patients undergoing head and neck radiotherapy.
Due to the heterogeneity between studies in terms of diagnose methods; it is hard to compare all of them directly. ICDAS scoring system seems to the most complete examination for diagnosing dental caries activity, especially because it allows the scoring of caries in very early stage, which is important to prevent irreversible demineralization by caries progression. However, this method still need more research regarding its application in root caries diagnose, since no studies that used ICDAS had enough findings for root caries. Only one study had a specific diagnose method for root caries [8, 27]. Regardless of this heterogeneity between studies, all methods used had good reproducibility levels and were enough to provide diagnose of dental caries. Nevertheless, more research on methods that can diagnose root caries lesions, especially in very early stages are necessary.
In summary, 38% SDF seems to be the best option to treat and prevent root caries in older adults. Despite the anti-esthetic result, this agent is the fastest and easiest treatment, since it requires only one application per year and demonstrates almost 100% of effectiveness in arresting root caries. If the root lesions are in an aesthetically compromised area and/or prevention is necessary, the use of toothpastes for daily brushing (with 1.5% arginine or 5000ppm F) is also effective and easy to use, since it only requires a simple substitution of the regular toothpaste. Nevertheless, it could be a problem for debilitated patients that are not able to brush their own teeth or do not have someone to do that for them. The use of fluoride varnish, chlorhexidine varnishes and xylitol are not yet proven to be efficient and need more root-caries-specific research.