From Volume 47, Issue 2, February 2020 | Pages 103-114
The elderly population is increasing and they have a higher retention of natural teeth than previous cohorts. The increased prevalence of root caries in this group presents challenges to all those concerned in its management. In this article, aetiology, risk factors and diagnosis of root caries are discussed with the aim of implementing effective approaches in its management.
The population of the elderly is increasing worldwide and they are experiencing a higher retention of natural teeth than previous cohorts. The increased prevalence of root caries is multifactorial and treatment success may be compromised by many factors, including difficulties with diagnosis and poor non-operative management. The consequent upsurge in root carious lesions (RCLs) presents demographic and procedural challenges, with implications for all those involved in the delivery of effective treatment. The problems in diagnosing root caries and the associated aetiology and risk factors are outlined. Deciding on how best to manage these lesions, with the emphasis on non-operative approaches, is discussed.
The proportion of edentulous adults is decreasing in the UK, having reduced from 28% in 1978 to 6% in 2009. Additionally, 86% of adults had 21 or more natural teeth whilst, in 1978, this was the case for only 74% of adults.1 In 1900, 3% of the population of North America was over 60 years old, by 2000 this was 13% and, by 2030, it is estimated that at least 20% of the population will be 60 years of age or older.2 Findings of a 2009 Adult Dental Health Survey published in the BDJ in 2013 showed that, in the UK, there are currently 11 million people aged over 65, 70% of which are functionally independent.3 There is an expected 40% rise to 16 million by 2040, according to Age UK.3 However, teeth retained into older age are at an increased risk of root caries.4
The prevalence of root surface caries among non-institutionalized elderly people over the age of 60 years in Western countries has been reported to be 60−70%.5 Winston and Bhaskar found that approximately 38% of patients between the ages of 55 and 64 have root caries, whereas 47% of those between 65 and 74 have experienced root caries.6 It has been written that ‘the aged patient will grow into the root caries problem and not out of it’ − a succinct observation of the serious consequences of the combined demographic and dental changes in the elderly.7
A wide range of factors contribute to the resultant increased susceptibility and prevalence of root caries and management is often compromised by problems with diagnosis, access, moisture control and bonding to dentine. Consequently, there is a great need for strategies to control caries that have an acceptable efficacy in order to reduce the burden of restorative treatment. There will therefore be an additional need for training in the non-operative and operative management of root caries.
There has been an increased interest in the study of root caries since the 1980s for a number of reasons:
Management will inevitably be needed as there is a greater frequency of root caries on proximal surfaces,8,9 with diagnosis, access and moisture control especially difficult in certain cases.
The consequent upsurge in root caries presents challenges with implications for all those involved in delivery of effective management.10 These include:
Root caries has been defined as ‘a cavitation below the cemento-enamel junction (CEJ) which did not include the adjacent enamel. Lesions are usually discoloured, softened, ill-defined and involved both cementum and underlying dentine’.11 Root caries has also been defined as ‘a cavitation or softened area in the root surface, generally well established, discoloured and characterized by penetration and destruction of the root surface and underlying dentine, which might or might not involve adjacent enamel or existing restorations (primary and recurrent caries). The point of the explorer can easily be inserted into the carious area’12 (Figure 1 a−h).
Katz et al defined root caries as ‘soft progressive destructive lesions either totally on the root surface or undermining the enamel at the CEJ, but classically indicating that the lesion initiated on the root surface’.13 Nyvad and Fejerskov differentiated between active and passive or non-active lesions based on colour and consistency assessed by blunt probing.14 Active lesions were described as yellowish or light brown in colour, softened or leathery when gently probed but without obvious cavitation. Passive lesions were considered to be more darkly stained, often dark brown or black and smooth. On probing, they might be softer than sound cementum, shiny and smooth but relatively hard when probed, even though cavitation might be present. However, the use of the dental probe in this way is contentious and considered to be outdated, but can be beneficial when the probe is blunt and used gently. It can be used to remove plaque that may be covering the lesion, to check for signs of demineralization, and thereby assess colour, texture and surface roughness of a lesion.15
Root caries, like coronal caries, is a plaque-associated disease and the main aetiologic factor for the initiation and development of root caries is the presence of microbial plaque and free sugars.16 However, the aetiology of root caries is multifactorial and should include consideration of three general categories of risk factors – biological, behavioural and intrinsic17 (Tables 1, 2 and 3).
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Biological
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Behavioural
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Intrinsic
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The microbial aetiology of root caries in the elderly is complex and there are a number of microbes which are involved in the disease process.18,19Streptococcus mutans (SM) is found in high numbers in lesion sites, higher than on sound root surfaces in the same subject. In studies on root surface caries, both Lactobacilli (LB) and SM have been implicated, especially if present simultaneously.18,19 LB produces metabolic acid from dietary sucrose and extracellular polysaccharides, which facilitate bacterial colonization of tooth surfaces. Eliminating or reducing the number of SM reduces the number of root carious lesions and can even result in reversal of incipient lesions. LB is also important in the pathogenesis of root caries by virtue of its association with SM in these lesions.20 SM alone or in combination with LB were detected more frequently in plaque overlying carious surfaces than on healthy root surfaces.21
Although there is some controversy with respect to whether root caries is essentially a demineralization or a proteolytic process, it is important to be aware that the critical pH at which point dentine demineralizes is 6.7, whereas that of enamel is 5.2.22 Susceptibility to root caries is considered to be dependent on exposure of the root of the tooth to the oral environment through attachment loss, usually a consequence of periodontal disease.23 Attachment loss is typically associated with gingival recession (defined as the apical migration of the gingival margin beyond the CEJ) with a prevalence range from 15−90%, and is more common in elderly individuals.22 However, it is important to distinguish between attachment loss and gingival recession when discussing root caries because it is possible to have a clinical situation where there is attachment loss and yet the crest of the gingiva is coronal to, or at the same level as, the CEJ. Of RCLs, 10−20% may then present subgingivally23 (Figure 2).
Patients suffering from advanced periodontal disease may therefore be more at risk from developing root surface caries. Hix and O’Leary found approximately twice as many decayed and filled root surfaces in patients with untreated periodontal disease when compared with patients who had treatment for moderate to severe periodontitis.12 Ravald and Hamp reported two thirds of adults treated for advanced periodontal disease develop root caries affecting about 5% of their periodontally treated teeth.20 Many of these patients may have diabetes, which is linked to the progression of periodontal disease and a greater number of exposed root surfaces with consequent increased risk of root caries.24
Xerostomia is characterized by decreased salivary flow of which there are many causes, including the use of medications, systemic diseases that may accompany ageing and radiation therapy.23 It has been shown that individuals who suffer from low salivary flow rates have a higher caries incidence than those with normal salivary flow rates.25,26 However, salivary flow rates were found to be poor predictors for the number of RCLs,27 a finding consistent in another study that reported no significant relationship between diminished saliva flow and caries.28 Närhi et al also found that there was no correlation between the presence of root caries and the number of daily medications used and salivary flow rates.29 Beighton et al reported higher root caries prevalence in men, although salivary flow was significantly lower in women.30 It was found that stimulated salivary flow rate was inversely correlated with microbial counts and flow rates were also found to be significantly lower in women than men.29 A further study determined that the effect of saliva composition on RCL development was independent of flow rate of unstimulated whole saliva. However, it was shown that it may be difficult to separate the effect of saliva composition from that of saliva flow rate on caries lesion progression as saliva composition is a consequence of flow rate.31 Nevertheless, saliva composition has been shown to have an effect on demineralization parameters, such as mineral loss, lesion depth and mineral content of the surface layer in experimental root caries in situ.31 In this context, the unstimulated rather than stimulated saliva composition was found to be considerably more important and high microbial counts have been associated with decreased salivary flow rate.30
In a study by Hiriyani et al smokers were found to be twice as likely to have untreated root caries as non-smokers.32 The higher prevalence and severity of root caries in smokers and older adults could partly be explained by the effects of smoking and age on gingival recession. The oxygen concentration in healthy gingival tissues appears to be lower in smokers than non-smokers, thereby influencing the inflammatory process and gingival recession.33 Research has found that smoking was related to elevated levels of SM and LB in saliva, which are associated with the initiation and progression of dental caries.34
Denture-wearing may adversely affect the condition of the natural teeth as plaque levels tend to be higher among removable partial denture (RPD) wearers (Figure 3). RPDs substantially increased and, in some cases, doubled the odds of a subject having root caries.35 The wearing of RPDs was therefore found to be significantly associated with root caries, and close proximity of a tooth to a removable prosthesis could indicate a tooth level risk factor rather than a patient level risk indicator.36 RPDs are an important independent indicator of risk for root caries and additional steps should be taken to prevent root caries, where possible.
Other factors to consider when determining a patient’s root caries risk include:
The clinical diagnosis of root caries is problematic and presents many challenges to the dentist as it is not easy, clinically, to distinguish the sound area from the carious lesion which may often extend onto proximal surfaces and subgingivally.43 As a result, the reliability of clinicians in detecting and classifying root caries has been shown to be poor, so that root caries can be erroneously classified as active or inactive.44 Katz has documented a number of methods of root caries detection in vivo including:45
Diagnoses are complicated by the presence of plaque and previously-placed restorations, poor resolution of root caries on radiographs and the relation to the gingivae, both sub- and supragingival.45 In a study on root caries experience, root caries cases were defined using softness and discoloration of dentine as the main features. There is general agreement that the use of a combination of visual and tactile criteria (ie soft or leathery to slight gentle probe pressure) is more indicative of root caries than the use of visual criteria alone.32 Furthermore, colour of the lesion was found to be a weak predictor of caries activity.46,47 There is also a poor correlation between the colour and hardness of root caries.48 Therefore, care must be taken when using colour as a guide to the status of early RCLs, since lesion colour is also influenced by bacterial metabolism, as well as by extrinsic staining.49
Radiographs are important in the diagnosis of root caries, although it is never possible to diagnose lesion activity from a radiograph alone because the radiograph will only show demineralization.50 Incipient lesions limited to enamel may not be apparent until approximately 30% to 40% demineralization has occurred.51
Cervical burnout appears as a radiolucent band around the necks of teeth. It is more pronounced at the proximal edges and may mimic cervical caries. Resultant false positive diagnoses can lead to unnecessary treatment.52 Detection of root caries by radiographs is therefore often difficult for early lesions on proximal surfaces.
The gentle use of a dental explorer has been the accepted technique for root caries diagnosis as changes in colour and appearance are much more subtle than coronal caries and tactile feedback must be relied upon for diagnosis43 However, probing as reported in a study by Ekstrand et al, can be subjective and there is a risk of missing small changes in texture of dentine with implications for under-treatment and over-treatment.53 Concerns about the accuracy and reliability of root caries diagnosis based on probing have also been raised by Rosen et al.54 Nevertheless, interproximal root caries may be difficult to detect any other way than by probing. The use of an explorer, modified to produce a 30° angle at the tip of the explorer prong, was found to be considerably more favourable in diagnosing root caries, especially in interproximal areas where visual inspection can be restricted.8 Warren et al agreed that probing with a dental explorer is the preferred method of root caries diagnosis.55 However, they investigated the effect of probing on remineralization of root surface lesions in vitro and found that probing root surfaces may create defects that do not fully remineralize. Existing clinical methods of diagnosing root caries are unable to discriminate between lesions with or without a remineralized surface layer without damaging the tooth surface. It has therefore been recognized that there is a potential for iatrogenic damage to root surfaces from the use of a dental probe, all the more significant when primary prevention strategies may be compromised and the clinician is then faced with inadvertent challenges of root caries treatment.55
Other studies have shown that gentle probing does not disrupt the surface integrity of non-cavitated lesions, while forceful use of the probe can cause irreversible damage to the surface of a developing lesion.56,57
In summary, when following non-operative root caries control, it is important to avoid damaging the surface by forceful probing with a sharp probe. Using a blunt probe applied with a gentle force is recommended to avoid creating small cavitations on the root surface.
Researchers have developed several root caries scoring methods for objective decision-making on whether or not to restore such lesions.58,59 The use of dyes to stain dentinal lesions was proposed, stating that the uptake of dyes is correlated with severity of the lesion.60,61 Fluoroscein was chosen because it is non-toxic, does not adhere to dentine, enamel or soft tissues and can easily be removed from lesions. The uptake of fluoroscein into dentinal tubules in vitro was found to be well correlated with mineral loss.62 However, mineral loss is not a good indicator of caries activity, may lead to invasive treatment and therefore the use of detection dyes is not recommended.
Ekstrand et al devised a reliable scoring system in which four variables are used53 (Table 4). This provides an indicator of active root caries.
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Texture
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Caries risk is the probability that caries will develop or progress.63
The concept of a caries risk assessment is to:
A risk model can identify who is at high risk and when it is important to identify one or two risk factors. This should exclude predictors such as past disease or number of teeth that do not cause further disease.64 A systematic review on root caries risk indicators suggested that future research should focus on variables which were found to be significant.65 Thirteen articles were used to extract data and over 90 clinical and non-clinical risk indicators were measured and tested. Of these, 30 were significantly associated with root caries incidence at least once in at least one study. It was concluded that root caries incidence can be predicted by risk models and, in published studies, the most frequently described predictors are:65
By identifying high risk individuals this guide can target and optimize root caries prevention.65
Another approach to caries risk assessment was through the development of a Cariogram programme using a weighted evaluation of nine caries-related factors.66 The Cariogram can be created using the data as detailed in Table 5.
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This information can be used in daily practice for motivating the patient and for use in clinical decision-making when selecting preventive strategies. In addition to a Cariogram, the following should be considered when carrying out a caries risk assessment:66
The dental profession can expect more demand and need for management of root caries as the elderly dentate population is increasing, with the increased risk of developing root caries.67 Preventive strategies should focus on targeting health behaviour improvement.31 Kidd et al state that ‘changing a patient’s behaviour is the cornerstone of preventive treatment. Advice should always be relevant and if there is a problem, individuals should be made aware.’50
However, it is important for the clinician to use various motivational approaches and monitor the patient’s progress.68 Motivational interviewing has been found to be the most effective method of altering health behaviours in the clinical setting and should form the basis of oral health promotion with elderly patients.69
It has been argued that ‘when the patient does not desire to change, or does not perceive that a problem worth acting on exists, there is little a practitioner can do’.70 This is especially salient when managing root caries in the elderly, who may have cognitive impairment, physical disability and a host of risk factors all of which present a challenge. Moreover, the clinical management of root caries is usually difficult and treatment methods should therefore be directed at remineralization of incipient lesions through non-operative approaches.71
Demineralization and remineralization is a dynamic process of mineral loss from the hard tissue of the tooth and of its repair. These are not distinct processes as both occur to some extent on tooth surfaces at any given time.72 Theoretically, root caries is a preventable disease73 which can be arrested through changes in the oral environment from one that favours demineralization to one that promotes remineralization.74 Clearly, the clinician’s objective should be to help the patient maintain an oral environment by implementing caries control through non-operative measures. A principle of modern preventive dentistry is ‘to avoid intervening before prevention has been given a chance to work’.75
It is well known that prevention can be divided into three phases:
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There are number of non-operative preventive measures as listed in Table 7. Plaque removal plays an important role in the prevention of root caries. In fact, it has been shown that active root caries can be converted into inactive root caries by good oral hygiene.76 Patients should be shown how to clean proximal and smooth exposed root surfaces effectively to reduce the risk of developing root caries. The use of plaque disclosing agents and interdental brushes should be recommended.
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Toothbrushing followed by interdental cleaning is the standard way of removing dental plaque, although new research has shown that interdental cleaning before brushing is the best way to ensure more effective cleaning.77
However, in most patients, substantial levels of plaque remain after toothbrushing, all the more likely in elderly patients who may be physically or cognitively impaired and struggle with manual toothbrushing and avoid interdental cleaning altogether.78
This was evident in a 2005 systematic review in which it was concluded that the quality of self-performed mechanical plaque removal was ineffective.79
There is good evidence available that, despite poor compliance, interdental brushes should be recommended for elderly patients who are likely to struggle when using floss to clean interdental spaces.80 Powered toothbrushes with features such as oscillation-rotation action, timers and force control have been shown to be more effective than manual toothbrushes.81 The wearing of partial dentures can lead to a six-fold increase in the prevalence of root surface caries on the adjacent teeth. Emphasis should therefore be placed on good denture hygiene as it is common for patients to neglect those parts of partial dentures that come into contact with teeth.82 The use of disclosing dyes applied to dentures can highlight retained plaque and ensure more effective cleaning.
Plaque retentive factors in incipient RCLs can be removed by recontouring and polishing such lesions to facilitate remineralization. Furthermore, subsequent improvement in periodontal health through scaling, root planing and effective oral hygiene measures will often convert subgingival RCLs into more manageable supragingival lesions, should they need to be restored.83
As clinicians, we need to be aware of functional, behavioural and situational factors that can have a negative impact on the oral health of elderly patients.84 One of the most significant factors contributing to dental caries is the frequency of ingestion of fermentable carbohydrates.72 Patients should be made aware that frequent sugar intake is a risk factor for root caries and that such intake should be restricted. However, this is a behavioural matter72 and it may be difficult to change the diet of the elderly when, for example, they are habitual comfort eaters and may manage their dry mouth by sucking mints. In such cases, saliva stimulants and substitutes should be recommended (Table 8).
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Substituting non-cariogenic sweeteners, such as xylitol, for the fermentable carbohydrates including glucose, sucrose and fructose, has been shown to be effective in reducing root caries incidence.85 In general, dentists are now less likely to intervene with early carious lesions and adopt a more conservative, non-operative approach for caries control.86
Unequivocal evidence has revealed that fluoride is effective in the prevention of root (and coronal) caries. Fluoride alters ionic saturation with respect to tooth mineral, aids remineralization and prevents demineralization. At high concentrations, fluoride may interfere with bacterial metabolism. Dentine is more caries susceptible than enamel due to the difference in mineral composition, and recent research has investigated the effects of fluoride on dentine and root caries.87 A laboratory study showed that 5000 ppm fluoride toothpaste (FTP) was more effective for controlling root caries formation and progression than a fluoride concentration of 1300 or 1500 ppm.88 The effectiveness of FTPs could be related more to the frequency of use rather than the fluoride concentration. However, there was no significant association found between the frequency of use and the remineralization of existing carious lesions.89 A pilot study has shown that 1100 ppm FTP was enough to reduce root dentine demineralization in a highly cariogenic environment, although the sample size was small.90
For primary prevention of root caries, the recommended regimen for older and vulnerable adults is an annual application of a 38% Silver Diamine Fluoride (SDF) solution while, for the secondary prevention of root caries, the best protocol is the professional 3-monthly application of a 22,500 ppm Sodium Fluoride varnish.91 The addition of xylitol to toothpastes can inhibit glycolysis and enzymes involved in the metabolism of SM. FTPs containing 1.5% arginine can help to reduce plaque acids and reduce caries initiation and were shown to reharden more root caries than a matched fluoride toothpaste.92,93
The presence or absence of cavitation was found to be an important predictor of whether or not a lesion hardened. In the high F group, 39 (55%) of the 71 non-cavitated lesions at baseline had hardened after 3 months, increasing to 54 (76%) after 6 months. In comparison, only 10 (19%) of 54 cavitated lesions had hardened after 6 months in this group. The less favourable response of cavitated lesions may indicate that dentine is more demineralized and less able to provide a suitable substrate for remineralization.94 Alternatively, it may be more difficult to maintain effective plaque control in such lesions. In summary, the frequency of use of both low and higher FTP is important for prevention of new RCLs (Figures 4 and 5). However, high FTPs are better at remineralizing RCLs.
The population of functionally independent elderly is increasing and they are retaining their teeth longer, so those seeking treatment from the GDP is also increasing. The aetiology of root caries is multifactorial and risk factors should be considered when developing a preventive treatment plan. Diagnosis can be fraught with difficulties and deciding when and how to manage can be equally as difficult. Associated problems of ageing may include cognitive impairment, lack of mobility, drug-induced xerostomia and reduced manual dexterity, all of which can present a challenge to effective treatment strategies, especially in the management of root caries. Treatment planning and caries control are all significantly different from the approaches used 30 years ago, when the interest in root caries intensified. Non-operative approaches, aimed at arresting and remineralizing RCLs, should be implemented whenever possible. In part 2 the challenges associated with restoration of root caries are discussed.
