From Volume 47, Issue 3, March 2020 | Pages 199-212
With the increasing prevalence of root caries of varying complexity, clinicians will face challenges in deciding how best to manage such lesions. Non-operative caries control should be used whenever possible. In this paper factors that can affect success when restoring root caries are discussed.
Restoration of root caries can present a number of problems even for the most experienced clinician. It is well known that the failure rate of Class V root carious lesions (RCLs) can be high.1 In this article, difficulties in the restoration of root caries are discussed, factors affecting success are reviewed and treatment approaches with the aim of improving treatment success are considered.
Root surface caries has been defined as a soft progressive lesion that is found anywhere on the root surface that has lost connective tissue attachment and is exposed to the oral environment.2,3,4
Banting and Courtright have classified RCLs as round, elliptical or band-like.5 The band-like lesion has been described as the most invasive, usually involving more than one root surface. The majority of lesions are between 0.5 and 1 mm deep, but may range from slight surface etch to a 3 mm cavity, and discoloration is a prominent feature. Historically, a root surface has been diagnosed as carious when the following conditions are met:6
However, the use of a probe in this way is controversial (as discussed in Part 1)7,8 and the current evidence indicates that gentle probing with a blunt probe should be used and forceful probing with a sharp probe should be avoided when diagnosing root caries. The Root Caries Index (RCI) was proposed by Katz in 1980 as an objective classification to enable a more complete epidemiologic description of root caries and could be used for monitoring the regression of lesions following non-operative management.9 (Again, based on current evidence,7,8 suggested recommendations to this Index are italicized):
However, current scoring systems for dental caries do not differentiate between cavitated and non-cavitated, active and inactive carious lesions and do not consider the dynamic nature of the disease. More recently, there has been an interest in developing clinical diagnostic criteria for assessing the activity state of carious lesions.10 This is reflected in the surface features of the lesion with the knowledge that non-operative management of ‘active’ lesions, such as effective oral hygiene or through the use of fluoride toothpastes, can tip the balance from demineralization to remineralization.11
It is necessary to have well-defined criteria for deciding when to attempt to arrest and when to restore a RCL.12 There are a number of indications for restoring RCLs as listed in Table 1.
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Root surface lesions are difficult to restore and recurrent lesions are frequently observed.13 Both access and cavity preparation can become complex problems for the clinician. Unfortunately, clinicians have been provided with very little useful information for diagnosing, managing and restoring root surface caries. ‘Contemporary principles for cavity preparation and restoration with guidelines for the choice of restorative materials are incompletely developed. Both are fertile areas for pioneering efforts and are urgently needed’.14 Over 30 years later there is still scope for further development in materials and techniques for managing RCLs.
Problems associated with the management of root caries include:15
Further considerations include:
In addition to primary caries, secondary caries is frequently found on root surfaces, recurring more frequently at cervical margins than on occlusal surfaces.16 Could this in fact be residual caries left at the time of preparation?16 A carious dentinal lesion consists of two layers with different characteristics.
The outer layer is infected with bacteria and should be removed as it cannot be remineralized. The inner layer is partially demineralized without bacterial contamination: it can be remineralized and should therefore not be removed.17 As previously discussed, clinicians may experience difficulty in detecting cariously affected dentine by tactile discrimination or visual cues based on natural discoloration.18 Unsurprisingly, a significant number of failed restorations reported as caused by recurrent caries may result from residual caries: ie caries not removed at the initial excavation. Whilst dyes have been investigated to enhance visual recognition of carious dentine, their efficacy is controversial.
It is pertinent to consider the background research in the use of dyes to emphasize how little progress has been made in their use over the last 30 years. During the preparation of a carious tooth for restoration, removal of all carious dentine from the amelo-dentinal junction (ADJ) and cemento-enamel junction (CEJ) is considered imperative. In order to provide a more objective guide, attempts have been made to develop caries detector dyes (CDDs) to enhance the visual recognition of carious dentine. In a study by Anderson and Charbeneau, fuchsin-stained dentine was most commonly observed in the ADJ. Both colour and hardnesss/texture are inconsistent guides for caries removal, as indicated by the finding that, in 72% of the prepared teeth, fuchsin-stained dentine was present at the completion of caries removal.18 However, a later study on propylene-based indicator dyes developed to act as a CDD found the evidence on their efficacy to be conflicting19
Kidd et al published a study which compared the conventional visual and tactile method of detecting carious dentine during cavity preparation with a visual method enhanced using a dye. The results indicated that dye stain could be seen in the ADJ in 57 cavities out of 100 (57%) prepared by students, in cavities which had been assessed as caries free by visual and tactile means and passed as clinically satisfactory by their teachers. Subsequent laboratory work on extracted carious teeth confirmed histological evidence that dye stains demineralized dentine.20As it is well recognized that all caries should be removed from the ADJ, Kidd et al concluded that it might be prudent to use a CDD as an aid to diagnosis when restoring carious lesions.20 In a 2015 paper, Kidd et al stated that ‘caries disclosing dyes are notoriously contra-indicated. Originally designed to stain infected dentine, they encourage overcutting of tissue that should not be removed…and there is no need to remove all infected dentine prior to placing the restoration’.21 The original rationale in using CDD for identifying caries-infected dentine was based on preferential staining of demineralized dentine.22 However, the increased porosity of the dentine substrates following caries removal can result in staining, which may mislead the clinician and lead to subsequent removal of demineralized yet caries-free dentine.23 CDDs with a higher molecular weight than earlier conventional CDDs have been developed which, in the long term, may be more effective in correctly identifying infected dentine by minimizing over-staining of uninfected porous dentine.24 Excessive removal of sound dentine can therefore be reduced or avoided when removing caries, which can be more objective with less chance of false positive results. The problem for the clinician is to distinguish between dentine which should be removed and dentine that is safe to leave, none more so than when restoring RCLs. At best, colour and hardness are only guides for caries removal, as judgements on these criteria are subjective. It is therefore clear that detection and removal of all cariously affected dentine during operative procedures is uncertain. Nevertheless, based on current evidence, the use of CDDs is not recommended.21
Many restorations end on dentine or cementum where access is difficult and adequate isolation, determination of appropriate caries removal and satisfactory restoration are problematic. Restoration of RCLs can also present problems as the cavities may be broad and saucer-shaped with ill-defined margins which can be positioned in enamel as well as dentine.25 Dentists should aim to improve longevity of restorations in order to protect the pulp, promote patient satisfaction, limit the enlargement of cavities which often accompanies replacement and reduce the overall cost of dental care.26 There is a need for a good understanding of biological failure to control caries through the patient's efforts in diet control, good oral hygiene and effective use of toothpastes in order to reduce restorative interventions and improve the longevity of restorations. Awareness of the mechanical and technical factors associated with restoration failure may guide clinicians to use more reliable materials and techniques and identify situations which demand greater skill or specific management options to improve success. Factors associated with failure of RCLs are listed in Table 2.
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There have been several studies on the failure of Class V restorations in which many variables were considered in an attempt to understand how to improve success and longevity of dental restorations.27,28 However, whilst the studies include cervical carious and non-carious lesions, the findings can, to some extent, be extrapolated to improve restoration success of RCLs, as there are no clear guidelines on the restorative management of root caries.
Stewardson et al 2011 compared the survival rate of Class V restorations placed by UK GDPs and found that 32/272 (10.5%) Class V carious restorations failed.27 Within this group of dentists, significant associations were identified between failure of Class V restorations within two years and included the dentist who placed the restoration, the cavity preparation method, the restoration material used and the age of the patient. Amalgam and resin-modified glass ionomer recorded the smallest proportion of early failure, while glass ionomer restorations (GICs) showed the greatest failure.27 In a later study, the findings relating to the 5-year survival of Class V restorations could also be applied to reduce failure rate of these restorations; after five years 275/989 restorations had failed (27.8%).28 However, for carious cavities, there was insufficient evidence of a significant difference in the time to failure of restorations being prepared with or without rotary instruments, although only 16 carious cavities were not prepared with a bur.
Amongst the variables that can affect treatment success when restoring Class V cavities are:28
Some or all of the above variables could impact on longevity of restorations like the one shown in Figure 1. Recommendations for improving success when restoring RCLs are listed in Table 3.
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In a systematic review of the literature, different restorative treatments of RCLs were compared. Failure rates were found to be high across all restorative materials and, at present, it was found that there is no gold standard restorative material.32 However, only five clinical trials were identified and these were confined to post-radiation, xerostomic patients, and may be atypical of the older adult dental patient.32 Nevertheless, it was concluded that there is insufficient evidence to recommend any specific material for routine use in the restoration of RCLs and highlighted the need for further research to guide dentists in the evaluation of restorative materials.32 This has implications on treatment outcome and efficacy, especially in the light of high failure rate of Class V restorations, which appears to be a common occurrence in practice.1 Restoration of RCLs can be challenging, especially as they may have dentine and enamel cavity margins, and because of the lack of restorative materials which bond equally well to both tissues.25 Deciding when and how to treat may improve operator skill in developing effective treatment protocols for the management of Class V root caries. There is a poor evidence base for the choice of restorative material for the treatment of RCLs1 restored with amalgam, glass ionomer cement(GIC), resin-modified glass ionomer cement (RMGIC), modified polyacid resins (‘compomers’) or composite resins, all of which have been considered in previous studies.33,34,35
Age-related changes in the structure of teeth may contribute to high restoration failure. Over time, dentine tubules decrease in diameter and number,36 with decrease in permeability,37 water content38 and altered mechanical properties.39 Consequently, clinicians need to modify their approach when restoring the teeth of older patients to provide longer lasting restorations.28
Glass ionomer cements (GICs) were first described in the dental literature by Wilson and Kent 1972.40 Since then the physical properties and potential uses of GICs have been extensively investigated and reported. McLean et al, in 1985, described GICs as a ‘replacement dentine’.41 They are self-adhesive to contaminated tooth structure and release fluoride into the restored tooth, thereby remineralizing and slowing caries progression.42,43 Chemical adhesion of GIC to the tooth tissues is the most important advantage of GICs.44 These well-established attributes should make GIC the material of choice for restoring RCLs. Unfortunately, early problems, such as high solubility, surface crazing and porosity, have not been overcome and restoration longevity is poor.28 Glass ionomer therefore requires careful handling to improve success. Even with contemporary GICs, there is a limited choice and shade matching can sometimes be a problem, resulting in poor aesthetics (Figure 2). RMGIs have been shown to give much better results.28
The new systems are encapsulated and, when triturated, produce a homogeneous and consistent mix. They can be overlaid with composite, are water resistant, set quickly and can be finished in a wet field after initial set.45 Applying GIC in thin layers onto exposed root surfaces, as shown in Figure 2, is an effective preventive measure when the patient is at risk of developing root caries at these sites due to deteriorating health and dexterity.46 In addition to its use to protect sound roots, GIC can also be applied in thin layers over incipient lesions of root surface caries which have an intact leathery surface. Such lesions can remineralize over time, obviating the need for more involved restorative procedures.47 The inherent adhesion of these materials enables them to be used with relatively minimal cavity preparation.44 However, bonding to dentine is known to be a particular challenge because this tissue contains more water than enamel and less mineral phase for bonding.44 Whilst GICs appear to be relatively simple materials to use, they exhibit low fracture strength and low tensile strength, which results in a much lower effective bond strength than other adhesive materials.48 GIC demands careful handling and the high failure rate of GIC restorations reported in a recent study indicates that this is not fully appreciated by some clinicians.27
Therefore, to optimize bonding, the smear layer blocking the dentinal tubules on the cut dentine surface should be removed. This allows the GIC material to penetrate the surface with development of a micromechanical bond.49
Removal of the smear layer before placing RMGI and GIC is usually carried out through surface pre-treatment, or conditioning with 10% or 20% polyacrylic acid solutions applied for 20 seconds prior to rinsing.50 Conditioning partially demineralizes the dentine substrate and increases the surface area and exposure of micro-porosities, which allows micro-mechanical attachment.49
Restoring Class V root caries can be challenging, because many lesions are subgingival and usually located in dentine or cementum, factors that can affect bond strength and marginal adaptation. It may be possible with OHI to improve gingival health and convert subgingival lesions to more accessible supragingival lesions. Whilst resin composites may be considered to be the material of choice for the restoration of these cavities, when aesthetics is most important, inherent polymerization shrinkage is a major disadvantage that can result in microleakage at the tooth-restoration interface.51,52 The consequent restoration failure can be minimized by good isolation, which is frequently difficult, and careful placement technique restoring in incremental multiple layers to reduce the risk of polymerization shrinkage. Figures 3 and 4 show approaches to restoring subgingival root caries.
Flowable composite resins (FCRs) can be used for the restoration of a Class V RCL, involving enamel and dentine, to facilitate adaptation due to their low viscosity.1 Moreover, FCRs have often been advocated for Class V restorations of RCLs because of their lower modulus of elasticity than hybrid resin composites.53 The results of an in vitro study indicated that FCR and dentine adhesive may be suitable for restoring advanced root caries when the proximal carious lesion is large, is wrapped around the root surface and is exposed to flexural load.53 An improved flow is likely to facilitate adaptation, and the reduced elastic modulus may provide the material with stress absorbing ability, demonstrated mostly in non-carious lesions but, nevertheless, applicable to restoration of root caries.54,55,56,57 Restorations in close proximity to gingival tissues require surface smoothness for optimal gingival health. As with all other restorative materials, special attention is needed when using FCR flowable composites to create smooth surfaces in order to avoid plaque retention, surface discoloration and gingival inflammation.58,59 Finishing and polishing of cervical restorations are important procedures that enhance aesthetics, gingival health, periodontal integrity and longevity of restorations and restored teeth. However, achieving an optimal finish can be problematic, especially when restorations extend subgingivally. The smoothest surfaces are achieved when resin material is cured against a cellulose strip or cervical former. However, their use is not always possible and, therefore, properly contoured restorations are seldom achieved without the need to remove excess material.60,61,62 Consequently, finishing and polishing Class V restorations carries a high risk of iatrogenic damage to the soft and hard tissues. In some cases, it may be prudent to recall the patient to ensure finishing is optimal and reinforce oral hygiene measures.
In a 2016 review, Hayes evaluated biodentine, a quick-setting, calcium silicate-based cement which was developed in 2011 as a dentine replacement material.63 As RCLs are often confined to dentine and biodentine produces mineral tags in dentinal tubules, it has the potential to offer high microleakage resistance. As many of the RCLs were typically found to be broad and shallow, conservative preparation resulted in restorations with a thin cross-section, which may have contributed to the high failure rate. The risk of failure was found to be higher when placed in a cavity that was in close proximity to the gingival margin within 1 mm or that extended subgingivally. The subsequent poor moisture control may be detrimental to biodentine restorations, which demonstrate a high level of washout.64 Furthermore, the caries-affected dentine substrate was thought to affect the bond strength and restoration success. The poor aesthetics of biodentine can be another disadvantage. It was therefore concluded, based on this limited evidence, that biodentine cannot be recommended for restoration of RCLs and Fuji products continue to be the best options for operative treatment of root caries.63
Minimally invasive dentistry is a philosophy of healthcare provision and can be defined as ‘the maintenance and monitoring of oral health through continuous care, comprising comprehensive preventive management, a longitudinal approach to risk assessment and diagnosis of chronic disease with a minimally interventive approach to any necessary operative intervention’.43 Minimally invasive treatment should be at the forefront of management of all patients, including the elderly, as decisions to drill and fill RCLs may not always be the best options when less invasive, non-operative management aimed at improving oral hygiene and remineralization of incipient lesions may be more appropriate, less challenging and more cost-effective. However, even when the decision to restore RCLs has been made, the clinician can often be faced with a dilemma as the clinical guidelines used by dentists in caries removal are based on subjective criteria that can vary from one operator to the next and, if inadequate, can lead to early restoration failures.65 The use of rotary instruments to remove carious tissue has often resulted in considerable removal of tooth structure and extensive tissue loss, which is now considered to be overly destructive.65 Ideally, only caries infected dentine should be removed as a principle of modern minimally invasive caries removal.66 Deciding on how best to remove carious dentine and, in fact what constitutes infected dentine, has to be determined to ensure effective treatment protocols. Undoubtedly, tactile appreciation with various patterns of hand excavators (Figure 5) should optimize treatment aims and outcomes to include removal of infected dentine and create a sound substrate to which restorations can be bonded.
Alternative approaches in the management of root caries can range from conventional removal with rotary instruments and restoration to the use of fluoride toothpastes aimed at remineralizing RCLs. Atraumatic restorative treatment (ART) can be used for root carious management when it may not be feasible to use rotary instruments in some older individuals who may be cognitively or physically impaired and unable to visit a dental practice. ART involves removal of softened tooth tissue with hand instruments followed by sealing of the partially demineralized dentine defect with GIC.67 Fure et al conducted a study to evaluate the clinical efficacy, treatment time and patient perception of Carisolv, a chemo-mechanical method of primary caries removal that could be used in ART, that was compared to conventional use of rotary instruments.68 The Carisolv group of patients were treated without anaesthesia and none experienced any pain during caries removal. There were no complications or adverse effects found in follow-up a year later. In conclusion, whilst Carisolv was found to be an effective method of root caries removal, it entailed a longer duration of treatment.68 This technique is advantageous insofar as only the softened tissue is removed, the cavity is prepared according to the shape of the lesion, anaesthesia is normally unnecessary, expensive equipment is not required, it has a low cost and reduced patient anxiety.69 However, the failure rate was found to be higher in restorations in close proximity to the gingival margin, within 1 mm or those that extended sub-gingivally. Many of the RCLs are shallow and it has been confirmed that caries-affected dentine as the bonding substrate could affect bond strength.65 So two questions remain unanswered:
Banting and Courtright have pointed out that proximal lesions start as small circular lesions at the cemento-enamel junction and then spread laterally onto facial and lingual surfaces.5 When proximal root caries develops in this way, extensive sound tooth tissue often has to be removed to gain access following a conventional Class II cavity. Figures 6 and 7 show cases in which tunnel restorations (TRs) were contra-indicated and conventional access cavities were prepared.
Figures 8 and 9 illustrate use of amalgam and composite in TRs.
However, there are cases when a minimally invasive cavity preparation, such as the more conservative tunnel restoration (TR) can be used. The TR was first described in 1963 for the restoration of distal proximal surfaces of deciduous second molars70 and was further developed in the 1980s using glass ionomers.71,72 GIC attributes of fluoride release and adhesion to enamel and dentine, as already discussed, are well known and should improve success, provided correct protocols are followed. Proximal carious lesions were accessed and prepared by approaching the lesion from the occlusal aspect, using rotary and hand instruments beneath the marginal ridge, but leaving it intact. Preserving the marginal ridge is the main advantage of the TR over the conventional box preparation.73 However, the TR can be challenging and difficult to prepare, particularly for inexperienced clinicians, often necessitating additional training. Success can therefore be operator-dependent. The marginal ridge can be undermined, resulting in fracture. Due to the limited access, recurrent caries caused by inadequate caries removal can develop and remains a key concern of this technique, as well as inadequacy in filling the prepared cavity.73 Therefore, proper case selection, having the appropriate armamentarium, including magnifying loupes and attention to detail, are imperative to improve success when restoring proximal root caries (Figure 10).
Whilst the 2-year clinical success rate of composite TRs was 96%, there was no significant difference with that of conventional composite box restorations.74 The most common cause of failure of TRs has been reported to be caries found clinically or radiographically adjacent to the TR.75 It was also demonstrated that the only factor significantly associated with failure of TRs was tooth type, with molars five times more likely to fail than premolars. In summary, problems associated with TRs include:75
The decision on when and how best to restore active, cavitated root caries, once diagnosed, is fundamental to efficacy. Management of RCLs should, when possible, be non-operative. As discussed in Part 1, being aware of risk factors and educating patients on the importance of reducing the frequency of sugar intake, effective oral and denture hygiene, especially interdental cleaning and the use of high fluoride toothpastes and saliva substitutes, when appropriate, will help to reduce the restorative needs of the elderly which, as illustrated in Figure 11, can be extremely complex. There are a number of factors that can affect restorative treatment success and careful consideration of treatment protocols will improve outcome. Whilst the restorative materials available, especially the RMGIs, have many favourable attributes, further developments are needed to reduce failure. Caries removal is subjective and knowing how to create an effective substrate to ensure good bond strength under difficult conditions of access and moisture control are just some of the challenges clinicians face in restoring RCLs. Frequently updated approaches of the dental team to include teachers of restorative dentistry will be needed to meet future challenges in root caries management of the elderly.
