Abstract

This publication describes the history of minimal intervention dentistry (MID) for managing dental caries and presents evidence for various carious lesion detection devices, for preventive measures, for restorative and non-restorative therapies as well as for repairing rather than replacing defective restorations. It is a follow-up to the FDI World Dental Federation publication on MID, of 2000. The dental profession currently is faced with an enormous task of how to manage the high burden of consequences of the caries process amongst the world population. If it is to manage carious lesion development and its progression, it should move away from the 'surgical' care approach and fully embrace the MID approach. The chance for MID to be successful is thought to be increased tremendously if dental caries is not considered an infectious but instead a behavioural disease with a bacterial component. Controlling the two main carious lesion development related behaviours, i.e. intake and frequency of fermentable sugars, to not more than five times daily and removing/disturbing dental plaque from all tooth surfaces using an effective fluoridated toothpaste twice daily, are the ingredients for reducing the burden of dental caries in many communities in the world. FDI's policy of reducing the need for restorative therapy by placing an even greater emphasis on caries prevention than is currently done, is therefore, worth pursuing. Key words: Minimal intervention dentistry, caries lesion detection, caries risk assessment, caries preventive measures, restorative care, plaque control, repaired restoration Minimal Intervention Dentistry (MID) is a response to the traditional, surgical manner of managing dental caries, that is based on the operative concepts of G.V. Black of more than a century ago. MID is a philosophy that attempts to ensure that teeth are kept functional for life. This term, therefore, is not restricted to the management of dental caries but is also applicable to other areas of oral health; such as periodontology, oral rehabilitation and oral surgery. Dental caries is the most prevalent of the oral diseases worldwide. This paper presents the rationale and content of MID for managing dental caries, using evidence-based information whenever available. RATIONALE OF THE MID PHILOSOPHY Without doubt, the many studies assessing the effect of water fluoridation on the progression of carious lesions have contributed greatly to the development of the MID philosophy. The one study that stands out in terms of importance is the Tiel-Culemborg study from the Netherlands 1 . This study, like many others, showed that the fluoridation of water reduced the prevalence of cavitated dentine lesions by approximately 50%. It also showed that the main long-term action of fluoride is retarding the progression of a carious lesion, rather than prevention of its *This is not an official FDI document. The content is the sole responsibility of the authors. © 2012 FDI World Dental Federation 223 International Dental Journal 2012; 62: 223-243 doi: 10.1111/idj.12007 development 2 . This outcome became evident as ample time was spent assessing not only cavitated dentine lesions, but also enamel carious lesions. The secondary study outcome was confirmed in later studies that researched the effectiveness of fluoride in varnishes, gels and mouth rinses 3 . These data led to a change in the cariology paradigm: fluoride appears not to act pre-eruptively, as was thought, but mostly post-eruptively by changing the mineral saturation characteristics at the tooth surface The remainder of this paper will discuss in detail the five strategies that make up the MID philosophy using, as much as possible, evidence-based information available in the peer-reviewed literature. EARLY CARIES DETECTION AND CARIES RISK ASSESSMENT Detection devices The oldest device used for detecting carious lesions, apart from the probe, is the X-ray machine. Radiography is reliable for detecting carious lesions in approximal tooth surfaces but considered unreliable in occlusal surfaces, particularly for diagnosing carious lesions in enamel and in the outer one-third to one half of the dentine 224 © 2012 FDI World Dental Federation Frencken et al. particularly in anterior teeth A new system using light fluorescence technology (Sopralife; Acteon, Bordeaux, France) utilises a different wavelength than QLF to detect carious lesions, in conjunction with a camera. Currently, the value of QLF systems for carious lesion detection in clinical practice seems to be limited. Other methods, such as electrical impedance (CarieScan PRO TM ; CarieScan Ltd, Dundee, UK) and photothermal radiometry (Canary System TM ; Quantum Dental Technologies, Toronto, ON, Canada) have recently been developed. However more research is required before they can be advised. It appears that both X-ray and FOTI devices are suitable for use for carious lesion detection on approximal surfaces and that infrared laser fluorescence and light-induced fluorescence devices are not sufficiently reliable for assessing carious lesions in pits and fissures of occlusal surfaces 27 . This also applies to the deciduous dentition, in which newer technologybased systems have not been found to be reliable for the accurate detection of carious lesions on approximal surfaces Visual-tactile methods Perhaps because of the absence of a properly validated and reliable carious lesion detection device, early enthusiasm dimmed, and the emphasis shifted back to visual-tactile detection methods in the second half of the 1990s. The World Health Organisation (WHO) had propagated its method, which was based on a 'yes/no' clearly cavitated dentine lesion, as a reliable data base was required for comparison of decayed, missing and filled (DMF) teeth scores among member countries and because DMF data from decades earlier were available Carrying out an oral investigation on the basis of assessing teeth with cavitated dentine lesions only (DMF) should be considered a screening exercise. If the investigation is conducted for healthcare planning purposes, enamel carious lesions should be assessed as well, whether in clinical practice or when conducting an epidemiological survey. The ICDAS II and Nyvadindex may be suitable in a clinical practice setting, although the number of studies supporting this assumption is low. The same caveat applies to the recently developed epidemiological indices PUFA and CAST, which appear to be promising, but need further research. Caries risk assessment The caries disease process is dynamic and multi-factorial in nature. Caries risk is defined as 'the probability of future caries disease development'. Disease development includes both primary disease (new carious lesions) and secondary disease (lesion progression or reactivated carious lesions). Risk assessment for such a dynamic disease is complex as it is only able to MID for managing dental caries provide a snapshot at that particular moment and risk factors may change over time. Most importantly, for assessing lesion activity accurately in one session, using a combination of indicators (visual appearance, location, tactile sensation and gingival health) might still provide the best way to determine lesion activity. Moreover, activity criteria are not designed to quantify lesion progression, with regard to either size or depth. Despite its current shortcomings, however, risk assessment and caries prediction is a crucial part of contemporary clinical decision-making that dental professionals apply on a daily basis. It serves as the foundation for the patients' prognosis for caries and is embodied in the individually tailored oral health management plan provided to the patients. A strong body of evidence exists that at all ages the 'past and present caries experience' (and in particular the presence of active carious lesions) is still the most accurate and powerful, single predictor of risk of future carious lesion development Caries risk prediction is still a work-in-progress. A recent publication provides an excellent concise and thorough overview of the evidence related to patient caries risk assessment 46 . 'Whole-population' approach and 'risk-based' strategy Caries-risk assessment is usually described at the level of the individual patient The 'whole population' approach is appropriate for the prevention of oral diseases and applying it is the only way to reduce the burden of these diseases and the cost of oral care In a balanced view, the advantages and disadvantages of both the 'high-risk' strategy (seeks to protect susceptible individuals) and 'population' approach (seeks to control the causes of incidence) have been considered It may be concluded that although the caries risk prediction may guide the best use of available funds to support preventive caries management, the dwindling financial means for the same, or even increasing, needs continue to call for the 'high-risk' strategy as well as the 'whole-population' approach. While the Frencken et al. dental profession needs to embrace a more primary preventive approach to caries management based on common risk factors, secondary prevention and management will continue to focus on patient-centred caries management, including both preventive and minimally invasive tissue-preserving operative interventions 53 . These interventions will be discussed later in this paper. REMINERALISATION OF ENAMEL AND DENTINE CARIOUS LESIONS Dental plaque and dental caries Dental caries is a complex process of cyclical enamel de-and re-mineralisation. Streptococcus mutans and Streptococcus sobrinus are two putatively important bacteria in the initiation of enamel demineralisation, with Lactobacillus caseii assuming greater importance after initial progression of the carious lesion. This is Loesche's so-called 'specific plaque hypothesis' Mechanisms of action of fluoride in enamel The presence of fluoride during the remineralisation/ demineralisation cycle leads to its incorporation into the crystalline structure of the carbonated hydroxyapatite, which not only decreases crystal solubility, but also increases the precipitation rate of enamel mineral in the presence of calcium and phosphate due to the lower solubility of fluorapatite Role of calcium and phosphate The pre-eminent role of fluoride in preventive dentistry remains valid. However, the effectiveness of fluoride to remineralise enamel and obtain net mineral gain is limited by the bio-availability of calcium and phosphate ions In order to manage caries lesion development through minimising the solubility of enamel during an acid attack, the individual's tooth surfaces should be exposed to supersaturated levels of calcium, phosphate and fluoride that are available in products containing these ions in a bio-available form. OPTIMAL CARIES PREVENTIVE MEASURES Different measures have been proposed for preventing and arresting carious lesions. It is the task of the dental professional to select, based on evidence and on the patient's profile, which preventive measure(s) is most appropriate for a specific clinical situation. In many cases, more than one preventive measure needs to be applied. The whole population approach and individual caries risk assessment are essential activities, alongside with the provision/usage of personalised preventive measure(s) that will ultimately determine the level of reduction of carious lesions in patients and populations. Dental caries is a preventable disease. Therefore the best strategy for managing the disease is to intervene before its signs and symptoms are clinically detected. Disturbance of the biofilm (dental plaque) by brushing teeth with a sufficiently-fluoridated toothpaste on a daily basis is an effective measure which contributes to the control of enamel carious lesion development 84 . Even disturbing the biofilm from cavitated dentine lesions appears to arrest further progression of such lesions Effectiveness of caries-preventive measures Diet counselling and sugar substitutes The assumed relationship between carious lesion development and consumption of fermentable sugars used to be stronger in the past than currently. The extensive exposure to different kinds of fluoride vehicles is considered the main reason for this situation 86 . Diet control, in terms of intake of sugars and other fermentable carbohydrates, is still an important factor in managing carious lesion development. Individuals at high caries risk, and/or those that do not use fluoride agents, will benefit from dietary control measures. The interplay between consumption of cariogenic food, oral hygiene, availability of saliva and fluoride is nicely modeled by Van Loveren and Duggal 87 . They state that as long as saliva and fluoride are available in the mouth in abundance, and if biofilm control is performed properly at the same time, the detrimental effect of cariogenic food consumption on demineralising enamel and dentine can be considered low. The use of sugar substitutes is a preventive measure that assists individuals in reducing total cariogenic sugar intake. Xylitol and sorbitol are the sugar alcohols most frequently added to 'sugar-free' products Although the consumption of xylitol-based candies and lozenges favours a reduction in carious lesion increment, in general, this effect is not seen on approximal tooth surfaces Frencken et al. advised to restrain their sugar-containing food intake to a frequency of not more than five times daily 94 . Fluoridated agents Fluoride can be provided via water, milk or salt, or be administered topically by professionals and through self-application devices (toothpaste, gel, varnish and mouthwash). Fluoride is found naturally in the environment (water and plants) and can be added to consumer products, such as infant formulas and beverages. Water fluoridation is a method of making fluoride accessible to an entire community without requiring individuals to change their behaviour in order to obtain the benefits of fluoridation Results show a dose-dependent relationship between carious lesion reduction and severity of dental fluorosis. Adults also benefit from water fluoridation 100 . With respect to milk fluoridation, the Cochrane Collaboration review 101 concluded that there is insufficient evidence to show the effectiveness of fluoridated milk in controlling dental caries, despite a beneficial effect for school children, mainly observed in the permanent dentition. Controversy exists regarding the effectiveness of salt fluoridation 102 . A systematic review on the topic favoured salt fluoridation versus no exposure to fluoride for caries prevention in permanent teeth A series of Cochrane reviews on self-and professionally applied fluoride agents has been published during recent years. The main results have been summarised by Marinho 3 and showed that the use of fluoride toothpaste, fluoride mouthrinses, fluoride gels and fluoride varnishes are able to reduce the incidence of dental carious lesions, irrespective of whether other fluoride vehicles are being used at the same time. The use of fluoridated toothpaste is the most widespread method used for maintaining a constant level of fluoride in the oral cavity. It is considered to be one of the major factors that has contributed to the decline of the prevalence of dental caries in high-income countries Chlorhexidine-containing agents Chlorhexidine is available in mouth rinses, gel and varnish. A systematic review was aimed at determining the carious lesion-inhibiting effect of chlorhexidine varnishes on the permanent dentition of children, adolescents and young adults. Chlorhexidine varnish showed a moderate caries-inhibiting effect when applied every 3-4 months, but this effect had diminished 2 years after the last application. Studies that test chlorhexidine effectiveness with longer application intervals are required Silver diammine fluoride Silver diammine fluoride (SDF) is a combination of silver nitrate and sodium fluoride (Ag(NH 3 ) 2 F) that, when applied to carious tissues, inhibits carious lesion progression by its interaction with bacteria 114 . Very few studies assessing the effect of SDF as a carious lesion control agent in non-cavitated lesions have been conducted. Braga et al. 115 investigated the effect of SDF in arresting enamel carious lesions in pits and fissures of permanent molars for up to 30 months. The results were no different from those achieved by plaque control through tooth brushing and the use of glass-ionomer sealant; two approaches which are largely used for enamel carious lesion management. In another study, the effectiveness of an annual application of SDF solution and of quarterly application of sodium fluoride varnish and chlorhexidine varnish were tested on sound and carious root surfaces in an institutionalised elderly population 116 . After 3 years there was no difference in carious lesion incidence between the three preventive measures observed but all three measures reduced carious incidence better than plaque control alone. It appears that evidence for the effectiveness of SDF solution in preventing carious lesion development is weak. Its effectiveness in cavitated carious lesions is presented later on. MID for managing dental caries Casein phosphopeptide-amorphous calcium phosphate agents CPP-ACP is usually incorporated in chewing gum or in prophylactic dental paste with or without fluoride added, but tests have been also carried out on hard candy confections, sports drinks and milk incorporating CPP-ACP in their formulation. The effectiveness of such products in remineralising enamel is still being investigated, but results from in-situ and clinical studies show that CPP-ACP has a short-term remineralisation effect and a promising caries control effect for long-term clinical use 117 . Many laboratory and in-situ studies on the effectiveness of CPP-ACP have been published in the last two decades. As part of the process of obtaining clinical evidence, the number of clinical studies is currently still low. Studies show different outcomes, ranging from a superior effect of CPP-ACP to the control group(s) Ozone Ozone gas, the tri-atomic state of di-oxygen, was proposed as an antimicrobial agent that could reduce the number of micro-organisms on tooth surfaces. It is naturally produced in the presence of light or by different industrial processes. In dentistry, ozone is claimed to have a sterilising effect, killing cariogenic bacteria and subsequently leading to the arrest of carious lesions 123 . However, clinical studies have not achieved the same efficacy found in laboratory studies. Three systematic reviews concluded that there is no reliable evidence that the application of ozone gas to the surface of cavitated teeth arrests or reverses carious lesions. It does not appear to be a cost-effective additional step to the existing carious lesion management approaches Infiltration method Caries infiltration has been proposed as an alternative for management of non-cavitated enamel carious lesions on approximal and buccal surfaces Pits and fissure sealants Pits and fissures of permanent molars are particularly vulnerable to carious lesion development during and after tooth eruption Resin composites and glass-ionomer cements are the dental materials generally used to seal pits and fissures. A high-viscosity glass-ionomer is indicated for use with the ART sealant technique. It is generally accepted that resin composite sealants are retained longer than low-to medium viscosity glass-ionomer sealants 230 © 2012 FDI World Dental Federation Frencken et al. technique showed higher retention rates than lowand medium viscosity glass-ionomers 145 . The preventive effect of these ART sealants was high; the annual mean dentine lesion incidence rate over the first 3 years was 1% The preventive effect of the glass-ionomer sealant could be clarified by the presence of the material in the bottom of the fissures, even though the material could not be detected clinically MINIMALLY INVASIVE OPERATIVE APPROACHES FOR MANAGING CAVITATED DENTINE CARIOUS LESIONS Despite the plea made by WHO, the FDI World Dental Federation (FDI) and IADR to reduce the use of restorative materials, especially amalgam, through placing much greater emphasis on caries preventive measures, the need for treating cavitated teeth will remain into the foreseeable future. Remineralisation of demineralised dentine Continued presence of cariogenic plaque is the principal aetiological factor for demineralisation of both enamel and dentine. It seems obvious that depleting or reducing the cariogenic potential of dental plaque/ biofilm is the most important activity for the maintenance of a healthy dentition. Whether this activity is being achieved at the plaque development site, through reduction of the frequency of sugar intake, or at the plaque destruction level through disturbance or removal of it, or by increasing the acid resistance of tooth tissues through mineralising agents, or by reducing the micro-organisms in plaque through disinfecting agents, tooth surfaces ought to be free from cariogenic plaque. This fact is also applicable to the tooth surfaces that give a dentinal cavity its shape. Clearly, a major reason for restoring a tooth cavity, from a cariology and preventive point of view, is to seal it and allow easy removal of dental plaque from the restored surfaces of the tooth. Concurrently, cavities are also restored to alleviate toothache and to restore form, function and aesthetics. Similar to remineralisation of enamel carious lesions, remineralisation of dentine carious lesions is possible. The evidence for this phenomenon in open cavities is still very weak, but evidence for closed cavities that had remnants of dental plaque and retained decomposed dentine, and were filled with a restorative material, is abundant 159 showed decades ago. Remineralisation of demineralised dentine occurs through: (i) the function of the odontoblast process, providing calcium and phosphate from the vital pulp 159 ; (ii) diffusion of ions (fluoride, calcium and phosphate) from materials placed on the floor of a restored cavity Appropriate excavation methods According to the concept of Minimal Intervention Dentistry (MID), only the decomposed dentine needs to be removed from within the cavity. This then poses the question: which method removes decomposed dentine most effectively? In aiding this process, cariesdetector dyes were introduced decades ago 9 . The dyes are very popular in certain parts of the world. However, as opposed to the initial intention to stain micro-organisms in decomposed dentine, subsequent studies have demonstrated that the dyes do not stain micro-organisms but rather stain the organic matrix of less mineralized dentine A number of laboratory studies, using different detection techniques and endpoints to delineate decomposed dentine, have investigated the efficacy and effectiveness of methods for its removal. Considering the variation in study designs, it appeared that rotating round metal burs have the tendency to overprepare cavities Disinfecting excavated cavities Earlier it has been stated that micro-organisms, retained under a well-sealed restoration, are reduced in numbers over time and have no potential to further demineralise the dentine, provided that the seal remains secured. It is often noticed that in such a situation the demineralised dentine remineralises over time Restorative materials In past decades amalgam and silicate cement were the two most popular dental materials used for restoring cavities in posterior and anterior teeth respectively, and these materials have been superseded to a large extent by resin-based and glass-ionomer-based materials. Both types of adhesive material are constantly being modified to mimic the physiological (behavioural) and physical characteristics of enamel and dentine. In particular, glass-ionomer restorative materials have undergone major changes during the last decades. Medium-viscosity glass-ionomer was recommended initially for non-stress bearing surfaces. However, the latest systematic review on restoration comparison concluded that the survival rates of high-viscosity glass-ionomer restorations placed in stress-bearing surfaces in both deciduous and permanent dentitions were equal to or higher than those of comparable amalgam restorations 176 . Minimally invasive operative treatment approaches and adhesive materials and systems go hand-in-hand. 232 © 2012 FDI World Dental Federation Frencken et al. Resin-based and glass-ionomer-based materials have their advantages and disadvantages. The dental practitioner ought to know the chemistry, characteristics and handling features of the restorative material that (s)he is using. Proper application of that knowledge in clinical practice is the basis for a long lasting restoration. Restorative therapy Deciduous dentition According to a systematic review, covering studies carried out between 1988 and 2003, the mean annual failure rate for Class I and Class II amalgam restorations in deciduous posterior teeth was 6.6% and 7.6%, respectively 177 . The mean annual failure rate for comparable resin composite restorations (Class I and Class II combined), assessed according to the Ryge and USPHS criteria, varied between 0% and 15% 177 . Many of the included studies had assessed restorations placed in cavities designed according to the principle of 'extension for prevention'. It goes without saying that those cavity designs, proposed by G.V. Black, have no place in MID. On the contrary, the contemporary design principles is tissue-saving: 'prevention of extension' 7 . In addition to the traditional techniques of excavation with a round bur or hand excavator and restoration of the cavity with preformed crowns, amalgam, resin-based or glass-ionomer-based materials in a tooth tissue-preserving manner, minimally invasive treatment approaches that do not use electrically driven equipment and running water are available. These are presented below. Atraumatic restorative treatment (ART) This approach uses hand instruments for opening cavities further, only to the extent required for removing decomposed carious dentine. The cavity is then cleaned, restored with a high-viscosity glass-ionomer and adjacent pits and fissures are sealed concurrently 178 . Evidence-based studies have shown ART restorations in single-surface cavities in deciduous posterior teeth to survive as long as comparable amalgam restorations 176 . The mean annual failure rate of these ART restorations over the first two years was 3.5% 146 . Multiple-surface ART restorations in deciduous posterior teeth have a lower survival rate than single-surface ART restorations but they appear not to differ from either comparable resin-composite restorations In comparing restoration survival rates of ART high-viscosity glass-ionomer and those produced through use of the traditional therapy using either amalgam or resin-composite, one has to take into account the evaluation criteria that have been used in these studies. ART restorations have predominantly been evaluated according to the ART restoration criteria, while traditionally produced restorations have mainly been evaluated according to the United States Public Health Service criteria or the FDI criteria. The ART restoration criteria turned out to be more stringent than both the FDI criteria 182 and the USPHS criteria 183 for restorations in permanent teeth. The difference in restoration survival rates, assessed by both the ART and the USPHS criteria was 22% and 27% for single-and multiple surfaces, respectively being higher for restorations assessed using the US-PHS criteria over a 10-year period. This large difference in outcome shows that evaluating a treatment, whether it concerns a restoration, a crown or a sealant, should be done by internationally accepted appropriate criteria. Furthermore, restoration survival rates of different restorative materials should only be compared if the same assessment criteria have been used. Hall technique Another minimally invasive restoration therapy that may be helpful in reducing the treatment burden of cavitated dentine carious lesions is the Hall technique Non-restorative therapy Plaque removal from cavities in deciduous teeth The vast majority of cavitated carious lesions in deciduous teeth are being neither restored nor extracted, a finding which is prevalent in all countries in the world. Figures based on the WHO data base vary from, on average, 80% in high-income countries to 95% in low income countries Application of silver diammine fluoride Consistent with the rationale for stopping the demineralising effect of cariogenic plaque in cavities by removing it, 38% silver diammine fluoride (SDF) has been used in cavitated carious lesions. Three studies have been published, all with different application frequencies Permanent dentition Carious lesions in anterior teeth should preferably be restored using a proven anterior resin composite because of its superior aesthetic performance. According to a systematic review regarding effectiveness of adhesive materials bonded to enamel and dentine in non-carious cervical lesions, the glass-ionomers were superior to resin-based adhesives According to a systematic review, the mean annual failure rate for single-surface amalgam and resin composite restorations in permanent posterior teeth, evaluated according to the USHPS criteria, are 2.1% and 1.8%, respectively Restoring multiple-surfaces in posterior teeth is best done using amalgam or resin composite materials following 'the box only' cavity design 17 . Evidence regarding the success of tunnel restorations has not been increased since a previous publication on this minimal intervention approach 17 . Therefore, this procedure cannot be recommended for general use. Studies that have assessed multiple-surface high-viscosity glass-ionomer restorations in permanent teeth are negligible and evidence for a predictive outcome, if this material is used in multiple-surfaces, is not available. 234