The ART approach: clinical aspects reviewed.

ABSTRACT The success of ART as a caries management approach is supported by more than 20 years of scientific evidence. ART follows the contemporary concepts of modern cariology and restorative dentistry. It challenges treatment concepts such as step-wise excavation and the need for complete removal of affected dentine. The ART approach so far has mainly used high-viscosity glass-ionomer as the sealant and restorative material. Cariostatic and remineralization properties have been ascribed to this material which requires further research to establish its clinical relevance. The adhesion of high-viscosity glass-ionomer to enamel in pits and fissures is apparently strong, as its remnants, blocking the pits and fissures, have been considered a possible reason for the low prevalence of carious lesion development after the glass-ionomer has clinically disappeared from it. encapsulated high-viscosity glass-ionomers may lead to higher restoration survival results than those of the hand-mixed version and should, therefore, not be neglected when using ART. Similarly, the use of resin-modified glass-ionomer with ART should be researched. The effectiveness of ART when compared to conventional caries management approaches has been shown in numerous studies. Proper case selection is an important factor for long-lasting ART restoration survival. This is based on the caries risk situation of the individual, the size of the cavity opening, the strategic position of the cavitated tooth and the presence of adequate caries control measures. As the operator is one of the main causes for failure of ART restorations, attending a well-conducted ART training course is mandatory for successful implementation of ART.


INTRODUCTION
The Atraumatic Restorative Treatment (ART), by definition, has features that characterize this approach and differentiate it from what we know as "conventional" operative dentistry for the management of carious lesions. Frencken and Holmgren 26 (1999) defined ART as a "maximally preventive and minimally invasive approach to arrest further progression of dental caries.
It involves the removal of soft, completely demineralised carious tooth tissues with hand instruments, followed by the restoration of the cavity with an adhesive dental material that simultaneously seals the remaining pits and fissures that remain at risk." Risk assessment is also the driving force behind the use of the preventive aspect of ART. This is achieved through sealing pits and fissures prone to development of carious lesions.
The purpose of this paper is to analyze and discuss the components that define ART, using published study outcomes, to discuss the contribution of ART to the management of carious lesion development in general and to identify issues that require further research. effective tools for preventing carious lesion development in (newly) erupted molars and premolars exposed to potential caries-risk factors. They appear to be more effective than the common fluoride varnishes but the evidence is not substantial and is dependent upon local circumstances 30 .
Retention of a sealant is usually considered the most important variable indicating its effectiveness. Those who disagree with this view have postulated that its carious lesion preventive effect is the real endpoint and that sealant retention is merely its surrogate 26 . These two variables do not necessarily correlate well, as is shown in the following example. A comparison between ART sealants using two types of glassionomer in a high caries-risk population was carried out in Brazil 54 . The study showed a high preventive effect (98.5%) for both type of sealants, whilst the retention rates of both types was lower than 50% after 1 year. Obviously, the level of caries risk in an individual and the level of professionalism of the practitioner have an important impact upon the relative contributions of both variables to the effectiveness of a sealant.
High-viscosity glass-ionomers are used in placing ART sealants. In the only comparative clinical trial published so far, they prevented carious lesion development in re-exposed pits and fissures of occlusal surfaces more effectively than resin composite sealants did 5  The meta-analysis by Van't Hof, et al. 53 (2006) concluded that although the number of studies reporting on the retention and caries preventive effect of ART sealants was low, the retention of high-viscosity glass-ionomer ART sealants was higher than that of medium-viscosity glassionomer ART sealants. Furthermore, the caries preventive effect was high: 99%, 98% and 97% after 1, 2 and 3 years, respectively. This meta-analysis showed that only high-viscosity glass-ionomer should be used for sealing pits and fissures using ART.

USINg ART IN MANAgINg CAVITATED DENTIN LESIONS
Hand instruments are used for cavity cleaning in accordance with ART. Although hand excavators have been used to clean cavities for more than a century, many dental practitioners resort solely to rotary equipment when "preparing and cleaning" a cavity, thinking that using hand instrumentation alone will lead to insufficient results. In light of this, issues related to the use of the ART approach will be discussed.

MICROORgANISMS LEFT IN ThE CAVITY
A recently published critical review stated that cariogenic bacteria, once isolated from their source of nutrition by a restoration of sufficient This implies that, in essence, there is no need to try to remove all microorganisms from within the cavity. If this is attempted, potentially remineralizable and sound dentine is sacrificed, which would inevitably lead to a reduction in the strength of the tooth. This argument is supported by Maltz, et al. 36,37 (2002, 2007), who concluded that incomplete removal of carious affected (demineralised) dentin and subsequent restoration of the cavity with a material that seals the cavity tightly results in the arrest of the lesion. The authors suggested that complete removal of affected (demineralised) dentin is not essential for controlling the progression of dentine carious lesions. This evidence shows that when a cavity is securely restored with a material having a good and long-lasting bond to the cavity walls, micro-organisms unintentionally left behind will not restart the caries process. This does not, however, mean that cavities should be left full of infected (decomposed) dentine and then filled with a restorative material. The intention when using ART is to remove as much infected (decomposed) dentine from the cavity as possible, in order to create the largest possible intra-cavity surface for a secure bonding. Thus production of ART restorations follows the same principles as those of contemporary cariology and restorative dentistry 32 .

STEPWISE-EXCAVATION VERSUS ONE-SESSION ART APPROACh
In managing deep carious lesions, the risk of pulp exposure during the removal of infected (decomposed) dentinal tissues led to development of a biological approach intended to preserve tooth tissues and promote the defence of the pulp by a total seal of the cavity and by the stimuli of calcium hydroxide cement.
This approach challenged the belief that the infected (decomposed) dentin had to be removed In conclusion, considering all the biological aspects discussed above, it is important to ensure that as much as possible of the infected, softened (decomposed) dental tissue is removed, in order to obtain adequate adhesion of the restorative material to the cavity walls over a long period, irrespective of the restorative material used.

CASE SELECTION OF CAVITIES TREATABLE WITh ART
It is obvious that the cavity size, selection of restorative material, clinical skills and knowledge of the dental practitioner will determine the success of a restoration, whether conventional, ART or any other cavity cleaning method is used.
The meta-analysis showed that the highest survival rates for ART restorations using high-

hAND-MIXED VERSUS ENCAPSULATED gLASS-IONOMERS
encapsulated high-viscosity glass-ionomer has been on the market for a decade or so. According to Dowling and Fleming 18,19 (2008,2009), encapsulated anterior and posterior glass-ionomer restoratives outperform their hand-mixed equivalents with regard to the range of powder to liquid mixing ratios routinely encountered clinically. Therefore, if electricity is available, encapsulated high-viscosity glassionomers are preferable to hand-mixed glassionomers with ART. However, if electricity is not available, it is mandatory for the operator to use the correct liquid to powder ratio, in order to obtain optimal properties from the cement.
Being careless and mixing less powder into the drop of liquid, as often happens in practice, will lead to a weak glass-ionomer and consequently, to a poor restoration or sealant.
The only study in which encapsulated highviscosity glass-ionomer was used with ART showed a cumulative survival rate for single-and multiple-surface ART restorations in permanent teeth of 85% and 77% after 5 years 25 .
Dowling and Fleming 18,19 (2008,2009) further conclude that anhydrous glass-ionomer restorative formulations are more susceptible to clinically-induced variability in hand-mixing, in contrast to conventional GI restorative formulations that contain a polyalkenoic acidic liquid. Therefore, if hand-mixed glass-ionomers are used for ART, using those with formulations containing the acid in the liquid is preferable to using those containing it in the powder. Thus, if encapsulated high-viscosity glass-ionomers can be used, these are to be preferred over handmixed high-viscosity glass-ionomers. The results of these few short-term studies are encouraging. Further research into the use of resin-modified glass-ionomers with ART is therefore warranted.

ACKNOWLEDgEMENTS
We are grateful to Ignacio Mazzola and Laura Brain for their assistance with searching the literature.