ATRAUMATIC RESTORATIVE TREATMENT (ART) – FACTORS AFFECTING SUCCESS

he success of tooth restorations rendered according to principles of the Atraumatic Restorative Treatment (ART) approach is dependant on various clinical factors. The most common failures, due to these factors, are partial material loss; complete material loss; caries related to restoration margin and material wear > 0.5mm. The main reason for clinical ART failures are related to operator skills and performance. The prevention and management of ART failures includes emphasis on correct clinical indication and the repair of failed restorations. A new caries classification may provide guidance for clinical indication. The classification combines site and size of a lesion, which is reflected in a dual coding system. In addition, ART training and diligence during ART application are important for clinical success. Uniterms: Atraumatic Restorative Treatment; Minimum intervention; Glass-ionomer cements.

The success of tooth restorations rendered according to principles of the Atraumatic Restorative Treatment (ART) approach is depended on various clinical factors.The most common failures, due to these factors, are: Partial material loss Complete material loss Caries related to restoration margin Material wear >0.5 mm In contrast to other ART failures, the occurrence of failures related to recurrent caries has steadily decreased due to improvements in restorative materials and operator skills 1 .ART failures may occur in combination or lead to each other, e.g.material loss may promote occurrence of secondary caries, or partial defects may lead to complete loss of the restorative material over time.
During caries progression beyond the enamel-dentin junction, dentine is first exposed to bacterial acids resulting in extensive demineralization of peritubular dentine and partial mineral loss of intertubular dentine.This early exposure is followed by bacterial invasion, together with the denaturation of dentinal collagen by proteolyic enzymes.As result carious dentine can be divided into affected dentine (a partially deminerialized thus harder inner layer, containing only few bacteria) and infected dentine (a largely dematerialized, thus much softer denatured outer layer).The outer layer contains the majority of bacteria.In addition, the complete loss of odontoblast

Atraumatic restorative treatment (ART) -factors affecting success
Mickenautsch S  1 .Hence, a loss of GIC filling material would also result in the loss of caries-arresting factors.Therefore, a good chemical bond between material and tooth tissue appears to be important for the success of ART restorations.
Clinical factors responsible for ART failures are 1.Material Factor 2. Operator Factor 3. Technique Factor

Material factor
Material factors are directly related to material (GIC) properties, such as physical strength, flow rate and Material consistency.With the development of newer high strength glass ionomer cements, physical properties have been improved.However, the strength of GIC remains inferior to traditional restorative materials, particularly amalgam and composite resin.The flow rate of GIC is directly related to the adaptability to the cavity surface.Improved GIC flow rate may reduce void formation.In addition, small void formation (diameter < 0.1 mm) within the restoration, may depend on the type of material mix, capsule or hand mix.Hand mix is operator depended and thus may incorporate more air entrapments then capsule mixing.A large number of voids may weaken the material and make it prone to higher wear and material loss on restoration margins 5 .

Operator factors
Operator factors relate to failures caused by insufficient operator performance, particularly in the areas of incorrect clinical indication, caries removal, moisture control, cavity conditioning, material mixing (hand mix) and material insertion 1 .Operator decisions leading to incorrect application of ART under clinical conditions not favourable for ART may result in a too large restoration, with constant exposure to masticatory forces, exceeding GIC strength.In combination with limited physical strength of GIC (material factor) this may lead to restoration fracture and subsequent loss of restorative material.Insufficient removal of infected dentine, particularly on the cavity circumference may cause a reduced chemical bond between tooth tissue and material, higher residual bacteria count and the access of those bacteria to substrates via occurring leakage with subsequent further caries progression.
Insufficient cavity conditioning, as well as saliva contamination of the prepared cavity through insufficient moisture control supports the retaining of a smear layer attached to tooth tissue.Such smear layer compromises the chemical bonding process of GIC to the cavity walls.Weak bond strength causes an increased likelihood of material loss.In contrast, the reduction of the smear layer through effective dentine conditioning using a 10% poly acrylic acid (PAA) for 10-15 seconds improves the bond strength between material and tooth tissue.
The correct material consistency is vital for effective material retention and physical strength.A too dry mixture has limited bond strength, a too moist mixture reduced resistance to wear and compressive strength.Furthermore, GIC needs to be inserted into the cavity in increments and condensed.Incorrect insertion and /or condensation will cause air entrapments, causing reduced physical strength of the restoration 2 .
A study, measuring operator performance in relation to the level of void avoidance, showed that initial training is needed.It was also shown that after training, experience levels are less important than operator diligence during the ART procedure 5,6 .

Technique factors
Hand excavation and press finger technique are both components, unique to clinical ART protocol 1 .Hand excavation causes enamel fracturing and irregularities in dentine.Both manifest as challenges to a good marginal GIC adaptation, important for effective bond strength of the material to the cavity walls.In addition, press finger technique causes a rough restoration surface with irregular margins, supporting potential plaque and bacteria retention.
However, selfsmoothening occlusal forces and the antibacterial action of GIC may counter act such negative effect 6 .

Failure prevention and management
The prevention and management of ART failures includes emphasize on correct clinical indication and the repair of failed restorations.A new caries classification may provide guidance for clinical indication.The classification combines site and size of a lesion, which is reflected in a dual coding system and expressed in the form of a grid (Table 1) 7,8 .The classification of sites follows the three surface areas on which caries occurs: Extensive cavity, with at least one cusp or incisal edge which is lost Clinical studies on the success rates of ART fillings show a higher success related to one surface restoration, without any occlusal or proximal contact with antagonistic or neighbouring teeth (Site 1 / Size 1 and 2), particularly in the permanent dentition 1 .

Journal Of Minimum Intervention In Dentistry
The management of ART failures follows principles of restoration repair instead of replacement 1 .Table 2 provides an overview how to repair failed ART restorations.
at least one cusp which is undermined and which needs protection from occlusal load Size 4:

Conclusion
The main reason for clinical ART failures are related to operator skills and performance (operator factor).nueva clasificación de las caries, puede proveer de una guía para la indicación clínica.La clasificación combina la ubicación y el tamaño de la lesión, lo que se refleja en un sistema de codificación dual.Además, para obtener el éxito clínico, son importantes el entrenamiento en el ART y diligencia durante su aplicación.

Table 1 .
New caries classification / Summary of classes

Table 2 .
ART failure management