Composite resin is a suitable restorative material to restore an existing failed restoration; However, it is not suitable for repairing a carious lesion due to the large amount of remineralisable dentine required to achieve a reliable bond base.
Glass ionomer (GIC) cements adhere to decayed dentin and minimize the tooth extraction required to restore the tooth. Glass ionomer cement can be used alone as a restorative material or as a base for a composite resin layer (sandwich restoration) when the remaining tooth structure is unsupported and requires an adherent composite to maintain its structural integrity.
Glass ionomer cements are the material of choice to treat an active carious lesion for the following reasons:
• The poor bond strength of glass ionomer cement to healthy and caries affected tooth structure does not compromise the integrity of the restoration as there is no polymerization shrinkage stress with composite resins.
• Glass ionomer cement, both self-cure and light-cure, bonds to carious and infected dentin.
• Glass ionomer cements release approximately 1 percent (more than 5,000 parts per million) of fluoride ion, which effectively kills any cariogenic bacteria remaining at the outer edge of a carious lesion.
• Glass ionomer cements protect the margins of a restoration from recurrent caries.
The release of fluoride from glass ionomer cements on a sealed carious lesion hardens the carious dentin and promotes the formation of caries-resistant arrested caries in existing carious dentin and converts the carbonate-apatite in affected dentin to fluoride-apatite, creating a caries-resistant base under the restoration . .
Rationale for using GIC to restore dental caries
A schematic diagram of a carious lesion prepared for a GIC restoration is shown in the figure.illustration 1.Note that a thin layer of decayed dentin may remain as the fluoride ions released from the GIC penetrate the decayed dentin at a concentration that kills any bacteria present.
Figure 2shows schematically what happens when a GIC restoration is placed in a cavity prepared in this way. Strontium and fluoride migrate from the VIC into the affected and infected dentin to combine with calcium and phosphate ions from the dentinal tubular fluid to allow the formation of arrested caries enriched with fluoride in infected dentin and fluorapatite in affected dentin.(Abb. 3).
Figure 4Figure 12 shows schematically the amount of extracted tooth needed for a GIC restoration compared to the amount of extracted tooth needed for a composite resin restoration under similar circumstances(Figure 5).
illustration 1
Schematic representation of a carious lesion prepared for a GIC restoration, showing the amount of tooth extraction required.
Figure 2
The remineralization process when a GIC restoration is placed on decayed dentin.
Figure 3
The schematic result of a GIC restoration that remineralizes caries-affected dentin.
Figure 4
The amount of extracted tooth needed for a GIC restoration: Leave some infected dentin and all affected dentin in the cavity preparation.
Figure 5
A cavity prepared for a composite restoration where all affected and infected dentine must be removed to obtain a reliable bond base.
Restoration of a carious lesion with a self-curing glass ionomer cement or a resin-modified glass ionomer cement
Self-curing GIC is preferred as a restorative material over light-curing GIC or resin-modified glass ionomer cement (RMGIC).
RMGICs have poor wear resistance on occlusal surfaces and for larger restorations, the curing light does not penetrate to the base of the restoration (due to high opacity). This leaves uncured HEMA in the RMGIC, which absorbs moisture from the tooth into the material and can cause post-operative sensitivity.
restorative technique
Figure 6shows two small occlusal carious lesions prepared for a GIC restoration.Figure 7indicates the number of cavities to be removed. At the perimeter of the preparation, a pit is prepared directly in healthy dentin using a #3 round bur to ensure a biological seal with the GIC restoration.
Figure 6
Two small occlusal carious lesions to be prepared for GIC restorations.
Figure 7
How to identify the different types of dentin affected by caries and how much should be left in the restoration base.
Outside the perimeter of the preparation, the base is affected dentin (determined by the color and hardness of the tissue). Because the collagen fibers remain intact, this dentin remineralizes as fluorapatite when calcium and phosphate ions from the dentinal tube fluid combine with fluoride from the GIC.
A thin layer of carious dentin approximately 0.5 mm thick is left in the center of the preparation just above the pulp tissue. The fluoride ions from the GIC penetrate the remaining tooth decay at a concentration that kills any bacteria present and supports fluoride-enhanced tooth decay.(Figure 8).
After cavity preparation, the tooth is etched with 37% phosphoric acid for five seconds to clean the cavity and remove any residue, including oil, from the restorative interface handpiece.(Figure 9). Polyacrylic acid conditioning does not remove oil from the handpiece; which, if left behind, significantly reduces the binding strength of the GIC.Figure 10shows how oil from a high and low speed handpiece can contaminate the tooth surface, a fact apparently overlooked by manufacturers of self-etch bonding.
Figure 8
Cavity preparation before seating the restoration.
Figure 9
Etching for five seconds with phosphoric acid removes handpiece oil and other contaminants from the cavity surface.
After the cavity has been washed and gently dried, the GIC can be placed by inserting the nozzle to the bottom of the cavity and filling the preparation from the base to the top to avoid entrapping air. High viscosity glass ionomer cements available today allow a physician to pack the GIC into the cavity similar to an amalgam restoration.
The setting time of the GIC can be shortened by preheating the capsule and/or light-curing the restoration, as the released energy accelerates the chemical setting reaction of the GIC.
After curing, the restoration must be contoured to fit the occlusal tray. Some manufacturers recommend a protective varnish layer, but clinically this seems to have little effect on the success of the restoration.
GIC restorations on occlusal surfaces are recommended if there are no cantilevered cusps and the restoration does not encroach on a centric stop.(Figure 11).
Figure 10
The polyacrylic acid, which cares for the tooth, does not remove oil from a high and low speed handpiece, which can reduce the adhesion strength of the GIC.
Figure 11
GIC restorations on occlusal surfaces are recommended if there are no cantilevered cusps and the restoration does not encroach on a centric stop.
If any of these conditions are present, a sandwich restoration with a layer of composite is indicated to protect the tooth from possible cusp fracture and excessive occlusal wear at the centric stop.
Conclusions
Composite resin may not be appropriate as a restorative material for carious lesions due to the large amount of remineralisable tissue that must be removed when using these materials.
Self-curing glass ionomer cement allows a restorative dentist to leave small amounts of infected dentin in the cavity and remineralize all affected dentin.
With the advent of pharmacological treatment of caries, little or no removal of carious dentin will be required; However, GICs will continue to be the first layering material of choice to replace missing tooth structures with this restorative technique.OH
Oral Health appreciates this original article.
Geoff Knight is a General Dentist based in Melbourne, Australia with an interest in Cosmetic and Minimally Invasive Dentistry. He has introduced a number of innovative clinical techniques and is featured on several dental patents. dr Knight speaks internationally with a focus on high-efficiency, minimally invasive dentistry. He was state president of his dental association and has extensive political and economic experience within the profession. Among the leisure activities of Dr. Knight is passionate about mountaineering, an interest that has taken him to some of the highest peaks on multiple continents.
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