Surface Treatments for Tooth-Colored Restorations

[drmithila]

 SURFACE TREATMENT OF COMPOSITE RESTORATION FOR ADHESIVE RESIN CEMENTATION

Adhesive bonding of laboratory-processed composite resins increases their resistance to fracture. A principal determinate in the long-term success of these restorations relies on the strength and durability of the interface between the resin cement and the bondable surface of the processed resin. The surface of laboratory-processed composite resins is highly polymerized with minimal unreacted free-end radicals for bonding to the resin cement. 
     While microleakage has been reported to occur at this interface between the internal surface of the inlay/onlay and the resin cement in the absence of composite softening agents, several surface treatments have been advocated to promote adhesion between the resin cement and the indirect composite restoration. Mechanical roughening of the internal surface of the inlay can be accomplished with small particle diamond burs or microetching with either 50 µm aluminum oxide particles or 30 µm silanized silica-coated aluminum oxide particles, which creates a micromechanical retention bond at a microscopic level between the restorative material and the resin cement. In addition to mechanical roughening, an application of proprietary softening agents, wetting agents, or silane has been reported to enhance the bond strength between the restoration and the resin cement.
     Various precementation protocols have been recommended by the manufacturers of indirect resin systems. The authors’ standard cementation protocol for laboratory-processed composite resins includes microetching with a silicate ceramic sand (Cojet-Sand [3M ESPE]), and then a subsequent application of silane to restore any coating on the original fillers that may have been removed by sandblasting. As a bifunctional molecule, the silane acts as a coupling agent between the filler particles on the indirect resin surface and the resin cement. Newer formulations of silane that include a monomer (ie, unfilled resin) further simplify the bonding process. Microetching of aged composite resin with silica-coated aluminum oxide particles results in higher bond strengths compared to other surface treatments for intraoral repair of composites. CoJet, a tribochemically assisted bonding system is designed to create potential micromechanical retention and a chemical bond between composite and most types of restorations. The mechanism of action allows the silicate particles to become embedded in the surface of the restoration during sandblasting, which then reacts with the silane to improve bond strengths. Reports indicate, however, that etching or rinsing after such surface treatment can significantly decrease shear bond strengths (Figures 1 to 7).

CONCLUSION
The restorative success of any indirect restoration begins and ends at the adhesive interface. While new products and technological advances impact our profession positively, a new burden rests on clinicians to continually educate themselves on the properties and applications of the new materials. This discussion has defined adhesion at the restorative interface and provided the standard surface treatment and adhesive cementation protocol for laboratory processed composite resin restorations.

        

[drmithila]

 

Figure 1. Preoperative occlusal view of a maxillary left second premolar with recurrent decay that was previously restored with a gold inlay restoration.

Figure 2. Proximal caries was removed on the mesial and distal aspect of the premolar, and an inlay preparation design was completed. The preparation was cleaned with a 2% chlorhexidine and rinsed with water.

Figures 3a and 3b. The internal surface of the laboratory-processed composite inlay was microetched with silicate ceramic sand (Rocatec/Cojet System [3M ESPE]) for to 2 seconds and air-dried (a). A silane coupling agent (Silane primer [Kerr]) was applied to the internal surface of the restoration with a brush and then air-dried (b).

Figure 4. The preparation was etched for 15 seconds with a 37.5% phosphoric acid semi-gel (Gel Etchant [Kerr]), rinsed for 5 seconds, and lightly air-dried.

Figure 5. A thin layer of adhesive was applied to the preparation with an applicator for 20 seconds with continuous motion, lightly air-thinned for 5 seconds, and light-cured for 10 seconds per surface.

Figure 6. A resin cement (NX3 Nexus [Kerr]) was injected into the entire preparation, and the restoration was positioned firmly in place. The excess resin cement was removed with a No. 000 sable brush using the “wet brush” technique. This procedure involved applying a small amount of bonding resin to the tip of the sable brush, then wiping it over the restorative interface to remove any excess resin cement. (Note: A residual amount of resin cement is left at the interface to compensate for polymerization shrinkage.)

Figure 7. Postoperative view of the definitive restoration. Note the harmonious integration of the composite resin with the existing tooth structure.

        

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