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One of the most important aspects in the success of a restoration is the bond between the tooth and the restoration. There are many luting agents currently on the market with differing formats of adhesion and techniques for use.
Adhesively bonding ceramic restorations with composite resin cements allows for the achievement of the best bond strength. This advantage in using a resin-based luting material allows for a decrease in fractures of the ceramic restoration. Adhesive cements provide many other benefits including great color matching, margins that can be polished, biocompatibility and great bond strength to both tooth and ceramic.
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A general rule of bonding has been that the more steps involved, the better the bond strength. Dental manufacturers have been developing simpler adhesive systems that are less technique-sensitive to help prevent the problems with dental adhesives. Carrying out the multi-step adhesive procedure is difficult and can be critical to the strength of the bond. Using self-etching adhesive cementing agents eliminates the conditioning, rinsing and drying steps that are associated with the multi-step adhesives. This can eliminate the over-drying factor that forms from dentin conditioning, which causes the collapse of the collagen fiber network that is associated with the multi-step technique. The breakdown in the collagen network can result in the incomplete resin infiltration that leads to postoperative sensitivity.
Futurabond DC (VOCO), a self-etching system for direct or indirect restorations, is available for adhesive luting with Bifix QM resin cement (VOCO). Futurabond DC can be used with light-cure, dual-cure and self-cure resin cements. The use of self-etch adhesives addresses the concerns of postoperative sensitivity and allows for a more efficient cementation process. This adhesive bonding agent can wet a cavity preparation with a single coat. Its SIO2 nanoparticles (20 nm) enable cross-linking of the resin components and enhance its film-building properties. These nanoparticles fortify the hybrid layer, helping produce high bond strengths. As this adhesive is applied to the surface of the tooth, it will solubilize the smear layer, penetrate and demineralize the dentin surface.
Bifix QM (VOCO), a radiopaque dual-cured resin luting system, comes in three shades: universal, white opaque and translucent with corresponding try-in pastes. This luting system can be used universally for non-metal (ceramics, composites) and metallic restorations. Bifix QM has a 10+ year success record and cleans up very easily.
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The clinical case illustrates a 77-year-old patient who presented with a gold crown on tooth No. 19 that had lingual decay at the crown margin. The crown was also abutted by the patients lower removable partial denture (RPD).
1. The patient was interested in having a tooth-colored, all-ceramic crown to replace her gold crown, as she had replaced other work in her mouth in the past. She also wanted to keep her current lower RPD as it was only two years old. As with all cases to be treated, the patient is asked to bite on articulating paper before they are anesthetized.
2. This allows us to try and replicate the patient’s contact points in the final restoration as this patient has a stable occlusion and no para-functional habits. The gold crown and decay are removed and a crown preparation for a chairside CAD/CAM (CEREC Bluecam, Sirona Dental Systems) crown is finalized.
3. It is important to remember that conservation of tooth structure is of utmost importance when preparing any tooth. A conservative approach where only decayed tooth structure and refinement of the margins is the method used in this case.
4. A trough is made in the gingival tissue using a diode laser (Picasso, AMD Lasers). The patient’s crown is replicated in the design of the restoration so that the new crown may fit in exact alignment with the patient’s RPD.
5. A lithium disilicate material, IPS e.max (Ivoclar Vivadent), was selected to fabricate the crown. The restoration is tried in to verify full seating and to make any minor adjustments. It is then further crystalized, after glazing, in a porcelain oven to reach its final strength of up to 360 MPa at 850°C.
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6. The restoration is removed from the oven, allowed to cool and then steam cleaned before preparing for cementation. The internal surface of the restoration was etched with 5% hydrofluoric acid and allowed to react for 20 seconds per manufacturers instructions.
7. It was then rinsed and dried and treated with a silane coupler for 60 seconds to create an optimal surface for bonding.
It is of utmost importance to try and maintain a clean and dry field in the mouth especially during the cementation procedure. In this case an Isolite (Isolite Systems) was used to help keep the mouth dry and illuminated. A 2% chlorhexidine solution, Cavity Cleanser (BISCO Products), was used to enhance long term bonding. It has been well proven that a solution of this type can enhance the long-term in-vivo bond to dentin through the inhibition of enzymes (matrix metalloproteinase-2 [MMP-2, MMP-8, MMP-9]) that breakdown the collagen scaffolding below and within the hybrid layer over time.
8. The self-etching adhesive bonding agent, Futurabond DC, was activated to mix within the unit-dose blister package. It was then applied and agitated for 20 seconds over the entire surface of the preparation.
9. The self-etch adhesive was lightly dried for five seconds and then cured with a halogen curing light for 10 seconds. A dual-cured adhesive resin luting agent, Bifix QM, was dispensed with its automix syringe in the crown.
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10. The crown was seated and then light-cured for two seconds on the buccal and lingual surfaces to allow for an easy and speedy clean up. Final curing of the luting agent occurs after the use of an oxygen-impermeable protective gel, DeOx (Ultradent Products). Occlusion was checked and a final polish was applied.
Adhesive materials using self-etch or total-etch techniques can provide excellent retention to direct and indirect ceramic restorations. Using cements that have dual-cure resin capabilities can also enhance the clinician’s outcomes. These materials allow us to accomplish great results in what was once a laborious procedure of retrofitting a crown to an existing RPD.