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SURFACE TREATMENT FOR CERAMIC RESTORATIONS

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  • 13/02/2012 at 4:24 pm #10344
    drmithiladrmithila
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    SURFACE TREATMENT OF ALL-CERAMIC RESTORATIONS FOR ADHESIVE RESIN CEMENTATION

    Adhesive cementation typically involves surface treatment of the restoration and the tooth structures, application of primers and adhesives and the use of composite resin luting agents. Different ceramic surface treatments have been introduced to pretreat the intaglio ceramic surface and improve the bond at the ceramic-resin interface.5-9 The adhesion between ceramic material and composite resins is the result of a physicochemical interaction at the ceramic-resin interface involving 2 simultaneous mechanisms—chemical bonding and micromechanical interlocking.10 Because of the different chemical structure between silica-based and high-strength ceramics different surface treatments are required.

    SILICA-BASED CERAMIC RESTORATIONS 
    Silica-based ceramic restorations, because of their optical and aesthetic properties, are used to a great extent for porcelain laminate veneers, inlays and onlays, and full-coverage crown restorations. This brittle restorative material derives its strength from the adhesive bond of the definitive restoration and the supporting tooth structure.11,12 Proper surface treatment of the ceramic surface prior to cementation is therefore rudimentary for their long-term clinical success.12,13 Bonding to silica-based ceramics is usually obtained by the 2 aforementioned simultaneous mechanisms.14-25 The hydrofluoric acid (HF) attacks the glassy phase of the ceramic material, dissolving the surface and exposing the silicate crystals in the matrix, while the silane coupling agents provide a chemical covalent bonding between the silica in the ceramic matrix20-22 and copolymerizes with the methacrylate groups through siloxane bonds.26,27 The authors’ recommend acid-etching with 4% to 9.8% HF to create surface roughness and the application time depends on the crystalline content of the specific ceramic substrate. A higher crystalline content requires less acid etching time and concentration. A silane coupling agent is then applied to the etched ceramic surface. It is important not to place an excess or thick layer of silane because additional layers of hydrolyzed silane will not bond to the porcelain surface and can result in a less than optimal porcelain bond28,29 (Figures 1 to 4).

            

    13/02/2012 at 4:25 pm #15180
    drmithiladrmithila
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    Figure 1. The patient presented with no posterior disclusion or anterior guidance after orthodontic treatment. A prepless veneer was placed (tooth No. 6) to establish the proper function and to improve the aesthetics.
    Figure 2. The internal surface of the silica-based ceramics (Willi Geller Creation [Creation International]) was etched with a 9% buffered hydrofluoric acid (Porcelain Etch [Ultradent Products]) for 2 minutes, rinsed, and air-dried (2a). An application of silane (Porcelain Bond Activator mixed with Clearfil SE Bond Primer [Kuraray]) was applied. Some manufacturers add a silane coupler to their bonding system that is mixed with the other components (eg, bonding agent/primer) during ceramic adhesion (2b). A clear translucent light-cure resin cement (Illusion [BISCO]) was applied to the internal surface of the veneer (2c).
    Figure 3. Once the disinfectant step was completed, the enamel was etched using a 37.5% phosphoric acid (Gel Etchant [Kerr]). The gel was placed several mm beyond the anticipated restorative margin (3a). An adhesive agent (Optibond Solo Plus [Kerr]) was applied to the etched enamel, air-thinned, and light-cured for 40 seconds (3b). The veneer was positioned into place and the excess resin cement was removed using the "wet brush" technique and was light-cured for 40 seconds. It is important to leave a residual amount of resin cement at the interface to compensate for polymerization shrinkage (3c).
    Figure 4. Function and aesthetics were improved using a noninvasive preparation-less 
    procedure.
            

    13/02/2012 at 4:26 pm #15181
    drmithiladrmithila
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     HIGH STRENGTH CERAMIC RESTORATIONS

    High strength nonsilica-based ceramic restorations such as zirconia and alumina have increased in utilization by the clinician and technician because of the material’s strength, multitude of clinical indications and applications, and its cost effectiveness compared to precious metals.30 Of course, when preparation designs are retentive, nonadhesive cements (ie, glass ionomer cements) or moderately adhesive cements (ie, self-adhesive resin cements) can be used successfully to retain these nonsilica-based restorations. However, when the retention/resistance form is compromised, adhesive cementation with surface treatment of the ceramic material can improve the durability and reliability of the bond for nonsilica-based restorations.30 The excellent optical properties of high-strength ceramic materials are especially advantageous for indirect resin-bonded restorations such as resin-bonded fixed partial dentures. These types of restorations, however, rely on stable and long-term durable resin bonds. 
    Although the surface treatment for the tooth substrate remains the same (ie, self-etch or total etch), the surface treatment procedures known for silica-based ceramics cannot be utilized for high strength ceramic materials (ie, alumina, zirconia). Traditional bonding procedures (ie, acid etching and silane application) for silica-based ceramics cannot provide long-term durable bonds to the silica-free, acid resistant, high-strength ceramic materials. Conventional acid etchants do not sufficiently roughen the dense surface31 of these materials and the chemical reaction from silanization of these nonsilica-based ceramics is not possible. However, silane application can provide increased wettability.16-27,31,32 Silica/silane coating or application of a phosphate-monomer-containing ceramic priming agent after airborne particle abrasion increases the shear bond strength between zirconium-oxide ceramic and a resin luting agent.33,34 In addition, several in vitro studies have indicated that air-particle abrasion and a phosphate-modified resin luting agent have the potential to provide long-term durable resin bonds.35 Another long-term in vitro study found that silica coating and silanization increases resin bond strength to zirconia (Lava [3M ESPE]) with different resin cements.36,37 While silica/silane coating failed to provide durable bonds to densely-sintered aluminum-oxide ceramics, it was successfully implemented for zirconia ceramics.38,39 In an in vitro investigation on the fracture strength and marginal leakage of densely-sintered alumina crowns after aging in an artificial chewing simulator, fracture strengths were well above natural chewing forces for all cementation methods. However, adhesive bonding with a composite resin luting agent and ceramic primer containing adhesive phosphate monomers after air-particle abrasion of the crown intaglio surface significantly increased fracture strength and decreased marginal leakage as compared to conventional cementation methods. The current evidence supports the use of modified priming and/or resin composite luting agents containing special adhesive monomers (eg, MDP [Kuraray]) that provide chemical bonds to metal oxides and, therefore, long-term durable resin bonds to high-strength ceramic materials.33-35,38,40-49 Airborne-particle abrasion and an MDP-containing priming agent (Porcelain Bond Activator mixed with Clearfil SE Bond Primer [Kuraray]) followed by application of an MDP-containing resin composite luting agent (Panavia F 2.0 [Kuraray]) revealed the highest shear bond strength in one study, although not significantly different from some combinations with Rocatec silica/silane coating.50 

     

            

    13/02/2012 at 4:26 pm #15182
    drmithiladrmithila
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    Figure 5. Preoperative facial view of existing ceramo-metal restorations with open margins, recurrent caries, and inadequate epithelial attachment. Patient presents with sensitivity and requests an aesthetic improvement. Treatment required connective tissue grafting and replacement of the existing crowns with zirconium restorations and a Class V composite restoration on the second premolar.
    Figure 6. The internal surface of the high strength ceramic crown (Lava [3M ESPE]) was microetched using a silica coating, CoJet-Sand (Rocatec/CoJet System [3M ESPE]) (6a). A silane coupling agent (ESPE Sil) was applied onto the internal surface of the restoration (6b). Application of a methacrylate based self-etch cement (G-Cem [GC America]) onto the internal aspects of the porcelain crown for final cementation (6c).
    Figure 7. Postoperative facial view of the final restorations. Notice the soft tissue biocompatibility at the restorative interface. Figure 8. Patient presents with a fractured all-ceramic crown on the maxillary right first molar after endodontic treatment. Treatment involved replacement of existing crown with all-ceramic restoration fabricated with a zirconium internal substructure and Vita surface ceramics (VITA VM9 [Vident]).

            

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