SURFACE TREATMENT FOR CERAMIC RESTORATIONS

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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