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Inside Dentistry

April 2008, Volume 4, Issue 4
Published by AEGIS Communications


CLINICAL ROUNDTABLE

David Avery; Gary M. Radz; Bruce Small


What is the optimal way to treat the surface of indirect laboratory-processed composites, porcelains, and core-based crowns before placement?

David Avery, AAS, CDT

Indirect composite resin restorations are rapidly diminishing in popularity. That said, the best way to treat these surfaces is, after try-in and proximal refinements, clean with alcohol, silanate, and bond with dual-cure resin adhesive cement.

For pressed or feldspathic ceramic restorations, after try-in and interproximal refinements, assuming the laboratory has etched the restoration with hydrofluoric acid, etch with phosphoric acid and silanate. Then, for pressed ceramics, bond with dual-cure adhesive cement. For feldspathic porcelain, bond with light-cured adhesive cement to eliminate potential shade shift from the combination of thin porcelain and the effect of the tertiary amines found in auto-cure resins.

For alumina or zirconia core-supported crowns-and-bridges, after try-in and interproximal and occlusal refinements, clean with alcohol and cement with a resin-modified glass-ionomer cement. If desired, these restorations can be bonded using a self-adhesive resin cement or a phosphonated resin cement. Importantly, do not sandblast the intaglio surface with aluminous oxide, as this may lead to phase transformation and potential clinical failure.

Gary M. Radz, DDS

Indirect composite is a resin material just as the direct material. It does not require a surface-etch. Simply clean the surface after try-in and cement to place with a bonding agent and a compatible resin cement.

Feldspathic and synthetic porcelain restorations are glass. The internal surface must be etched with a hydrofluoric acid. A 9% buffered solution is preferred. These restorations are required to be bonded to place with a resin cement system.

Lucite-reinforced core restorations also require acid-etching of the internal surface and need to be bonded to place with a resin cement.

Fluoroapatite glass ceramics have been designed to press over metal or zirconium. However, they may be used as a stand-alone material. If used in this fashion, this material will also be required to be acid-etched and bonded to place with a resin cement.

Lithium disilicates are a higher-strength pressed ceramic and the manufacturers state that they may be conventionally cemented. Therefore, the internal surface needs to be cleaned after try-in before using a conventional cement. With this material there is general agreement that the restoration is stronger if the internal surface is etched regardless of the cement used. Personally, I request my ceramist to etch the internal surface of these restorations in the laboratory.

Alumina-core restorations are a high-strength material. In general, these do not need to be etched and can be confidently cemented using conventional cementation systems.

Zirconia-core restorations are an extremely high-strength material. Etching is not required and generally considered ineffective if tried. These restorations may be ce-mented with conventional cement systems.

Please note that when discussing conventional cements, resin-modified glass ionomers are not included in this category.

Bruce Small, DDS, MAGD

When dealing with indirect composites, the best way to treat the surface is by sandblasting the internal surface using an aluminum-oxide or silica-dioxide powder and then steam cleaning. This should not be done for longer than 15 to 20 seconds to prevent the dissolution of the surface from decreasing marginal adaptation.

In addition, Valandro1 has reported that the use of the CoJet™ or Rocatec™ system (3M ESPE, St. Paul, MN) can also be used with composite and increases the bond strength when compared to acid-etching using a 37% phosphoric acid. The CoJet and Rocatec systems are basically a type of sandblasting using 30-µm to 110-µm size aluminum oxide coated with silica or silicon dioxide. The CoJet can be used intraorally for repair of porcelain fractures while the Rocatec is only used in the laboratory.

For feldspathic and pressed porcelain, it is generally accepted that the internal surface should be etched using 10% hydrofluoric acid for 60 seconds followed by silanization. Lithium-disilicate porcelain needs to be etched with 10% hydrofluoric acid for only 15 to 20 seconds.

High-strength alumina-based ceramics and all-zirconia are extremely dense and will not be affected by any etchant. Current dental literature2-5 and a manufacturer (3M ESPE) recommend that the CoJet or Rocatec systems be used for 15 to 20 seconds to sandblast the internal surface followed by silane treatment. These units coat the internal surfaces of the zirconia with a layer of tribochemical silica, which allows a chemical bond with the silane.

References

1. Valandro LF, Pelogia F, Galhano G, et al. Surface conditioning of a composite used for inlay/onlay restorations: effect on muTBS. J Adhes Dent. 2007;9(6): 495-498.

2. Della Bona A, Borba M, Benetti, Cecchetti D. Effect of surface treatments on the bond strength of a zirconia reinforced ceramic to composite resin. Braz Oral Res. 2007;21(1):10-15.

3. Blatz MB, Chiche G, Holst S, Sadan A. Influence of surface treatment and simulated aging on bond strengths of luting agents to zirconia. Quintessence Int. 2007;38(9);745-753.

4. Bitter K, Paria S, Hartwig C, et al. Shear bond strengths of different substrates to lithium disilicate ceramics. Dent Mater J. 2006;25(3);493-502.

5. Valandro LF, Ozcan M, Bottino MA, et al. Bond strength of a resin cement to high alumina and zirconia reinforced ceramics: the effect of surface conditioning. J Adhes Dent. 2006;8(3):175-181.

About the Authors

David Avery, AAS, CDT
Director of Training and Education
Drake Precision Dental Laboratory
Charlotte, North Carolina

Gary M. Radz, DDS
Associate Clinical Professor
University of Colorado School of Dentistry
Denver, Colorado

Private Practice
Cosmetic Dentistry of Colorado
Denver, Colorado

Bruce W. Small, DMD, MAGD
Private Practice
Lawrenceville, New Jersey


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