J O U R N A L OF ESTHETIC DENTISTRY

Ask the Experts

ENAMEL AND DENTIN BONDING

Associate Editor Edward J. Swift Jr., DMD, MS

DR. BERTHA BARRIGA, Seattle.

Washington: With today’s adhesives, it is recommended to leave the dentin moist after etching. In leaving the dentin moist, the adjacent enamel is also moist. Is this a problem?

DR. POONAM JAIN‘: This is an excellent question. Yes, leaving enamel moist could be a major problem, especially if you are using a multicomponent bonding system (i.e., primer and adhesive resin in separate bottles). Of course, in clin- ical situations, where enamel and dentin are juxtaposed, it is difficult to treat each substrate differently. It is impractical to leave dentin glisteningly moist and, at the same time, completely dry the enamel next to it. Composite resin does not bond well to moist enamel. Jain et al obtained low (3-8 MPa) bond strengths between moist enamel and 2-100 composite resin, using two different adhesive resins. However, they also reported bond strengths of 25 to 30 MPa when

the dentin primer of each system was applied to moist enamel before application o f the bonding resin. These results are logical, as the hydrophilic primer would act as a link between moist enamel and the hydrophobic adhesive resin.

Clinicians using single-bottle bonding agents (i.e., primer and adhesive combined in one bottle) should not have to worry about leaving enamel moist. The single- bottle systems ensure the applica- tion of hydrophilic primer resins to enamel. Bond strengths of com- posite resin to enamel do not seem to be affected by moisture if these single-component systems are being used.

Therefore, when restoring a prepa- ration with enamel and dentin juxtaposed, the entire preparation may be left moist. Simply apply dentin primer on enamel as well as dentin, or use a single-component bonding agent.

SUGGESTED READlNG I. Kanca J Ill. Resin bonding to wet sub-

strate. II. Bonding to enamel. Quintessence Int 1992; 23:625-627.

2. Wakefield CW, Sneed WD, Draughn RA, Davis TN. Composite bonding to dentin and enamel: effect of humidity. Cen Dent 1996; 44508-5 12.

3. Barghi N, Knight CT. Berry TC. Compar- ing two methods of moisture control in bonding to enamel: a clinical study. Oper Dent 1999; 16:130-135.

4. Hayakawa T. Horie K. Effect of water- soluble photoinitiator on the adhesion between composite and tooth substrate. Dent Mater 1992; 8:351-353.

5. Jain P, Stewart CP. Effect of dentin primer on shear bond strength of composite resin to moist and dry enamel. Oper Dent 2000; 25:.51-58.

“Assistant Professor, Department of Restorative Dentistry, School of Dental Medicine, Southern Illinois Uniwrsity. Alton. Illinois

DR. RICHARD TRUSHKOWSKY, Staten Island, New York: Some research suggests that formation of a hybrid layer in the etched dentin surface is not necessary for good rcsin-dentin bonding. Would there be any clini- cal benefit in removing exposed

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collagen from the dentin surface after acid-etching?

DR. ROLAND FRANKENBERGER.: Dentin bonding using the total-etch technique is a common and clinically recommended procedure. Total-etch adhesive systems are based on the penetration of ambiphilic molecules into acid-demineralized dentin. High vapor-pressure solvents, such as ethanol or acetone, enable resin monomer penetration of dentin, resulting in formation of a hybrid layer, or a mixed zone of resin and decalcified dentin.

Such adhesive systems have pro- duced high bond strengths in numerous investigations. However, infiltration of the demineralized dentin surface is tremendously sensitive to desiccation or imprecise application of bonding agents. As a result, incomplete infiltration of the collagen network and poor adhesion can occur. Therefore, some authors have suggested the use of 5% sodium hypochlorite (NaOCl) to remove collagen after etching. Eliminating the collagen- rich zone produces a rough surface with widely opened, funnel-shaped dentinal tubules. Some studies of shear bond strengths to dentin with and without hybrid layer have shown better results when the colla- gen was removed prior to bonding.

However, such results might reflect the increased cohesive strength of the resin tags, which are larger in diameter when NaOCl is used after etching. A study of tensile bond strength by Pioch et a1 demonstrated no differences between bonding with and without a resin-collagen hybrid layer.

A major problem of shear and ten- sile tests, in which resin composites are debonded from flattened sur- faces, is that polymerization shrink- age has essentially no influence on the results. The resin can shrink toward the interface without being stressed. The effect of a hybrid layer as an assumed intermediate elastic zone can be determined only when shrinkage of the resin is suffi- ciently considered. Some studies use cavity simulation tests (in vitro and in vivo) to include the effects of polymerization shrinkage stress. These report that removing the col- lagen, and thus preventing hybrid layer formation, generally produces inferior results in dentin bonding.

A recent study from our laboratory confirms these findings. In evaluat- ing simulated cavities with "push- out" bond strength and marginal adaptation, all investigated total- etch adhesive systems had lower bond strengths and fewer gap-free margins when the dentin was treated

with NaOCl for 60 seconds after etching for 15 seconds.

Perdig50 and Lopes recently dis- cussed an interesting aspect of the use of NaOCl on etched dentin. A commercially available NaOCl gel does not fully eliminate collagen and leaves a certain amount of col- lagen fibers on the dentin surface. Perhaps with fluid solutions like those used in our recent study, this will not occur; however, this has not been investigated thoroughly.

In conclusion, based on the results of recent studies, treatment of dentin with sodium hypochlorite after etching cannot be recommended.

SUGGESTED READING 1. Inai N, Kanemura N, Tagami J, Watanabe

L, Marshall SJ, Marshall GW. Adhesion between collagen-depleted dentin and dentin adhesives. Am J Dent 1998; 11:123-127.

2. Vargas MA, Cobb DS, Armstrong SR. Resindentin shear bond strength and interfacial ultrastructure with and without a hybrid layer. Oper Dent 1997; 22:159-166.

3. Uno S, Finger WJ. Function of the hybrid zone as a scress-absorbing layer in resin- dentin bonding. Oper Dent 1996; 2 1 :733-738.

4. Pioch T, Kobaslija S, Schagen B, Gotz H. Interfacial micromorphology and tensile bond strength of dentin bonding systems after NaOCl treatment. J Adhes Dent 1999; 1 :13S-142.

5. Vichi A, Ferrari M, Davidson CL. In vivo leakage of an adhesive system with and without NaOCl as pretreatment. J Dent Res 1997; 76:398. (Abstr)

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A S K THE E X P E R T S

6. Frankenberger R, Kramer N, Oberschacht- 7. PerdigPo J, Lopes M. Dentin bonding: siek H, Petschelt A. Dentin bond strength and marginal adaptation after NaOCl pre- treatment. Oper Dent 1999; 24:40-45.

questions for the new millennium. J Adhes Dent 1999; 1:191-209.

‘Assistant Professor, Department of Opera- tive Dentistry and Periodontology, Dental School, University of Erlangen-Nuremberg, Erlangen, Germany 02000 B.C. Decker Inc.

Editor’s Note: If you have a question on any aspect of esthetic dentistry, please direct it to the Associate Editor, Edward J. Swift Jr., DMD, MS. We will forward questions to appropriate experts and print the answers in this regular feature. Ask the Experts Edward J. Swift Jr., DMD, MS Department of Operative Dentistry University of North Carolina, CB#7450, Brauer Hall Chapel Hill, NC 27599-7450 Telephone: 919-966-2773; Fax: 91 9-966-5660 E-mail: Ed-Swift@dentistry.unc.edu

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