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Ask the Experts
DENTIN BONDING
Associate Editor Edward J. Swift Jr., DMD, MS
QUESTION: Is there any evidence that a filled adhesive provides bet- ter clinical performance than an unfilled adhesive?
DR. STEVE ARMSTRONG*: Bond- ing to tooth structure is accom- plished through steps not dissimilar to those followed in any other adhesive procedure (i.e., surface preparation, wetting, and solidifica- tion). The newly formed adhesive resin bond is immediately challenged by the contraction stresses of the polymerizing resin composite, sub- sequent finishing and polishing pro- cedures, and masticatory loading. The reader’s question addresses the desire to optimize the clinical bond to tooth structure. This is an impor- tant question and especially perti- nent when bonding to dentin, a challenging substrate for adhesion.
Several laboratory studies have demonstrated that an elastic inter-
mediary layer between the tooth structure and resin composite can absorb the shrinkage stress of the polymerizing resin composite. This is referred to as the elastic wall concept. In general, filled adhesive resins form thicker layers than unfilled adhesives and, therefore, preserve the adhesive bond to tooth with a greater elastic buffering capacity. Loaded with filler, the adhesive resin is stiffer, which is counter to the desired effect of elas- ticity. However, it also is thicker, resulting in a greater overall strain energy capacity to protect the adhe- sive bond.
In vitro studies have demonstrated higher shear bond strength and reduced dentin marginal leakage with filled adhesives. If adequately loaded, filled adhesive resins have greater strength and stiffness and reduced contraction upon curing -properties that should improve clinical performance. Bear in mind that filler type and amount vary considerably from product to product, so generalizations may not be applicable.
Another potential advantage of filled adhesive resins is radiopacity. Restorations must not be misdiag- nosed as having recurrent caries or marginal defects. Standardized test- ing of several restorative materials, including an unfilled and filled adhesive resin, found that all mate- rials were at least as radiopaque as dentin except for the unfilled adhe- sive resin.
As with many issues in clinical dentistry, the question raised has not been adequately addressed with controlled clinical trials. As previously indicated, a great deal of in vitro evidence points to the advantage of filled adhesives over unfilled adhesives; however, it would be premature to state this as a clinical fact.
A 3-year clinical trial in noncarious cervical lesions found a 93.3% and 89.4% retention rate for a filled and unfilled adhesive, respectively; however, the difference was not sta- tistically significant. Even if a sig- nificant difference could be demon- strated, considerable variation
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exists among manufacturers’ prod- 5
ucts. A proposed research design to adequately address this question would be to restore noncarious cer- vical lesions using a single adhesive system with and without the filler. This type of scientific study has not been traditionally funded federally and lacks manufacturer’s market appeal; don’t hold your breath waiting for the results.
iUGGESTED READING 1. Van Meerbeek B, Willems G, Celis JP,
et al. Assessment by nano-indentation of the hardness and elasticity of the resin- dentin bonding area. J Dent Res 1993; 72:1434-1442.
2. Fortin D, Swift EJ Jr., Denehy GE, Reinhardt JW. Bond strength and micro- leakage of current dentin adhesives. Dent Mater 1994; 10:253-258.
4. Browning WD, Bracken WW, Gilpatrick RO. Two-year clinical comparison of a microfilled and a hybrid resin-based com- posite in noncarious Class V lesions. Oper Dent 2000; 25:46-50.
5. Swift EJ Jr., Perdiggo J, Wilder AD Jr., Heymann HO, Sturdevant JR, Bayne SC. Clinical evaluation of two one-bottle dentin adhesives at three years. J Am Dent Assoc 2001; 132:1117-1123.
3. Bouschlicher MR, Cobb DS, Boyer DB. Radiopacity ofcomPomers, flOwable and conventional resin composites for pos- terior restorations. Oper Dent 1999;
*Assistant Professor, Department o f Opera- tive Dentistry, The University of Iowa, Iowa City, Iowa 0 2002 BC Decker Inc 24:20-25.
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: 919-966-2770; Fax: 919-966-5660 E-mail: [email protected]
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