Stability of wet versus dry bonding with different solvent-based adhesives.

OBJECTIVE: To evaluate the effects of surface moisture (wet or dry) and storage (24h or 3 months) on the microtensile bond strength (BS) of resin/dentin bonds mediated by two water/ethanol based adhesives Single Bond, 3M-ESPE, (SB) and Opti Bond Solo Plus, Kerr, (OB), and two acetone-based adhesives, One Step, Bisco, (OS) and Prime&Bond NT, Caulk/Dentsply, (PB). MATERIALS AND METHODS: Flat dentin surfaces were polished with 600-grit SiC paper, etched with 35% phosphoric acid for 15s and rinsed for 20s. Half the surface was maintained moist and the other half was air-dried for 30s. Each adhesive was applied simultaneously to both halves, left undisturbed for 30s and light-cured. Four-mm resin build-ups were constructed incrementally. After storage in water at 37 degrees C for 24h, slabs were produced by transversal sectioning and trimmed to an hourglass shape (0.8mm2). Half of the specimens were tested in tension at 0.6mm/min immediately after trimming and the other half after 3 months of water storage. Data were analyzed by two-way ANOVA and SNK for each material. RESULTS: Both moisture and storage affected BS to dentin, and was material-dependent. Dry bonding affected mostly the acetone-based adhesives. Larger reductions in bond strength were associated with dry bonding after 3 months of water storage. SIGNIFICANCE: Wet bonding resulted in more stable bonds over 3 months of water storage for most of the materials tested.

Adhesive-composite incompatibility, part II.

Apart from some questions related to the repairability of resin composite restorations, dentists have always assumed that methacrylate-based resins are compatible with each other. For example, there is no clinically relevant problem in using a microfilled composite to laminate a Class IV restoration made with a hybrid composite, even if they are not of the same brand or manufacturer. In the context of adhesive systems, we have always believed that resin composites, regardless of their type or composition, bond well to all types of bonding agents. However, unexpected debonding of self-cured, core buildup composites that had been bonded with single-bottle adhesive systems was reported about 5 years ago. Subsequent studies demonstrated that there were, indeed, compatibility problems between simplified adhesive systems and self- or dual-cured resin composites. Apparently, when such combinations are used, reduced bond strengths and subsequent failures at the resin-adhesive interface can occur because of adverse reactions between the acidic resin monomers, an integral part of the simplified adhesive systems, and the chemicals involved in the polymerization mechanism of the self- or dual-cured composites, particularly the basic tertiary amines.

Critical appraisal: adhesive-composite incompatibility, part I.

Apart from some questions related to the repairability of resin composite restorations, dentists have always assumed that methacrylate-based resins are compatible with each other. For example, there is no clinically relevant problem in using a microfilled composite to laminate a Class IV restoration made with a hybrid composite, even if they are not of the same brand or manufacturer. In the context of adhesive systems, we have always believed that resin composites, regardless of their type or composition, bond well to all types of bonding agents. However, unexpected debonding of self-cured, core buildup composites that had been bonded with single-bottle adhesive systems was reported about 5 years ago. Subsequent studies demonstrated that there were, indeed, compatibility problems between simplified adhesive systems and self- or dual-cured resin composites. Apparently, when such combinations are used, reduced bond strengths and subsequent failures at the resin-adhesive interface can occur because of adverse reactions between the acidic resin monomers, an integral part of the simplified adhesive systems, and the chemicals involved in the polymerization mechanism of the self- or dual-cured composites, particularly the basic tertiary amines. At least one research group has expanded the information on this issue by further investigating the mechanisms involved in this phenomenon. This group demonstrated that not only adverse chemical reactions but also the permeability of such simplified systems contribute to the compromised bonding. This issue has profound clinical implications in view of the wide use of self- and dual-cured composites as core buildup materials and in the bonding of indirect restorations and endodontic posts. Some of the most representative studies of this group are described in this Critical Appraisal. Part II will appear in the next issue of the Journal.