Dental Adhesives: A Review and Case Report
John O. Burgess, DDS, MS; and Deniz Cakir, DDS, MS
The newest dental adhesives have fewer components and fewer steps. Older total-etch adhesives are generally classified into two-bottle (primer and adhesive separated) and one-bottle (primer and adhesive combined) systems. More recently, two-bottle, self-etching adhesives that eliminate the phosphoric acid-etch and rinse step have evolved, and the most recent development for self-etching adhesives is the single-bottle system that etches, primes, and binds in one bottle and one step.
It would seem that simplified bonding agents would lead to improved bond strengths and better clinical efficiency. However, a recent study reported that simplified systems do not produce improved results compared to older total-etch, two-bottle bonding agents in inexperienced and experienced operators.1
Bonding to dentin and enamel is essential in adhesive restorative dentistry, and questions remain about the newest single-bottle, self-etching systems. In single-bottle systems, the acid used to etch enamel and dentin in the total-etch technique is incorporated in a single-component system. It is more difficult for self-etching adhesives to remove or partially dissolve the smear layer than it is for phosphoric acid-etching systems. Tay et al investigated the effect of smear layer thickness prepared with 60-, 180- and 600-grit SiC paper and showed that the bond strength was significantly lower in the thickest smear layer group (60-grit).2
Self-etching adhesive systems use two basic methods to aid in the removal of the smear layer. One method, such as in the Adper™ Prompt™ L-Pop™ (3M ESPE, St. Paul, MN) system, is to decrease the pH of the self-etching system. In other systems, such as Clearfil® SE Bond (Kuraray America, Inc, New York, NY), agitation or scrubbing the self-etching com-ponent is accomplished during its applica-tion. Mechanical agitation helps to remove the smear layer, allowing the adhesive to coat the exposed collagen fibers and also to create a thicker hybrid layer.3
In part, the durability of the bond produced by single-component, self-etching systems is decreased by the hydrophilic components in the bonding agent that remain in the tooth. When single-bottle, self-etching bonding agents are polymerized, water is trapped in the hybrid layer, and slowly evaporates.4 Bubbles representing water evaporated from the bonding agent and from water in the tubules slowly coalesce, making the hybrid layer permeable.5 Fluid from the dentin tubules moves through the permeable, cured hybrid layer, forming water channels. Drying the self-etching bonding agent after it is applied to dentin for longer times appears to reduce the residual water in the hybrid layer and helps to preserve the bond strength of the bonding agent.6,7 Residual water retained in the bonding agent causes three things: it inhibits polymerization of the bonding agent; it produces water channels (essentially increasing porosity); and it softens the resin.8 Water absorption plasticizes polymers and lowers their mechanical properties.9 As a result, the adhesive weakens with time and reduces bond strengths. When bonded specimens were thermocycled and load cycled, total-etch, two-step, self-etch adhesives showed better marginal adaptation to dentin than all-in-one, self-etching bonding agents.10
Other studies11,12 have measured the reduced polymerization of the adhesive because of water-inhibiting effects and have evaluated methods to improve the polymerization of the adhesive. Because poorly cured adhesives are weaker and have greater permeability, increasing curing time to gain additional polymerization of the adhesive may improve its du-rability. Simplified adhesives—especially one-bottle bonding agents—cure less, even when the cure time is increased to 60 seconds. These studies demonstrate that additional curing of the adhesive layer is required especially when the curing light tip is some distance away from the surface being polymerized, such as the gingival margin. Increasing the curing time makes adhesives less permeable and more durable.
In an attempt to seal and make the bonding layer less permeable, additional coats of the bonding agent were applied.13 Ito et al applied a single coat or up to five coats of iBond™ (Heraeus Kulzer, Armonk, NY) or Xeno® III (DENTSPLY International, York, PA) to dentin, drying each coat separately. Applying additional coats of single-bottle adhesives improved bond strength. The best bonds were recorded with three layers. Therefore, application of additional coats of the bonding agent, thorough air drying of the adhesive, agitation during application, and adequate light-curing are essential steps when applying a bonding agent. It was recently demonstrated that water trees form and that bonds degrade in vivo with self-etching adhesives. Bond degradation seems to occur by the same mechanisms in vivo and in vitro.14
A highly recommended review of adhesives was written by De Munck et al.15 Interested clinicians or investigators should make this mandatory reading. Their review reports that total-etch, two-bottle, and two-step (primer bottle and resin bottle that are applied separately and cured) bonding systems are the most durable of all adhesives. One clinical study reported 3-year retention rates of total-etch, one-bottle bonding agents (fifth generation) of 88%.16 Gallo et al17 reported less marginal leakage clinically at a 2-year recall with a fourth-generation (total-etch, prime, and bond) adhesive compared to a fifth-generation system (total-etch, prime, and bond in one bottle) in class II restorations.
Clinical studies evaluating the total-etch, single-bottle (fifth generation) adhesives One Coat® Bond (Coltène/ Whaledent Inc, Cuyahoga Falls, OH) and Adper™ Single Bond (3M ESPE) have reported a 94% retention rate at 1 year18 and Single Bond a 90% retention rate at 3 years.19 The importance of moist and dry dentin on the clinical performance of two total-etch, single-bottle adhesives (fifth generation) bonding agents at a 18-month recall has also been studied.20 The effectiveness of the bonding agent seemed to depend upon its solvent. Single Bond (an ethanol- and water-containing material) exhibited an 89% retention rate when bonded to dry dentin, and a 100% retention rate when bonded to wet dentin. Prime and Bond® NT™ (DENTSPLY Caulk, Milford, DE) had a 94% retention rate to dry dentin and a 92% retention rate to moist dentin. However, and perhaps most importantly, moist dentin produced less sensitive restorations with both adhesives. Self-etching bonding agents have shown less success,21 with one study reporting retention rates of 56% at 18 months.
A Swedish study22 reported an 18-month evaluation of Adper Prompt, a self-etch, single-application adhesive, and Single Bond (a total-etch, single-bottle adhesive). A microfilled composite resin (Filtek™ A 110, 3M ESPE) was applied to all prepared noncarious cervical lesions. At 18 months, Adper Prompt retention rates were 93%, 30% had marginal discoloration, and 30% had marginal breakdown. Single Bond bonded restorations were 100% retained, 10% had marginal discoloration, and 13% had marginal breakdown.
This article describes the proper placement of a self-etching, single-bottle adhesive (Futurabond NR, VOCO America Inc, Sunnyside, NY) used to bond a class II composite resin restoration. The techniques used are designed to improve its clinical performance.
The tooth to be restored had a small carious lesion on the mesial surface. The tooth was in occlusion and the proximal surface was in contact with tooth No. 13. The cavity preparation was prepared for the restoration after rubber dam isolation (Figure 1). The cavity preparation was made using 330 burs (Brasseler USA, Savannah, GA) with a high-speed handpiece (Figure 2). All prepared margins were placed 90° to the external tooth surface; no bevels were placed on any surface. Because the cavity preparation was estimated to be more than 1 mm of the pulp clinically, no liner was used. The matrix used was Composi-Tight (Garrison Dental Solutions, Spring Lake, MI) sectional matrix (Figure 3). The restoration was bonded with a new self-etching bonding agent (Futurabond). The self-etching adhesive was applied to the tooth with a scrubbing motion for 10 seconds (Figure 4). The adhesive was dried by moving the air syringe from its initial position about 6 inches away from the tooth to its final position almost touching the tooth. In this manner the solvent is removed without displacing the resin monomer that is necessary for coating the tooth. The adhesive was light-cured for 10 seconds (Figure 5) with a G Light (GC America Inc, Alsip, IL). This curing light had an output of 1,024 mW/cm2.
The composite (Grandio® Flow, VOCO America Inc) was placed in increments beginning with the gingival increment and proceeding until the restoration was complete (Figure 6). Increments were placed in heights no more than 2 mm. After the restoration was completed, the matrix was removed and carbide finishing burs were used to remove the excess composite (Figure 7). These burs were followed by Cosmodent (Cosmodent, Chicago, IL) discs to develop the occlusal embrasure (Figure 8), followed by finishing strips and disks (Sof-Lex™, 3M ESPE), and the Enhance® system (DENTSPLY Caulk). All polishing was done at slow speed without water spray (Figure 9). After removing the rubber dam and adjusting the occlusion, a surface sealer was applied and cured for 20 seconds (Figure 10).
Dr. Burgess has received grant/research support from 3M ESPE, DENTSPLY Caulk, GC America Inc, and VOCO America Inc.
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|Figure 1 The tooth is properly isolated.||Figure 2 The tooth is prepared for a posterior composite resin restoration.|
|Figure 3 A sectional matrix is applied.||Figure 4 Futurabond is applied with a scrubbing motion and the adhesive is dried until nothing moves. The resulting surface should be shiny.|
|Figure 5 Light-curing of the bonding agent. Curing time depends on the distance of the light from the surface being cured.||Figure 6 Incremental placement of the composite resin.|
|Figure 7 The matrix is removed, and the restoration is ready for finishing.||Figure 8 The occlusal embrasure is established.|
|Figure 9 The restoration is finished and polished.||Figure 10 The final restoration.|
|About the Authors|
John O. Burgess, DDS, MS
Assistant Dean for Clinical Research
University of Alabama at Birmingham
School of Dentistry
Deniz Cakir, DDS, MS
Department of Prosthodontics and Biomaterials
University of Alabama at Birmingham
School of Dentistry