Bonding Agents
The Dental Advisor dishes on what reps need to know about bonding agents
By John M. Powers, Ph.D. and John W. Farah, D.D.S., Ph.D.
Editor’s Note: At The Dental Advisor, not a day goes by without our phone ringing from a customer asking for the “best.” As a dental publication that was designed after Consumer Reports, over the past 25 years we have learned one thing – the best changes from day to day. Providing relevant and timely information to customers is something we strive for. This series of Tech Talks focus on educating dental sales professionals on the products and technology they are selling so they can in turn educate their customer.
Bonding agents are represented by five distinct generations (4th, 5th, 6th-Type I, 6th-Type II, and 7th). Products range from total-etch (etch-and-rinse) systems that are used with phosphoric acid and require rinsing to self-etch systems that do not use phosphoric acid and do not require rinsing. In addition, light- and dual-cured bonding agents are available for different applications.
Total-etch bonding agents
The total-etch bonding agents were introduced in the 1990s with 4th-generation systems. These systems have components (primer and adhesive) in separate bottles, and these components are applied in separate layers after tooth structure is etched with phosphoric acid. Some products are light-cured and others are dual-cured. The light-cured products typically require four steps, whereas the dual-cured products typically require six steps.
In the mid-1990s, the single-bottle 5th-generation bonding agents were introduced. These systems combined the primer-adhesive monomer in one bottle to make bonding less complicated and quicker. These bonding agents are applied in one or more layers after tooth structure is etched with phosphoric acid. Both light-cured and dual-cured systems are available. The light-cured products typically require three steps, whereas the dual-cured products typically require four steps.
Self-etch bonding agents
The first self-etch bonding agents (6th-generation) were introduced in the 2000s. These systems eliminate the need for etching with phosphoric acid. The 6th-generation, Type I, bonding agents have a self-etching primer and a resin adhesive, which are applied in separate layers. Both light-cured and dual-cured systems are available. The 6th-generation, Type II, bonding agents combine the self-etching primer and adhesive in one component and were intended to simplify the bonding procedure even more. The light-cured 6th-generation, Type I, products typically require two steps, whereas the dual-cured products typically require three steps. The light-cured 6th-generation, Type II, products typically require two steps.
The 7th-generation, self-etching bonding agents were introduced in the mid 2000s. Both light-cured and dual-cured systems are available. The light-cured products typically require one step, whereas the dual-cured products typically require two steps.
Components in bonding agents
Bonding agents are formulated from complex chemicals. Etchants demineralize and clean enamel and dentin. Phosphoric acid, used with the “total-etch” or “etch-and-rinse” technique, removes the smear layer, whereas self-etch primers-adhesives penetrate and re-precipitate the smear layer. Strong acid solutions are mainly based on phosphoric acid (typically 35-37 percent). Self-etching primers are acidic monomers that combine the etchant with the primer or primer-adhesive. Some acidic primers have higher pH than phosphoric acid.
The primer promotes good wetting of enamel and dentin. It is composed of hydrophilic monomers usually carried in a water-soluble solvent (acetone, ethanol, water) to promote good flow and penetration into hydrophilic dentin. Self-etch bonding agents utilize primers that are acidic monomers. The adhesive promotes bonding between enamel or dentin and resin composite restorative material or resin cement. Adhesives are typically dimethacrylate monomers that act as a link between the hydrophilic resin primer and the hydrophobic resin composite. Seventh-generation bonding agents utilize primer-adhesives that are acidic monomers.
The initiator and accelerator promote curing by light- or dual-cured mechanisms. In light-activated products, these components are typically camphorquinone and organic amine. Fillers are sub-micron glass particles and nanofillers ranging from 0.5 percent to 40 percent by weight. Fillers control handling and may improve strength. Fillers may increase film thickness of the adhesive layer.
Solvents include acetone, ethanol and water. One recently introduced product is solvent-free. The solvent affects the evaporation rate. The effectiveness of drying can influence the resulting bond strength and is related to the amount of air applied to the teeth with a three-way syringe. Acetone evaporates quickly and requires the shortest drying time. Ethanol evaporates more slowly and requires moderate drying time. Water evaporates very slowly and requires the longest drying time. Other ingredients include: fluoride, desensitizers, and antimicrobial ingredients. The effectiveness of the release of these ingredients from bonding agents has not yet been demonstrated clinically.
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