Dental bonding agents continue to evolve. Both total-etch (4th- and 5th-generation) and self-etch (6th- and 7th-generation) bonding systems are in use. New bonding systems include self-etching products with dual-cured capabilities as well as simplified total-etch systems.
This issue of THE DENTAL ADVISOR (June 2008, Vol. 25:5) reports the characteristics and compares 65 bonding agents. Clinical tips are given for a number of clinical techniques for restorative procedures requiring bonding. Effects of contamination on bond strengths to dentin are also discussed.
Eugenol-based materials can lower bond strength to dentin.
If a eugenol-based material must be used, pumice the tooth before bonding.
Residual chemicals from hemostatic agents (ferric sulfate, aluminum chloride or other chemicals) can lower bond strength to dentin.
Rinse contaminated areas for at least 10 seconds with water, acid etch or scrub before bonding.
Saliva, Blood and Plasma
Contamination with these fluids can lower bond strength.
Rinse contaminated areas for at least 10 seconds with water before bonding.
Most bonding agents with water solvent bond well to dry or moist dentin.
Avoid over-wet (pooled water) or over-dry (desiccated) dentin before application of the bonding agent.
Residual oxygen from take-home or in-office whitening can lower bond strength.
Wait several days to one week after whitening before a bonding procedure.
Etching with Phosphoric Acid
Most manufacturers of self-etching bonding agents recommend the use of phosphoric acid to etch uncut enamel before application of the self-etching primer or self-etching adhesive. Even so, the improvement in bond strength may not be large. If the phosphoric acid also etches dentin, the bond strength of the self-etching adhesive to dentin may be reduced. This reduction may occur if the self-etching adhesive fails to completely penetrate the additional demineralized dentin produced by the phosphoric acid etch.
Apply extra coat(s) of bonding agent as needed to obtain a shiny surface.
Pumice technique – pumice can be used on uncut enamel before applying the bonding agent to improve bond strength.
Pre-etch technique – apply phosphoric acid to enamel before preparing the tooth. This technique eliminates the need to etch uncut enamel while the dentin is exposed, avoiding possible contamination of dentin with phosphoric acid.
Apply bonding agent to tooth and resin cement to veneer, place veneer and then light cure.
Veneers greater than 1.0-mm thick
Use a two-step, light-curing technique.
Apply bonding agent to tooth and light cure, apply resin cement to veneer, place veneer and then light cure.
Be sure to thin the bonding agent with air before light curing.
Note: Instructions for some resin cements recommend additional application of the bonding agent to the veneer without separate light curing before cementation (3M ESPE RelyX Veneer Cement, 3M ESPE; Variolink Veneer, Ivoclar Vivadent;
Variolink II, Ivoclar Vivadent).
Carefully follow instructions on application time and use of air to thin the adhesive and evaporate the solvent. With less volatile solvents (water, ethanol), more air is needed for evaporation and should be used within three minutes of dispensing. Bonding agents with acetone should be used immediately after dispensing.
Some bonding agents etch the surface of the metal matrix band, making it difficult to remove the band. Scratching the surface of the metal band with a spoon excavator after bonding but before placement of the composite is helpful.
Re-emergence of 4th- and 5th-generation bonding agents Total-etch (etch and rinse) bonding agents that use phosphoric acid have a long, successful record and considered particularly desirable for anterior restorations. New 4th-generation systems (ALL-BOND 3) are easier to use than previous systems.
Light-cured 7th-generation bonding agents are not
compatible with dual- and self-cured composite cores and resin cements. The dual-cured 7th-generation bonding agents (Clearfil DC BOND, Futurabond DC, Xeno IV DC) solve this problem.