20 Tips on Bonding
Things You Might—or Might Not—Know
Edward J. Swift Jr., DMD, MS

Buonocore introduced the acid-etch technique for bonding resin-based materials to enamel in 1955.1 It took nearly a quarter-century for this technique to be widely accepted and another 10 years before predictable dentin bonding became a reality.

We have learned much about enamel and dentin bonding over the years, but it is easy to be overwhelmed by the sheer volume of information available on this topic. For example, a recent Medline search revealed that more than 6,500 papers have been published on dentin bonding alone. This brief article summarizes some of what you already know, and perhaps a little of what you don’t already know, about bonding.
  1. One of the difficulties with dentin bonding is the inherently complex composition and structure of dentin itself—and adhesion to sclerotic or caries-affected dentin is more difficult than bonding to normal dentin.
  2. Adequate light activation is required to optimize bond strengths of any adhesive. Consider a longer exposure time if the distance between the light guide and the bonded interface is more than 2 to 4 mm (e.g., in a Class II preparation).
  3. Bonds of etch-and-rinse adhesives to dentin are more durable when the resin-dentin interface is surrounded by a rim of etched and bonded enamel.
  4. Many etch-and-rinse systems rely on a moist bonding technique for optimal dentin bonding. This is particularly true for systems that have an acetone solvent, less so for those containing ethanol, and even less so for those that contain water.
  5. Avoid extended etching times on dentin when using etch-and-rinse adhesives. Over-etching can demineralize dentin to a greater than desired depth, making penetration of the resin primer and bonding agent more difficult. Collagen left uncoated by resin provides a potential location for bond degradation.
  6. Isolation is important; contamination of tooth surfaces with saliva or blood during bonding procedures reduces adhesion of the resin.
  7. Chlorhexidine inhibits a class of intrinsic dentinal enzymes that are released by etching and can cause degradation of the hybrid layer, so it can improve the durability of the resin-dentin bond formed by an etch-and-rinse adhesive.
  8. The use of a glass ionomer liner, especially in deeper dentin, can reduce postoperative sensitivity with etch-and-rinse adhesives.
  9. Re-wetting agents containing glutaraldehyde and hydroxyethylmethacrylate (HEMA) stabilize the hybrid layer formed by etch-and-rinse adhesives and help to reduce postoperative sensitivity.
  10. Self-cure and dual-cure composite should not be used with some light-cured adhesives because of chemical incompatibilities related to pH of the adhesive.
  11. Despite much anecdotal evidence that self-etch systems have less postoperative sensitivity than etch-and-rinse systems, this has never been verified in clinical trials. The incidence of postoperative sensitivity is small if either type of system is used properly.
  12. Although the bond of resin to tooth structure is primarily mechanical, one monomer present in some mildly acidic self-etch primer systems provides a chemical bond to hydroxyapatite. This improves the durability of the resin bond.
  13. Roughening enamel improves adhesion of self-etch systems.
  14. Selective etching of enamel margins improves the bond of self-etch systems, but contact of the etchant with dentin should be avoided because it reduces dentin bond strengths for most (not all) self-etch materials.
  15. Agitation of most self-etch primers and self-etch adhesives improves their bond strengths.
  16. Coating an all-in-one self-etch adhesive with a layer of hydrophobic bonding resin can improve its dentin bond strengths and clinical performance. (Of course, by adding this extra layer, you have converted the self-etch adhesive into a self-etch primer!).
  17. A technique called immediate dentin sealing has been introduced for use with bonded indirect restorations. It reduces sensitivity during the provisional phase and has been shown to provide excellent bond strengths.
  18. Bond strength tests are a useful tool for evaluating dental adhesives and they provide reasonable information about the likely clinical performance of a material. Materials that achieve high bond strengths in independent testing by multiple investigators are more likely to perform well clinically than materials that achieve low bond strengths under the same conditions. That said, a high average bond strength in the laboratory is not necessarily a guarantee of excellent clinical performance, nor does it make a particular adhesive the best choice for a particular clinical indication.
  19. Newer does not necessarily mean better. Based on their clinical performance, the so-called fourth-generation materials (three-step etch-and-rinse) are better than the so-called seventh-generation materials (all-in-one self-etch).
  20. Fortunately, the all-in-one self-etch materials are getting better.

Reference: Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res. 1955;34:849-53.
First published in the Journal of Cosmetic Dentistry