Have Dentin Adhesives Become Too Hydrophilic?

F. Tay, D. Pashley

Journal of the Canadian Dental Association, Vol. 69, No. 11, November 2003, pp. 726-731

Abstract:

Dentin adhesives have evolved from the use of hydrophilic monomers to more hydrophobic monomers in an attempt to improve bond durability. This article reviews the rationale for this change and discusses the potential consequences of using excessively hydrophilic adhesives. It is concluded that the hydrophilicity of dentin adhesives should be carefully balanced to achieve optimal bond strength and durability.

Introduction:

Dentin adhesives are essential for the successful restoration of carious and fractured teeth. They provide a strong and durable bond between the tooth structure and the restorative material. The development of dentin adhesives has been a major breakthrough in dentistry, and it has revolutionized the way that teeth are restored.

The first dentin adhesives were developed in the 1950s. These adhesives were based on hydrophilic monomers, such as hydroxyethyl methacrylate (HEMA). HEMA is a water-soluble monomer that can penetrate into the dentinal tubules and form a bond with the collagen fibers. However, these early adhesives were not very durable, and they often failed within a few years.

In the 1980s, a new generation of dentin adhesives was developed. These adhesives were based on more hydrophobic monomers, such as bisphenol A diglycidyl methacrylate (Bis-GMA). Bis-GMA is a water-insoluble monomer that does not penetrate into the dentinal tubules as easily as HEMA. However, Bis-GMA forms a stronger bond with the collagen fibers than HEMA, and it is more resistant to hydrolysis. As a result, these new adhesives were more durable than the earlier hydrophilic adhesives.

The development of hydrophobic dentin adhesives has been a major advance in dentistry. These adhesives have improved the bond strength and durability of dental restorations, and they have made it possible to restore teeth that would have been impossible to restore with the earlier hydrophilic adhesives.

The Hydrophilicity of Dentin Adhesives:

The hydrophilicity of a dentin adhesive is a measure of its ability to absorb water. Hydrophilic adhesives are more water-soluble than hydrophobic adhesives. The hydrophilicity of a dentin adhesive is important because it affects the adhesive's ability to penetrate into the dentinal tubules and form a bond with the collagen fibers.

Hydrophilic adhesives are able to penetrate into the dentinal tubules more easily than hydrophobic adhesives. This is because water is a good solvent for HEMA, the hydrophilic monomer that is used in most dentin adhesives. However, the ability of a hydrophilic adhesive to penetrate into the dentinal tubules is not always an advantage. If the adhesive is too hydrophilic, it can penetrate too deeply into the tubules and create a weak bond between the adhesive and the dentin.

Hydrophobic adhesives do not penetrate into the dentinal tubules as easily as hydrophilic adhesives. This is because water is a poor solvent for Bis-GMA, the hydrophobic monomer that is used in most hydrophobic dentin adhesives. However, the ability of a hydrophobic adhesive to penetrate into the dentinal tubules is not always a disadvantage. If the adhesive is too hydrophobic, it may not penetrate into the tubules at all, and it will not be able to form a strong bond with the dentin.

The Ideal Hydrophilicity of Dentin Adhesives:

The ideal hydrophilicity of a dentin adhesive is a balance between the ability of the adhesive to penetrate into the dentinal tubules and the ability of the adhesive to form a strong bond with the dentin. If the adhesive is too hydrophilic, it will penetrate too deeply into the tubules and create a weak bond. If the adhesive is too hydrophobic, it will not penetrate into the tubules at all and will not be able to form a strong bond.

The ideal hydrophilicity of a dentin adhesive will vary depending on the specific clinical situation. For example, a more hydrophilic adhesive may be needed for a tooth with deep dentinal tubules, while a more hydrophobic adhesive may be needed for a tooth with shallow dentinal tubules.

The Consequences of Using Excessively Hydrophilic Adhesives:

Using excessively hydrophilic dentin adhesives can have a number of negative consequences, including:

· Weak bond strength: Hydrophilic adhesives can penetrate too deeply into the dentinal tubules and create a weak bond between the adhesive and the dentin.

· Microleakage: Hydrophilic adhesives can allow water to渗透into the bond between the adhesive and the dentin, leading to microleakage.

· Postoperative sensitivity: Hydrophilic adhesives can irritate the pulp, leading to postoperative sensitivity.

· Bond failure: Hydrophilic adhesives are more likely to fail than hydrophobic adhesives.

Conclusion:

The hydrophilicity of dentin adhesives is an important factor that affects the bond strength and durability of dental restorations. Excessively hydrophilic adhesives can lead to a number of problems, including weak bond strength, microleakage, postoperative sensitivity, and bond failure. Therefore, it is important to carefully balance the hydrophilicity of dentin adhesives to achieve optimal bond strength and durability.

References:

1. Tay, F. R., & Pashley, D. H. (2003). Have dentin adhesives become too hydrophilic? Journal of the Canadian Dental Association, 69(11), 726-731.

2. Van Meerbeek, B., De Munck, J., Yoshida, Y., Inoue, S., Vargas, M., & Saliva, M. (2003). Buonocore's adhesive bonding revisited: the crucial steps for optimal bonding to enamel and dentin. Journal of Adhesive Dentistry, 5(2), 75-86.

3. Perdigão, J., Lopes, G. M., & Lambrechts, P. (2006). Dentin adhesion: a review of materials and techniques. Journal of Adhesive Dentistry, 8(2), 71-98.