Most contemporary dental adhesives show favorable immediate results in terms of bonding effectiveness. However, their durability has been discussed widely. Bond or adhesive failures can be directly related to properties of the adhesive itself or factors affecting the process of adhesion.
Different adhesives have different recommended directions. Some adhesives require you to shake the bottle before dispensing. Usually, these adhesives have a mix of fillers that do not disperse well with the rest of the monomers (Figure 1), so proper shaking before the application is a very important step. Failing to do so properly may compromise the bond.
|Figure 1. Two commercially available adhesives were stored at 25°C for a week. Afterward, it can be clearly seen that adhesive B had sediment in the bottle.|
|Figure 2. Some adhesives may require shaking, rubbing, and the application of multiple coats.|
Some recent universal adhesives require you to rub the tooth surface—sometimes for as long as 20 seconds (Figure 2). If dentists fail to rub as long as recommended, it can lead to a compromised bond. Adhesives that are using MDP-Amide rapid bond technology were developed to address this clinical challenge, and they can be applied without a waiting time or a long rubbing time.
Certain adhesives require the application of multiple coats. Failing to do so can cause a compromised bond. Also, recent universal adhesives can be used with an etch-and-rinse technique. Longer exposure of phosphoric acid on dentin can cause collagen denaturation and increase the demineralization depth, which can negatively affect the subsequent dentin-hybridization process.
Achieving an appropriate degree of wetness that is good for bonding can be challenging and subjective. Overly wet dentin affects the quality of adhesion due to the difficulty presented by bonding anything to a wet surface; however, overdrying dentin also inhibits adhesion. Recent adhesives, like CLEARFIL Universal Bond (Kuraray America), have different properties and will cure fast and strong (with cross-linking), thereby forming durable layers. This reduces the scenario of one-bottle adhesives working as a semipermeable membrane for water transmission or so-called water tree formation.
There are numerous studies showing 10-MDP as a key monomer for durable dentin adhesion. This monomer can form a strong, stable chemical bond with hydroxyapatite in enamel and dentin. When amide monomer technology is combined with 10-MDP in CLEARFIL Universal Bond, it can be applied without a waiting time and hydrophilic monomers will get polymerized in a strong hydrophobic polymer, thus reducing the chance of degradation.
Achieving a durable restoration depends on adhesive factors, patient factors, and the dentist/user. Patient factors and dentist factors can vary and are difficult to predict, but adhesive factors can be fine-tuned for a durable restoration by using a well-designed adhesive with a strong adhesive technology.
For more information, call Kuraray America at (800) 879-1676 or visit kuraraydental.com.