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Dentin-Resin Bonding
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Question #1: I was told by a manufacturer to use my dentin bonding agent on etched enamel too. Is it better than the old unfilled resin enamel bond?

Answer: Probably not. Resins used for dentin bonding are hydrophilic and generally have more air inhibition than enamel bonding materials.
Although being hydrophilic is helpful in dentin bonding, these materials are not as color stable toward water soluble stains as the more hydrophobic unfilled resin enamel bonding agents. However, this does not seem to be a problem clinically.
Increased air inhibition prevents the initial bond from forming prior to composite polymerization contraction. This can increase the contraction gap.
Conventional unfilled enamel bonding agents with the same resin matrix as the composite, are the safest for bonding composite to etched enamel. However, they are rarely used anymore in favor of materials than bond to dentin.

Question #2: Can the adhesive with the dentin bonding agents be used to reseal the margins as you discussed?
Answer: Usually not. Most are not very durable for surface use. The conventional unfilled and fuild filled resins, now called glazes and filled sealants, are better suited for rebonding and surface coating applications.

Question #3: Are composite resins placed with dentin bonding agents better than glass ionomers for my older patients who have numerous Class V erosions? My major concern is longevity.

Answer: With mature patients most Class V erosions are not in highly esthetic areas and longevity is a primary criterion.
Unfortunately, we do not know enough about the long term clinical effects of newer dentin–resin bonding systems to compare. With the information presently available, most knowledgeable authorities agree that if longevity is the primary concern, glass ionomers have a more established track record of retention and preventing recurrent decay. Resins stain more at the gingival margins and are less retentive to dentin over time.

Question #4: If I bond only to etched enamel, always line my dentinal margins with glass ionomer and use mechanical retention, do I need to use a dentin–resin bonding agent?

Answer: Probably not. Dentin–resin bonding agents are not essential. They are alternatives for occasional use on Class Vs and for bonding veneers and cast metal restorations to dentin.

Question #5: I have not had much success with a dentin–resin bonding to erosions. My composites have been falling off. What am I doing wrong?

Answer: First reread the directions. Most of these systems are technique sensitive. A few steps will improve results with most of these materials.
1) With secrolic dentin roughen the surface and provide mechanical undercuts alone the gingival margin.
2) When applying primers continually replenish the surface to improve penetration into the dentin and to allow the primer to wash away surface debris.
3) Thoroughly dry the dentin primed surface before adding the resin adhesive. Primers usually contain water or alcohol which in excess reduces bonding. Primers increase adhesive penetration and should not be used in place of adhesives.
4) Overly–thin adhesive (or unfilled resin) increases air inhibition and prevents the resin from fully curing.
5) Cure the bonding agent before placing the composite to reduce the likelihood of polymerization shrinkage pulling the composite from the dentin before a bond can be formed.
6) The first layer of composite should be placed in a very thin layer.
7) Check the occlusion for fremitus since tooth flexure can dislodge cervical restorations.

Question #6: Which is the better restoration, a Class V glass-ionomer or a Class V composite resin bonded with a dentin–resin bonding agent?

Answer: That depends on your criteria. Glass ionomers have fewer placement steps and have demonstrated long–term retention. Composite resins are smoother and more resistant to stains and abrasion, although a well placed glass ionomer can be virtually invisible.
Glass ionomers have established long term clinical success. This may be partly because glass ionomers, unlike composite resins, expand and contract to hot and cold similarly to natural tooth. This reduces stress at the bonded interface from the normal hot and cold cycling which occurs in the mouth.

Question #7: I'm confused. What do all the bonding numbers mean and how much is necessary for clinical success?

Answer: The bond strength of resin to etched enamel is about 2000–3000 PSI. We know that this is adequate for bonding resin to enamel. Some studies have shown that high bond strengths are associated with reduced contraction gaps and microleakage. The problem with dentin bonding agents is that unlike enamel bonding, bond values decrease over time. Thus the stability of the bond is as important as the strength of that bond. Unfortunately, laboratory studies do not mimic clinical performance in this regard since intraoral conditions are not reproducable in the dental laboratory.
Only clinical studies can confirm the success of dentin bonding materials. Unfortunately, these take years to complete and most do not compare competitive products. In addition, most of these are funded by the product manufacturers which occasionally, but not usually, can influence the results. Because of these concerns only long term clinical success by practicing dentists will demonstrate the usefulness of these materials.

Question #8: One manufacturer claimed that their dentin bonding agent was better because it sealed best to the tooth even though it had a lower bond strength than other materials. How important is sealing compared to bonding?

Answer: Most clinicians agree that sealing is considerably more important than bonding since a restoration which remains attached and does not seal is highly susceptible to recurrent caries.
Many researchers feel there is a linear relationship between bond strength and marginal adaptation when studying a single material. However, sealing (as measured by microleakage) is usually unrelated to bond strength, especially between different materials (e.g. glass ionomers can have a lower bond strength than composite but can seal better in some studies). Most would agree that long term clinical studies are the best way to measure the sealing abilities of these materials. Unfortunately clinical sealing studies are difficult to do and few long term (5 to 10 years) are available on newer dentin bonding materials to determine the ultimate clinical effect on teeth in terms of recurrent caries and pulp pathology. Laboratory evaluations have shown that all products show significantly increased leakage over time.

Question #9: If newer dentin bonding agents are solutions containing only water, methacrylate monomer, and other trace elements why do they cost so much?

Answer: Clinical research is expensive and costs must be recovered. However, even with quality companies this represents only about 10% of product revenue. Much more is spent on packaging, advertising, and dealer profits (usually 40% plus gifts for high volume sales).
It is unfortunate that a larger percent of our dental material dollar is not spent on developing new products.
Despite this, many manufacturers have not entered or have left the dental field because profit margins are too low. Medical devices have been more attractive for many where greater returns on investment can be realized.

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