Restorative Procedure - Kerr Hawe

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Adhesives
Restorative Procedure
Adhesives
Bonding & Adhesion
Prof. David Watts, Dr. Nick Silikas, University of Manchester, UK
The mechanism of enamel bonding is based on a
micro-mechanical bond between the resin and the
phosphoric acid conditioned rough surface of the
enamel.Enamel conditioning remains the most
commonly used method to bond resin-composites
to enamel surface. It provides strong bonds.
Enamel conditioning may be regained by re-etching
the surface and applying the resin, thus recovering
the required shear bond strength at the enamel-resin
interface, and allowing the resin to mechanically
bond onto its surface.
Dentine however has a much more complex
structure than enamel. Prior to dentine-bonding,
the removal or modification of the smear layer is
indicated to clear the openings of the dentine
tubules by conditioning the surface of the dentine.
A fluid adhesive is then applied over the dentine
and cured, ensuring that optimum wetting of the
surface and absorption into the dentinal tubules
is achieved; thus creating an inter-penetrating
network with the demineralised collagen in the
dentinal tubules, hence forming the hybrid layer.
Preservation of the hybrid layer prior to the
application of the hydrophobic resin restoration
is imperative for an efficient bond to form between
the resin and dentine. Therefore, any contamination
of any region of the adhesive system would
evidently jeopardise the integrity of the bond.
The mechanism proposed for this material was
to bond to the organic component of the dentine,
namely the collagen. The first work to investigate
the mechanism of bonding to the dentine was by
Nakabayashi (1). He first identified a layer between
the resin and dentine substrate referred to as
“hybrid” dentine, in that it was the organic components
of the dentine that had been permeated by
resin.
The term “hybrid layer” has now become synonymous
with bonding of resins to etched dentine.
There has been a tremendous amount of research
done on the hybrid layer, its structure, formation
and how it can be improved. This layer has also
been referred to as the “resin-dentine interdiffusion
zone” (2).
Classification
Numerous dentine bonding agents have been
commercially introduced. These changes have
been referred by some people as “generations”,
implying that there was a chronological development.
This can be very confusing. A more consistent
and logical approach is to classify bonding
agents by the number of steps needed to complete
the bonding process.
“Three-step” or “Conventional” systems
This group typically consists of three separate
application steps: etching, priming and adhesive
resin. They are also known as “etch-and-rinse”
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