Restorative Procedure - Kerr Hawe

systems. Although they were the first ones
introduced, they are still widely used and have
been shown to provide reliable bonding. Their
main drawback seems to be technique sensitivity,
since any deviation from the recommended
procedure will result in inferior bonding.
“Two-step” systems
This group can be subdivided into two subgroups:
i) they have a separate etch and have combined
the priming and bonding steps. These systems
are often referred to as “Single-bottle” systems.
Similar problems found with the “Three-step”
system can also be seen here.
ii) etching and priming steps are combined together
and bonding is separate. This is referred to as
“Self-etching primers”. An acidic resin etches and
infiltrates the dentine simultaneously. The tooth
does not need to be rinsed which decreases
the clinical application time and also reduces
technique sensitivity by eliminating the need to
maintain the dentine in a moist state.
“One-bottle” or “All-in-one” systems
This is when all steps are combined into one
process. Their mode of action is similar to that of
the “self-etching primers”, but the bonding resin is
also incorporated. It is considered that these do
not etch as effectively as the previous ones. They
are the most recently introduced so limited clinical
data is available.
Bonding mechanism
This micromechanical coupling of restorative
materials to dentine, via an intermediate adhesive
layer, is referred to as dentine bonding (3). The
resin in the primer and bonding step penetrates
the collapsed collagen fibrils (after demineralisation),
and forms an interpenetrating network. This
layer had been described extensively and in great
detail (4, 5). The thickness of the hybrid layer
ranges from less than 1 µm for the all-in-one
systems to up to 5 µm for the conventional systems.
The bond strength is not dependent on the
thickness of the hybrid layer, as the self-etching
priming materials have shown bond strengths
greater than many other systems but exhibit a
thin hybrid layer. The etching, rinsing and drying
process cause the dentine to collapse due to the
loss of the supporting hydroxyapatite structure.
The collapsed state of collagen fibrils was hindering
the successful diffusion of the resin monomers.
To overcome this problem, two approaches were
introduced. The first one is called “dry-bonding
technique” and involves air-drying of dentine after
etching and subsequent application of a waterbased
primer that can re-expand the collapsed
collagen (6, 7). The second one is the “wet bonding
technique” in which the demineralized collagen is
supported by residual water after washing (8). This
allows the priming solution to diffuse throughout
the collagen fibre network more successfully.
However, when it comes to clinical practice, it is
very difficult to find the correct balance of residual
moisture. Excess water can be detrimental to
bonding and these problems have been described
as “overwetting phenomena” (9). Since the
“dry-bonding technique” is considered to be
significantly less technique sensitive, it should
be preferred over the most difficult to standardize
“wet bonding technique” (2).
Relevant in-vitro bond strength studies can provide
a useful indication of the prospective clinical
success of a system. However, the highest level of
evidence for comparing the efficiency of a bonding
system is obtained from randomised clinical trials.
Randomised clinical trials with elongated the
treatment periods will be very useful in assessing
both the effectiveness of a particular group and
a particular method of application.
References
1. Nakabayashi N, Kojima K, Masuhara E. The promotion of adhesion by
the infiltration of monomers into tooth substrates. J Biomed Mater Res
1982;16:265-273.
2. Van Landuyt K, De Munck J, Coutinho E, Peumans M, Lambrechts P,
Van Meerbeek B. Bonding to Dentin: Smear Layer and the Process of
Hybridization. In: Eliades G, Watts DC, Eliades T, editors. Dental Hard
Tissues and Bonding Interfacial Phenomena and Related Properties Berlin:
Springer; 2005. p. 89-122.
3. Eick JD, Gwinnett AJ, Pashley DH, Robinson SJ. Current concepts on
adhesion to dentin. Crit Rev Oral Biol Med 1997;8:306-335.
4. Van Meerbeek B, Braem M, Lambrechts P, Vanherle G. Morphological
characterization of the interface between resin and sclerotic dentine.
J Dent Res 1994;22:141-146.
5. Van Meerbeek B, Inokoshi S, Braem M, Lambrechts P, Vanherle G.
Morphological aspects of the resin-dentin interdiffusion zone with
different dentin adhesive systems. J Dent Res 1992;71:1530-1540.
6. Finger WJ, Balkenhol M. Rewetting strategies for bonding to dry dentin
with an acetone-based adhesive. J Adhes Dent 2000;2:51-56.
7. Frankenberger R, Krämer N, Petschelt A. Technique sensitivity of dentin
bonding: effect of application mistakes on bond strength and marginal
adaptation. Oper Dent 2000;25:324-330.
8. Kanca JI. Effect of resin primer solvents and surface wetness on resin
composite bond strength to dentin. Am J Dent 1992;5:213-215.
9. Tay FR, Gwinnett JA, Wei SH. Micromorphological spectrum from
overdrying to overwetting acid-conditioned dentin in water-free acetonebased,
single-bottle primer/adhesives. Dent Mater 1996;12:236-244.
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