Biomedical Engineering Reference
In-Depth Information
CHX) and a substrate (e.g., oral mucosa, oral proteins, dental plaque, or dental surface), an associa-
tion that can be greater and more extended than would be expected from a simple deposition mech-
anism. It is considered that the delivery of an agent to its site of action in a biologically active
form and in effective doses increases the effects for prolonged periods of time. Substantivity of
CHX or its ability to be retained in dentin matrices could be the reason why CHX-treated acid-
etched dentin may form hybrid layers that are more stable over time. Recently Breshi et al.
[61]
investigated the pretreatment of dentin with a specific MMP inhibitor galardin (
Figure 7.23
). The
inhibitory effect of galardin on dentinal MMPs was confirmed by zymographic analysis as com-
plete inhibition of both MMP-2 and -9 was observed. The use of galardin had no effect on immedi-
ate bond strength while it significantly decreased bond degradation after 1 year. Interfacial
nanoleakage expression after aging revealed reduced silver deposits in galardin-treated dentin com-
pared to untreated dentin.
7.8.4
Improved impregnation
Various methods have been recently proposed to enhance dentin impregnation, i.e., prolonged
application time, vigorous brushing technique, and electric impulse assisted adhesive application
[62]
. The latter technique recently revealed increased bond strength and reduced nanoleakage
expression if adhesives are applied under the effects of an electric signal. Junior et al.
[63]
improved impregnation of dentinal collagen by adhesives via the evaporation of adhesive solvent
by a stream of warm air (
Figure 7.24
). The use of a warm air-dry stream to evaporate the solvent
of adhesives seems to be a clinical tool to improve the bond strength and the quality of the hybrid
layer (less nanoleakage infiltration).
Another approach to improve impregnation of collagen by the adhesive after acid etching was
the simultaneous acid etching and deproteinization suggested by Nassif and El Korashy
[64]
. The
simultaneous etching and deproteinization by NaOCl/phosphoric acid for 15 s showed a hybrid
layer with improved bond strength. This was attributed to removal of shredded collagen found in
the smear layer that could not be removed by acid etching only. Removal of this disorganized col-
lagen would give more open structure to the collagen network and improve its impregnation by the
adhesive.
7.8.5
Wet ethanol bonding approach
Tay et al.
[65]
proposed the ethanol-wet bonding technique. Ethanol is used to replace water just
prior to bonding, thus avoiding the collapse of the collagen matrix. Ethanol-wet dentin may permit
the infiltration of hydrophobic monomers to disperse into the demineralized dentin, creating a
hydrophobic hybrid layer. Since the concept of ''ethanol-wet bonding'' was proposed, various
ethanol-wet protocols have been developed to optimize this technique
[66,67]
. The ethanol-wet
bonding is a time-consuming technique since it needs consecutive application of ascending concen-
trations of ethanol. A simplified protocol for wet ethanol bonding to dentin was suggested by
Sadek et al.
[68]
. They suggested a protocol of reduced time for each ascending ethanol concentra-
tion application to dentin prior to bonding. This technique achieved high bond strengths, minimal
nanoleakage infiltration, and maintained bond stability after 6 months of artificial aging. A shorter
dehydration period (135 s) may render the bonding of hydrophobic monomers to dentin easily.
