Biomedical Engineering Reference
In-Depth Information
FIGURE 7.18
(A) SEM photomicrograph of nanofilled RMGI/dentin interface treated with Ketac nanoprimer. No evidence of
hybrid layer or resin tag extensions, with a gap (G) between the restoration and underlying dentin. Smear
layer remnants (arrows) are noticed over the dentin surface. RMGI, nanofilled resin-modified glass ionomer;
D, dentin. (B) SEM photomicrograph of nanofilled RMGI/dentin interface treated with 35% phosphoric acid
before the application of Ketac nanoprimer. Numerous long, funnel-shaped resin tag extensions (RT) with a
thick hybrid layer (H). Fillers distributed at the bottom of and within the hybrid layer as well as around the
orifices of the dentinal tubules (arrows).
From Ref.
31
.
7.6
Nanoleakage
Nanometer-sized porosities within the hybrid layer were first described by Sano et al.
[33
35]
.By
observing the penetration of silver nitrate along gap-free margins with several dentin bonding sys-
tems under SEM or transmission electron microscopy (TEM), they described a leakage pattern
occurring within the nanometer-sized spaces around the collagen fibrils within the hybrid layer.
They termed this phenomenon as “nanoleakage.” This represents permeation laterally through the
hybrid layer and may be the result of incomplete infiltration of adhesive resin into the deminera-
lized dentin. This kind of leakage may allow the penetration of bacterial products and dentinal
or oral fluid along the interface, which may result in hydrolytic breakdown of either the adhesive
resin or collagen within the hybrid layer, thereby compromising the stability of the resin
dentin
bond
[36]
.
Recently, a 50 wt% ammoniacal silver nitrate solution has been used to detect nanometer-sized
defects in bonds analyzed by SEM
[37]
or TEM
[38]
. Several recent TEM studies (
Figure 7.19
)
[39]
have revealed several types of nanoleakage (i.e., spotted, reticular patterns, and water tree). Recently
developed resin adhesives contain more acidic hydrophilic monomers and higher amounts of water to
improve monomer impregnation into wet dentin substrate, resulting in lower degrees of polymeriza-
tion of adhesive resin. This results in increased silver uptake into the hybrid and adhesive layers (i.e.,
increased nanoleakage). In addition, it has been reported that there is often a discrepancy between the
depth of acid etching and the degree of resin infiltration and exposed collagen network
[40]
.This
