Nanotechnology and Nanoparticles in Contemporary Dental Adhesives - Nanobiomaterials in Clinical Dentistry - page 133

FIGURE 7.10
SEM micrograph of resin dentin interface when the adhesive was air dried at short distance using high air-

drying pressure. C, composite; A, adhesive, and D, dentin. Black oval represents area without the adhesive
layer.

From Ref. [21] .

the adhesive layer. A recent study [21] demonstrated that even with adding nanofillers to the adhe-
sive, excessive air-drying procedure through the use of high air-drying pressure did not only exces-
sively thin the adhesive layer but also it completely washed away the adhesive to the level that
resin composite was directly bonded to dentin ( Figure 7.10 ). Unfortunately, this result did not con-
firm whether this problem was related to the tested self-etching adhesive used in this study or it
could be a general problem related to all self-etching adhesives.
Fillers are also added for therapeutic purpose. The presence of prereacted glass ionomer micro-
fillers offers the advantage of fluoride releasing from some adhesive systems [22] . Fillers are also
added to improve the radiopacity of the adhesives [23] . Improving the radiopacity of the adhesives
helps in the evaluation of recurrence of decay under resin restorations.

7.4.3.2 Effect of filler composition and particle size
Different fillers are used, which are incorporated for two purposes: (i) to reinforce the adhesive
layer and (ii) to perform a specific function. As mentioned before, there is a wide range of role for
the fillers in the adhesives. Based on the “adhesion/decalcification concept” [24] , Zhang and Wang
[25,26] incorporated HAP microfillers into two commercially self-etching adhesives. The aim of
their study was to evaluate the reaction/interaction of monomer and HAP fillers on the DC and PR
of the two adhesives. They found that HAP fillers significantly increased the DC and PR of the
aggressive self-etching adhesive; on the contrary, they had no significant effect on the DC and PR
of the mild one. A 7 nm silica filler size of 10 wt% concentration had a significant effect on the
cohesive strength of the adhesive with no effect on DC [20] .
When 0.2 0.5 wt% of HAP nanorods ( Figures 7.11 and 7.12 ) were incorporated into an experi-

mental adhesive, the study results showed a significant positive effect on both the diametral tensile
strength (DT) and flexure strength (FS) of the adhesive. A 5 wt% of the nanorods dramatically