Biomedical Engineering Reference
In-Depth Information
composites shall not be used as a simple bioinert way of enamel/dentin replacement, but as a com-
plex, biomimetic, and biointeractive material.
4.4
FILLERS IN COMPOSITE RESINS
Since the first formulation of composite resins in the 1960s, a basic triad is used: monomer, silane
treated filler, and initiators. The filler used by Bowen
[1]
, in 1963, consisted of milled quartz particles
with average size ranging from 8 to 12 μm (8,000-12,000 nm) as shown in
Figure 4.2
.
Due to the aesthetic limitations of macrofilled composites (lack of surface gloss), the minifilled
composites were introduced in the 1970s. The filler material was produced by a pyrogenic method
allowing a maximum load of 55 wt%, with better polishability, however with a significantly lower
mechanical strength.
It was only in the 1980s and 1990s, mixtures of previous filler materials were tested. These hybrid
fillers (600-2,000 nm) were commercialized as hybrid, microhybrid, and condensable (whisker-
shaped) composites. Improvement in the mechanical strength was achieved; however, the polishabil-
ity was still a limitation. A maximum load of filler from 70 to 77 wt% was recorded then. Still, the
particle size of conventional composites were not similar to the size of the hydroxyapatite crystal,
dentinal tubule, and enamel rod, and that there was a potential for compromise in adhesion between
the macroscopic restorative material and the nanoscopic (1-10 nm in size) tooth structure
[6]
.
1
µ
m
P : 10,000 x
10.0 kV
AMRAY
#0000*
FIGURE 4.2
SEM of irregular macrofiller.
Source: Hörlle, Hirakata, and Mota (2008).
