Biomedical Engineering Reference
In-Depth Information
Fig. 10.5
The cross-linking molecule di-HEMA phosphate. 2-hydroxyethyl methacrylate
(HEMA) is the part left of the dashed line and the right half substituted by hydrogen -H
Fig. 10.6
TEM micrograph of a moderately strong self-etch-adhesive.
Left
: overview of a restora-
tive composite (C) bonded to dentin (Ud: unaffected dentin) with as intermediates the hybrid layer
(Hy) and the adhesive resin (Ar); (
b
) detail of the hybrid layer. The dark conglomerates in (
a
)result
from silver infiltration but not discussed any further in the present context. The filler particles in C
can be clearly distinguished. By courtesy of K.L. Van Landuyt [328]
with a hydrophilic monomer(2) with on top the adhesive(3). To make a long story
short, we selected, out of a mishmash of possible procedures, one modern
self-etch
adhesive
, a one-step procedure, combining the
surface conditioning
(the first step in
3-step procedures by etching with phosphoric acid), the
priming
(second step with
monomethacrylate+initiator+inhibitor) and the
adhesive
(third step with a mixture
of methacrylates, initiator, inhibitor and filler).
Etching demineralizes the surface by extraction of calcium from the mineral
phase, mainly hydroxyapatite and carbonate and is freeing the collagen bundles of
dentin (typically collagen type I). The hydrophilic monomers with viscosity similar
to water act as wetting agents and diluting solvents (MMA, HEMA). They diffuse
into the wetted zone to form a hybrid transition layer, clearly shown at low and high
magnification in Fig.
10.6
.
Derivatives of these basic components are monomers whose main function is
demineralization. Another example is
10-methacryloylodecyl dihydrogeniumphos-
phate
(10-MDP) with at one end the methacryl group and at the other end a
phosphate group as shown in Fig.
10.7
.
The end groups in 10-MDP are separated by an alkyl chain of ten methyl groups,
called
spacer groups
. Because spacers modify the interaction between the end
groups and the flexibility of the molecule, they co-determine the over all properties
of the monomer as well as of the polymer!
