Biomedical Engineering Reference
In-Depth Information
that cell-biological
in vitro
techniques are suitable for the prediction
of tissue reactions toward implant coatings
or
mechanically altered
NiTi-surfaces. The surface morphology (platelets versus globular
particles) appears to play a signiicant role that supersedes that of
the chemical composition of the surface [9
].
3
.
4 Polymers
Polymers used in today's dentistry, commonly known as “dental
resins”, are used in all specialties of the profession, whether
restorative, prosthodontics, or surgical (Table 3.29) [4, 84, 86, 140].
Ta b l e 3
.
29
Requirements for a denture polymers [4, 80, 92, 106, 140]
Properties Characterization
Biocompatibilty Biocompatibility is the ability of a polymer material or a
device to remain biologically inert during its functional period.
Possible effects of biomaterials on the living environment due
to a lack of blood compatibility are thrombogenicity, and the
induction of hemolysis. In addition, the biomaterial must not
be carcinogenic, immunogenic, antileukotactic, or mutagenic.
In turn, the environment should not cause degradation or
corrosion of the biomaterial that would result in loss of physical
and mechanical properties.
Physical
properties
A denture polymer should possess adequate resilience and
strength to biting, chewing, impact forces, and excessive wear
under mastication. It should be stable under all conditions of
service, including thermal and loading shocks. Mechanical
properties increase considerably with an increase in number
average molecular weight.
Aesthetic
properties
The resin should exhibit suficient translucency and
transparency (hue, chroma and
,
value) to match the adjacent
structures and tissues. It should be capable of being pigmented
or tinted to camoulage the surroundings. Once fabricated,
it should maintain the appearance and color and not change
subsequently.
Chemical stability The biomaterial should be chemically stable and not deteriorate
inside the oral cavity by inducing some chemical reaction or an
adverse event. It should preferably polymerize to completion,
without leaching any residual monomers.
Rheometric
properties
The low behavior in polymers involves elastic and plastic
deformation (viscous low) and elastic recovery when stresses
are released. Molecular weight, chain length, number of cross
linkages, temperature, and applied force greatly determine
the typical behavior. Plastic low is irreversible and causes
permanent polymer deformation, compared to elastic recovery in
certain polymers, when applied stress is removed. Biopolymers
exhibit complex combined elasticplastic deformation called as
visco-elastic recovery.
(
Contd
)
