Biomedical Engineering Reference
In-Depth Information
1.3
Finite Element Modeling of the Mandible
Numerical pre-clinical testing using Finite Element Models (FEM), for example,
is becoming more important as an alternative to animal testing. This numerical
technique has no ethical requirement or patient involvement in clinical trials [
1
,
18
].
In this respect, computational modeling will be one of the most important tools
for detecting implant performance in the short and long term. The design of TMJ
prostheses presupposes the use of numerical tools like finite element analysis (FEA)
[
19
,
20
]. The finite element simulation has been criticized because of the lack of
validation; however, it is the only way forward to explore 'possible' solutions.
These FE models must be applied carefully and it is sensible that they should be
“calibrated” using an experimental model. Some studies have been carried out with
the mandible, applying experimental techniques to validate numerical models [
21
].
However, numerical or experimental simulation can influence and undermine the
results of biomechanical analyses, by introducing configurations into the problem
and associated variables. There are many issues in Finite Element Analysis [
19
,
22
-
27
] that one must be aware of as well as data resulting from commercial FEA
applications. FEM results must be examined with care, because this model presents
some variables associated with the solution.
The FEM model results depend on simulation parameters like geometry repli-
cation, bone properties, boundary conditions and type of elements. The geometry
of bone is irregular and finite element modeling is increasingly carried out using
digitized images generated from computer tomography scanning [
28
-
30
]ormicro-
computer tomography for better resolution with small problems [
30
].
Another variable in FEM is bone materials, which are normally assumed to be
isotropic and homogeneous, whereas it is known that they are highly anisotropic
and inhomogeneous. This variable is a limitation when using FE models, because it
is very complex to simulate the biological process and bone evolution.
Boundary conditions are relevant input conditions that can considerably alter and
undermine the reliability of results. Loads applied to finite element models have
been very much simplified and many published papers have analyzed all sorts of
loading configurations. The model in [
22
,
31
-
34
] presents 10 muscles, but other
models present more [
35
]. Thus, there is a degree of uncertainty in determining
which muscles are important, and their relevance to mechanical testing.
The biomechanics of the mandible and the TMJ is an extremely complex problem
and the correct knowledge of the functioning of muscles and ligaments is unknown.
Predicting muscle forces should be treated with caution since many assumptions are
made when calculating them.
The finite element mesh is a key factor for an efficient analysis and much research
has been done on meshing and element performance. Finite element models must
be sufficiently refined to accurately represent the geometry [
36
,
37
]. The results
of these models are meshing sensitive and ideally a convergence test should be
performed to test the model's accuracy [
38
].
