Biomedical Engineering Reference
In-Depth Information
Tabl e 1
Jaw-closing muscle
forces (N)
Loads (N)
Muscles
Ref.
x
y
z
Deep masseter (dm)
M1,2
7:8
127:2
22.7
Superficial masseter (sm)
M3,4
12:9
183:5
12.1
Medial pterygoid (mp)
M5,6
140:4
237:8
77.3
Temporal anterior (ta)
M7,8
0:06
0:37
0.13
Medial temporal (mt)
M9,10
0:97
5:7
7.4
The directions of the forces exerted by the masseter and the medial pterygoid
muscles remained almost parallel and it is thus possible to consider substituting
the pterygoid electrode in the oral cavity by assigning a corrected section to the
masseter.
Six jaw-closing muscles have been selected here, while the jaw-opening muscles
have not been taken into account. Since a muscle does not act in isolation but
in synergy with several other muscles, the protocol described in this paper is not
limitative and does offer equally the possibility of taking jaw-opening muscles into
account. The next step will be to quantify the relative contribution of the opening
and closing muscles and test the hypothesis formulated by Caix [
46
]. We will also
improve numerical results by using a larger population sample [
47
].
3
Finite Element Model
The mandible bone presents a complex geometry and boundary conditions need to
be correctly specified, otherwise these can undermine the reality of results. In this
sense, it is essential that numerical models are tested and validated experimentally
[
27
,
48
,
49
]. Finite element and experimental models have been used to determine
stresses and strains on the surface of bone structures with relevant conclusions [
35
,
50
,
51
]. These models can be used for different biomechanical analyses and to
predict the performance of implants. Defining numerical models needs to be broken
down into stages; the first stage involves the geometric model or a CAD model.
3.1
CAD Model
The geometry of the mandible is the first step in constructing the FE model, and
geometry acquisition was normally by CT scan. In this work the model of the
mandible was based on a polymeric replica of a human mandible from Sawbones
®
(model 1337 was selected). This model has adequate geometric accuracy for the
experiments [
52
]. The geometry of the model was obtained using a 3D laser
scanning device (Roland LPX 250 machine). The complexity of the geometry
required ten scans with different orientations. The scan resolution was 0.2 x 0.2 mm
and the final geometry is shown in Fig.
2
.
