Biomedical Engineering Reference
In-Depth Information
Fig. 1
TMJ prostheses [
8
]
The first type of prosthesis, characterized by introducing an alloplastic material
between the fossa and condyle, was used before the 1950s before 50th years. The
applied materials were Tantalum, Cr-Co alloy, UHMWPE by different commercial
prosthesis. The prosthesis used to replace the condyle was made of Titanium and
Cr-Co alloy, and normally consisted of a plate with a flat geometry and fixed by
screws.
Reconstruction with metallic materials modifies the physiological behavior of the
mandible (stress and strain patterns and condyle displacements). As a result of the
changing bone strains the TMJ and articular contacts must be adapted. Replacing
a single condyle is preferable as a temporary TMJ replacement, maintaining the
glenoıd fossa. Another type of TMJ implant is the custom-made variety; this may
have some advantages related to its being a perfect fit [
9
], but they have to be
evaluated in a long term-study to justify the extra costs.
Comparative studies of recent prostheses [
3
,
10
] point out that the inter-incisor
opening is almost 20 mm. Occlusion corrections clearly give the patient both
psychological and physical comfort. On the other hand, these studies and Karray
[
11
] point out different cases of failures that sometimes require additional surgical
procedures:
-
Inflammation
can occur due to the choice of material, with persistence of pain
revealing imperfect osteointegration (bone screws) consequently accompanied
by implant micro-displacements with respect to the bone [
12
],
-
Prosthesis fracture
(rare) happens near a screw or in a sharp variation of the
implant section where stresses tend to concentrate,
-
Bone connection fracture
is the result of an insufficient number of screws and/or
a too high intensity of loads on the mandible condyle [
13
,
14
].
There are several solutions available to improve the TMJ survival rate, but the
most frequent consists of a plate and fixation screws [
13
,
14
].
