Biomedical Engineering Reference
In-Depth Information
within an overall agreement level of 10%. The model correctly reproduced bone
strains under different load configurations. For this reason, it adequately reproduces
the mechanical behavior of the mandible and has therefore become an essential tool
for predicting biomechanical changes in the mandible and long-term failure.
First, we describe mandible strains under natural loads. Using simulations
we were able to define the worst boundary conditions for the condyle and the
associated mandible behavior. Next, a plate implant was screwed onto one of the
mandible ramus. The results were then used to determine the strains at the end
of the plates and around the screws; the modified mandible strain patterns and
mandible displacements are compared to demonstrate the influence of the implant
on mandible behavior.
1
Introduction
The most common reason for replacing the temporomandibular joint (TMJ) is to
relieve pain and to improve reduced function caused by arthritis [
1
].
Total replacement of the TMJ involves removing the non-functional joint and
replacing it with an artificial one [
2
]. Due to the nature of the bone structures
involved in this joint, prosthesis design is somewhat complex, and materials and
geometry play an important key role in enhancing the long-term life of the artificial
joint [
1
]. The most commonly applied TMJ implants are plates that are flat and rigid
and surgeons can spend some hours bending a plate to fit it to the contours of the
patient's bones [
3
].
Total TMJ replacement has seen several different stages of development from
1945 until now [
4
]. In the 1990s a negative experience with the Vitek-Kent pros-
thesis brought some discredit to TMJ replacements [
1
] and some were abandoned
[
5
,
6
]. The new prosthesis introduced in the last decade has increased its application
in Europe [
7
].
1.1
Prosthesis Design
TMJ prosthesis design can be categorized into prostheses providing replacements
for the fossa only (Fig.
1
a), reconstruction plates to replace the condyle, and
combined prostheses for fossa and condyle (Fig.
1
b, c).
The evolution of TMJ joints in the UK resulted in a reevaluation of the principal
models applied, the Christensen and Vitek-Kent prostheses. The TMJ-concept is the
most popular, with a current estimated annual total of between 60 and 65 patients in
the UK. The most common problem in TMJ revision is infection in 2% of cases, with
problems occurring overall in around 9% or 170 cases (1999-2006) [
1
]. Surgeons
are currently reported to charge from £15,000 to £19,000 for a TMJ prosthesis
procedure.
