18 CHAPTER 1. THE TEMPOROMANDIBULAR JOINT
successful management of patients with severe TMDs. The following section recaps the description
of the history and current use of alloplastic devices found in the book chapter of Wong et al. in
Tissue Engineering and Artificial Organs [28].
1.10.1 PAST EXPERIENCES
Experiences with different alloplastic materials for TMJ disc replacement have been characterized
by a number of significant failures resulting in severe joint resorption, alteration of mandibular
skeletal relationships, compromised motion, pain, and even systemic immune compromise. These
surgical disasters and the resultant lawsuits have unfortunately tainted all forms of TMJ surgery
and discouraged many surgeons from seeking alternative methods to reconstruct the joint. Before
the controversy surrounding the implantation of medical-grade silicone, interpositional implants
(silastic) were available for disc replacement. As permanent replacements, these devices were prone
to fragmentation, but when used as a temporary interpositional implant (“pull-out technique),
they were observed to provoke the formation of a dense fibrous tissue capsule, which served as an
interarticular cushion. Their relatively successful use following discectomy might be attributed to
this reaction.
One of the alloplastic replacements of a disc with the most litigation occurred with the use
of a Teflon–Proplast implant in the late 1980s and early 1990s. Produced by the Vitek Corpora-
tion, fragmentation of the implant under functional and parafunctional loads was associated with
an exuberant foreign body giant cell response and significant osteoclastic activity, resulting in the
resorption of condylar and fossa surfaces and severe local inflammatory events. Despite the immense
suffering experienced by the patients who were unfortunate enough to be treated with this implant,
the lessons learned from this experience are essential, and include the significance of characterizing
the loading patterns within a joint, and the importance of recognizing the effects of degradation
products upon the local joint environment.
1.10.2 CURRENTLY APPROVED THERAPIES
The TMJ hemi-arthroplasty was a procedure popularized by Christensen and Morgan in the 1960s,
in which the superior articulation of the joint was replaced with an implant fabricated out of chrome–
cobalt alloy. The Christensen implant reconstructed both the fossa and articular eminence while the
Morgan implant covered the eminence only. Concerns over accelerated degeneration of the natural
condyle articulating against a less-deformable surface eventually resulted in the replacement of
the hemi-arthroplasty with total joint reconstructive procedures utilizing both prosthetic fossa and
condylar components. Currently, three total joint replacement systems are licensed by the Food and
Drug Administration (FDA) for implantation into patients, though limitations have been imposed
on surgeons wishing to use these devices and the selection of patient candidates. Stringent follow-up
of patients treated with these implants form the basis of various clinical trials designed to test not
only the ability of the procedure to improve a patients condition, but also the integrity of the devices
over time.
1.10. TMJ REPAIR USING ALLOPLASTIC DEVICES 19
Customization of alloplastic implants: The ability to customize an alloplastic device is also useful for
correcting a skeletal discrepancy that may occur in patients with severe degenerative joint disease,
where retrusion and rotation of the mandible is the result of decreased posterior vertical support
(Figure 1.8). Customized prosthetic devices involve complex surgical techniques. In order to accu-
Figure 1.8: Rapid prototype of skull obtained from computer tomography (CT) scans.
rately reproduce the skeletal bases to which the devices will be attached, two separate surgeries are
ideally required. During the first procedure, the diseased joint (or failed implant) is removed and
the area debrided. A temporary alloplastic space maintaining implant is used to reduce the amount
of soft tissue in-growth into the resulting space. Following this surgery, a thin-cut computerized
tomography (CT) scan is obtained using a protocol devised by companies specializing in the fabri-
cation of stereolithographic models. The anatomically accurate model is sent to a joint fabrication
company where CAD–CAM technology is used to produce a prototype of the final device. Each
device is composed of a prosthetic fossa and eminence as well as a condylar head attached to a ramus
component.The prototype is returned to the surgeon who confirms that the surgical defect has been
correctly reconstructed.
At this time, minor modifications to the skeletal defect may be proposed to better accommo-
date and fit the implant. Once the customized implant has been completed, the patient undergoes
a second surgery during which the surgical sites are adjusted to match the defect created on the
stereolithographic model before the prosthetic fossa and condyle are attached to their bony bases.

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