The prosthetic must be able to act as a TMJ immediately after surgery so that patients can eat, speak, and move their jaw properly. The prosthetic must be biomechanically suitable as a TMJ to allow for full function and structural support. Both the shape and material of the prosthetic must be considered in order to develop an effective replacement for the TMJ. The second design criterion is that the device must be easy to implant and remove. The current prosthetic is not biodegradable, meaning that it will remain in the body permanently and will not facilitate any ossification. In order to create a more effective replacement for the TMJ, the implanted device must biodegrade over time as the TMJ regenerates. This brings up the third design criterion, which is that the device must encourage regeneration of the TMJ. The current prosthetic stays in the body permanently. Our device, however, would use Mesenchymal stem cells which are precursors to osteoblasts, allowing for regeneration of the TMJ as ossification occurs at the site of implantation. In order to incorporate these three design criteria, we will create a device with a hard outer shell that is biomechanically suitable as a TMJ with an interior scaffold that can facilitate bone growth using mesenchymal stem cells.
- Full structural support
The design of our device is very similar to the current TMJ prosthesis out right now. However, the format of the screws connecting Component 1 and Component 2, the material used, and the function would be different. In the current prosthesis, component 2 would be screwed on the inside of component 1. In our device, component 2 would be screwed to the outside of component 1 in order to prevent damage to the scaffold on the interior. As shown in Figure 2, the central screw marked with the asterisk is where component 2 is attached and it is able to move horizontally as the jaw opens and closes itself. Component 1 itself is a hollow thermoplastic. All sides are covered with this protective layer except the side facing the mandibular bone. This is done in order to prevent the bone from attaching itself to the temporal bone and only allowing it to attach itself to the mandibular bone. This protective layer is made from the thermoplastic polyetheretherketone (PEEK), a mechanically strong plastic that would serve well to protect the scaffold placed in the interior of component 1 and to serve as a temporary replacement to the temporal mandibular joint.
2. Ease to Implant/Remove
Components 1 and 2 will be surgically implanted into their proper locations, which would be the temporal bone for C1 and mandible for C2. Both components will be screwed in. We designed the prosthesis out of polyetheretherketone in order to easily remove the prosthesis around newly formed bone, so it does not damage the tissue. Once tissue regeneration is complete and the bone has reformed, both components will need to be removed surgically. First, C2 can be removed by unscrewing its attachment to the mandible. C1 will be cut out and separated from the newly formed bone.
3. Regeneration of the TMJ
In order to support tissue regeneration, the scaffold must be biocompatible and biodegradable. The material we chose for this device was chitosan, as it is structurally sound as well as biocompatible and biodegradable. This scaffold, along with mesenchymal stem cells and biological signals, will facilitate the maturation of the MSCs into osteocytes. Over time, the TMJ will regenerate itself, offering the patient a functional TMJ of their own.