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Connecting Teeth to Artificial Bone
Large Image Display: Connecting Teeth to Artificial Bone

As covered inTeeth Designed for Prosthetic Jaws, connecting the child prosthetics to the main prosthetic, is just as important as the main prosthetic itself. In the case of a jaw prosthesis, removing the old jaw removed the teeth as well. So, when a new jaw is put in, these dependent systems must also be replaced. However, since they are separate systems to the jaw itself, and serve a very different function, they are by definition, separate prosthetics. Still, without these dependant systems, the jaw would never reach full potential - the patient would be unable to chew.

The tooth bridge slots downwards into the mouth. The jaw was inserted under the chin. Trying to tie these two pieces together into a single implant, would result in a very unwieldy piece of titanium, and an extremely messy, complex operation that would be extremely delicate and drawn out, requiring a long recovery time. Instead of going down that route, if you create them as separate pieces, you preserve the dependencies, and allow for multiple small operations, with a fast recovery time. The jaw goes in first, and the teeth go in later, when the wound has healed and the swelling has abated. But, in order to do this, both implants must be designed from the get-go, to work together as parent and child. They must be designed to mesh together with no room for error, and to hold strongly as a single unit when in place, whilst allowing for the possibility of one to be removed without dislodging the other.

This rendered image shows the basic design of the jaw and connector implant. It was created prior to the patient data for the prototype being collected, and so serves as an overview for all such jaws, rather than an individual implant.


Creating two separate prosthetics that merge as one is a relatively straightforward feat when you have the patient's medical scan data to work with, and each piece will be custom made to that data. It is a relatively minor matter to create two separate prosthetics, molded to the exact shape of the skeletal structure you are presented with. The interesting part comes in fixing them.

As shown in the top image, the LayerWise system handled this by surgical screws. Made out of titanium, the six screws are a part of the dental bridge they hold. All seven components were 3D printed together as a single unit, using additive manufacturing technology. Basically, individual grains of titanium are heat-fused to one another, building up a complex 3D shape. If you fdon't apply the heat, the grains do not stick. You can use this basic concept to create single pieces with multiple moving parts, by sticking a layer of grains to each other, but not to the grains below. You create two separate pieces of titanium, yet they remain linked together in ways it would be impossible to achieve if you had to assemble them later on. Namely, with this method they can be designed so that it is impossible for the screws to fall out as they were literally grown in place.


Here we see the main LayerWise jaw implant with the screw holes in the fore. These are what the connector piece for the teeth screws down into. As with everything else in the main implant, they were 3D printed as part of the single piece.


Likewise, the screw threads were printed into the earlier implanted jaw, which was itself also created as a single piece of 3D printed titanium. Whilst the jaw was made before the bridge, both were made from the same medical data. The virtual versions of both were shown to mesh long before either were printed out, and by use of a physics simulation in virtual reality, it was possible to tell for absolute certain if it was possible to screw the screws in without hitting obstructions. Again the medical data was invaluable, as the entire mouth area can be simulated with the prosthetics in place, along with the screwdriver itself. The surgeon can make absolutely sure they have enough room to proceed, by operating on the virtual patient before they operate on the actual patient.

The connector is implanted by making an incision in the floor of the mouth, and slotted down into the jaw. Once it is in place, it sits flush with the floor of the mouth, all six screws tightened into the jaw, without compromising the jaw's integrity. All that pokes up are tiny cradles, designed to affix to the dentures, and hold them in place.

This model does not have any capability to funnel nerve endings to the individual teeth, so the patient loses the sense of pressure when biting down on something, at least with their lower teeth, but that is no different than with any normal dental bridge. The basic design of this system does not preclude such things, it is more a case that such fine nerve routing is presently beyond us, rather than a limitation of the technological concept. The whole system is designed such that any individual piece can be removed with minimal disruption to the other implants, should damage occur, or a more advanced replacement be developed. So long as the original medical data and CAD data is preserved, replacement implants of any type can be manufactured in hours, to the same exacting standards, and implanted with a guarantee they will interconnect on that patient, and that patient only.

Further Reading

Large Image Display: Making a Bespoke Jaw

Large Image Display: Prosthetic Jaw Hinging

Large Image Display: Teeth Designed for Prosthetic Jaws

References

Form Fitting Prosthetics Using DICOM Data