Patent Application
20080090209
The preferred embodiment of this invention is shown in
The base and its legs may be used as a reinforcing structure, or more frequently as a root or base for other structures. In
In fact, the base may have drilled and threaded-taped holes in it so as to receive appurtenances such as teeth, brace wires, and whatever else may be of use.
The gist of this invention is its capacity to change the shape of the implant from its interim condition which enables it to be inserted into the jaw, to its set condition in which it is positively, structurally, retained in the jaw.
In
These could, if desired, both be inserted in the same socket or recess, but more often would be in a slot. For that matter, the base could extend a substantial distance away from any of them, and may have a set shape of its own, for example an arch.
As shown in
While any biocompatible alloy that exhibits suitable shape memory properties, perhaps the most completely studied and accepted is the alloy of Nickel and Titanium commercially available under the name Nitinol. This alloy is available with various transformation temperatures and temperature spans for the transformation of the alloy to or from heating from martensite to austenite, and cooling from austenite to martensite.
The basic process is to form a blank or other article to a desired set shape (sometimes called a “trained” shape). This is the ultimately desired configuration after implantation. It is formed to this shape, constrained to this shape and heat treated to permanently set the shape into the material. Then it is annealed and cooled.
It is then mechanically shaped to a desired interim shape such as by pressing. It retains this interim shape until heated to its transition temperature, upon which it will return to its set shape.
It is interesting and important that the entire implant need not be heated to the temperature that was needed to train the body to its set condition. Instead it has been found that a very brief and local burst of heat to some part of the implant can cause the entire implant to transform to the set condition.
Because these implants are intended to be placed in the mouth, the implant cannot be heated in its entirety to an elevated temperature. It has been found, however, that a very high, very local, application of heat can function for this purpose, and will not harm surrounding tissue.
For example, there exists a cordless soldering tool which applies two spaced-apart electrodes to a conductive metal surface and applies a voltage across them which produces a very hot local region in the workpiece. Often the workpiece is a solder. This is so efficient that it can be powered by four AA batteries. Still the heat for these implants needs to be applied only very locally and for such a short period of time that the highest temperature reached by the implant where it contacts tissue or bone remains well within tolerable limits.
The specific alloy to be used will be selected for the ability to transform it from its interim shape to a set shape by a brief local application of heat. Useful alloys, commonly referred to as Standard SMA Ni Ti alloys code S, C or M may be obtained from Johnson Matthey Company, San Jose, Calif.
Accordingly, in accordance with this invention, a blank form is shaped to a set shape while heated to a temperature above the transition temperature to austenite. Then it is annealed, cooled, and processed to a different interim shape in the martensite range of temperature. This interim shape will be retained until suitable heat is applied locally to start the transition back to martensite, when it returns to its set shape, the implant having been inserted while in the interim shape. When it is appropriately heated to resume its set shape, it retains the shape and is fixed in place.
It is an important feature that if some of the dimensions of the set condition are somewhat “oversize”, then when the implant is heated and the implant enlarges, but is restrained by surrounding structure such as the walls of a jaw, the implant will continue to exert a prevailing force tending to hold the implant in place. This greatly reduces the tendency of the implant to come loose. Of course the expansive force must not be so great as to crack surrounding bone, but this can readily be designed for.
This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.
