1. Field Of The Invention
This invention relates to a method for molding surgical implants and more particularly relates to a vacuum technique for molding an implant of polymer beads.
2. Description Of The Prior Art
In certain surgical applications such as prosthetic implantation to fill bone defects caused by trauma, tumor resection, congenital defects, infections, etc., it is desirable to have a prosthetic implant which can be molded to any desired shape. Ideally, such an implant should be porous to allow for bone growth, malleable to allow it to conform to various shapes, yet firm and rigid when fixed to the bone to provide for a strong, solid support.
A material which has been used successfully in bone implantation is described in Ashman et al. U.S. Pat. Nos. 4,728,570 and 4,535,485, and in Bruins et al. U.S. Pat. No. 4,536,158. The material disclosed therein is a conglomerate of polymethylmethacrylate beads coated with polyhydroxyethylmethacrylate. The beads may be joined into a unitary structure as disclosed in U.S. Pat. No. 4,536,158, or they may be used in granular form as disclosed in U.S. Pat. No. 4,535,485.
When used as granules, the beads are packed into a cavity, such as the cavity in the gums remaining after a tooth extraction, and the cavity is sewn closed. When used as a unitary porous mass a separate mold must be fabricated based on the extracted tooth. The mold is then filled by packing it with the polymer beads which have been wetted with polyhydroxyethylmethacrylate, and heated in a dielectric oven to polymerize and/or sinter the beads into a unitary porous mass.
Such techniques are useful in dental procedures like tooth extraction where it is possible to fill a void, or to make a separate mold based on an extracted tooth. In other applications, however, it is not possible to make a separate mold, or to pack a cavity and sew it closed. Certain procedures, such as augmentation of bony structures for cosmetic purposes, or implantation to fill bone defects, require the implantation of a unitary structure which has been custom shaped in situ, i.e., which as been molded within the surgical site where it will be implanted. In situ shaping of implant material is not possible with the modalities disclosed by the above-mentioned references.