Current implant techniques—an overview 9

The splint is then fixed temporarily over the prepared anterior abutment teeth and the implants in the following manner. Temporary cement is applied only to the portion of the acrylic splint that fits over the prepared abutment teeth. Because these teeth are tapered, the temporary splint can be easily removed later. Cement should not be applied to the areas of the splint that fit over the implant posts, because they are not tapered and thus might be loosened during the removal of the splint. Instead, cold cure acrylic is placed inside the holes that cover the implant posts. The splint is placed in the mouth, left for 20 seconds, and taken out. The excess acrylic is removed, and the splint is placed back in the mouth. The process is repeated until only enough acrylic is left to hold the implants by a passive, frictional grip. The acrylic should finally set outside the mouth. At the end of the second visit, the patient is sent home with the implanted abutment posts in his mouth, held securely in place and protected by the acrylic splint.

Third visit. On the third and final visit, the temporary splint is removed and the finished pros-thesis is carefully put into place (Fig. 1-20) and radiographed. After all occlusal adjustments have been made, the prosthesis is permanently cemented into place with oxyphosphate of zinc cement (Fig. 1-21), and the final result is checked again roentgenographically for any cement that may remain under the bridge (Fig. 1-22) . Most patients will experience little pain and will be able to masticate forcefully immediately after the prosthesis has been cemented into place.

Vent-plant implants

The vent-plant is similar to the spiral-shaft implant in that a space in the bone must be prepared for its insertion. Its eventual stability in the bone also relies upon the regrowth of hard and soft tissue around it. However, the vent-plant is designed to take better advantage of the tendencies of bone regrowth.

Bone tends to regenerate first around the deepest portion of the implant. At the apex of the vent-plant is an open portion, the so-called vent. Blood can flow freely through this vent, promoting faster bone regrowth. The unique design of the vent can also be used to create greater stability by leaving in the site a cylinder of bone over which the vent can slip or by reimplanting a bone core by placing it inside the vent. Thus bone immediately takes up the space of the vent, providing a skeletal matrix

for new bone regrowth. The bone core, of course, is itself eventually replaced by new bone or fibrous tissue.

The spiral portion of the implant, which lies closer to the soft tissues, is wider in diameter than the vent, so that it grips the bone and provides immediate retention of the implant. This portion is also solid, so that no soft tissues can invaginate into it and cause failure of the implant. Also, because the spiral portion is solid rather than hollow and contains sluiceways, it is sturdy enough for self-tapping.

At the coronal portion of the implant is the solid shaft that anchors the prosthesis. This shaft is narrower than the other parts of the implant. If part of it is buried into the bone, a bony shelf will grow over the lower and wider portions, making vertical exfoliation difficult. A round neck between the spirals and protruding square shaft is less irritating to the bone because it lacks sharp angles.

Materials and equipment required. The materials required for setting vent-plants in bone are similar to those needed for the spiral-shaft implant procedure except that no taps are needed since the implants are self-tapping. In addition to the materials listed on p. 3, various sized helical burs (to coincide with the different sized vent-plants) and hollow-mill drills or trephines for creating the solid core of bone (if this technique is desired) are needed.

Procedures. The procedures for installing a fixed splint secured to vent-plant implants are similar to those followed using spiral-shaft implants. The major differences, of course, involve the techniques for installing the implant itself. These differences are, however, only variations of the basic endosseous shaft implant procedure.

First visit. Three visits are usually required. On the first visit, periapical x-ray films and lateral plates are taken of the edentulous areas in which the vent-plants are to be installed. This is a crucial step, be-cause the success or failure of any type of implant relies upon selecting the best location. Anatomic landmarks, such as the mandibular canal, are to be avoided, and the positions of neighboring teeth should be noted as important guides.

Two anterior abutment teeth should be prepared for full crown restorations (Fig. 1-23) and impressions and bites of them taken to provide crown castings. In addition, an alginate impression and a bite of both the prepared abutment teeth and the edentulous area are made. A stone cast is prepared, then a temporary acrylic splint is made for