Mandibular endosseous implant interventions 351

Fig. 9-53. The markings are transferred to the tissue-bearing surfaces of the pontics and then the properly sized holes are made. (From Linkow, L. I.: Prefabricated mandibular prostheses for intraosseous implants, J. Prosth. Dent. 20 [4] : 365-375, 1968.)

Fig. 9-55. The fibromucosal tissue in the area of the mandibular symphysis is incised and the tissue reflected, ex-posing the underlying bone. A "hollow-mill" trephine is attached to the contra-angle. (From Linkow, L. I.: Pre-fabricated mandibular prostheses for intraosseous implants,

Fig. 9-54. The starting holes are made with spear-point burs followed with helical type burs. (From Linkow, L. I.: Prefabricated mandibular prostheses for intraosseous implants, J. Prosth. Dent. 20[4]:365-375, 1968.)

Since vent-plants were to serve as the implant abutments, helical burs of a corresponding size were employed. One of the round burs was removed and the other one was left in position as a parallel guide for the helical bur.

If the "hollow-mill" technique is to be used, as it was in this case, the operator has two choices. He can try to get a good bone plug from the implant site itself or from the symphysis area, just behind the cortical plate of bone on the labial aspect of the mandible. In obtaining a plug from the site itself, the hole made by the helical bur is restricted to the same depth reached by the round bur. A "hollow-mill" trephine the same diameter as the implant is inserted with a slow-running contra-angle to

Fig. 9-56. The trephine is rotated through the cortical plate and into the deeper alveolar bone. (From Linkow, L. I.: Prefabricated mandibular prostheses for intraosseous implants, J. Prosth. Dent. 20[4]:365-375, 1968.)

the depth where the vent-plant will rest. When this depth is reached, the hollow mill is carefully taken out of the bone. The core of the patient's bone is then set inside the vent-plant, which is then screwed into the artificial socket to its predetermined depth.

If the bone in the region where the vent-plant is to be placed is too cancellous, an autogenous plug of bone can be obtained from the mandibular symphysis. To do this, the tissue in the mouth over the symphysis is incised to expose the underlying bone (Fig. 9-55) . A "hollow-mill" trephine is placed in a contra-angle handpiece and is slowly drilled into the exposed bone, cooled continuously with water, to a depth of 1/8 to 1/4 inch to create a bone plug (Fig. 9-56). The bone plug is removed from the trephine