Ramus hinges for excessive movements of the condyles: a new dimension in mandibular tripodal subperiosteal implants

Abstract

Some subperiosteal mandibular implants of the earlier designs failed because of bone resorption beneath the posterior portions of the implant. Conversely, bone loss was observed rarely in the anterior region. The resorption was more profound posteriorly because there can be as much as 250 lb. of biting force per square inch and the bone is more porous than in the symphyseal region, which receives about 25 lb. per square inch. The independent movements of the condyles and the inferior border of the mandible at the gonial angles have dictated the success or failure of conventional mandibular subperiosteal implants in many of the earlier designs. Often, the rigidity of the implant framework prevents its posterior portion from moving in unison with the flexion and flexibility of the condyles upon the opening and closing of the mouth. Flexure usually is 2-4 mm in range and varies according to the quality of bone, age, sex, and musculature of the patient. Approximately 2% of these patients demonstrate movements of up to 4 mm. This has influenced an altered approach to posterior design-especially with tripodal mandibular subperiosteal implants. A brief history of the contributions of the earlier pioneers and their important contributions to the subperiosteal implant follows: G. Dahl inserted the first mandibular subperiosteal implant and was awarded his patent in 1941. Gershkoff and Goldberg, were the first to report clinical cases with mandibular subperiosteal implants in the United States. N. Berman reported on a direct bone impression of the mandible and transosseous wiring of the implant to the bone for stabilization. I. Lew introduced his own surgical bone impression technique for the mandibular subperiosteal implant and had published case histories on maxillary and mandibular implants. B. D. Weinberg reported an early unilateral subperiosteal implant consisting of a latticework portion that seated over the bone connected to the protruding post by four uprights. Leonard I. Linkow reported on the posterior unilateral mandibular subperiosteal implant. He followed up with a 5-year report, an 8-year follow-up report, and a 12-year report. R. L. Bodine reported his experiences with mandibular subperiosteal implants. A. N. Cranin and P. Schnitman introduced the Brookdale bar for an improved support of an overdenture for the mandibular subperiosteal implants. L. I. Linkow made some significant changes in the mandibular subperiosteal implant. D. D'Alise reported on the O-ring design for retention of implant dentures. R. A. James reported on the support system and perigingival mechanism surrounding oral implants and changed the subperiosteal based on peri-implant tissue behavior. L. I. Linkow reported on an entirely new mandibular tripodal design concept as well as a distinct change in the surgical protocol for obtaining the bone impressions without exposing those parts of the body of the mandible from the mental nerves to the ascending rami.