46 Theories and techniques of oral implantology

treme cases, a part of the mandibular canal may be exposed at the upper surface of the mandible. With loss of the entire alveolar process and sometimes parts of the body of the upper and lower jaws, the lips lose their support and sink inward. The nose and chin then appear more prominent, thus creating the typical picture of the senile face.

Stress and dental prostheses. Because bone loss may result from dysfunction, it seems likely that artificially restoring stress to an area will retard or even stop resorption. It has been claimed that a re-movable prosthesis in good occlusion can lessen or eliminate bone loss. This statement bears analyzing from a mechanical viewpoint. First, the role of stress in maintaining alveolar bone in good health and preventing its resorption is well established. Second, it is known that this stress must be distributed as tension within the bone. This is accomplished naturally by Sharpey's fibers. Third, to retard the re-sorption of the alveolar crest, transverse and tangential stresses must be suppressed.

The design of a conventional removable appliance prohibits meeting any of the mechanical criteria fulfilled by natural dentition. In fact, the saddles encapsulating the soft tissue overlying the

edentulous area create osteoclastic activity by the abnormal pressures caused during lateral and occlusal articulation. When a prosthesis is unstable, re-sorption is not only unretarded, it is promoted by displacements causing irritation. Furthermore, there is often floating fibrosnucosa in the edentulous jaw that encourages continual displacement of a removable prosthesis. Experience also shows that maxillary crest resorption is accelerated by a mobile prosthesis that, because of gravity alone, is difficult to immobilize.

A means of effectively redistributing pressure throughout bone, not just on top of it, has obvious advantages. It is our opinion that bone will not resorb as readily in edentulous areas where endosseous implants are inserted, providing that the implants are well placed and stabilized and that the final prosthesis is carefully occluded and properly balanced. From the point of view of masticatory biomechanics alone, the endosseous implant reestablishes conditions as close to normal as is possible with an artificial prosthesis. It is in the very ground of the lost organ that the new substitute element is going to work, in the same axis and on the same plane as a natural tooth (Fig. 2-27).

Fig. 2-27. An endosseous implant in a healed site closely approximates a natural tooth. Al-though Sharpey's fibers do not exist in the dense fibrous tissue that tenaciously binds itself to an implant, this connective tissue acts in the same manner. Pressure exerted on the implant is transferred to the connective tissue, which pulls on the bone, thereby providing the necessary stimulation for osteogenesis. The only true way alveolar bone can stay completely healthy is by being stimulated by the suspensor type ligaments found with teeth and certain endosseous implants.