Management of the Posterior Maxilla in the Compromised Patient: Historical, Current, and Future Perspectives.
Thomas J. Balshi & Glenn J. Wolfinger
Periodontology 2000, Vol 33, 2003, 67-81.
The posterior maxilla has been described as the most difficult and problematic intraoral area confronting the implant practitioner, requiring a maximum of ingenuity for the achievement of successful results(39, 59). Both anatomical features and mastication dynamics contribute to the challenge of placing titanium implants in this region.
Anatomic factors include decreased bone quantity, especially in older edentulous or partially edentulous patients who have experienced alveolar resorption in the wake of tooth loss. The antrum also tends to enlarge with age, as well as with edentulism, and this further decreases the amount of available bone. In addition to the diminished quantity, bone in the posterior maxilla often is softer and of poorer quality. Radiographs typically reveal a dearth of trabeculations, and the tactile experience of drilling here often more closely resembles the penetration of styrofoam rather than anthracite. Limited access to the pterygomaxillary region constitutes yet another problem.
Mastication dynamics also affect the long-term stability of implants placed in the posterior maxilla. Whereas masticatory forces of 155N have been reported in the incisor region, the premolar and molar regions have exhibited forces of 288N and 565N, respectively3. Parafunction can increase these forces as much as three-fold(4-6), applying significant stress to the bone-implant interface and the component hardware.
Despite the biomechanical impediments to creating prostheses in the posterior maxilla, patients who have lost teeth in this area have sought some means of restoring both their chewing ability and their appearance. One solution has been the use of posterior cantilevers on implant prostheses. When designed to minimize the occlusal forces applied to the pontic, short cantilevers can function successfully. One key is the availability of several long and strong implants anterior to the cantilever. The author also suggests the use of implants of 4mm diameter or greater, if the intent is to create a cantilevered prosthesis.
If sufficiently strong anchors are unavailable or longer cantilevers are required, problems are likely to ensue. Complications associated with posterior cantilevers include screw loosening and fracture, bone loss around the most distal fixtures, and loss of osseointegration(7) (Figure 1). As awareness of such consequences has grown, the alternative of creating non-cantilevered bone-anchored restorations has become increasingly desirable.
The following discussion reviews the development of implant solutions in the posterior maxilla and examines the feasibility of applying these solutions to the compromised patient. Future prospects are also briefly assessed.