Management of the Posterior Maxilla in the Compromised Patient: Historical, Current, and Future Perspectives
CONTINUED (Page 6)
Thomas J. Balshi & Glenn J. Wolfinger
Periodontology 2000, Vol 33, 2003, 67-81.
The volume of bone in the pterygomaxillary area is not always sufficient to support placement of implants. In such cases, when patients have severely atrophic maxillas and are unwilling or unable to undergo extensive bone grafting, Zygoma fixtures (Nobel Biocare, Göteborg, Sweden) may provide an alternative.
Ranging in length from 30mm to 52.5mm, Zygoma fixtures are anchored in two different types of bone. The head of the fixture normally emerges in a slightly palatal position in the second premolar or first molar area of the maxilla, while the other end of the fixture engages the very dense midfacial zygomatic bone. The body of the fixture thus traverses the posterior portion of the maxillary sinus, ideally avoiding penetration of the sinus mucosa. Initial sinoscopic studies of patients treated with Zygoma fixtures indicate that the presence of a titanium foreign material inside the sinus cavity does not appear to increase the risk of inflammatory reactions in the nasal and maxillary sinus mucosa.
Preparation of the fixture sites is accomplished with the patient under deep sedation or general anesthesia. After determining the exact point on the alveolar crest to start the drilling sequence and the direction of the long axis of the fixture, a series of long twist drills of increasing diameter is used to prepare the receptor sites. A Zygoma fixture is then placed and allowed to heal for five to six months before being loaded.
Because of the greatly increased length of the fixtures and the limited bone support commonly found in the alveolar crest, Zygoma fixtures have an increased tendency to bend under horizontal loads. Since bending forces can jeopardize the long-term stability of implant-supported restorations, Zygoma fixtures must be placed in combination with at least two, and preferably more, standard implants in the anterior maxilla, in order to distribute the functional load and prevent rotation. The restoration should ideally include cross-arch stabilization (Figures 6,7), decreased buccal lever arms, decreased cantilevers, balanced occlusion, and decreased cuspal inclination.
Placement of the Zygoma fixtures is demanding and difficult, requiring considerable surgical expertise. On the other hand, this approach offers patients and implant practitioners a number of advantages, including shorter treatment and hospitalization times than that required by most grafting procedures, as well as reduced pain and risk of morbidity. The ability to use fewer implants may also result in lower treatment cost.
One study of the Zygoma fixture by Brånemark has indicated an overall success rate of 97 percent38, but this evaluation is only preliminary.