Standard Implant Placement Studies of the long-term success of osseointegrated implants placed in the posterior maxilla have painted a mixed picture. Jaffin and Berman, reporting specifically on implants used in this region8, noted a higher failure rate related to Type IV bone. Schnitman9 showed that only 72 percent of implants placed in the posterior maxilla achieved osseointegration. When Widmark et al studied the results of implants placed in the severely resorbed maxillae of 36 patients (16 of whom received bone grafting and 20 of whom did not), they found that after three to five years, the success rates in the two groups were 74% and 87%, respectively10.
Other investigators, however, have found significantly higher success rates. Bahat11, analyzing the experience with 660 Brånemark System implants placed in the posterior maxilla and followed in 202 patients for up to 12 years after loading, found a cumulative success rate of 94.4 percent at five to six years and a 93.4 percent rate after 10 years. Lazzara and coworkers found a success rate of 93.8 percent among 529 implants placed in the posterior maxilla12. The Kaplan-Meier success rate for 167 IMZ posterior maxillary implants after 80 months was 96.9 percent, according to Haas and colleagues13. And when Buchs and associates studied Steri-Oss HA-coated threaded implants, including 416 placed in the posterior maxilla, their life-table analysis indicated a 96.6 percent five-year success rate14.
A number of recommendations for achieving predictable implant osseointegration in the posterior maxilla have been made. To obtain a greater surface area for bone contact, Langer et al suggested the use of wider diameter implants15. More recently, Bahat recommended placement of a sufficient number of implants to support the occlusal load in a way that avoids nonaxial loading11.
In the author’s experience, standard implant placement in the posterior maxilla is indicated if at least 8mm of bone is available below the sinus. In such cases, a 10mm implant can be utilized. The apical threads of the implant will engage the layer of cortical bone that forms the antral floor, thereby creating bi-cortical stabilization of the fixture and a slight apical tenting of the sinus membrane. This tenting, or mini sinus lift, is similar in effect to the osteotome technique for fixture placement16.
Another alternative is to utilize longer implants, tilting them anteriorly between the floor of the sinus and the apex of the canine or other anterior teeth. Such off-axis loading of maxillary anterior implants has been shown17,18 to achieve osseointegration and create a stable support system for the prosthesis.
Immediate extraction sites also offer opportunities for standard implant placement in the posterior maxilla because residual bone usually exists around the extraction site.
When standard implants are placed in the posterior maxilla of partially edentulous patients, the final prosthesis will not enjoy the benefit of cross-arch stabilization. Therefore, more implants are recommended to prevent the overload bending moment forces that can cause bone loss around the implants (Figure 2).