[Radionuclide imaging in oral implantations. Personal experience in maxillary sinus elevation].

Purpose: Presently nuclear medicine techniques are not very popular in oral implantology, but they can play an interesting role in this surgical field too. In particular bone scan with 99mTc-MDP allows to evaluate the function of oral implants and the survival of bone grafts. We report our experience with skull bone scan in maxillary sinus lifting.
Material and Methods: We performed a three-year follow-up on 13 patients treated with inlay-one stage uni- or bilateral sinus lifting with a mixture composed of 90% bovine bone powder and of 10% small bone splinters and autogenous fibrin glue. We performed imaging studies and quantitated implant MDP uptake from the mean values at the surgical site to the 5th neck vertebral ratio (M/V index). The M/V index was also statistically compared with the one measured in 13 patients with severe resorption of distal upper dental arches (bone height less than 0.5 cm) and in 63 patients with normal dental status. Scintigraphic data were interpreted in the light of clinical, radiological and histologic findings.
Results: All oral implants appeared to be fixed and radiographs showed good positioning and bone adhesion; bone height exceeded 1 cm. Peri implant biopsy material was formed by normal mature bone tissue without bovine bone granules, necrotic areas and inflammatory cells. The highest bone activity (M/V index: 1.54-2.57) was observed 1-4 months after sinus lifting. Then MDP uptake decreases and 18 months after surgery radionuclide uptake in maxillary arches is homogeneous, with M/V values of 0.81-0.88. The average M/V value in the 18 surgical sites was clearly higher than in the resorbed (1.44 vs 0.64; Kruskall-Wallis ANOVA test; Dunn's method; p < 0.05) and normal (1.44 vs 0.73; p < 0.05) maxillary arches.
Discussion and Conclusions: 99mTc-MDP can show the transformation of newformed into mature bone and then allows in vivo visualization of implant osteointegration. The importance of our work lies in the use of radionuclide imaging to assess both the function of oral implants inserted by a complex surgical technique and the expected bioactive properties of the filling mixture. Nevertheless the strong active autogenous compounds do not permit to detect the real agent of local bone induction. An interesting finding is that implant stability is biologically gained 18 months after intervention and that the uptake index facilitates comparison of sequential scans and confirmation of local bone growth. Therefore high MDP uptake by the implant 2-3 years after surgery can suggest mechanical or septic bone injury which can lead to implant failure if not treated promptly. In conclusion we believe that quantitative bone scan is a valid diagnostic tool in the follow-up of oral implants inserted with sinus lifting, though our experience needs confirmation on larger series and new research is warranted to understand the real mechanisms of assisted bone regeneration.