Assessment of accuracy of navigated implant placement in the maxilla

The use of computed tomography (CT) based intraoperative navigation has greatly improved surgery in many specialties. In this study, the precision of the SMN system (Zeiss, Oberkochen, Germany) for navigated drilling and following implant placement in the maxilla was evaluated. This study should demonstrate the suitability of navigation systems for computer-assisted implantation in the maxilla to avoid perforation of the maxillary sinus.

Sixty target drillings were carried out on 10 standardized polyurethane milling models after CT scanning. The models were produced with cranial open maxillary sinuses. The CT scans were performed with a slice distance of 1 mm. Then the CT data were transferred to the workstation of the SMN system and registration of the reference markers (fiducials) for superposition of the native and CT model was done. Referencing of the model was performed with the aid of a drilling tool. This drilling tool was used for later navigation-assisted drilling into the maxilla. The target of drilling was the maxillary sinus floor. The aim was to come as near as possible without perforation. The distance from the bottom of the drilling holes to the maxillary sinus floor was measured after sectioning of the model. In another 10 models, implants were placed after performing 60 navigated drilling holes.

In the first part of the study, an average drilling depth of 6.97 mm and a mean distance to the sinus floor of 0.11 mm (standard deviation = 0.2) was found. In 13 specimens, the inferior border of the sinus was perforated. In the second part of the study, a perforation of the sinus floor by the implants was seen in 47 cases. The mean distance to the maxillary sinus was 0.25 mm (standard deviation = 0.2).

High precision of CT-based navigation for controlled preimplant drilling was seen, but a high incidence of penetrations into the maxillary sinus was caused by the subsequent implant placement.