Transfer precision of three-dimensional implant planning with CT assisted offline navigation

Computer-assisted surgery (CAS) is used in implant dentistry for preoperative planning and intraoperative transfer of the correct implant position. Implant placement is performed via sleeve-guided templates in the case of static navigation procedures by taking into consideration prosthetics and the amount of local bone. The aim of the present in vitro study was to analyze the transfer precision of the computer-aided planning system Med3D as well as the possible improvement of transfer accuracy by using a second, template-guided drilling during osteotomy.

A total of 48 implants were placed into 8 study models from calf ribs. Preoperative computed tomography (CT) scans were imported via the respective software and used for virtual planning of the implant position on the computer. CT control images were taken after the actual implant site preparation via sleeve-guided drilling templates and subsequent implant placement. The preoperative CT scans were compared to the post-operative CT images in order to analyze transfer precision. Vertical, radial and axis deviations were calculated for each implant.

The minimal deviations obtained between the planned and the achieved implant position have shown that a transfer accuracy within the range of 0.1 mm is feasible when utilizing the MED-3D system. However, maximal vertical deviations of up to 2 mm have to be considered. The maximal axis deviation may reach 16 degrees. Deviations from the planned implant position seem to be influenced especially by the local bone quality and quantity. Transfer precision may be significantly improved by adopting a second, sleeve-guided implant site preparation.

Static procedures allow for a precise transfer of the virtual, computer-assisted implant planning to the surgical site. However, transfer deviations of up to 2 mm in all directions should be considered in order to prevent impairment of anatomical structures. Local bone quality and quantity seem to influence the deviations from the implant position planned. A significant improvement of the transfer precision can be achieved by applying a second sleeve-guided site preparation.