Transtomography for implant placement guidance in non-invasive surgical procedures.

Objectives: To illustrate the use of transtomography for the placement of implants using a radiopaque radiographic guide and to evaluate the accuracy of transtomography.

Methods: The study included 11 implants inserted with minimally invasive procedures. Pre-operative, intraoperative and post-operative examinations were performed with a ProMax panoramic unit implemented with transtomographic technique (Planmeca Oy, Helsinki, Finland). At each implant site, cross-sectional and longitudinal intraoperative transtomograms were taken through a radiopaque reference guide to control and adjust the drilling axis. The effective axis on post-operative transtomograms was compared with the planned axis correction estimated on intraoperative images. Radiopaque guides, used as the gold standard, were measured on intraoperative cross-sectional slices to evaluate image distortion.

Results: Intraoperative transtomograms, with the reference guide inserted in the bone, gave clear images of the cortical plates and accurate information of drilling length and axis, which allowed the surgeon to adjust pilot drilling axis in 6 sites (54.5%) out of 11 sites, including sites with narrow bone ridges. The implant axis on the post-operative tomogram compared with the planned axis correction showed an angle difference ranging from 0.8 degrees to 3.4 degrees. The image distortion on cross-sectional slices ranged from 0.03 mm to 0.52 mm, resulting in a distortion ratio ranging from 0% to 6% when expressed in percentages.

Conclusions: Transtomographic examination performed with a radiographic reference guide during implant surgery can provide the necessary and accurate information for implant placement. Transtomography distortion appears to be less important than in other conventional tomographic systems and comparable with CT scan distortion.