Comparison between planned prosthetic trajectory and residual bone trajectory using surgical guides and tomography--a pilot study

Implant treatment is a highly technical and complex form of dentistry. Research and experience have shown that the success of dental implant treatment relies on a well-developed treatment plan approach that takes into account factors such as systemic condition, anatomical landmarks, occlusion, shape and density of the jawbone, and type of implant system. Historically, once the tissue was reflected, implant placement was guided by residual bone height and width, using the trajectory that was compatible with the location and direction of available bone, at times compromising prosthetic needs. The purpose of this study was to measure the amount of deviation between planned prosthetic trajectory (PPT), perpendicular to the plane of occlusion, and residual bone trajectory (RBT) in different areas of the maxillary and mandibular dental arches, using tomography in conjunction with surgical guides. Twenty-five patients with a total of 66 implant sites were selected for this study. A surgical guide with a radiopaque indicator was constructed to determine the PPT. Cross-sectional tomograms were taken through the indicator at each implant site. The outlines of the available bone, PPT and RBT, were traced, and the difference in the angulation between the two trajectories was determined. Results showed discrepancies between the PPT and the RBT to be greater in the mandibular molar areas. Further study of such pre-implant diagnostic procedures is needed to understand the relation between the PPT and RBT, thus increasing the predictability of implant success.