Comparison of Restoratively Projected and Surgically Acceptable Virtual Implant Position for Mandibular Overdentures

Purpose: To compare differences between restoratively projected and surgically acceptable virtual implant positions at sites identified by cylindric radiopaque markers on diagnostic templates for implant-retained mandibular overdentures using cone beam computed tomography (CBCT). Materials and Methods: A retrospective chart audit of a CBCT database identified 77 subjects who had been imaged to assess the residual alveolar ridge in the completely edentulous mandible prior to implant placement for mandibular overdentures. Individuals had been scanned with a diagnostic template using cylindric markers to identify the restoratively derived locations and trajectories for implants. Qualitative and quantitative differences between restoratively projected and surgically acceptable positions on transaxial CBCT images were recorded using implant planning software based on a standard implant. Results: Only 6.4% of restoratively projected positions were within the criteria for surgically acceptable implant placement. However, most implant placement plans (77.9%) could be modified to fulfill surgically acceptable criteria. Of the projected implant positions, 15.7% were deemed inadvisable because of potential anatomical complications. Restoratively projected implant position was more likely to deviate buccally than lingually to the available residual alveolar ridge, as determined by CBCT. The mean angular deviation of the clinical prediction from ideal was 14.0 ± 5.5 degrees, the mean platform translation was 2.1 ± 1.3 mm, and the mean apex translation was 2.3 ± 1.5 mm. The average residual alveolar ridge reduction required in the posterior segment was 3.9 ± 2.5 mm. Conclusion: The restoratively projected trajectory for implant placement determined by visual inspection, diagnostic casts, and panoramic radiography deviated from the surgically acceptable location determined using CBCT data sets. Keywords: cone beam computed tomography, dental implants, dental prosthesis, edentulous jaw