On Demand Primary Stability for Dental Implants

Objectives: Using a calcium phosphate-based adhesive cement to glue implants in place, factors influencing the resulting primary stability, including implant diameter, length, thread design and the distance from the implant surface to the simulated bone wall (cement gap size), were examined. As the adhesive is a viscous paste upon placement, insertion torque cannot be used to assess primary stability. Therefore, the potential for using removal torque as a surrogate measure for primary stability was also evaluated.
Methods: Cylindrical osteotomies were prepared in PUR plates, yielding cement gap sizes of either 0.5, 1.0, 1.5 or 3.0 mm. The adhesive cement was injected into the osteotomies and implants were placed by submerging the endosteal area into the center of the cement filled defect, using a jig to ensure alignment. Following 15 minutes of curing, removal torque was measured. For each parameter, 10 samples were tested.
Results: Increasing cement gap size did not significantly affect the primary stability, however, it was associated with a larger spread of the data. For same diameter implants, a direct correlation between torque-out values and implant surface area was observed. Increasing the diameter of the implant yielded higher torque-out values, relative to lower diameter implants, having the same surface area. The results from different thread designs indicated that lower removal torque values might be associated with more pronounced thread designs. Overall, the lowest median value (39 Ncm) was found for the implant with the lowest endosteal area, placed with the largest cement gap size (3 mm).
Conclusions: The obtained removal torque values indicate that the adhesive cement is a potent candidate for enhancing primary implant stability under non-optimal geometrical conditions. Additionally, removal torque was found to be a suitable surrogate measure for assessing primary stability. Further testing of the material, in vivo, is ongoing to determine the clinical relevance of the cement.