The Effect of Implant Design and Bone Quality on Insertion Torque, Resonance Frequency Analysis, and Insertion Energy During Implant Placement in Low or Low- to Medium-Density Bone

Purpose: This study investigated the effect of implant design and bone quality on insertion torque (IT), implant stability quotient (ISO), and insertion energy (IE) by monitoring the continuous change in IT and ISO while implants were inserted in artificial bone blocks that simulate bone of poor or poor-to-medium quality. Materials and Methods: Polyurethane foam blocks (Sawbones) of 0.16 g/cm(3) and 0.32 g/cm(3) were respectively used to simulate low density and low- to medium-density cancellous bone. In addition, some test blocks were laminated with a 1-mm 0.80 g/cm(3) polyurethane layer to simulate cancellous bone with a thin cortical layer. Four different implants (Nobel Biocare Mk III-3.75, Mk III-4.0, Mk IV-4.0, and NobelActive-4.3) were placed into the different test blocks in accordance with the manufacturer's instructions. The IT and ISO were recorded at every 0.5-mm of inserted length during implant insertion, and IE was calculated from the torque curve. The peak IT (PIT), final IT (FIT), IE, and final ISO values were statistically analyzed. Results: All implants showed increasing ISO values when the implant was inserted more deeply. In contrast to the ISO, implants with different designs showed dissimilar IT curve patterns during the insertion. All implants showed a significant increase in the PIT, FIT, IE, and ISO when the test-block density increased or when the 1-mm laminated layer was present. Tapered implants showed FIT or PIT values of more than 40 Ncm for all of the laminated test blocks and for the nonlaminated test blocks of low to medium density. Parallel-wall implants did not exhibit PIT or FIT values of more than 40 Ncm for all of the test blocks. NobelActive-4.3 showed a significantly higher FIT, but a significantly lower IE, than Mk IV-4.0. Conclusions: While the existence of cortical bone or implant designs significantly affects the dynamic IT profiles during implant insertion, it does not affect the ISO to a similar extent. Certain implant designs are more suitable than others if high IT is required in bone of poor quality. The manner in which IT, IE, and ISO represent the implant primary stability requires further study.