Effects of screw and host factors on insertion torque and pullout strength.
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OBJECTIVE: To experimentally study the effects of altering implant length, outer diameter, cortical bone thickness, and cortical bone density on the primary stability of orthodontic miniscrew implants (MSIs). MATERIALS AND METHODS: Maximum insertion torque (IT) and pullout strength (POS) of 216 MSIs were measured in synthetic bone with different cortical densities (0.64 g/cc or 0.55 g/cc) and cortical thicknesses (1 mm or 2 mm). Three MSIs were evaluated: 6-mm long/1.75-mm outer diameter, 3-mm long/1.75-mm outer diameter, and 3-mm long/2.0-mm outer diameter. To test POS, a vertical force was applied at the rate of 5 mm/min until failure occurred. RESULTS: The 6-mm MSIs displayed significantly (P < .001) higher IT and POS than the 3-mm MSIs did. The 3-mm MSIs with 2.0-mm outer diameters showed significantly higher (P < .001) IT and POS than the 3-mm MSIs with 1.75-mm outer diameters. The IT and POS were significantly (P < .001) greater for the MSIs placed in thicker and denser cortical bone. CONCLUSION: Both outer diameter and length affect the stability of MSIs. Increases in cortical bone thickness and cortical bone density increase the primary stability of the MSIs.
author list (cited authors)
Shah, A. H., Behrents, R. G., Kim, K. B., Kyung, H., & Buschang, P. H
complete list of authors
Shah, Ankit H||Behrents, Rolf G||Kim, Ki Beom||Kyung, Hee-Moon||Buschang, Peter H