Effects of Stainless Steel Miniscrew Length on Primary Stability: An in vitro Study

Abstract

The aim of the study was to determine the effects of different stainless steel miniscrew implant lengths on maximum insertion torque and pull-out strength in a location with relatively low bone density and cortical bone thickness. Thirty six stainless steel miniscrew implants were evenly assigned to three groups (n=12) according to size: 2 mm x 8 mm, 2 mm x 10 mm, and 2 mm x 12 mm. The implants were wrenched into artificial bone blocks. The artificial bone blocks were made of two different densities, 20 pounds per cubic foot (pcf) and 10 pcf, to replicate the cortical and cancellous bone in the posterior maxilla, respectively. The maximum insertion torque and pull-out strength were measured using a digital torque gauge and universal testing machine, respectively. One-way analysis of variance (ANOVA) and Tukey's multiple comparisons test were performed. The significance level was determined at 5%. The results showed that the 2 mm x 12 mm miniscrew implants had significantly greater maximum insertion torque than the 2 mm x 8 mm and 2 mm x 10 mm implants, whereas there was no significant difference between the 2 mm x 8 mm and the 2 mm x 10 mm implants. The pull-out strength significantly increased in a length-dependent manner. In conclusion, all tested miniscrew implant lengths provided appropriate acceptable maximum insertion torque and pull-out strength for miniscrew implant placement in a location with relatively low bone density and cortical bone thickness.