Effects of Pre-drilled Pilot-hole Diameters on Miniscrew Implant Primary Stability: An In vitro study
Objective: To evaluate the effects of pre-drilled pilot-hole diameters on the primary stability of palatal miniscrew implants in synthetic composite palatal bone substitute using maximal insertion torque and pull-out strength measurements.
Materials and Methods: Sixty titanium alloy miniscrew implants, with a length of 6.0 mm and a diameter of 1.8 mm, were divided into six groups, 10 each, of different-sized pre-drilled pilot-hole (1.1-mm, 1.2-mm, 1.3-mm, 1.4-mm and 1.5-mm diameters, and no pilot-hole as a negative control group). The different sizes of pre-drilled pilot holes were created in synthetic composite palatal bone blocks (bone density of 0.32 g/cc for cancellous bone, and 0.64 g/cc for cortical bone). The maximal insertion torque was recorded as the implant threads were engaged into the bone block at a depth of 5.0 mm. The vertical pull-out strength was measured at a 10 mm/min rate of removal until the implant was separated from the block.
Results: Mean maximal insertion torque showed significant differences (p<0.001) among the six groups. The control group showed the greatest maximal insertion torque (11.58 Ncm). This torque decreased with increased pilot-hole diameter. The 1.5-mm pilot-hole exhibited the least maximal insertion torque (4.08 Ncm). There were no significant differences in pull-out strength between the no-pilot-hole and 1.1-mm and 1.2-mm pre-drilled pilot-hole diameters (61.1% and 67.7% of the implant outer diameter, respectively) (p>0.05). However, the significant differences were found between 1.3-mm, 1.4-mm, and 1.5-mm pilot-hole diameters, (72.2%, 77.8%, and 83.3% the implant outer diameter, respectively) (p>0.001).
Conclusions: The maximal insertion torque and the pull-out strength decrease when pre-drilled pilot-hole diameter increases. The 1.1-mm- and 1.2-mm-diameter pre-drilled pilot-hole provide optimal primary stability and are suggested for 1.8 mm x 6 mm titanium alloy implant placement in synthetic palatal bone.
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