INFLUENCE OF DIFFERENT PILOT HOLE SIZES ON TORQUE MEASUREMENTS AND PULLOUT ANALYSIS OF OSTEOSYNTHESIS SCREWS

When screws are inserted in thick cortical bone, a small pilot hole si ze, corresponding to the care diameter of the screw, can result in hig h torsional stress, leading to screw fracture, The aim of this study w as to enlarge the drill size up to a critical pilot hale size (CPHS) w hich, if exceeded, means a rapid decrease in the screw holding power, 1.5 and 2 mm titanium screws were inserted in discs of polyvinylchlori de (PVC), wood and porcine mandibular bone with thicknesses differing between 2 to 4 mm, using an increasing pilot hole size between 66% and 95% of the screw external diameter, Torque measurements and pullout t ests were performed and the CPHS was calculated, In torque measurement s, the CPHS of microscrews ranged between 83% and 85% of the screw ext ernal diameter (SED). The CPHS of miniscrews lay between 80% and 90% o f SED. In pullout analysis, the CPHS of microscrews ranged between 83% and 89% of SED; the CPHS of miniscrews lay between 79% and 91% of SED , The mean of the CPHS was calculated to be approximately 85% of the S ED, Up to this critical point, the pilot hole size may be increased wi thout affecting the holding power of the screws.