title: Effect of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws.
abstract: OBJECTIVE
  To evaluate the effects of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws in a synthetic canine cancellous bone substitute.
  
  
  METHODS
  75 synthetic cancellous bone blocks (15 blocks/group).
  
  
  METHODS
  For groups 1 through 5, screw size-pilot hole diameter combinations were 3.5-2.5 mm (cortical screws), 4.0-2.5 mm, 4.0-2.5 mm, 4.0-2.0 mm, and 4.0-2.0 mm, respectively. Holes were tapped in groups 1, 2, and 4 only (tap diameter, 3.5, 4.0, and 4.0 mm, respectively). One 70-mm-long screw was inserted into each block; in a servohydraulic materials testing machine, the screw was extracted (rate, 5 mm/min) until failure. Mean group values of maximum insertion torque, axial pullout strength, yield strength, and stiffness were determined.
  
  
  RESULTS
  Mean maximum insertion torque differed significantly among the 5 groups; the group 5 value was greatest, followed by group 3, 4, 2, and 1 values. Group 3, 4, and 5 axial pullout strengths were similar and significantly greater than the group 2 value; all values were significantly greater than that for group 1. Group 5 and 4 yield strengths were similar and significantly greater than the group 3, 2, and 1 values. Stiffness in group 3 was similar to group 4 and 2 values but significantly greater than the group 5 value; all values were significantly greater than that for group 1.
  
  
  CONCLUSIONS
  These synthetic cancellous bone model findings suggested that tapping a 2.0-mm-diameter pilot hole when placing a 4.0-mm screw is the optimal insertion technique.
authors: South Carolina Veterinary Specialists, 3912 Fernandina Rd, Columbia, SC 29210, USA. karkdvm@hotmail.com
authors: Kevin A R
authors: KA
authors: Kunkel
authors: Jonathan T
authors: JT
authors: Suber
authors: Patrick D
authors: PD
authors: Gerard
authors: Michael P
authors: MP
authors: Kowaleski
mesh_terms: D000818:Animals; D001863:Bone Screws; D018786:Bone Substitutes; D001842:Bone and Bones; D004285:Dogs; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005592:Fracture Fixation / Q000295:instrumentation / Q000379:methods* / Q000662:veterinary; D016268:Internal Fixators; D008422:Materials Testing; D011140:Polyurethanes; D013314:Stress, Mechanical; D013718:Tensile Strength; D019415:Torque
chemical_list: D018786:Bone Substitutes; D011140:Polyurethanes