Effects of thread shape on the pullout strength of miniscrews

Am J Orthod Dentofacial Orthop. 2012 Aug;142(2):186-90. doi: 10.1016/j.ajodo.2012.03.023.

Abstract

Introduction: The aim of this study was to determine the effects of variations in thread shape on the axial pullout strength of orthodontic miniscrews.

Methods: A total of 35 miniscrews, 7 of each design being considered, were tested by performing pullout tests on a synthetic bone support. We used self-tapping and self-drilling miniscrews having a diameter of 2 mm and a thread shaft length of 12 mm (the longest and the largest supplied by the manufacturer). A buttress reverse thread shape served as the control design and was tested against 4 experimental designs, each manufactured with a modification in thread shape while maintaining all other characteristics. The experimental groups had the following thread designs: buttress, 75° joint profile, rounded, and trapezoidal.

Results: The control group with a buttress reverse thread shape had consistently higher pullout strength values than did the other designs. A statistically significant reduction in pullout force was found between the buttress reverse and the buttress thread miniscrews.

Conclusions: Thread design influenced the resistance to pullout of the orthodontic miniscrews. The buttress reverse thread shape provided the greatest pullout strength.

MeSH terms

  • Bone Screws*
  • Bone Substitutes / chemistry
  • Dental Stress Analysis / instrumentation
  • Humans
  • Materials Testing
  • Orthodontic Anchorage Procedures / instrumentation*
  • Orthodontic Appliance Design*
  • Polyurethanes / chemistry
  • Stress, Mechanical
  • Surface Properties
  • Torque

Substances

  • Bone Substitutes
  • Polyurethanes