title: Effects of thread shape on the pullout strength of miniscrews.
abstract: BACKGROUND
  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.
authors.affiliation: Department of Orthodontics, School of Dentistry, University of Ferrara, Ferrara, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Gracco
authors.forename: Costantino
authors.initials: C
authors.lastname: Giagnorio
authors.forename: Serena
authors.initials: S
authors.lastname: Incerti Parenti
authors.forename: Giulio
authors.initials: G
authors.lastname: Alessandri Bonetti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Siciliani
mesh_terms: D001863:Bone Screws; D018786:Bone Substitutes / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D016382:Orthodontic Appliance Design; D011140:Polyurethanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque
chemical_list: D018786:Bone Substitutes; D011140:Polyurethanes