title: Effects of tooth root contact on the stability of orthodontic anchor screws in the maxilla: Comparison between self-drilling and self-tapping methods.
abstract: BACKGROUND
  We evaluated the effects of screw placement angle on the frequency of root contact and the effects of root contact on screw stability, comparing self-drilling and self-tapping methods.
  
  
  METHODS
  In total, 80 patients with 142 screws (diameter, 1.6 mm; length, 8.0 mm) were included. Cone-beam computed tomography images were taken. Cortical bone thickness, interroot distance, shortest distance between the screw and adjacent tooth root, and screw placement angle were measured.
  
  
  RESULTS
  The success rates of the screws were 91.5% for the self-drilling method and 94.4% for the self-tapping method (P >0.05). The self-drilling screws tended to contact the distal tooth roots in the right maxilla. In the self-drilling method, the failure rate was significantly higher in the root contact group than in the no-contact group (P <0.05).
  
  
  CONCLUSIONS
  The success rate was not significantly different between the self-drilling and the self-tapping methods in the maxilla. Avoidance of tooth root contact may improve the success rate more in the self-drilling method than in the self-tapping method.
authors.affiliation: Postgraduate student, Department of Orthodontics, School of Dentistry, Nihon University, Tokyo, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Iwai
authors.affiliation: Associate professor, Department of Orthodontics, Division of Clinical Research, Dental Research Center, School of Dentistry, Nihon University, Tokyo, Japan. Electronic address: motoyoshi.mitsuru@nihon-u.ac.jp.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Motoyoshi
authors.affiliation: Resident, Department of Orthodontics, Division of Clinical Research, Dental Research Center, School of Dentistry, Nihon University, Tokyo, Japan.
authors.forename: Yasuki
authors.initials: Y
authors.lastname: Uchida
authors.affiliation: Assistant professor, Department of Orthodontics, School of Dentistry, Nihon University, Tokyo, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Matsuoka
authors.affiliation: Professor and chair, Department of Orthodontics, Division of Clinical Research, Dental Research Center, School of Dentistry, Nihon University, Tokyo, Japan.
authors.forename: Noriyoshi
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D000328:Adult; D001863:Bone Screws; D002508:Cephalometry / Q000379:methods; D054893:Cone-Beam Computed Tomography / Q000379:methods; D003724:Dental Arch / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008437:Maxilla / Q000000981:diagnostic imaging / Q000601:surgery; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods; D016382:Orthodontic Appliance Design; D013499:Surface Properties; D016019:Survival Analysis; D014092:Tooth Root / Q000000981:diagnostic imaging*; D055815:Young Adult