title: Primary failure rate for 1680 extra-alveolar mandibular buccal shelf mini-screws placed in movable mucosa or attached gingiva.
abstract: OBJECTIVE
  To compare the initial failure rate (≤4 months) for extra-alveolar mandibular buccal shelf (MBS) miniscrews placed in movable mucosa (MM) or attached gingiva (AG).
  
  
  METHODS
  A total of 1680 consecutive stainless steel (SS) 2 × 12-mm MBS miniscrews were placed in 840 patients (405 males and 435 females; mean age, 16 ± 5 years). All screws were placed lateral to the alveolar process and buccal to the lower first and second molar roots. The screw heads were at least 5 mm superior to the soft tissue. Loads from 8 oz-14 oz (227 g-397 g, 231-405 cN) were used to retract the mandibular buccal segments for at least 4 months.
  
  
  RESULTS
  Overall, 121 miniscrews out of 1680 (7.2%) failed: 7.31% were in MM and 6.85% were in AG (statistically insignificant difference). Failures were unilateral in 89 patients and bilateral in 16. Left side (9.29%) failures was significantly greater (P < .001) compared with those on the right (5.12%). Average age for failure patients was 14 ± 3 years.
  
  
  CONCLUSIONS
  MBS miniscrews were highly successful (approximately 93%), but there was no significant difference between placement in MM or AG. Failures were more common on the patient's left side and in younger adolescent patients. Having 16 patients with bilateral failures suggests that a small fraction of patients (1.9%) are predisposed to failure with this method.
authors.affiliation: a   Private Practice, Beethoven Orthodontic Center, Hsinchu City, Taiwan.
authors.forename: Chris
authors.initials: C
authors.lastname: Chang
authors.affiliation: b   Assistant Professor, Department of Orthodontics and Orofacial Genetics, Indiana University School of Dentistry, Indianapolis, Ind.
authors.forename: Sean S Y
authors.initials: SS
authors.lastname: Liu
authors.affiliation: c   Professor Emeritus of Orthodontics and Adjunct Professor of Mechanical Engineering, Indiana University and Purdue University, Indianapolis, Ind.
authors.forename: W Eugene
authors.initials: WE
authors.lastname: Roberts
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D002648:Child; D004868:Equipment Failure; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000601:surgery*; D052280:Orthodontic Anchorage Procedures / Q000379:methods; D012189:Retrospective Studies; D055815:Young Adult
keywords: Alveolar mucosa; Attached gingiva; Extra-alveolar orthodontic anchorage; Mandibular buccal shelf; Miniscrews; Skeletal anchorage