title: Effects of insertion angle and implant thread type on the fracture properties of orthodontic mini-implants during insertion.
abstract: OBJECTIVE
  To determine the effects of insertion angle (IA) and thread type on the fracture properties of orthodontic mini-implants (OMIs) during insertion.
  
  
  METHODS
  A total of 100 OMIs (self-drilling cylindrical; 11 mm in length) were allocated into 10 groups according to thread type (dual or single) and IA (0°, 8°, 13°, 18°, and 23°) (n = 10 per group). The OMIs were placed into artificial materials simulating human tissues: two-layer bone blocks (Sawbones), root (polymethylmethacrylate stick), and periodontal ligament (Imprint-II Garant light-body). Maximum insertion torque (MIT), total insertion energy (TIE), and peak time (PT) were measured and analyzed statistically.
  
  
  RESULTS
  There were significant differences in MIT, TIE, and PT among the different IAs and threads (all P < .001). When IA increased, MIT increased in both thread groups. However, TIE and PT did not show significant differences among 0°, 8°, and 13° IAs in the dual-thread group or 8°, 13°, and 18° IAs in the single-thread group. The dual-thread groups showed higher MIT at all IAs, higher TIE at 0° and 23° IAs, and longer PT at a 23° IA than the single-thread groups. In the 0°, 8°, and 13° IA groups, none of the OMIs fractured or became deformed. However, in the 18° IA group, all the OMIs were fractured or deformed. Dual-thread OMIs showed more fracturing than deformation compared to single-thread OMIs (P < .01). In the 23° IA group, all OMIs penetrated the artificial root without fracturing and deformation.
  
  
  CONCLUSIONS
  When OMIs contact artificial root at a critical contact angle, the deformation or fracture of OMIs can occur at lower MIT values than those of penetration.
authors.affiliation: Department of Orthodontics, School of Dentistry, Seoul National University, Seoul, South Korea.
authors.forename: Il-Sik
authors.initials: IS
authors.lastname: Cho
authors.forename: Tae-Woo
authors.initials: TW
authors.lastname: Kim
authors.forename: Sug-Joon
authors.initials: SJ
authors.lastname: Ahn
authors.forename: Il-Hyung
authors.initials: IH
authors.lastname: Yang
authors.forename: Seung-Hak
authors.initials: SH
authors.lastname: Baek
mesh_terms: D001842:Bone and Bones / Q000033:anatomy & histology; D019245:Compressive Strength; D015921:Dental Implants; D003760:Dental Impression Materials / Q000737:chemistry; D055119:Elastic Modulus; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008904:Miniaturization; D008953:Models, Anatomic; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation / Q000379:methods*; D016382:Orthodontic Appliance Design; D010513:Periodontal Ligament / Q000033:anatomy & histology; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012826:Silicone Elastomers / Q000737:chemistry; D013499:Surface Properties; D013718:Tensile Strength; D013997:Time Factors; D014092:Tooth Root / Q000033:anatomy & histology; D019415:Torque
chemical_list: D015921:Dental Implants; D003760:Dental Impression Materials; C521416:Imprint II; D011140:Polyurethanes; D012826:Silicone Elastomers; D019904:Polymethyl Methacrylate