title: Insertion Torques of Self-Drilling Mini-Implants in Simulated Mandibular Bone: Assessment of Potential for Implant Fracture.
abstract: OBJECTIVE
  Fracture of orthodontic mini-implants during insertion is a limiting factor for their clinical success. The purpose of this study was to determine the fracture potential of commonly used self-drilling orthodontic mini-implants when placed into simulated thick, dense mandibular bone.
  
  
  METHODS
  Six mini-implant systems were assessed for the potential for fracture (Aarhus, Medicon; Dual-Top, Jeil Medical; OrthoEasy, Forestadent; tomas-pin, Dentaurum; Unitek, 3M; and VectorTAS, Ormco). First, mini-implants were inserted manually, without predrilling, into bone substitutes (Sawbones) with a 3-mm-thick, dense (1.64 g/cm(3)) cortical layer. A custom-made insertion device was used for placement of mini-implants. A sixaxis force/torque transducer was secured at the base of the bone blocks to measure the maximum torque experienced during insertion. Measured insertion torques were compared with previously reported fracture torques, yielding a torque ratio (insertion torque as a percentage of fracture torque), which was used as an indicator of the potential for mini-implant fracture. Mini-implants that experienced torque ratios ≥ 75% upon insertion underwent further testing, following the manufacturer's recommendations for predrilling in thick, dense bone conditions.
  
  
  RESULTS
  Significant differences in torque ratios were found among all mini-implants, except between OrthoEasy and Dual-Top, and OrthoEasy and VectorTAS. Overall, Aarhus had the highest torque ratio (91% ± 3%), with Unitek showing the lowest ratio (37% ± 3%). Aarhus and tomas-pin mini-implants displayed torque ratios ≥ 75% and experienced fracture upon insertion. When the manufacturer's specific predrilling recommendations were followed, no changes in torque ratio were found for Aarhus and tomas-pin. However, while Aarhus continued to fracture upon insertion, all tomas-pin mini-implants were inserted fully without fracture following predrilling.
  
  
  CONCLUSIONS
  These findings support the safe use of Unitek, VectorTAS, Dual-Top, and OrthoEasy self-drilling mini-implants in areas of 3-mm-thick, 1.64 g/cm(3) dense cortical bone without predrilling. Following predrilling, fractures did not occur with tomas-pin. For implants that continued to fracture after predrilling, other strategies may be required, such as the use of larger-diameter mini-implants in thick, dense bone conditions.
authors.forename: Yara K
authors.initials: YK
authors.lastname: Hosein
authors.forename: Angie
authors.initials: A
authors.lastname: Smith
authors.forename: Cynthia E
authors.initials: CE
authors.lastname: Dunning
authors.forename: Ali
authors.initials: A
authors.lastname: Tassi
mesh_terms: D000704:Analysis of Variance; D001863:Bone Screws; D018786:Bone Substitutes; D003722:Dental Alloys; D003758:Dental Implantation, Endosseous / Q000295:instrumentation / Q000379:methods*; D015921:Dental Implants; D003799:Dental Stress Analysis; D004868:Equipment Failure; D008334:Mandible / Q000601:surgery; D008422:Materials Testing; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D013314:Stress, Mechanical; D019415:Torque
chemical_list: D018786:Bone Substitutes; D003722:Dental Alloys; D015921:Dental Implants