2 ORTHODONTICS he Art and Pratice of Dentofacial Enhancement Scienti ic Innovation 1 [au: title?], Department of Orthodontics, School of Dental Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2 [au: please provide professional afiliation.] 3 Assistant Professor, Babol University of Medical Sciences, [au: location?]. 4 [au: please provide professional afiliation.] CORRESPONDENCE Dr Allahyar Geramy Department of Orthodontics School of Dental Medicine Tehran University of Medical Sciences North Kargar Tehran 14176-14411 Iran Email: gueramya@yahoo.com, gueramya@tums.ac.ir Mini-implant loosening: 3D analysis using the inite element method Allahyar Geramy 1 Jean Marc Retrouvey 2 Reza Jelodar 3 Hasan Salehi 4 [au: please provide academic degrees (ie, DDS, DMD) for each author] Aim: Mini-implants are a relatively new method for absolute anchorage control in orthodontics. Their failure due to loosening is a multifactorial problem. Improper positioning of mini-implants with different diameters is evaluated in this study via the inite element method. Methods: Twelve 3D inite element models of a mandibular posterior segment were designed and included the irst molar, a mini-implant, the periodontal ligament, and spongy and cortical bone. They were similar except for the mini-implant position and diameter (1.3, 1.6, and 2.2 mm). A vertical force of 300 N was applied to the occlusal molar surface. The von Mises stress and energy produced by the applied occlusal forces were assessed in the mini-implant and bone. Results: The stress indings were between 15.284 and 359.77MPa for the mini-implant based on their diameters and locations.The mini-implant energy indings were between 0.00084 and 0.258 mJ. These ranges for the bone stress and energy changes were 17.611 and 129.45Mpa and 0.296 and 1.575 mJ, respectively. Conclusion: A decrease in the distance between the mini-implant and tooth root has a direct effect on different parameters to explain mini-implant loosening. Orthodontics (Chic) 2012;13:xxx–xxx. Key words: absolute anchorage, inite element method, mini-implant loosening A nchorage control is one of the most important aspects of orthodontic biomechanics. Poor anchorage control during tooth movement may increase treatment time and lead to unfavorable results. Mini-implants are used for absolute anchorage control in orthodontic treatment. The suc- cess rate for mini-implants has been reported to be 87.5% to 100%. 1–3 A mini-implant’s stability is correlated to the degree of inlammation, 4 local irritation, 5 excessive orthodontic load, 1 quality and quantity of cortical bone, 6 design and shape of screw thread, 7,8 and mini-implant proximity with adjacent tooth roots. 9–11 Other factors such as patient age [au: edit ok?], insertion site of the mini-implant, craniofacial pattern, 1,12,13 and the amount of the implant placement torque (IPT) have also been assessed. 14 Shan et al 15 showed that implanting angles have much more inluence on stress distribution and that the stress is located primarily at the neck of the mini-implant. Also, a decreased implant angle and a reduced angle between the load line and implant long axis can decrease peak stress. 15