ORIGINAL ARTICLE Sequential bone healing of immediately loaded mini-implants Glaucio Serra, a Liliane S. Morais, a Carlos Nelson Elias, b Marc A. Meyers, c Leonardo Andrade, d Carlos Muller, e and Marcelo Muller e Rio de Janeiro, Brazil, and San Diego, Calif Introduction: The relatively small size and the ability to load mini-implants without delay are important changes in the simplification of bone rigid anchorage. The purpose of this study was to analyze interfacial healing 1, 4, and 12 weeks after the placment of titanium mini-implants in New Zealand rabbits by removal torque test (RTT) and scanning electron microscopy (SEM). Methods: Eighteen animals were used in the experiment, in which 72 titanium grade 5 mini-implants 2.0 mm in diameter and 6.0 mm long, were placed. Each animal received 4 mini-implants; 2 were immediately loaded with 1 N. Results: The RTT means for the unloaded mini-implants at 1, 4, and 12 weeks were 15.2  4.2 N mm (n = 5), 13.1  5.7 N mm (n = 5), and 54.4  12.8 N mm (n = 4), respectively. The loaded groups had means of 12.7  5.1 N mm (n = 4), 11.1  5.4 N mm (n = 4), and 32.9  12.8 N mm (n = 5) for the same healing periods, respectively. The statistical evaluation indicated significance in the comparison between loaded and unloaded 12-week groups (P 0.05). SEM analysis in the loaded group showed the formation of less fibrous interfacial tissue after 4 weeks and more lamellar appearance after 12 weeks. Conclusions: The immediate 1-N load did not cause significant changes in the fixation of the mini-implants after 1 and 4 weeks of bone healing. Nevertheless, after 12 weeks, the loaded group had significantly lower RTT values than the unloaded group without compromising the stability of the mini-implants (P 0.05). (Am J Orthod Dentofacial Orthop 2008;134:44-52) C onventional implants have proved to be suc- cessful for orthodontic anchorage. 1-4 Neverthe- less, the substantially different needs between orthodontic and prosthetic implants resulted in the development of systems specific to orthodontic use, such as plates, 5 onplants, 6 bicortical screws, 7 and mini- implants. 8-11 Mini-implants became widely used because they have few limitations of placement sites, a simple surgical procedure, little postoperative pain, low cost, easy maintenance of oral hygiene, and easy attachment of elastics or springs. 8,10,11 The methodology for implemen- tation of mini-implants is continuously being devel- oped. The smaller implant size permits more placement sites but influences in the material of choice. 12,13 In addition, the required early load has an important influence on the characteristics of the newly formed bone. 2,14,15 Commercially pure titanium is the most used ma- terial in implantology, and, due to its particular fea- tures, excellent results were described in animal and human research. 7,16-18 However, the size reduction of titanium mini-implants could result in fracture during placement and removal. 12,19 The use of titanium alloys could overcome this disadvantage, 20-23 but osseointe- gration could be impaired. 24 Implants of 3 to 4 mm in diameter and 6 to 13 mm in length loaded just after an unloaded healing period were extensively tested and had high success rates. 4,15,25 Nev- ertheless, mini-implants have had more clinical failures than conventional implants. 13 Important changes in implant size and, consequently, in the bone contact and the force transmission could be related to these failures. Moreover, the anchorage value of implants depends on the response of supporting bone to applied loads. 26,27 Huja and Roberts 26 concluded that an elevated rate of remodeling within about 1 mm of the loaded implant surface is a long, continuous process that maintains the inert metal in compliant bone. The continuous remod- eling is a possible mechanism whereby loaded implants resist bone fatigue and maintain the integration in less a Postgraduate student, University of California at San Diego; Engineering Military Institute, Rio de Janeiro, RJ, Brazil. b Professor, Department of Mechanical Engineering and Materials Science, Military Engineering Institute, Rio de Janeiro, RJ, Brazil. c Professor, Department of Mechanical and Aerospace Engineering, University of California at San Diego. d Professor, Department of Biomineralization, University of Brazil, Rio de Janeiro, Brazil. e Reseacher, Department of Animal Experimentation, Oswaldo Cruz Institute, Rio de Janeiro, RJ, Brazil. Supported by CAPES, Ministry of Education and Culture, Brazil. Reprint requests to: Glaucio Serra, Av Nossa Senhora de Copacabana 1355, Apt 805, Copacabana, Rio de Janeiro, RJ, Brazil; e-mail, gserrag@ hotmail.com. Submitted, February 2006; revised August 2006; and accepted September 2006. 0889-5406/$34.00 Copyright © 2008 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2006.09.057 44