Titanium alloy mini-implants for orthodontic anchorage: Immediate loading and metal ion release - Corrective Dentistry (Orthodontics) Articles

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Titanium alloy mini-implants for orthodontic anchorage: Immediate loading and metal ion release
Acta Biomaterialia
Volume 3, Issue 3, May 2007, Pages 331-339

Liliane S. Morais, a, b, Glaucio G. Serra, a, b, Carlos A. Muller, c, Leonardo R. Andrade, d, Elisabete F.A. Palermo, d, Carlos N. Elias, b and Marc Meyers, a
a - Mechanical and Aerospace Engineering Department, University of California-San Diego (UCSD), San Diego, CA, United States
b - Mechanical Engineering and Material Science Department, Military Institute of Engineering (IME), Rio de Janeiro, RJ, Brazil
c - Oswaldo Cruz Institute (FIOCRUZ), Rio de Janeiro, RJ, Brazil
d - Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil
Received 23 June 2006; revised 19 October 2006; accepted 24 October 2006. Available online 25 January 2007.

Removable osseointegrated titanium mini-implants were successfully used as anchorage devices in orthodontics. The early load is necessary to simplify the mini-implant methodology, but can lead to failure during osseointegration. The TiÒ6AlÒ4V alloy was used instead of commercially pure Ti due to its superior strength. However, the corrosion resistance is low, allowing for metal ion release. The purpose of this work was to analyze the immediately loaded mini-implant fixation and to gauge the vanadium ion release during the healing process. Titanium alloy mini-implants were inserted in the tibiae of rabbits. After 1, 4 and 12 weeks, they were submitted to removal torque testing. There was no increase in the removal torque value between 1 and 4 weeks of healing, regardless of the load. Nevertheless, after 12 weeks, a significant improvement was observed in both groups, with the highest removal torque value for the unloaded group. The kidney, liver and lung were also extracted and analyzed by atomic absorption spectrometry. In comparison with the control values, the content of vanadium increased slightly after 1 week, significantly increased after 4 weeks and decreased slightly after 12 weeks, without reaching the 1 week values. A stress analysis was carried out which enables both the prediction of the torque at which commercially pure (CP) Ti and TiÒ6AlÒ4V deform plastically and the shear strength of the interface. This analysis reveals that the removal torques for CP Ti dangerously approach the yield stress. The results of this rabbit model study indicate that titanium alloy mini-implants can be loaded immediately with no compromise in their stability. The detected concentration of vanadium did not reach toxic levels in the animal model.

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