Effects of sodium fluoride mouth rinses on the torsional properties of miniscrew implants Takeshi Muguruma, a Masahiro Iijima, b William A. Brantley, c Toshihiro Yuasa, d Hee-Moon Kyung, e and Itaru Mizoguchi f Ishikari-Tobetsu, Japan, Columbus, Ohio, and Daegu, South Korea Introduction: Effects of sodium fluoride (NaF) mouth rinse solutions on torsional properties of a miniscrew implant were investigated. Methods: As-received Ti-6Al-4V miniscrew implants (AbsoAnchor [Dentos, Inc., Daigu, Korea]) were immersed in 0.1% or 0.2% NaF mouth rinse solution (pH 5.12 and 5.14, respectively) for 1 hour or 24 hours. Miniscrew implants selected as controls were not immersed. Each implant was subjected to increasing torque until fracture (n 5 5 in sample groups). Mean moment and twist angle for fracture were compared using 1-way analysis of variance (ANOVA). Surfaces of implants after immersion were observed with a scanning electron microscope (SEM). Electron microprobe and micro-x-ray diffraction analyses were performed to obtain composition information about deposits on implant surfaces. Results: Pits and cracks formed on the implant surfaces after immersion in both NaF mouth rinse solutions. Corrosion products, probably sodium aluminum fluoride (Na 3 AlF 6 ), were observed on the implants after immersion in both NaF solutions for both time periods. There were no significant differences for mean torque (P 5 0.063) and twist angle (P 5 0.696) at fracture compared with control implants. Conclusions: Although titanium alloy miniscrew implants corroded slightly from immersion in 0.1% or 0.2% NaF solutions, mouth rinsing by patients with the same fluoride solution concentrations should not cause deterioration of their torsional performance. (Am J Orthod Dentofacial Orthop 2011;139:588-93) S ince the technique employing implants for skele- tal anchorage was introduced, titanium miniscrew implants have become very popular because of lower cost, simpler placement, and removal with less traumatic surgery and less discomfort for patients. 1,2 However, we have experienced occasional fracture of the miniscrew implants during placement or removal. Recent clinical studies have also reported fracture of miniscrew implants. 3,4 Miniscrew implant fracture is a serious problem for the orthodontist and patient because it is sometimes difficult to remove the implant fragment from inside the bone. Because the demineralization of enamel adjacent to an orthodontic fixed appliance is a significant clinical problem, fluoride-containing products such as tooth- paste, bonding materials, and solutions for prevention of dental caries are commonly used in clinical orthodon- tics. 5-7 Mouth rinsing with fluoride-containing products is an effective method for prevention of caries because orthodontic fixed appliances have complicated morphol- ogies. 6 However, reduced corrosion resistance of pure titanium and titanium alloys in fluoride-containing envi- ronments that attack the protective surface oxide has been reported, 8-13 because F  ions in the solution combine with H 1 ions to form hydrogen fluoride (HF), even if the NaF concentration is low. 14 Clinically available fluoride-containing products have a variety of fluoride concentrations (250 to 10,000 ppm) and pH (approximately 3.5 to 7.0). 15 The corrosion of titanium is affected not only by fluoride concentration but also by pH. 10,12 Therefore, titanium corrodes in the a Instructor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan. b Associate professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan. c Professor, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University, Columbus, OH. d Instructor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan. e Professor, Department of Orthodontics, School of Dentistry, Kyungpook National University, Daegu, South Korea. f Professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan. The authors report no commercial, proprietary, or financial interest in the prod- ucts or companies described in this article. Reprint requests to: Masahiro Iijima, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Kanazawa 1757, Ishikari-Tobetsu, Hokkaido 061-0293, Japan; e-mail, iijima@hoku-iryo-u.ac.jp. Submitted, February 2009; revised, April 2009; accepted, May 2009. 0889-5406/$36.00 Copyright Ó 2011 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2009.05.042 588 ORIGINAL ARTICLE