Do miniscrews remain stationary under orthodontic forces?
Miniscrews have been used in recent years for anchorage in orthodontic treatment. However, it is not clear whether the miniscrews are absolutely stationary or move when force is applied. Sixteen adult patients with miniscrews (diameter = 2 mm, length = 17 mm) as the maxillary anchorage were included in this study. Miniscrews were inserted on the maxillary zygomatic buttress as a direct anchorage for en masse anterior retraction. Nickel-titanium closed-coil springs were placed for the retraction 2 weeks after insertion of the miniscrews. Cephalometric radiographs were taken immediately before force application (T1) and 9 months later (T2). The cephalometric tracings at T1 and T2 were superimposed for the overall best fit on the structures of the maxilla, cranial base, and cranial vault to determine any movement of the miniscrews. The miniscrews were also evaluated clinically for their mobility (0: no movement, 1: < or =0.5 mm, 2: 0.5-1.0 mm, 3: >1.0 mm). The mobility of all miniscrews was 0 at T1 and T2. On average, the miniscrews tipped forward significantly, by 0.4 mm at the screw head. The miniscrews were extruded and tipped forward (-1.0 to 1.5 mm) in 7 of the 16 patients. Miniscrews are a stable anchorage but do not remain absolutely stationary throughout orthodontic loading. They might move according to the orthodontic loading in some patients. To prevent miniscrews hitting any vital organs because of displacement, it is recommended that they be placed in a non-tooth-bearing area that has no foramen, major nerves, or blood vessel pathways, or in a tooth-bearing area allowing 2 mm of safety clearance between the miniscrew and dental root.
Liou
Eric J W
EJ
Department of Orthodontics and Craniofacial Dentistry, Chang Gung Memorial Hospital and Graduate School of Craniofacial Medicine, Chang Gung University, 199 Tung-Hwa North Road, Taipei 105, Taiwan. lioueric@ms19.hinet.net
Pai
Betty C J
BC
Lin
James C Y
JC
D000328:Adult; D001863:Bone Screws; D002508:Cephalometry; D000044:Dental Abutments; D003757:Dental Implantation / Q000295:instrumentation / Q000379:methods; D015921:Dental Implants; D003799:Dental Stress Analysis; D005260:Female; D006801:Humans; D008310:Malocclusion / Q000628:therapy*; D008437:Maxilla; D008904:Miniaturization; D016382:Orthodontic Appliance Design; D009967:Orthodontic Appliances; D014087:Tooth Movement Techniques / Q000295:instrumentation*; D015050:Zygoma / Q000601:surgery
D015921:Dental Implants