Experimental investigation of the fracture torque of orthodontic anchorage screws.
OBJECTIVE
In contrast to dental implants that remain in the bone, orthodontic anchorage screws serve as temporary anchorage for orthodontic tooth movement and are removed after completion of treatment. The aim of the present study was to evaluate the stability of various commercially available orthodontic anchorage screws against torsion.


METHODS
The torsional deflection of ten different orthodontic anchorage screws from different manufacturers [Ortho Easy Pin (Forestadent), Benefit, quattro (both PSM Medical Solutions), Vector TAS (Ormco), AbsoAnchor(®) (DENTOS Inc.), OrthoLox, Dual-Top JA (both Promedia Medizintechnik), TAD (3M Unitek), INFINITAS (ODS) and tomas(®) (Dentaurum)] was tested in vitro in relation to the rotation angle using a self-developed set-up. The screws were positioned in a resin model with bone-like material properties. Shear tests were performed using the manufacturers' own screwdrivers. Ten screws each were turned manually until a sudden drop in the measured torque occurred. At this point, the screw head was twisted off. Fracture torque and the torque at which the screws deformed plastically were evaluated. Mean values and standard deviations were calculated.


RESULTS
According to the German industrial standard, the torque of orthodontic anchorage screws should reach at least 20 Ncm. The majority of the screws reached this nominal torque; however, a few screws fractured before reaching this value. Five screw types displayed plastic deformation below the threshold, at approximately 16 Ncm.


CONCLUSIONS
The results suggest that orthodontic anchorage screws generally meet the requirements of the standard and ensure safe clinical use. However, according to the present data, it may be assumed that a portion of the screws will be plastically deformed upon removal.
Department of Orthodontics, University of Bonn, Bonn, Germany. susanne.reimann@uni-bonn.de.|Endowed Chair for Oral Technology, Rheinische Friedrich-Wilhelms University of Bonn, Welschnonnenstrasse 17, 53111, Bonn, Germany. susanne.reimann@uni-bonn.de.
Susanne
S
Reimann
Department of Orthodontics, University of Bonn, Bonn, Germany.
Mustafa
M
Ayubi
Department of Orthodontics and Craniofacial Development, Kings College London, London, UK.
Fraser
F
McDonald
Department of Orthodontics, University of Bonn, Bonn, Germany.
Christoph
C
Bourauel
D001863:Bone Screws; D019245:Compressive Strength; D015921:Dental Implants; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D019544:Equipment Failure Analysis; D017276:Friction; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013718:Tensile Strength; D019415:Torque
D015921:Dental Implants
Biomechanics; Deformation; Orthodontic anchorage screw; Patient safety; Stability