Study On Properties Of Orthdontic Rectangular Arch Wires In Torsion

Orthodontic treatment is a process of using forces. It is very important to grasp the sorts of physical properties of orthodontic applications and arch wires using methods of biomechanics. Torque moment is one of the most important orthodontic forces controling the three-dimension movement of tooth. The using of Torque moment mainly depends on orthodontic rectangular arch wires. In order to use the moment rationally one must know the properties of the arch wires on torsion deeply.To find out the torsional properties of torque angle and torque moments with sorts of dimensions and materials, 0.018×0.025, 0.019×0.025 inch stainless steel wire and nickel titanium archwire was selected to test their torsional properties of torque angles and torque moments in 0.022 inch bracket with one instrument measuring torsion which designed and made by ourselves. The conclusions of the study were drawn as followings:1. In order to study the tosional properties of orthodontic rectangular arch wires, one torsion measurement instrument was designed and made under the cooperation of orthodontic department of Huaxi stomatology with Shichuan machine research and design office. The instrument is able to measure the torque angles and torque moments in single bracket made by orthodontic arch wires and its precision of torque moment and torque angle are 30gmmm and 0.1° respectively. The instrument was tested in repeated experiment after assembled, the results show it has a good reliable character which achieve the require of design.2. The rectangular stainless steel arch wires with 0.025 inch width section have almost 4° play each 0.001 inch in one 0.022 inch bracket.3. The rectangular nickel titanium arch wires with 0.025 inch width section have almost 6° play each 0.001 inch in one 0.022 inch bracket.4. The study considers the reason of difference in play of rectangular stainless steel and nickel titanium arch wires is variability of edge bevels. The edge bevel of rectangular nickel titanium arch wire is larger than that of stainless steel arch wire.5. Because of the irregular contact of the arch wires and brackets, there would be some torque monents in initital period of arch wires in torsion when the plays is not erased completely.6. The torsional properties of arch wires are determined by the torsional stiffnesses in the period of elastic deflection. Thetorsional stiffness is affected by shear modulus, sectional dimension and length of one arch wire. With the same secitonal dimension, rectangular stainless steel arch wires have a larger torsional stiffness than nickel titanium arch wires. 7. Under the 20Nmm moment which is the optimal moment value for the torque movement of a maxillary central incisor, 0.018×.025 and 0.019×0.025 inch rectangular stainless arch wires and nickel nitanium arch wires are both at the period of elastic delection, will not have a permanent deformation.Some suggestions were also put forward for orthodontic clinic as follows:1. To maxillary central incisors, it is not recommended that add torque angle exceed 4° and 3° each time for 0.018×0.025 and 0.019×0.025 inch rectangular stainless steel arch wires respectively.(If the interbracket distance is less than 14mm, the reference values must be reduced accordingly.)2. It is recommended that the best choice of orthodontic arch wires using for torsional movement of tooth must have the properties with low torsional stiffness, high formability and low edge bevel.