Elementary Research Of The Changes In Mechanical Properties And Surface Frictional Forces Of SS Archwires Exposed To Oral Conditions

Objective: The main purpose of this study was to investigate the changes in mechanical properties , surface frictional forces and surface topography of various orthodontic SS arch wires used in the anteriorteeth-retraction or canine-distalization period .Materials and Methods: Two types of 0.019×0.025-in rectangular SS arch wires ( marked with A and B respectively ) and two types of 0.020-in round SS arch wires ( marked with C and D respectively ) used in the comprehensive treatment with four first premolars extracted were selected .The posterior portion of each wire was segmented . The unused segments and these used ones were separated into 6 groups respectively : as-received condition ( T0 , control group ) , exposed to oral conditions for 4 weeks ( T1 ) , for 8 weeks ( T2 ) , for 12 weeks ( T3 ) , for 16 weeks ( T4 ) and for 20 weeks ( T5 ) . Changes in yield strength and modulus of elasticity were observed by tensile testing , and deflections were tested by deflection test , and static frictional coefficients by friction test . Surface topography was assessed by scanning electron microscope ( SEM ) . Results: Our findings showed that there were no statistically significant differences between the unused wires and the ones exposed to oral conditions for 4 , 8 , 12 , 16 , 20 weeks in yield strength , modulus of elasticity , and deflection ( P >.05 ) . Two types of 0.019×0.025-in rectangular SS arch wires ( i.e. A and B ) and 0.020-in round SS arch wire D showed no significant differences in static frictional coefficients after they were exposed to oral conditions for 4 , 8 weeks ( P >.05 ) , but demonstrated significantly greater static frictional coefficients compared with the control wires after their intraoral exposure for 12 , 16 , 20 weeks ( P <.01 ) . However , the static frictional coefficient of 0.020-in round SS arch wire C was greater than that of the control group after their exposure to oral conditions for 8 , 12 , 16 , 20 weeks ( P <.01 ) . Surface roughness of the wires A,B,C,D exposed to oral environment for 20 weeks was significantly greater than that of the control wires .Conclusions: During the anteriorteeth-retraction or canine-distalization period , the mechanical properties of 0.019×0.025-in rectangular SS arch wires A and B and 0.020-in round SS arch wires C and D weren't affected significantly by many oral environmental factors . It indicated that all these SS arch wires could stable the dentition and guide the tooth movement well when they were exposed to oral conditions for 4 , 8 , 12 , 16 or 20 weeks . However , oral conditions affected the surface structure of these SS arch wires and then increased their surface roughness and the frictional forces between brackets and wires after their exposure to oral environment for 12 , 16 , 20 weeks ( A , B , D ) or 8 , 12 , 16 , 20 weeks ( C ) . The greater friction opposed the free sliding action of teeth guided on appropriately shaped SS archwires .