Effects Of Different Rocking Chair Curvature Archwire On Frictional Forces Of Space Closure Using Sliding Mechanics

In clinical,for orthodontic patients who pursue a better facial profile,we usually extract4first premolars, then retract anterior teeth and close extraction space using slidingmechanics. In order to avoid overbite increasing, different rocking chair curvature archwiresis usually co-used during space closing.So far,the effects of different rocking chair curvaturearchwire on frictional forces during space closing using sliding mechanics has not carriedout.Doctors simply adopt different forces based on clinical experiences. Studying the effectsof different rocking chair curvature archwire on frictional forces of space closing usingsliding mechanics could provide orthodontists with a reference basis.Objectives: This study aims to investigate the effects of different rocking chaircurvature archwire on frictional forces of space closure using sliding mechanics,analyze thefactors of frictional forces, and provide orthodontists with a reference basis.Methods: Divide five0.018x0.025inch stainless steel wires of the same batch into4groups with different rocking chair archwire (0°、5°、10°、15°).The same division andgroups with0.019x0.025inch stainless steel wires. The samples be investigated bymicro-structure analyze。 Each rocking chair archwire is placed on the model and measuredthe maximum static frictional forces. Then the data were analysed using SPSS17.0software.Results：The microscopic structure of the braces and arch wires show that there aremany irregular bumps and cracks on the surfaces. The chemical composition of braces andarch wires is1Cr18Ni9Ti which is not toxic.The more nickel and chromium in the bracesand arch wires, the better corrosion resistance is. There are many directional micro-cracks onthe surfaces of stainless steels. According to the direction of the cracks we determine thesliding direction of the arch wire while space closing.The0.019×0.025inch stainless steel archwires with0°,5°,10°,15°rocking chairarchwire produce the higher frictional forces than0.018×0.025inch stainless steel with thesame degree rocking chair curvature. There were significant difference in the statistics (p<0.05) of different size stainless steel aichwires with the same rocking chair curvaturearchwire. With the curvature increasing, the frictional forces of the Rocking Chair Archwiregradually increase. Paired t-test showed that there were significant difference in the statistics (p <0.05).But There were not significant difference in statistics(p=0.126) between the5°and10°rocking chair archwire of0.019×0.025inch stainless steel. It may be caused byoperational errors. The frictional force of0.018×0.025inch stainless steel with15°rockingchair curvature archwire is243.2±38.61(g).The force of0.019×0.025inch stainless steelwith5°rocking chair archwire is148.53±31.97(g).Both are more than150g.Conclusion: Many factors can affect the friction force,which varies in a large range.The size and curvature of archwire play an important role in the friction force. The greaterfriction force is accompanied with the bigger size and the larger rocking chair curvature.In clinical, we often extract4first premolars, then close space using slidingmechanics.In order to prevent the anchorage loss,0.018×0.025inch stainless steel archwirewith smaller than15°rocking chair curvature and0.019×0.025inch stainless steel archwirewith no more than5°rocking chair curvature is recommended for use.