Study On Effect Of Surface Microtexture On Friction And Wear Behaviors Of Orthodontic Brackets

Orthodontic archwires and brackets are important appliances for the treatment of dentofacial deformities,the teeth can be aligned neatly under the relative movement between the archwire and brackets.The effect of orthodontic treatment could be enhanced by improving the friction and wear performances between the archwire and brackets.Laser microtexturing technology has become a research focus in tribology field,because it can reduce friction and wear,improve lubrication performance and enhance surface load bearing capacity.To further improve the friction and wear performances between the archwire and brackets,the surface modification of the brackets was completed by applying laser microtexturing technology to the surface of the orthodontic brackets;and by designing the anti-friction scheme of micro-textured brackets,a stable and long-lasting low friction coefficient was achieved,and the low friction mechanism of the microtexture was discussed.In order to achieve the surface modification of orthodontic brackets,micro-grooves and micropits were manufactured on the surfaces of commercial brackets by using laser processing technology.The effects of microtexture and non-texture on the friction and wear behaviors of archwire-bracket contacts were investigated by using a home-built archwire-bracket reciprocating friction tester.The results showed that the average friction coefficient between archwire and bracket is reduced from 0.52 to 0.42 after the fabrication of micro-grooves on the brackets,and the degree of surface wear are lightened.Therefore,it was concluded that surface modification of the brackets is achieved.The minimum average friction coefficient of micropits was 0.52,thus it was argued that micro-grooves have better tribological properties than those of micro-pits.The friction and wear behaviors of micro-grooves were fruther evaluated in dry and wet environments.The results showed that the three-row groove has the best tribological properties in the artificial saliva environment,the micro-groove bracket has the lowest surface wear and the minimum friction fluctuation.To study the low friction behavior of microtextured brackets,three-row grooves with the best tribological properties were selected,and the areal density and spacing parameters of the microgrooves were optimized.The results showed that with the decrease of areal density of microgrooves from 46% to 35%,the average friction coefficient of the micro-grooves decreases from0.59 to 0.38,and the maximum static friction coefficient decreases from 0.69 to 0.55.With the decrease of spacing of the micro-grooves from 190 μm to 110 μm,the maximum static friction coefficient of the micro-grooves decreased from 0.64 to 0.43.In order to further reduce the friction coefficient,micro-groove with a spacing of 110 μm was selected for friction experiments in a dental wax environment.The micro-groove brackets exhibited low friction behavior.Specifically,the average friction coefficient was further reduced to 0.11,and the maximum static friction coefficient was reduced to 0.24.The artificial saliva in the environment will not make the low friction behavior of the micro-grooves disappear,even if the slding friction test was prolonged.The average friction coefficient was stabilized at approximately0.14,and the surface of the archwire and the brackets had no obvious wear marks.The microgroove releases the stored dental wax under the function of friction motion and load,together with flows and diffuses of the artificial saliva,and results in the formation of a stable and uniform dental wax-artificial saliva mixed lubricating layer the surface of the micro-grooves,and finally achievs a ultra-long and stable low friction behavior.