| Objective: The orthodontic force directly affects the orthodontic efficacy as well asdental and periodontal health.There are a variety of orthodontic arch wires. Nickel-titanium（NiTi） arch wires are very popular with orthodontists soon after they are developedbecause of their gentle orthodontic force, good elasticity, accurate and rapid aligned effect.At present， the superelastic(SE) nickel titanium arch wires and heat-activated(HA)nickel-titanium arch wires are regularly as the initial wires used in aligned phase oforthodontic treatment. The purpose of this experiment is to evaluate the mechanicalproperties of SE NiTi wires and HA NiTi wires by three point bending tests to helporthodontists select orthodontic NiTi wires.Methods: In this experiment, we selected15kinds NiTi arch wires commonly used inclinical orthodontic treatment of four manufacturers (TP, NIC, IMD and3M) and two sizes(0.014inches and0.016inches).The arch wires were subjected to bending at a constanttemperature of37°C test,including8kinds of SE NiTi wires and7kinds of HA NiTiwires.Then we obtained load–deflection curves, and compared the unloading plateau withthe plateau length, the plateau slope and average plateau force for each type of wires.Results: The unloading curves of15kinds NiTi arch wires all presented a plateau andthe superelasticity ratio（SER）of each wire was greater than2. Statistical analysis showedthat the plateau length, the plateau slope and average plateau force of different brands oforthodontic NiTi arch wires were statistically significant (p <0.05).Among differentorthodontic NiTi wires with the same dimension and type, the plateau length of NIC (SE2.45±0.05mm,HA2.87±0.05mm) and IMD NiTi wires (SE2.42±0.06mm, HA2.82mm±0.06mm)were significantly longer than TP and3M NiTi arch wires (p <0.05). The plateauslope of3M SE NiTi wires were significantly greater than other SE NiTi wires (p <0.05),but among the HA NiTi wires, the plateau slop of TP and3M company’s productswere much more flat (p <0.05).The average plateau force of IMD company’s products(0.014inch SE159.91±6.90g,0.016inch HA207.26±6.58g,0.014inch HA70.73±2.35g and0.016inch HA132.88±4.48g)were obviously greater than others (p <0.05),while3Mcompany’s wires produced the smallest force (107.85±5.40g) among the4kinds0.014inchSE NiTi wires and TP company’s wires produced the smallest force (153.02±5.30g) among the4kinds0.016inch SE NiTi wires. Among the HA NiTi wires, NIC company’s wiresproduced the smallest force(0.014inch64.96±2.16g and0.016inch93.42±3.54g). The TPand3M company ’s wires had the lowest hysteresis while IMD ’s wires had the highesthysteresis among SE NiTi wires.There were significant differences on mechanical properties (including the plateaulength, the plateau slope and average plateau force) between SE NiTi wires and HA NiTiwires(p <0.05).Compared with SE NiTi wires, HA NiTi wires had longer plateau andproduced lower discharge force. However，the HA NiTi wires did not always have thesmaller plateau slope. The slope of HA NiTi wires of TP, IMD and NIC companies weregreater than that of SE NiTi wires, while3M HA NiTi wires had the more flat plateau.The dimension had a significant effect on the discharge forces: with an increase in archwire dimension from0.014inch to0.016inch, the released force increased for both HA NiTiwires and SE NiTi wires (p <0.05). With increasing diameter of arch wires of the same typeand manufacturer from0.014to0.016inch, the trend was not constant for all wires anddifferences ranging from6%to46%were reported. On average, with increasing0.02inch,the average plateau force increased about30%.Conclusion:①15kinds of orthodontic NiTi arch wires selected in this experiment allhad superelasticity.②Comparison of SE NiTi arch wires and HA NiTi arch wires of thesame diameter showed that the latter exerted a significantly lighter force and generated asignificantly longer plateau than the former.③Totally speaking, with an increase in archwire dimension, the released average force increased. On average, a0.002inch increase incross-sectional diameter generated a30%increase in plateau force.④Significant differencesin mechanical behavior between almost all wires of equal section and type produced bydifferent manufacturers were seen for the parameters considered (mean force, plateau length,slope and hysteresis). |
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