Abstract
BackgroundTitanium-molybdenum alloy (TMA) and stainless steel (SS) wires are commonly used in orthodontics as arch-wires for tooth movement. However, plastic deformation phenomenon in these arch-wires seems to be a major concern among orthodontists. This study aimed to compare the mechanical properties of TMA and SS wires with different dimensions.Material and MethodsSeventy-two wire samples (36 TMA and 36 SS) of three different sizes (19×25, 17×25 and 16×22) were analyzed in vitro, with 12 samples in each group. Various mechanical properties of the wires, including spring-back, bending moment and stiffness were determined using a universal testing machine. Student’s t-test showed statistically significant differences in the mean values of all the groups. In addition, metallographic comparison of SS and TMA wires was conducted under an optical microscope.ResultsThe degree of stiffness of 16×22-sized SS and TMA springs was found to be 12±2 and 5±0.4, respectively, while the bending moment was estimated to be 1927±352 (gm-mm) and 932±16 (gm-mm), respectively; the spring-back index was determined to be 0.61±0.2 and 0.4±.09, respectively (p<0.001). There were no statistically significant differences in spring-back index in larger dimensions of the wires.ConclusionsSystematic analysis indicated that springs made of TMA were superior compared to those made of SS. Although both from economic and functionality viewpoints the use of TMA is suggested, further clinical investigations are recommended. Key words:Bending moment, optical microscope, spring-back, stainless steel, stiffness, titanium‒molybdenum alloy.
Highlights
In orthodontics, tooth movements are achieved by the forces developed in the deformed wire, which are transmitted to the teeth through fixed or removable appliances
The TiO2-based passive film on the surface of wires provides a good measure of biocompatibility [18]; Titanium‒molybdenum alloy (TMA) is described as having an excellent balance of properties, including high spring-back, low stiffness, high formability and the ability of direct welding [11,12,19,20]
Statistical analysis showed that the stiffness, bending moment and spring-back of TMA springs were significantly lower than those of stainless steel (SS) wires (P0.05)
Summary
Tooth movements are achieved by the forces developed in the deformed wire, which are transmitted to the teeth through fixed or removable appliances. SS wires are smooth wires with low friction and spring-back values, which are considered a reference material for comparing the characteristics of other types of orthodontic wire alloys [6] This drawback of SS led to the popularization of TMA with superelasticity, making it highly resistant to plastic deformation [15]. The TiO2-based passive film on the surface of wires provides a good measure of biocompatibility [18]; TMA is described as having an excellent balance of properties, including high spring-back, low stiffness, high formability and the ability of direct welding [11,12,19,20] They are considered superior to SS wires due to their favorable functional and aesthetic effects [21]. Both from economic and functionality viewpoints the use of TMA is suggested, further clinical investigations are recommended
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