Mechanical properties of orthodontic wires derived by instrumented indentation testing (IIT) according to ISO 14577

Abstract

BackgroundThe aim of this study was the characterization of mechanical properties of representative types of orthodontic wires employing instrumented indentation testing (IIT) according to ISO 14577.MethodsSegments were cut from ten wires. The first six are made of stainless steel (SS), two are made of Ni-Ti, and the last two are made of titanium molybdenum alloys (TMA). Then, the Martens hardness (HM), the Vickers hardness (HVIT) based on indentation hardness (HIT), the indentation modulus (EIT), the ratio of elastic to total work (ηIT), and the traditional Vickers hardness (HV1) were measured by IIT. The results were statistically analyzed by one-way ANOVA followed by Student-Newman-Keuls (SNK) test at a = 0.05. The HVIT and HV1 data were analyzed by paired t test (a = 0.05).ResultsSS wires showed the highest hardness followed by TMA and Ni-Ti alloys. However, all wires showed significantly lower HVIT compared to corresponding HV1, a finding probably appended to elastic recovery around the indentation. EIT for all wires tested was determined much lower than the nominal values of the corresponding alloys due to the implication of residual stress field at the slope of unloading curve. Elastic to total work ratio was ranged from 45.8 to 64.4 % which is higher than that expected for ductile alloys (<30 %).ConclusionsThe products tested illustrated significant differences in their mechanical properties. Although IIT provides reliable data for hardness and elastic index of materials tested, the intense residual stress field developed during the manufacturing process significantly affects the determination of modulus of elasticity.

Assessment of the hardness of different orthodontic wires and brackets produced by metal injection molding and conventional methods

“…Beta-titanium wire exhibited the lowest hardness value (334.65 VHN). These findings are consistent with previous findings with the SS wires that exhibited the highest hardness (468–601 hardness values)[ 15 16 17 18 19 ] compared to other two alloys. Ni-Ti (240–438 hardness values)[ 16 17 18 20 21 22 ] and TMA (292–378 hardness values)[ 15 17 18 20 23 24 ] exhibited lower values with overlapping ranges.…”

Forces in initial archwires during leveling and aligning: An in-vitro study

“…The former capitalizes on conventional variable cross-section orthodontics, which was tabulated many years ago in an orthodontic textbook. [15] The latter makes use of variable modulus orthodontics. [15]…”

A Comparison of the Compositional, Microstructural, and Mechanical Characteristics of Ni-Free and Conventional Stainless Steel Orthodontic Wires

“…All force-indentation depth curves were recorded and Martens Hardness (HM), indentation modulus (E IT ), and elastic index (η IT ), were estimated according to the ISO 14577-1 specification [14]. The analytical formulas were given by the ISO 14577-1 and can also be found in recent publications [7,15]. Then, Vickers hardness was determined by measuring the diagonal length of indentations.…”

“…In an effort to prevent the adverse effects of Ni in allergic patients, new orthodontic wires made of Ni-free SS alloys were introduced [7,8,9,10]. However, the substitution of Ni by other elements may provoke alterations in the microstructural, mechanical and corrosion resistance of SS alloys, as the presence of Ni has a notable effect on these aforementioned characteristics.…”