Forces of Various Nickel Titanium Closed Coil Springs

Abstract

Objective: To compare the forces generated by 14 different 9 mm springs supplied by five different companies. Materials and Methods: Five replicates of 14 different 9 mm springs were evaluated, resulting in 70 total specimens. Each was extended once from its resting length to 12 mm and then was deactivated. All tests were performed in a 37ЊC water bath. Forces were recorded at the 12 mm extension and deactivation distances of 9 mm, 6 mm, 3 mm, and 1 mm using an MTS force gauge. Data were collected with Testworks software, version 4.0, and were analyzed by analysis of variance (ANOVA) with one factor alternated. Results: Mean peak load forces at 12 mm were significantly different between springs, and these forces varied from 147 to 474 grams. Mean unload forces measured at 9 mm, 6 mm, and 3 mm of deactivation values were highly variable, and only 6 of the 14 springs exhibited a ''physiologic'' mean unload force of 50 grams or less over the total deactivation range. Conclusions: Few springs tested exhibited physiologic peak load forces and constant deactivation forces. This study suggests that labeling of nickel titanium closed coil springs is confusing and misleading. (Angle Orthod. 2010;80:182-187.)

In-vivo force decay of nickel-titanium closed-coil springs

“…5, 16, 22 However, the absolute value of our measured forces cannot be directly compared with their findings because all of our springs were not initially stretched to the full 12mm activation range that theirs were. It has been shown that the initial activation length of NiTi coil springs can have a significant influence on their force properties and effects both the length and absolute value of the constant force plateau regions of these springs.…”

“…23 However, an interesting finding of these studies that is in concordance with our results is that GAC NiTi springs do not exhibit constant force of the reported 150gm over the entire 12mm activation range as claimed by the manufacturer. 5, 16, 22 The super-elastic force plateau region occurs over a much more limited range than advertised.…”

“…1–4 Some common orthodontic materials used for space closure deliver very high initial forces that decay rapidly prior to re-activation. 5–8 NiTi materials are purported to overcome this rapid force decay problem and supply light, continuous forces over a long activation range. 9,10 The claim that they are able to deliver these more biologically favorable forces, and thus potentially lead to more efficient tooth movement, is how many clinicians have justified their use despite their relatively greater cost compared to other common space closing materials such as elastomeric chain or closing loops.…”

“…5, 13–17 Maganzini et al examined 14 different types of NiTi closed coil springs in vitro from five different companies and concluded that most of the springs tested did not exhibit constant deactivation forces or physiologic peak load forces. 5 …”

Deformation of nickel-titanium closed coil springs: an in vitro study

“…In those two clinical situations, deformations smaller than 7.4 mm and 5.7 mm, respective to each situation, would be considered clinically irrelevant. However, there are two other variables that should be considered when using nickel-titanium springs: one is the desired force, since the force plateau decreases with increased activation; 11 , 16 and the second is the relationship between the spring's clinical work range (Fig 3) and the SE plateau length, because even at a SIMT, the dimensions that are clinically used in Orthodontics could make the spring work outside its SE plateau (Fig 4), thus acting in a SE way only after some space is closed or even never acting in a SE way at all.…”