Abstract
abstractObjective: This paper analyzed whether nickel-titanium closed coil springs (NTCCS) have a different superelastic (SE) behavior according to activation and whether their force plateau corresponds to that informed by the manufacturer.Methods:A total of 160 springs were divided into 16 subgroups according to their features and activated proportionally to the length of the extensible part (NiTi) of the spring (Y). The force values measured were analyzed to determine SE rates and force plateaus, which were mathematically calculated. These plateaus were compared to those informed by the manufacturer. Analysis of variance was accomplished followed by Tukey post-hoc test to detect and analyze differences between groups.Results: All subgroups were SE at the activation of 400% of Y length, except for: subgroups 4B and 3A, which were SE at 300%; subgroups 4E and 4G, which were SE at 500%; and subgroup 3C, which was SE at 600%. Subgroup 3B did not show a SE behavior. Force plateaus depended on activation and, in some subgroups and some activations, were similar to the force informed.Conclusions: Most of the springs showed SE behavior at 400% of activation. Force plateaus are difficult to compare due to lack of information provided by manufacturers.
Highlights
In the 1980’s, two new nickel-titanium alloys were suggested for orthodontic use, the “Chinese NiTi”1 and the “Japanese NiTi”.2 These alloys had some advantages over the already existing nickeltitanium alloy used at the time, termed Nitinol;[3] one was the fact that they did not obey Hooke’s Law which determines proportionality between load and deflection of metals.This is due to a transformation in the crystallographic structure from a martensitic to an austenitic phase, which can be induced by changes in temperature and/or stress.[4,5,6] Since each of these two phases presents an inherent load-deflection rate, these alloys will behave differently depending on at which phase they are
At a given temperature above austenitic start” (As), a phase transformation could be induced by stress, transforming part of the alloy which is in austenitic phase into martensitic phase, e.g., when a nickel-titanium spring is activated,[2] changing the alloy’s properties
This is very important, since small springs, such as in subgroups 1A and 2A, will produce a plateau with smaller activations than what is normally used in Orthodontics,[17] and even if a 1000% of activation equals to 23 mm, as in subgroup 1A, reverse transformation occurs only after some deactivation, only producing a plateau after 10 mm of deactivation (Fig 4)
Summary
In the 1980’s, two new nickel-titanium alloys were suggested for orthodontic use, the “Chinese NiTi”1 and the “Japanese NiTi”.2 These alloys had some advantages over the already existing nickeltitanium alloy used at the time, termed Nitinol;[3] one was the fact that they did not obey Hooke’s Law which determines proportionality between load and deflection of metals. This is due to a transformation in the crystallographic structure from a martensitic to an austenitic phase, which can be induced by changes in temperature and/or stress.[4,5,6] Since each of these two phases presents an inherent load-deflection rate, these alloys will behave differently depending on at which phase they are. At a given temperature above As, a phase transformation could be induced by stress, transforming part of the alloy which is in austenitic phase into martensitic phase, e.g., when a nickel-titanium spring is activated,[2] changing the alloy’s properties
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