COMPARISON OF MANUFACTURED AND HAND-FORMED REVERSE CURVE OF SPEE NICKEL-TITANIUM WIRES
Date of Award
Summer 7-13-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Dentistry
First Advisor
David Berzins
Second Advisor
David Liu
Third Advisor
William Lobb
Abstract
Introduction: The reverse curve of Spee (RCOS) nickel-titanium (NiTi) archwire is a standard tool for leveling a deep curve of Spee, but it carries a substantial cost relative to a flat NiTi archwire. An infrequently shared clinical technique is to permanently shape a flat superelastic NiTi archwire chairside into a reverse curve of Spee. This study compared the mechanical and thermal properties of manufactured RCOS, hand-formed RCOS (hf-RCOS), and flat superelastic NiTi archwires to determine whether hand-formed archwires are clinically equivalent to their manufactured counterparts. Methods: Three 0.016 × 0.022-inch archwire groups were evaluated: a manufactured RCOS NiTi archwire, a hand-formed RCOS archwire shaped chairside from a flat superelastic NiTi archwire, and a flat superelastic NiTi archwire serving as a baseline. Deflection-load characteristics were assessed on a universal testing machine at 37°C using a 3D-printed mandibular model, with load applied at the midline and bilateral canine positions (n=15 per group per location). Phase transformation behavior was characterized by differential scanning calorimetry (DSC; n=5 per group) across a controlled −100 °C to 100 °C thermal cycle. Descriptive and inferential statistics (independent t-tests, Mann-Whitney U, and Wilcoxon signed-rank tests) were applied, with p < 0.05 considered statistically significant. Results: At the midline, the manufactured RCOS archwire delivered statistically significantly greater forces than the hand-formed archwire; at the canine positions the differences were smaller, and both groups exhibited left-right canine force asymmetry. Thermally, the flat and hand-formed archwires displayed nearly identical transformation temperatures (mean austenite finish of approximately 19 °C and 21 °C, respectively), consistent with a standard superelastic alloy. The manufactured RCOS archwire behaved markedly differently, with a strongly depressed austenite start, an elevated and broadened austenite finish (approximately 36 °C), a wide transformation hysteresis (approximately 77 °C on heating), and high specimen-to-specimen variability—features characteristic of a martensite-stabilized form. Hand-forming modestly reduced transformation enthalpy but did not meaningfully shift transformation temperatures. Conclusions: A reverse curve of Spee can be shaped chairside from a flat superelastic NiTi archwire while retaining the favorable superelastic thermal behavior of its parent wire, whereas the manufactured RCOS archwire behaves as a martensite-stabilized material. Although the manufactured archwire delivered greater forces, the thermal comparability of the hand-formed archwire supports its potential as a cost-effective alternative. Differences in force delivery should be weighed clinically, and in vivo investigation is warranted.