Friction forces generated by aesthetic Gummetal® (Ti-Nb) orthodontic archwires: A comparative in vitro study

Objective: The aim of this in vitro study was to compare friction forces generated by the following archwires: rhodium-plated aesthetic Gummetal® (E-GM), Gummetal® (GM), stainless steel (SS) and titanium-molybdenum alloy (TMA), according to bracket-wire angulation and archwire cleanliness. Methods: One hundred and ninety-two samples of four orthodontic alloys (E-GM, GM, SS, and TMA) were prepared. The samples were divided into two groups: uncleaned and cleaned using 99% isopropanol in an ultrasonic bath, then subdivided into three subgroups according to bracket-wire angulation: 0°, 5° and 10°. Using a universal testing machine, the wires were pulled through SS maxillary right canine brackets to test static friction forces according to bracket-wire angulation and wire cleanliness. Representative specimens were evaluated to assess surface morphology and roughness. Results: There were significant differences in static friction forces between archwires when analysed by bracket-wire angulation and cleanliness (P < 0.001) except for the 0° uncleaned group. Overall, TMA archwires produced the highest friction while SS wires showed the lowest friction at 0° and 5°. E-GM wires showed comparable friction to SS at 0^o (cleaned and uncleaned), but significantly higher friction than SS at 5^o (uncleaned) and 10° (cleaned). GM wires had comparable friction to SS at 0° (cleaned and uncleaned), but significantly less friction at the 5° (cleaned) and 10° (cleaned and uncleaned). Compared to GM, E-GM had significantly higher friction at 5^o and 10° (cleaned and uncleaned). Cleaning wires reduced surface roughness but increased overall friction. Conclusion: E-GM wires generate higher frictional resistance forces compared to GM and SS, especially at higher bracket-wire angulations and when cleaned. GM friction forces are comparable to SS and thus could be used for space closure with sliding mechanics. However, E-GM wires are not ideal for the same purpose.