Martensitic transformation of austenitic stainless steel orthodontic wires during intraoral exposure.
BACKGROUND
Our purpose was to study the mechanical properties and phase transformations of orthodontic wires submitted to in-vivo exposure in the mouth for different periods of time.


METHODS
Stainless steel wires were tied to fixed orthodontic appliances of 30 patients from the orthodontics clinic of Universidade Federal do Rio de Janeiro School of Dentistry in Brazil. According to the duration of the clinical treatment, the patients were divided into 3 groups. After in-vivo exposure, the samples were studied by mechanical testing (torsion) and ferromagnetic resonance. Statistical analyses were carried out to evaluate the correlation between time of exposure, mechanical properties, and austenite-to-martensite transformation among the groups.


RESULTS
The results were compared with as-received control samples. The torque values increased as time in the mouth increased. The increase in torque resistance showed high correlations with time of exposure (P = 0.005) and austenite-martensite phase transformation.


CONCLUSIONS
The resistance of stainless steel orthodontic wires increases as the time in the mouth increases; this effect is attributed to the austenite-to-martensite transformation.
Departamento de Ortodontia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil.
Paula P
PP
Izquierdo
Ronaldo S
RS
de Biasi
Carlos N
CN
Elias
Lincoln I
LI
Nojima
D055598:Chemical Phenomena; D003722:Dental Alloys / Q000737:chemistry*; D006801:Humans; D008280:Magnetics; D008422:Materials Testing; D055595:Mechanical Phenomena; D009055:Mouth / Q000502:physiology*; D016382:Orthodontic Appliance Design; D009969:Orthodontic Wires; D013193:Stainless Steel / Q000737:chemistry*; D013997:Time Factors; D019415:Torque; D054159:Torsion, Mechanical
D003722:Dental Alloys; C426023:austenitic steel; D013193:Stainless Steel