Document Type

Article

Language

eng

Publication Date

1996

Publisher

Elsevier

Source Publication

American Journal of Orthodontics and Dentofacial Orthopedics

Source ISSN

0889-5406

Abstract

The purpose of this study was to determine the transformation temperatures for the austenitic, martensitic, and rhombohedral (R) structure phases in representative as-received commercial nitinol (NiTi) orthodontic wire alloys, to reconcile discrepancies among recent publications. Specimens were examined by differential scanning calorimetry (DSC) over a temperature range from approximately −170° C to 100° C, with a scanning rate of 10° C per minute. Two different pathways, with the intermediate R structure either absent or present, were observed for the transformation from martensitic to austenitic NiTi, whereas the reverse transformation from austenitic to martensitic NiTi always included the R structure. The enthalpy (ΔH) for the transformation from martensite to austenite ranged from 0.3 to 35 calories per gram. The lowest ΔH value for the nonsuperelastic Nitinol wire is consistent with a largely work-hardened, stable, martensitic microstructure in this product. The DSC results indicate that the transformation processes are broadly similar in superelastic, body-temperature shape-memory, and nonsuperelastic NiTi wires. Differences in bending properties for the NiTi orthodontic wires at room temperature and 37° C are due to the relative proportions of the metallurgical phases in the microstructures.

Comments

American Journal of Orthodontics and Dentofacial Orthopedics, Vol 109, No. 6 (1996): pg. 589-597. DOI. © 1997 Elsevier. Used with permission.

Dr. T. Gerard Bradley was associated with Ohio State University - College of Dentistry at time of publication.

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