Review Article
Pseudoelasticity and thermoelasticity of nickel-titanium alloys: A clinically oriented review. Part I: Temperature transitional ranges*,**,*,**,*

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Abstract

The purpose of this review was to organize a systematic reference to help orthodontists evaluate commonly used orthodontic nickel-titanium alloys. Part I of the article reviews the data available in the literature regarding the temperature transitional ranges of the alloys. The thermomechanical behavior of these compounds is, in fact, strictly dependent on the correlation between the temperature transitional range and the oral temperature range. Part II of the article will focus on the mechanical characteristics of the alloys, such as the magnitude of the forces delivered and its correlations with temperature transitional range and oral temperature. (Am J Orthod Dentofacial Orthop 2001;119:587-93)

Section snippets

Thermoelasticity and shape memory effect

An ideal NiTi wire should retain a stable predesigned archform at mouth temperature and yet be formable at a lower room temperature. In other words, it should be possible to engage the wire into the brackets during a reasonable time interval, and only later should the wire recover its ideal arch form and apply light, predictable, constant, and continuous force to the dentoalveolar structures.3 Because of the most recent technological advancements, superelastic NiTi alloys that meet these

Review of available alloys

Pseudoelastic and thermoelastic properties are not always present in all commercial orthodontic alloys available on the market. Sometimes the product advertisements can be confusing or even misleading. In this review, we attempt to clarify a few points in this regard, and, we hope, simplify the clinical choice by attributing the correct properties to the most commonly used alloys.

NiTi orthodontic wires are generally classified as superelastic or nonsuperelastic. The original Nitinol, developed

Summary and conclusions

Two concomitant phenomena are responsible for the superelastic behavior of orthodontic NiTi alloys: a temperature-related phase transformation along a TTR (thermoelasticity), and the formation of SIM in localized areas of the archwire due to deflection (pseudoelasticity). The shape memory effect is derived from the thermoelastic transformation from martensite to austenite, and orthodontic clinical application requires setting the TTR of the alloys slightly below oral temperature. This type of

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    • Cited by (0)

    *

    aAssistant Professor of Clinical Orthodontics.

    **

    bAssociate Professor of Clinical Orthodontics.

    *

    cProfessor and Chairman.

    **

    Reprint requests to: Margherita Santoro, Division of Orthodontics, Columbia University, School of Dental and Oral Surgery, 635 W 168th St, P O Box 20, New York, NY 10032; e-mail, [email protected].

    *

    Am J Orthod Dentofacial Orthop 2001;119:587-93

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    Copyright © 2001 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.