Date of Award

Summer 2015

Document Type


Degree Name

Master of Science (MS)



First Advisor

Berzins, David

Second Advisor

Toth, Jeffrey M.

Third Advisor

Bradley, Thomas G.


ABSTRACT THERMOMECHANICAL CHARACTERIZATION OF VARIABLE FORCE NITI ORTHODONTIC ARCHWIRES Anjali Mehta, BDS MDS Marquette University, 2015 Introduction: Nickel-Titanium (NiTi) archwires, due to their properties of superelasticity and shape memory, have been extensively used in orthodontic mechanotherapy. However, one of the shortcomings of these wires is that they deliver constant forces across the entire arch. The amount of force needed to move a tooth is a function of the surface area of the tooth and its supporting bone; and is lesser for single rooted anterior teeth compared to larger molars. The introduction of heat treatment of NiTi wires and the influence of varying temperature and duration of heat treatment on the transition temperature range has provided wires with variable forces across different sections of the same archwire. Objectives: This study investigated the thermal behavior and load-deflection characteristics of different brands of variable force archwires across sections of the archwire. Materials and Method: Five brands of variable force orthodontic wires of 0.016 X 0.016 inch were compared against a non-variable force brand to evaluate their thermomechanical characteristics using Differential Scanning Calorimetry (DSC) and a three point bending test. Three segments (anterior, premolar and molar) of each type of wire were evaluated and compared. Two-way ANOVA was used to statistically analyze the thermal and bending measures. Results: The anterior segments of the variable force orthodontic wires exhibited significantly (p<0.05) greater austenite finish temperatures and lower loads compared to the molar segments. Significant (p<0.05) differences in thermal and bending values were observed between different brands of variable force wires and the control. Conclusion: Marketed variable force orthodontic wires do in fact deliver different force values depending on region (anterior, premolar, molar) and do so as a result of manufacturing steps that alter their thermal transitions. Differences exist among brands suggesting they are not interchangeable.