Effect of wire size on maxillary arch force/couple systems for a simulated high canine malocclusion.

AIMS: To better understand the effects of copper nickel titanium (CuNiTi) archwire size on bracket-archwire mechanics through the analysis of force/couple distributions along the maxillary arch. The hypothesis is that wire size is linearly related to the forces and moments produced along the arch. MATERIALS AND METHODS: An Orthodontic Simulator was utilized to study a simplified high canine malocclusion. Force/couple distributions produced by passive and elastic ligation using two wire sizes (Damon 0.014 and 0.018 inch) measured with a sample size of 144. RESULTS: The distribution and variation in force/couple loading around the arch is a complicated function of wire size. The use of a thicker wire increases the force/couple magnitudes regardless of ligation method. Owing to the non-linear material behaviour of CuNiTi, this increase is less than would occur based on linear theory as would apply for stainless steel wires. CONCLUSIONS: The results demonstrate that an increase in wire size does not result in a proportional increase of applied force/moment. This discrepancy is explained in terms of the non-linear properties of CuNiTi wires. This non-proportional force response in relation to increased wire size warrants careful consideration when selecting wires in a clinical setting.

Three-dimensional orthodontic force measurements.

INTRODUCTION: Until recently, much of the orthodontic biomechanics literature was restricted to 2-dimensional experimental studies and, more recently, to assumption-based 3-dimensional computer modeling. There is little evidence in the literature regarding 3-dimensional experimental measurements and analysis of orthodontic force systems. METHODS: The purpose of this study was the design, construction, and validation of a laboratory-based human mouth model capable of accurately measuring forces and moments applied by orthodontic fixed appliances on all teeth in 1 arch. A high canine malocclusion was simulated, and forces and moments acting on the canine, lateral incisor, and premolar were measured with passive and conventional ligation. RESULTS: We were successful in building this human mouth model. The error in force measurements of the 14 transducers was 1.54%. The force system resulting from passive ligation brackets was considerably different from that of conventional ligation. CONCLUSIONS: This method will allow us, for the first time in the history of our specialty, to determine with great accuracy the forces acting on orthodontically treated teeth. Future research will focus on simulating many types of orthodontic clinical applications of full-fixed or partial-fixed appliances.

Torque expression of self-ligating brackets.

INTRODUCTION: The labiolingual inclination of maxillary and mandibular incisors is considered by many orthodontists to be an important determinant of pleasing dental esthetics and ideal stable occlusion. In contemporary fixed appliances, attaching a rectangular orthodontic archwire to a bracket with a rectangular slot makes third-order control possible. The purpose of this study was to measure the difference in third-order moments that can be delivered by engaging 0.019 x 0.025-in stainless steel archwires to 2 active self-ligating brackets (In-Ovation, GAC, Bohemia, NY; Speed, Strite Industries, Cambridge, Ontario, Canada) and 2 passive self-ligating brackets (Damon2, Ormco, Orange, Calif; Smart Clip, 3M Unitek, Monrovia, Calif). METHODS: A bracket/wire assembly torsion device was developed. This novel apparatus can apply torsion to the wire while maintaining perfect vertical and horizontal alignment between the wire and the bracket. A multi-axis force/torque transducer was used to measure the moment of the couple (torque), and a digital inclinometer was used to measure the torsion angle. Fifty maxillary right central incisor brackets from each of the 4 manufacturers were tested. RESULTS: There was a significant difference in the engagement angle between the 2 types of brackets; on average, torque started to be expressed at 7.5 degrees of torsion for the active self-ligating brackets and at 15 degrees of torsion for the passive self-ligating brackets. The torque expression was higher for the active self-ligating brackets up to 35 degrees of torsion. Torsion of the wire past this point resulted in a linear increase of the measured torque for the Damon2, the Smart Clip, and the In-Ovation brackets. The torque was relatively constant past 35 degrees of torsion for the Speed bracket. CONCLUSIONS: We conclude that active self-ligating brackets are more effective in torque expression than passive self-ligating brackets.