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Thesis Format



Master of Clinical Dentistry




Tassi, Ali


This study aimed to compare torquing moments, engagement angles, and torsional stiffness generated by stainless steel (SS), titanium molybdenum alloy (TMA) and nickel titanium (NiTi) wires in three active self-ligating (ASL), one passive self-ligating (PSL), and a conventional twin orthodontic bracket system control. Brackets were tested in simulations of buccal and palatal root torque. A custom 3D printed testing apparatus was developed to measure torque. In general, the PSL and conventionally ligated systems generated significantly larger torquing moments than ASL systems, especially with stiffer wires and greater degrees of twist. Torquing direction only influenced torque expression with ASL systems. The PSL system demonstrated significantly smaller engagement angles than the ASL or twin bracket systems, especially with stiffer wires. Torsional stiffness values aligned with the expected modulus of elasticity of the given wire material. In addition to ligation modality, other aspects of bracket design likely contribute to these findings.

Summary for Lay Audience

Patients often seek orthodontic care to achieve a straighter, more esthetic smile, through which the orthodontist must properly position the teeth in the mouth in all three planes of space. Braces, or orthodontic brackets, are commonly used in conjunction with wires to move teeth into their ideal orientation. A common tooth movement achieved with braces, called “torque”, involves changing the angulation of teeth by moving the tooth roots toward or away from the lips or cheeks.

Three basic types of orthodontic brackets are available today, which differ in how the wire is secured to the bracket, or the “ligation method”. These different types of ligation methods are each suggested to have different advantages, with one type (active self-ligation, or ASL) suggested to add torque to teeth more efficiently than other methods. There are also different wire materials which are commonly used throughout orthodontic treatment, which vary in terms of their properties such as flexibility and stiffness. To test which bracket-wire combination produces torque most effectively, five different bracket systems representing the three ligation methods were tested by twisting brackets from -15 to 45 degrees, clockwise and counterclockwise, around a section of orthodontic wire and measuring resulting torquing moments. This was repeated in two directions (root towards the lips, and root away from the lips). Resulting torque moments were compared between different bracket types, wire materials, directions of twist, and system stiffness, to existing literature to determine if one ligation method was superior in producing torque.

In general, with higher degrees of twist, torquing moments increased for all bracket systems and wires tested. For a given degree of twist, torquing moments tended to be higher for stiffer wires than more flexible wires. In comparing different ligation types, tested ASL groups seemed to generate lower moments than other tested brackets, despite purported benefits of this ligation type. Direction of rotation affected only ASL systems. System stiffness values were lower in the ASL groups as well. These findings are likely the result of not only ligation modality, but other aspects of bracket design as well.