Electronic Thesis and Dissertation Repository

Thesis Format



Master of Clinical Dentistry




Tassi, Ali


This investigation aimed to compare engagement angles and torquing moments generated by stainless steel (SS) 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 using four sizes of SS wires (16x22, 17x25, 19x25, 20x20 mil). A custom 3D printed testing apparatus was developed to measure torque. After initial engagement within bracket slots, torquing moments increased with progressive rotation of brackets around wires. In general, the PSL and conventionally ligated systems generated significantly larger torquing moments than ASL systems, especially with larger 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 larger wires. In addition to ligation modality, other aspects of bracket design likely contribute to these findings.

Summary for Lay Audience

Many people visit the orthodontist for a straighter, more esthetic smile. Achieving desired outcomes requires we properly position the teeth in the mouth in all three dimensions of space. The most common way to accomplish this is using “braces”, which are orthodontic brackets and wires that move teeth into their ideal orientation. One type of tooth movement achieved with braces, known as “torque”, involves changing the inclination of teeth by moving the tooth roots toward or away from the lips or cheeks. Three basic types of orthodontic brackets are marketed today, differing in terms of how brackets are secured to the wire, or “ligation method”. These different types of ligation method are each suggested to have different advantages, with one particular type (active self-ligation, or ASL) suggested to add torque to teeth better than other methods. To test this claim, five different bracket systems representing all three ligation methods were tested by twisting brackets from 0 to 45 degrees around a section of orthodontic wire and measuring resulting torquing moments. This was repeated in both directions. Four common sizes of stainless steel orthodontic wires were considered. Resulting moments were compared between different bracket types, wire sizes, directions of twist, and to existing literature to determine if one ligation method was superior in producing torque. In general, with greater degrees of twist, torquing moments increased for all bracket systems tested, once the wire and bracket engaged one another. Likewise, for a given degree of twist, torquing moments tended to be higher for larger wires than smaller wires. However, 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 and not other ligation method groups. These findings are likely the result of not only ligation modality, but other aspects of bracket design as well. A prudent clinician should possess a full understanding of the appliances employed in clinical practice to treat patients efficiently. We hope orthodontists can use this information to optimize use of bracket systems and improve outcomes of orthodontic treatment.