While there are several key topics on the forefront of our profession (implant anchorage, polymer aligner systems, etc.), passive self-ligation, or “frictionless” orthodontics, is perhaps the most universal in application.
Many of these topics may prove their relevance only to the degree that the doctor participates in delivering care using these modalities. However, every doctor practicing orthodontics must acknowledge and critically evaluate the passive self-ligation concepts. Though we as orthodontists often consider ourselves to be progressive thinkers and advancers of our cause to better treat our patients, the reality is we resist change to some degree in the same fashion. Many practicing orthodontists will recall the radical shifts in thinking and practice that occurred with the introduction of straight wire orthodontics and direct bonding. While we recognize these concepts and practices as commonplace today, each required that practitioners step out of their comfort zones (at the time) for introduction and implementation into their individual practices.
The ideas and concepts behind passive self-ligation are all derived from the underlying principle that forces employed to position teeth should not overwhelm the supporting biological system (supporting periodontium, facial musculature). Rather, forces applied should be just great enough to stimulate cellular activity and thus tooth movement without compromising the vascular supply to the periodontium. To accomplish these goals, several key adaptations to our traditional orthodontic appliances are necessary. The most significant change is the alteration in thinking behind the force systems used in orthodontics. Additional changes to traditional systems include modifications in archwire, mechanics, and bracket design.
Traditional bracket systems rely on active ligation using colored or steel ligatures to hold the archwire in the bracket slot. While ligatures are applied around the circumference of the entire bracket, the two areas that hold the archwire most tightly are at the mesial and distal aspects of the bracket—where the ligature crosses the archwire. These contact points bind the archwire, creating friction during tooth movement and increasing the forces necessary for leveling/aligning and sliding mechanics during treatment. There is no question that overcoming these forces is achievable, but the question one must ask is at what expense?
Proponents of the self-ligating bracket systems will tout that their overall treatment times are reduced significantly. Studies are ongoing, but several practitioners have quantified in their practice a reduction of as much as 3-4 months in leveling and aligning and an overall treatment time reduction of 7 months with frictionless vs. traditional bracket systems. When cases are examined more closely, one quickly finds that the most significant reduction in time is during the initial leveling and aligning of the dentition. Without the friction/binding to overcome in the system, only very light forces are required to produce the desired tooth movement. Incisor proclination/flaring during leveling and aligning is also reduced with the frictionless systems by eliminating binding of the archwire. This reduces unnecessary “roundtripping” of incisors, or undesired flaring in patients with fuller profiles, and is of critical importance if one is giving facial esthetics the necessary consideration in treatment planning.
One of the greatest claims and reported benefits of these systems is the decreased need for extraction of permanent teeth during orthodontic treatment (this is obviously an ongoing debate/controversy for many). As mentioned above, a claimed benefit of these systems is the decreased flaring of incisors during leveling and aligning of cases. The natural question is, then, where is the arch length coming from to diminish the need for extraction therapy? The reported answer is in the “posterior transverse arch adaptation,” which occurs by using lighter forces to move teeth without overpowering the underlying supporting structures. Controlled studies are certainly needed, and are ongoing, to critically evaluate this adaptation of the supporting structures to the posterior expansion that is required in order to relieve crowding in what would otherwise be extraction cases. In this age of evidence-based dentistry it is important that we critically evaluate these claims; however, clinical results achieved show great promise for addressing these types of cases without extractions, while still maintaining optimum facial esthetics.
Other reported benefits of passive self-ligating bracket systems include: decreased number of visits for treatment, extended appointment intervals, decreased arch-leveling time, reduced overall treatment time, greater patient comfort, improved hygiene vs. elastomeric ties, anchorage conservation, and ease of chairside wire changes. While these benefits need further controlled study to substantiate anecdotal clinical evidence, there is no question that these systems offer a great deal of promise to clinical orthodontics.
Self-ligating bracket systems certainly will not necessarily make you a better clinical orthodontist. They will, however, challenge the orthodontist to consider new concepts and possibilities on what results may be achieved and how they may be realized. Whether the challenge presents itself under the guise of a new system, philosophy, concept, or individual product, each deserves a critical evaluation by the practitioner. Blind acceptance or rejection of any of these based solely on what we already “know” puts us at risk of letting ego and habit, rather than critical thinking, determine the direction of both our individual practice and profession as a whole.