February 2, 2015 in Articles
Introduction: I have been extremely fortunate to have traveled broadly in teaching orthodontics throughout my career. One of the aspects that seems to create a great deal of confusion among orthodontists around the world is the relationship between the means of using a “straight wire” appliance to align teeth and the contemporary clinical goals of excellence in both esthetics and occlusion.
Every orthodontist is familiar with the brilliant article by Andrews1, which introduced the basis of “straight wire” theory, which has dominated our profession for the last 40 years. Building tip, torque, and in/out into the bracket as a means of avoiding adverse “wagon wheel” effects of wire bending is the premise of every modern orthodontic appliance, and to this day, I use pre-adjusted appliances for this reason.
As with all great ideas, “Straight Wire” theory has some recognized limitations. Thomas Creekmore and Randy Kunik provided a good summary of these: inaccurate bracket placement, variation in tooth structure and tooth facial morphology, variations in the maxilla/mandible skeletal relationships, tissue rebound, mechanically deficiencies in the appliances2, and variable threshold of biological activation, to name a few. The combination of all these factors reduces the ability of the clinician to rely strictly on the appliance to guarantee an excellent occlusal result, with an even less likelihood of reaching superior esthetic goals.
For me, there are three significant considerations of straight wire theory as it applies to using a contemporary PSL appliances in esthetics based treatment:
• The first of these is revolves around the core straight wire principle that the wire plane parallel to the occlusal plane is a requisite for excellent occlusions. It is not, and failure to adjust bracket position to meet esthetic need can result in esthetic decline3 in many patients. The contemporary Orthodontist needs expand his/her diagnostic and mechanical understandings beyond reliance on improved “straight wire” appliances to attain superior esthetic results. David Sarver has led the charge on the impact on esthetics of orthodontic treatment mechanics4 where the vertical position of the upper incisor is the prime diagnostic criteria in developing superior esthetics in orthodontics, and I agree with this concept.
• The second involves the misconception that incremental increases in arch wires size is an effective means of controlling axial inclination. It is not, and failure to appreciate how to control axial inclination results in frustration in many orthodontists when reliance on “the treatment built into the appliance” fails to deliver.
• The third limitation involves the lack of appreciation of the pivotal role of case management in attaining superior aesthetic and occlusal results. The best orthodontic results are attained by the best case managers, regardless of the appliances they use.
Today I would like to explore briefly the elements that are within the control of the Orthodontist; bracket position, appropriate use of pre-adjusted appliances, and arch form as they relate to esthetic outcomes.