Straight Wire Appliance Straight Bow Technique
1.Introduction
Since its development by L Andrews in 1970, the “straight arch” has become a universally widespread technique.
With its advantages and disadvantages, this new “edgewise” has facilitated the considerable development of orthodontics throughout the world.
This opportunity, however, requires the practitioner to observe the patient more methodically and to establish a much more in-depth diagnosis, taking into account the initial morphological pattern
, the growth estimate and the mechanical needs to be implemented as a result.
2.history
As early as 1927, Angle angled brackets on rings to avoid certain 2nd order deformations. Jaraback in 1957, incorporated a groove inclination to reduce 3rd order deformations.
Andrews in 1970, designed, manufactured and then marketed new equipment which took into account the three senses of space, adapted to dental morphological standards which he called the “ Straight Wire Appliance”.
3. Presentation of SWA and Andrews’ ideas
To understand the evolution of pre-informed techniques, we must return to Andrews’ initial approach: his objective being to develop a device that could be used with classic treatment methods, he needed:
- Establish average morphology standards for each tooth;
- Define a precise system for placing the brackets, i.e. a standardized, easily identifiable position of the bracket;
The philosophy of Andrews’ appliance revolutionized orthodontics. Indeed, Andrews, after a study of casts of 120 ideal adult dentitions who had never undergone orthodontic treatment, identified certain constants of static occlusal meshing, which he called: “The six keys to normal occlusion”.
3.1. The six keys to optimal occlusion:
Key No. 1 specifies the inter-arcade relationships: it includes seven points including:
- The mesiovestibular cusp of the first permanent molar occludes in the vestibular groove of the first mandibular molar, between the mesial and medial cusps;
- the distal marginal edge of the maxillary first molar comes into contact with the mesial marginal edge of the mandibular second molar, which imposes a more distal position of the maxillary first molar than that described by Angle;
- the maxillary canine has a cusp-embrasure relationship with the mandibular canine and premolar, the tip of the cusp being slightly mesial to the embrasure, etc.
Key No. 2 determines the angulation of the crowns: all crowns in the sample have a mesial version, this version being similar for each type of tooth.
Key No. 3 determines the inclination of the crowns (improperly called torque). Andrews makes the following observations:
- The inclination is positive on most maxillary incisors, that is, they present a coronovestibular torque;
- The inclination is slightly negative on the mandibular incisors , that is to say they present a coronolingual torque;
- The inclination is negative on the upper lateral sectors , slightly more marked on the first and second maxillary molars;
- At the level of the mandibular posterior teeth, the inclination is negative, progressively more marked from the canine to the second molar.
Key #4 is no rotation.
Key #5 is the absence of diastemas if there is no dento-dental disharmony.
Key #6 is a flat or slightly concave Spee curve.
4. Advantages and disadvantages of the system
4.1. Advantages of the system:
With this device, it became possible to set up arches free of deformations with the advantage of eminently reproducible information without random adjustments from one arch to another.
The information being therefore in the bracket, the SWA allowed and still allows to relieve the practitioner in the making of these arches.
- At the 1st order level , the information programmed in the bracket allows a large part of the treatment to be carried out without deformation of the arch.
Straight Wire Appliance Straight Bow Technique
- At the 2nd order level , the angulation of the teeth is directly programmed and quickly put in place from the first arches, the average information thus incorporated allows in principle to maintain the physiological angulation of the tooth, even during translation movements. To respect this angulation, the axis of the bracket must be perfectly superimposed on the axis of the clinical crown; any placement error results in a modification of the programmed angulation.
Straight Wire Appliance Straight Bow Technique
- At the 3rd order level, the inclination of the teeth is fixed by programmed information that is read progressively by increasing the caliber of the arches. Another advantage of the straight arch is that regardless of the size of the crown, the value of the inclination remains identical if the bracket is correctly placed
Straight Wire Appliance Straight Bow Technique
4.2. Disadvantages of the system:
The first results were relatively disappointing, because this first SWA proved to be poorly adapted to the therapeutic constraints ; the initial approach presented certain drawbacks:
- Difficulty of precise placement to preserve the value of the programmed information and in particular the torque;
- The casts collected by Andrews and from which he defined his information were casts of adults, selected solely on static occlusion criteria (the six keys); without taking into account other criteria such as facial typology, age, etc.
5. Conclusion
Whatever the technique, the practitioner must choose between two systems:
- One with average information that will not fit all cases (edit arc).
- A seeker of individualization of information requiring great anticipation.
Straight arch orthodontic treatment requires determination of information and positioning of brackets before treatment begins for each individual patient.
The choice of information requires a precise diagnosis based on:
- The skeletal diagram.
- Dentoalveolar compensations.
- The functional environment.
- Future growth.