Tip is one of the strengths of the preadjusted appliance, especially when twin brackets with adequate width are used. Nearly full expression of the bracket tip is expressed with relatively little effort, and tip bends are normally not needed.
With the standard edgewise appliance, however, second order (tip) bends were placed in the archwires for two reasons. First, to properly move teeth relative to the 0° of tip in the bracket and, second, to compensate for the heavy forces used to move teeth. Therefore, unless overpowering forces are used during treatment with the preadjusted appliance, there should be little need to modify the tip measurements obtained by Andrews in his study of the non-orthodontic normal models. This has been the choice of the authors, and only minor tip modifications were made when developing the MBT™ appliance system, relative to the research figures.
Bracket tip is one of the main factors that influence the amount of space occupied by each tooth. This in turn influences the way the upper teeth fit with the lower teeth. When using anterior brackets with precisely Andrews' original tip measurements, a total of 40" of tip is placed in the upper anterior segment, and only a total of 6° in the lower anterior segment (Fig. 10.6). The resulting 34° of'tip differential' helps to increase the size of the upper anterior segment and decrease the size of the lower anterior segment. This helps to achieve improved tooth fit within the 60% group described above.
The shape of incisor crowns needs to be assessed during finishing. Tipping incisor crowns, which are barrel or triangular shaped, will have little effect on the arch length occupied (Fig. 10.7). However, barrel-shaped crowns are fortunately rare. Triangular-shaped crowns will normally be reshaped to a more rectangular form, by the orthodontist, for esthetic reasons. So crown shape is seldom an issue, except at the treatment planning stage.
When designing the MBT™ upper premolar brackets, the tip was slightly modified, relative to the research figures. The change was from 2° to 0° of lip. This was to help tooth fit, and to position the upper premolar crowns in a slightly more upright position, which is more toward a Class I position from a starting Class II malocclusion. The MBT™ lower bicuspid brackets have 2° of tip, which is the research figure, and this inclines them toward a Class I position from a starting Class II relationship.
Molar tip of 5° in the upper and 2° in the lower is required. These tip values position the molar cusps parallel to the occlusal plane, which is correct. This tip is achieved by using MBT™ 0° brackets on all molars, and placing the bands parallel to the cusp lips (pp 66 & 67). This positioning allows the molars to settle into an ideal Class I relationship.
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