Maxillary Intrusion Research Articles

Maxillary anterior intrusive forces generated by Begg Stage I appliances

The capability of Begg mechanotherapy to produce intrusion of the maxillary anterior teeth, particularly the incisors, has been questioned. Although the Stage I appliance opens the bite, this can be the result of one or a combination of several occlusogingival displacements, and the manner of bite opening continues to be a subject of discussion. Support in favor of anterior maxillary intrusion exists, at least in part, because of the potential for extrusion of these teeth during Stage III. However, the magnitudes of actual intrusive force generated by the Begg Stage I appliance apparently have not been investigated heretofore. The purpose of this experimental study was to quantify and compare on the bench the intrusion potentials of maxillary appliances used in Stage I by Begg practitioners. Five independent variables (size of anchor bend and gable bend, Class II elastic-force magnitude, anchor-bend positions, and archwire diameter) and a total of 135 appliance configurations were evaluated. The raw intrusive-force data were reduced and analyzed by means of accepted statistical procedures. The individual contributions of the independent variables in the appliance were investigated. Parametric relationships, developed within the experimental results, were compared to the predictions of the engineering bending theory for beams and arches. A force analysis of the appliance design was carried out toward evaluation of anchorage potential. This investigation revealed that the appliances generate light to moderate intrusive forces, that wire diameter, anchor-bend size, and elastic-force magnitude are the controlling parameters, and that several combinations of variable values may yield identical intrusive-force magnitudes as activated. For most of the appliance configurations tested, the results were in general agreement with the elastic bending theory. Although intrusive forces generated by the most commonly used Begg appliances were found to be rather light, factors inherent in the design-in particular the nonuniform distribution of the intrusive force throughout the anterior segment-tend to enhance the potential for intrusion. A systematic approach to the fabrication of the appliance is suggested.