Spatial changes in the relationship of the mandible and maxilla with different extraction patterns and techniques

To assess the spatial changes in the relationship of the mandible to the maxilla with different extraction patterns and techniques when treated Class II patients are compared with untreated subjects.

Pretreatment and posttreatment cephalometric radiographs of 125 Class II adolescent patients and 30 untreated Class II patients were traced. The treated patients were divided by technique and extraction pattern into four groups: preangulated appliance with four first premolar (4/4) extractions, preangulated appliance with maxillary first and mandibular second premolar (4/5) extractions, standard edgewise (Tweed-Merrifield technique) with four first premolar (4/4) extractions, and standard edgewise (Tweed-Merrifield technique) with maxillary first and mandibular second premolar (4/5) extractions. The mandibular displacement vector angle was determined by using two different superimposition methods: the superimposition on the cranial base and the superimposition on the maxillary base.

The differences in the mean vector angles of mandibular displacement in the two superimposition methods were statistically compared. There was a significant difference between the vector angle of mandibular displacement in each treated group when the superimposition techniques (ie, cranial base and maxillary base) were compared. Significant differences between the standard edgewise treated group and the preangulated treated group were found using both superimposition methods.

The standard edgewise appliance groups showed a more forward horizontal displacement of the mandible than the preangulated appliance groups. Within the standard edgewise sample, the patients with four first premolars extracted had a greater horizontal mandibular displacement than did the maxillary first, mandibular second premolar extraction sample.