Cephalometric changes in overbite and vertical facial height after removal of 4 first molars or first premolars

The objective of this study was to evaluate the outcome of standard edgewise orthodontic treatment with extraction of 4 first molars (6xT group) or Tweed edgewise treatment with extraction of 4 first premolars (4xT group).

A cephalometric analysis that isolated tipping and bodily tooth movements of the maxillary and mandibular incisors and measured vertical skeletal changes in the anterior region of the maxilla and mandible was used. Thirty subjects treated by 10 practitioners comprised the 6xT group, whereas 31 subjects treated in the Case Western Reserve University orthodontic clinic were used in the 4xT group. Control groups (6xC and 4xC) were selected from untreated subjects enrolled in the Bolton-Brush Growth Study and were matched on age and gender. Data were collected before (T1) and after (T2) treatment.

Analysis of the data showed no statistically significant changes between 6xT and 6xC for any of the variables studied. An increase in overbite of 2.1 mm in the 6xT group was the result of small but clinically significant changes in both tipping and extrusion of maxillary and mandibular incisors. In the 4xT group, statistically and clinically significant changes were observed for intrusion of the maxillary and mandibular incisors, resulting in a 4.1-mm decrease in overbite. Importantly, both the 6xT and the 4xT groups showed no increase in mandibular vertical height during treatment.

Both treatment strategies showed good control of vertical mandibular growth. Bodily intrusion of anterior teeth was the main contributor to correction of deep overbite in the Tweed edgewise sample.