The effects of three methods of orthodontic appliance therapy on some commonly used cephalometric angular variables

This investigation was undertaken to study the effects of the Andresen activator functional appliance therapy, Begg therapy, and cervically directed extraoral forces upon several commonly used cephalometric angular variables, with particular reference to the relationship between the maxillary plane (palatal plane) and anterior cranial base as represented by SN line. The material consisted of 107 cases taken from the files of patients who had attended the Orthodontic Department, Eastman Dental Hospital, London. Ninety of the cases had received orthodontic treatment. For each case pretreatment, posttreatment, and postretention radiographs were traced and angular measurements made by means of a Lysta-Dent digitizer linked to an on-line computer. Descriptive statistics and one-sample and two-sample Student's t tests were performed. None of the treatment methods under investigation had a clinically significant effect upon the maxillary plane. An increase in the inclination of the mandibular plane was a feature of Begg and headgear therapies but not of Andresen therapy. Any increase observed was of a temporary nature. While no change in SNA occurred with Andresen therapy, Begg and headgear therapies produced a permanent reduction in the variable. A small reduction was also produced in SNB by Begg and headgear therapies. The behavior of SNB following Andresen therapy was not significantly different from that in the group of untreated subjects. Each appliance method produced a permanent reduction in ANB; however, a similar reduction was also demonstrated in the control group.