SKELETAL EFFECTS INDUCED BY TWIN BLOCK IN THERAPY OF CLASS II MALOCCLUSION

The aim of this clinical study was to evaluate the treatment skeletal effects induced by Twin Block in the therapy of Class II malocclusion during or slightly after the onset of the puberal peak in the growth velocity. The study sample was obtained from the records of the author's private practice and consisted of a parent sample of 70 Class II division 1 subjects treated consecutively with the Twin-block appliance, from which good quality lateral cephalograms were available. From this sample, 23 subjects (Study Sample) 15 males and 15 females, were selected according to the following inclusion criteria: ANB greater than or equal to 4 degrees, full Class II or end-to-end molar relationships, no history of previous orthodontic treatment or surgery treatment, absence of congenital anomalies, same Caucasian race. All patients received active treatment with Twin-block before or during their pubertal growth spurt, as assessed by the cervical vertebral maturation (CVM) method. Lateral cephalograms for each subject was digitized by a single author (AL) respectively at time 1 (T1), immediately before treatment, (mean age 10.0 +/- 1.1years) and at time 2 (T2) immediately after treatment (mean age 12.0 +/- 1.1 years). The error of the method was calculated with the formula described by Dahlberg (1940). In addition systematic error and the coefficient of reliability were determined as suggested by Houston. The Control Group consisted of untreated Class II subjects (Michigan Standard). A modification of the Twin-block appliance, originally developed by Clark, was used in this study. In the present study the mean duration of the Twin -block treatment was 1.2 +/- 0.5 years. Results of the statistical comparisons between Study Sample (treated subjects) and Control Group (untreated subjects) on the changes for all cephalometric variables during the T1-T2 observation showed significantly favorable changes: the total mandibular length (Co-Me) and ramus height (Co-Go) and corpus length (Go-Me) increased more in cases than in controls. Our results show a significantly higher average answer in the Study Sample, both in the paired t- test, comparing pre and post treatment, and in the unpaired t- test, comparing the Study Sample and the Control Group. Paired t- test data for the variables Co-Me, Co- Go, Go- Me, with a P=.05 significance level, lead us to reject the null hypothesis (differences average = 0) in favor of the alternative of a positive differences average, meaning that the average of the values is higher after the treatment.