Stability of upper incisor inclination changes in Class II division 2 patients

The aim of this study was to evaluate the changes in incisor inclination following orthodontic treatment in Class II division 2 patients, and to assess the long-term stability after retention. Dental casts and cephalograms of 61 Class II division 2 patients (31 males and 30 females, mean age 13.4 years) with a closed lip seal were available before (T1), at the end of treatment (T2), and 3.5 years (mean) post-treatment (T3). A method of measuring upper incisor inclination on dental casts was developed for the purpose of the investigation. This involved placing markers on the study casts and then taking radiographs which were measured to establish the upper incisor inclination. Statistical analysis of the data included the calculation of mean values, standard deviation, standard errors, and ranges for each variable. Spearman ranked correlation coefficients were computed for selected model variables and scattergrams plotted. To investigate the influence of the chosen retention therapy, a Mann-Whitney U-test was used. The mean change in incisor inclination during orthodontic treatment was 15.2 degrees. There was a mean relapse of 2.2 degrees between T2 and T3, but this was not considered clinically relevant. The amount of relapse was independent of the type of the retention appliance (Hawley type retainer or lingual retainer). The relationship between long-term stability of the incisor inclination and between the lip line relative to the upper incisors was also investigated, based on cephalometric data. A mean decrease in lip line height of 0.6 mm was seen at T2 and, although the observed change was statistically significant, it would not be clinically relevant.