Evaluation of cervical spine posture after functional therapy with twin-block appliances: A retrospective cohort study

Introduction: It has been postulated that a change in cervical posture occurs as a consequence of forward repositioning of the mandible. Therefore, the objective of this study was to compare the cervical spine posture between subjects with and without functional appliance therapy. Methods: A retrospective cohort study was conducted with the use of pre- and post–functional therapy cephalograms of orthodontic patients. A total of 60 subjects was composed of 2 groups of 30 subjects each: those who underwent treatment with a twin-block (TB) functional appliance and a control group selected from the Bolton-Brush Growth Study. Three sagittal and 7 cervical vertebral parameters were compared between the groups. The Wilcoxon signed-rank test was used to compare pre- and postfunctional mean angular measurements. The Mann-Whitney U test was used to compare the mean changes in cervical parameters between the groups. Results: A significant difference existed between pre- and postfunctional SNB (P <0.001) and ANB (P <0.001) angles, showing a change in maxillomandibular relationship. Comparison of mean changes in angular measurements between the 2 groups showed a significant difference (P = 0.032) in the sella-nasion to odontoid process tangent (SN-OPT) angle. The SN-OPT angle predicted that the probability of developing an altered cervical posture with the TB appliance is 2.08 times greater than without the TB appliance. Conclusions: SN-OPT angle can predict a change in skeletal relationships after treatment with the TB functional appliance. The TB causes the craniocervical posture to be more upright. Subjects with reduced vertical dimensions have greater change in cervical posture.