The relationship between unilateral posterior cross bite, asymmetries in the craniofacial complex and postural disorders has been previously reviewed by Korbmacher et al.
]. As noted above, the current literature is lacking in randomized clinical trials addressing the development of the dental and craniofacial complex and its possible influence on the morphology of the cranio-cervical and vertebral column. Although the close functional and morphological relationship between the stomatognathic system and the vertebral column have been described
] to date no randomized trials have addressed the possible impact of that treatment of unilateral posterior cross bite could have on the vertebral column.
Our working hypothesis for this study was that early orthodontic treatment in preadolescents with unilateral cross bite could induce a negative change in vertebral alignment with respect to the thoracic and lumbar spine sections. To test this hypothesis, we analyzed the parameters quantifying the sagittal curvature in the kyphotic and lumbar spine in a randomized clinical trial, using rasterstereography to evaluate possible effects of treatment. Additionally, we assessed frontal plane effects based on surface rotation and lateral deviation. In this study, we found that in both the therapy and the control group, the kyphotic and the lordotic angle were within the limits of clinical tolerance. A significant difference was observed in the kyphotic angle between initial (T1) and follow-up (T2) examination; while in the control group the kyphotic angle slightly increases, the converse is observed in the therapy group. However, a change of 1 to 2 degrees in the kyphotic angle is not of clinical relevance, especially in a juvenile population.
No significant difference in the control and therapy group was observed in surface rotation. The control group and therapy group showed measurement values that did not differ significantly from the expected biomechanical value of zero. Nevertheless, in the therapy group, the distance from zero decreases between T1 and T2 – a decrease that is significant as assessed by the paired t-test. The distance from zero does not change significantly in the control group.
No significant changes were detected for the pelvic tilt, and no pelvic torsion was observed for the patient sample due to the small amount of pelvic tilt. The orthopedic data collected in this study reveal no manifest orthopedic illnesses; furthermore, no clinically relevant changes in the parameters of kyphotic angle, surface rotation and lateral deviation were observed.
Our results suggest that modern orthodontic treatments for unilateral posterior cross bite
] does not influence negatively the thoracic spine. The orthodontic treatment had no impact on impairing postural parameters. Therapy had no negative effect on several parameters of spinal positioning, including kyphotic and lordotic angle, surface rotation, pelvic angles and lateral deviation. We therefore conclude that our working hypothesis – namely, that early orthodontic treatment can induce negative therapeutic changes in body posture through thoracic and lumbar position changes in preadolescents with uniltaral cross bite– is not valid within the limitations of this study.
While it has been hypothesized that orthodontic treatment can influence the cervical spine, it seems likely that in lower segments, these effects disappear due to biomechanical effects or by inherent measurement limitations. According to the theory of scoliosis progression postulated by White et al.
], an imbalance in the thoracic spine can result in imbalanced loading of the spinal muscles and ligaments that finally results in a progression to scoliosis. Solow et al. proposed a similar theory about the development of the cranio-cervical complex based on the individual muscular balances
]. Local imbalances are suggested to contribute to the development of idiopathic scoliosis in the preadolescent growth phase
The effects of asymmetric loads on the spinal system were suggested by Roaf to be the major contributing factor in the development of juvenile idiopathic scoliosis
]. Idiopathic scoliosis in the preadolescent growth phase is believed to be reversible based on work in animal models
]. We therefore conclude that early treatment of unilateral cross bite is advisable since it does affect negatively the vertebral column. After the adolescent growth spurt, conservative correction of spinal postural disorders seems to be more difficult