Subjects
The investigation was planned as a randomized clinical trial and was approved by the local ethics committee with reference number “2IXEhm” (Ethics Committee of the Medical Faculty, Westfälische-Wilhelms-Universität Münster, Germany) and registred with the number: DRKS00003497. The study protocol was established and the number of patients needed for adequate statistical power was determined through assistance from Zentrum für Klinische Studien Münster (ZKS). A minimum of 30 patients each for the therapy and control group was established. Patients to be included were required to have late deciduous and early mixed dentition, unilateral posterior cross bite and functional mandibular asymmetry (according to Figure1). Patients with previous orthodontic treatment, ongoing habits, systemic illness under long-term therapy (e.g., diabetes mellitus), syndromes, cleft lip and palate, physical or mental handicaps and known structural orthopedic illnesses (e.g., Scheuermann’s disease, stiff neck) and spinal deformities were excluded. The subjects were screened for sport habits before and during the orthodontic therapy and it was recommended to them, not to change the initial sports habits in order to minimize this functional factor in the study. Parents gave their informed consent according to the requirements of the local ethics committee and the Helsinki criteria. The patients were initially randomized using block randomization (block length 20; allocation ratio 1:1) to either the control or therapy group. A total of 82 children (38 boys and 44 girls) met the above criteria; 40 were assigned to the therapy group, 42 were assigned to the control group and 77 children attended the initial examination appointment. Due to various personal reasons, 5 children dropped out after randomization. A total of 37 children remained in the therapy group, and 40 children remained in the control group. For the final examination, 11 children were excluded from the study for either personal reasons or for being unable to keep to the mandatory time schedule. Thus 66 children (30 boys and 36 girls) remained: 31 in the therapy group (13 boys and 18 girls) and 35 in the control group (17 boys and 18 girls). The children’s mean age was 7.3 (SD 2.1 years) at the beginning of the study and 8.3 years (SD 2.1) at the end of the study. The gender ratio was nearly equal in the groups. For all patients, two examination appointments were fixed: an initial examination appointment (T1) and a final examination appointment one year later (T2).
Orthodontic treatment
In the therapy group for slow expansion of the maxillary bone formation, a bonded palatal expansion appliance (Figure2a) was used as previously described by McNamara et al.[11]. After correction of the maxillary discrepancy, an orthodontic activator treatment (U-Bow activator Type 1) as described by Karwetzky[12] was applied to achieve midline coordination and to retain the amount of palatal expansion (Figure2b). Details are given by Lippold et al.[7].
3-D back shape measurement
To measure back shape and to determine three-dimensional orthopedic parameters of the back and spine, rasterstereography (Formetric 2, Diers International GmbH, Schlangenbad, Germany) was used. This optical contact-free photogrammetric method provides high accuracy of the surface data and good correlation with radiological findings[5, 13–15] for the spine reconstruction, but without the risk of radiation hazards. The recording required only 0.04 sec with the subject standing free without pads or trunk fixation.
Evaluating the record was accomplished in three steps. First, the back shape was reconstructed by photogrammetric methods that generated a list of 3-D coordinate data of back surface points in a regular array. Second, three anatomical landmarks – the vertebra prominens and the two spina iliaca posterior superior (lumbar dimples) – were detected and localized using automated mathematical procedures that scanned the reconstructed surface for its characteristic shape. When these three landmarks were localized, they spanned a body fixed coordinate system, which provided an objective and automated determination of the longitudinal, sagittal and lateral direction. Third, the symmetry line of the back was determined by mathematical shape analysis and model calculation based on the 3-D reconstruction of the back surface. The symmetry line is a reasonable estimate of the line of spinous processes[16]. Finally, the lateral projection of the symmetry line, which is virtually the sagittal back profile, was calculated and analyzed such that the appropriate shape parameters for the back could be determined.
The automated mathematical evaluation procedures necessitate a high level of accuracy of the input data: back shape and the sagittal profiles were therefore recorded with 0.25 mm accuracy. The precision in localizing the vertebra prominens landmark and the dimple landmarks was of high accuracy according to Hierholzer[17].
Shape parameters of the back were calculated from the sagittal profile and from the back shape. Geometric analysis of the sagittal profile was used to determine the kyphotic and lordotic angle. Geometric analysis of the profile provided the points of inflection and their respective inflection tangents in the cervico-thoracic transition (ICT), thoracic-lumbar transition (ITL) and lumbar-sacral transition (ILS). The kyphotic and lordotic angles are spanned by two of the inflectional tangents each (Figure3a). Additional parameters used in the characterization of back and spinal shape were the lateral deviation, the vertebral rotation, the pelvic tilt and the pelvic torsion[16]. These parameters rely on biomechanical modeling of the spine and on the shape analysis of the back with methods from differential geometry[18] and are consistent with radiological findings[14].
Lateral deviation suggests that at a given vertebral level, the distance between the center of the reconstructed vertebral body and the sagittal plane (Figure3b). Here, the parameter specifies the mean values of the measured distances between the vertebra prominens and the lumbar dimples midline.
Vertebral rotation at a given level was estimated from surface rotation at the pertinent point of the symmetry line, with the sagittal direction as the reference direction (Figure3c). Again, this parameter specifies the mean value over the same distance. Pelvic tilt was calculated from the height difference of the two lumbar dimples (Figure3d); similarly, pelvic torsion was calculated from the difference of surface orientations in the lumbar dimples (Figure3e). The latter has a positive value with posterior rotation of the right side of the pelvis and an anterior rotation of the left side of the pelvis. In the reversed configuration, the sign of the pelvic torsion is negative.
Data analysis
Statistical processing was performed with SPSS 12.0 (Lead Tech., Chicago, USA) under biomathematical assistance by “Zentrum für Klinische Studien Münster (ZKS)” at our university. The therapy and control groups were tested for normal distribution using the Kolmogorow-Smirnow test. SPSS 12.0 (Lead Tech., Chicago, IL, USA) software was used in the data analysis. The posture parameters involved in the measurements were as follows: UTI, KA, LA and PI. To determine the craniofacial morphology, the Angle Classification and the overjet were considered. ANOVA, Scheffé and Kruskal-Wallis procedures were used to test our hypothesis. Significance was set at p < 0.05.