INTRODUCTION

Correlations between the head posture and the craniofacial morphology are described in the literature.12 A number of studies used lateral cephalometric radiographs of the head to analyze the posture of the head and neck region (cranio-cervical angles and cervical inclination to horizontal or vertical reference planes).1–7 Festa et al2 used lateral cephalographs to evaluate the relationship between the mandibular length and the cervical inclination and could show significant correlations between these parameters in 70 Caucasian women (mean age 27.4 years) suffering from skeletal distal occlusion. Solow et al3 analyzed 120 Danish male dental students (age 20–30 years) and found low significant correlations between the head inclination and the craniofacial morphology.8 Also D'Attilio et al4 found a correlation between the cervical lordosis and the mandibular position, the mandibular length, the mandibular divergency, and the overjet.

Conversely, some studies negate the existence of specific orthopedic findings in patients with different sagittal jaw positions.910 In view of the close functional correlations of the cervical and thoracic spine, the back shape of the thoracic and pelvic region seems to be of interest with respect to relationships between the sagittal jaw position and the body posture.7

Michelotti et al11 stated in a review article that there is some evidence that correlations between the jaw position and the cervical inclination do exist; however, in the case of the lower vertebrae, these correlations tend to disappear.

The aim of the present study was to analyze the correlations between the kyphotic inclination, the lordotic angle, and the inclination of the pelvic derived form the sagittal back profile by means of rasterstereography and the craniofacial morphology by analyzing six cephalometric parameters in lateral cephalographs.

MATERIALS AND METHODS

The sample consisted of 53 healthy adults (32 women, 21 men; mean age 24.6 years, SD 9.0 years; mean body weight 64.5; mean height 170.6 cm). All patients had been admitted to the Department of Cranio-Maxillofacial Surgery and the Department of Orthodontics, University of Münster for combined orthodontic-orthognathic surgery. The patients had Class II or III malocclusions. None of the examined persons had a history of motor or neurological problems, internal disease, orthopedic trauma or impairment, spinal disorder, or spinal surgery. All patients gave their informed consent to the study design according to the local Ethics Committee and the Helsinki criteria.

Cephalometric Analysis

A standardized lateral skull radiograph (24 × 30-cm films; Planex Regular, Kodak, Germany) was taken (film focus distance 3.2 m; final enlargement 1%; exposure 15–25 mAs, 72–81 kV) of each patient. The radiographs were digitized (Power Look III scanner, Umax Systems, Willich, Germany; resolution 300 dpi), and a cephalometric tracing was performed with cephalometric analysis software (Onyx Ceph Version 2.7.8, Image Instruments, Chemnitz, Germany) (Figure 1).

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Six angular skeletal parameters12 were considered to be the most relevant for this study (facial axis, mandibular plane angle, inner gonial angle, lower facial height, facial depth, and maxilla position) and were determined according to Figure 1 and Table 1.

Table 1. Cephalometric Analysis: Definition of Reference Points, Lines, and Angles (I–VI)^a

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The patients' data were blinded before the cephalometric analysis was carried out. The method error in determining the cephalometric measurements was assessed using Dahlberg's formula13 (mean square error (SE²) = d²/2n (d = difference between repeated measurements; n = number of recorded radiographs). For the lateral cephalometric analysis, the method error was determined by repeating the measurements of the six variables on randomly chosen radiographs at 2-week intervals with the same operator.

Rasterstereography

Rasterstereography1415 (Formetric 2, Diers International GmbH, Schlangenbad, Germany) is a method based on photogrammetric principles that makes three-dimensional surface analysis possible. A multitude of light sections is projected on the patient's back from a different direction than that of the optical measurement unit, thereby compiling shape information along the section line.16 The measurement time is typically reduced to 1/25th of a second, and all sections are simultaneously registered. The patient is examined in a relaxed standing posture. Rasterstereography is accurate and reliable and therefore the best choice for back shape analysis (error < 0.1 mm). The automatic anatomical landmark localization (vertebra prominens or the spinae iliacae in the pelvic region) is the basis for an automatic reconstruction of the sagittal back shape. It provides a set of shape parameters characterizing the back profile.17 Figure 2a shows a typical plot of the rasterstereographic reconstruction in the three dimensions. Figure 2b shows the frontal and lateral view of the spinal shape.

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A two-dimensional sagittal back shape profile can be obtained by mathematical modeling. Three inflectional points along the profile are indicated: the cervicothoracic (ICT), thoracolumbar (ITL), and lumbo-sacral (ILS) inflection points. The tangents to the inflectional points span two characteristic angles of the profile: The kyphotic angle (KA) is spanned by the tangent lines in ICT and ITL; and in an analogous way, the lordotic angle is spanned by the tangents in ITL and ILS. The reproducibility of a single rasterstereographic measurement of the kyphosis or lordosis angle is determined to be 2.8°.18 Accordingly, the reproducibility of inclination measurements with respect to the vertical line is expected to be 2°. Two angles provide orientation data with reference to the vertical line (plumb line): the upper thoracic inclination (spanned by the plumb line and the ICT tangent) and the pelvic inclination (spanned by the vertical and the tangent ILS). The positioning with respect to the measurement system was carried out according to the recommendations of the supplier.

RESULTS

The standard errors of the mean values of the angular and linear measurements did not exceed 0.5° and 0.5 mm, respectively. These arbitrary levels were used according to Trpkova et al.19 The results of the cephalometric analysis are presented in Table 2, and those of the back shape analysis in Table 3.

Table 2. Cephalometric Measurement Data

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Table 3. Back Shape Measurement Data

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Statistically significant correlations were found between the facial axis and the lordotic angle (P = .022; R ² = 0.113), the facial axis and the pelvic inclination (P = .002; R ² = 0.178), the inner gonial angle and the lordotic angle (P = .048; R ² = 0.083), the inner gonial angle and the pelvic inclination (P = .014; R ² = 0.112), the mandibular plane angle and the lordotic Angle (P = .013; R ² = 0.18), the mandibular plane angle and the pelvic inclination (P = .032; R ² = 0.169), and the facial depth and the pelvic inclination (P = .021; R ² = 0.178).

DISCUSSION

In the literature, the documentation of significant correlations between the jaw position and the body posture often lack objective measurement methods to provide valid results.111

The present study is based on accurate skeletal cephalometric data, obtained by means of lateral cephalometric analysis, needed to evaluate the vertical and sagittal jaw positions. For the analysis of the sagittal alignment and the balance of the spine lateral cervical, it would have been possible to use thoracic and pelvic radiographs.20 However, in view of possible radiation hazards, such an attempt would not be justified. Therefore rasterstereography was performed because a back shape analysis can be accomplished without radiation exposure while achieving excellent accuracy.18

In the case of patients with idiopathic scoliosis, the system accuracy was clinically evaluated by Drerup et al21 and by Hackenberg et al,2223 and showed good accuracy compared with digitized radiographs, particularly for the sagittal profile. To simplify the examination technique, four parameters of the sagittal back shape profile were provided by Drerup et al21 to determine the back shape in a standardized manner.

In this study, correlations could be found between the measurement angles determining the vertical skeletal pattern of the craniofacial skeleton (facial axis, inner gonial angle, and mandibular plane angle) and the pelvic inclination and the lordotic angle. These craniofacial angles are determined by parameters that are based on the vertical relationship of the skull base to the mandible (facial axis) or the vertical type of the lower jaw itself (inner gonial angle and mandibular plane angle). It can be concluded that the vertical pattern of the mandible or the mandible in correlation to the cranium has a correlation to the vertical arrangement of the lower thoracic and lumbar vertebral regions and the inclination of the pelvis. The subjects analyzed in this study featuring a more horizontal type of craniofacial complex had lower inclination angles for the measured sagittal back shape parameters (upper thoracic inclination, lordotic angle, and pelvic inclination). By contrast, patients with a more vertical craniofacial pattern had greater values for these parameters.

Even the sagittal position of the mandible was positively correlated with the pelvic inclination. Subjects with a mesial mandibular position had lower pelvic angles than those with a more posterior oriented mandible (Figure 4a, b). In view of the results of this study, the mandible seems to be in a postural relationship to the lower part of the spine. However, it is not possible to deduce any information about the neurological or muscular balanced interactions. Further investigations are necessary to analyze this correlation and to understand the interactions between the craniofacial and lumbar and pelvic regions, respectively. Prospective clinical studies on growing children should be conducted to analyze the influence of growth stimulation on the lumbar and pelvic regions.

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The measurement of the lower face height (angle IV) is defined as the vertical arrangement of the maxilla in relation to the mandible, but no correlations with orthopedic measurement data could be observed. Even the sagittal position of the maxilla (maxillary position) did not show any correlation to the sagittal back shape parameters achieved in this study. It can be concluded that the vertical and sagittal position of the maxilla does not seem to be correlated with parameters of the back shape profile.

The results of our study are in agreement with studies by Solow et al3 and Huggare et al56 that showed a positive correlation between the different skeletal facial patterns and the cervical inclination. The possible explanation, termed “soft-tissue stretching” hypothesis, stated that differences in craniofacial morphology could be explained by the stretching of the soft tissue layer of the skin when the head is bent backward. The increased force level would restrict the forward growth of the maxilla and the mandible. However, this hypothesis could be used for the explanation of postural relationships between the facial and the craniocervical skeleton, but no explanation for correlation to body posture was given. Possibly, this hypothesis could be extended to other regions of the human body.

Nobili et al7 revealed positive correlations between the sagittal jaw position and the body posture. Class II malocclusion was correlated to anterior body posture and Class III malocclusion to posterior oriented posture. However, the main focus of these studies was on the upper part of the vertebral column.

The result of the present study is not in agreement with a critical review of the literature by Michelotti et al,11 who postulated that there is some evidence of a correlation between the sagittal jaw position and the cervical posture but not in relation to body posture. Our results show significant correlations between the craniofacial morphology and the lower spinal morphology.

It is known that the measurement of the body posture by means of rasterstereography instead of radiography provides accurate information on the back shape and the sagittal profile, avoiding radiographic load for the patient, and is therefore suitable for studies like this. Further prospective studies should be conducted to assess the possible influence of orthodontic therapy on body posture.

CONCLUSIONS

• The correlations between craniofacial parameters and thoracic, lordotic, and pelvic inclination suggest that there is some clinical evidence for a relationship between the jaw position and the body posture. However, in the case of the maxilla, these correlations were not observed.

• For accurate reproduction of the back shape profile, rasterstereography is a noninvasive and reproducible method. It can be used in interdisciplinary orthopedic-orthodontic studies for a valid reproduction of the body posture.