In a sample of 20 adults the associations between cervical lordosis, craniocervical inclination, position of the hyoid bone and cross-sectional dimensions of the pharyngeal airway were studied. Lateral skull radiographs were obtained in natural head posture and also at 20 degrees extension with the subjects' teeth in the intercuspal position. Cervical lordosis was measured from the second to the sixth vertebra and the position of the hyoid bone was calculated in horizontal and vertical directions. The dimensions of the free airway were measured between the dorsal tongue surface and the posterior pharyngeal wall and at the level of the second and fourth vertebra. A change from natural head posture to 20 degrees extension resulted in an increase in cervical lordosis and craniocervical inclination, changed position of the hyoid bone and increased cross-sectional dimensions of the pharyngeal airway. The changes in lordosis produced by changing natural head posture to 20 degrees extension showed significant correlations with the size of changed craniocervical inclination and free airway.

In a sample of 107 boys and girls registered at 8, 11, and 15 years of age and 22 adults the statural height and the height and length of the cervical vertebrae, measured from lateral skull radiographs, were studied. The height and length of the vertebrae increased with age among the children and were non-significantly higher for the girls in each age group. The 15-year-old girls matured earlier, reaching adult values at this age. The 15-year-old boys still showed significantly smaller values for vertebral height and length compared with the adult men. Statural height was significantly correlated with the variables for vertebral growth at 8 and 11 years, whereas there was no correlation at 15 years of age among the children who had passed the pubertal peak height. The development of the vertebrae showed similarities with earlier reported skeletal maturity indicators found in the hand-wrist area and could as such offer an alternative method of assessing maturity without the need for hand roentgenograms.

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The present investigation was undertaken in order to study the velocity of orthodontic tooth movement in rats and the effect of the hormonal changes that occur during pregnancy or with fluoride, which is one of several trace elements that affect hard tissue metabolism. Adult, female Sprague-Dawley rats were separated into three groups: non-pregnant, pregnant, and non-pregnant NaF-supplied. All rats were treated with a fixed orthodontic appliance which moved the upper first molars in a buccal direction during 21 days. The appliances delivered an initial force of 150 mN. Repeated intra-oral, standardized radiographs were taken during the experimental period, and at the end of the experiment the maxillae were examined histologically. The velocity of tooth movement was calculated after measurement of the radiographs. The first molars were moved in a buccal direction in all groups. The mean value of the expansion from day 0 to 21 was significantly higher among the pregnant rats (0.64 mm) compared to the non-pregnant, control animals (0.46 mm) while the NaF-supplied rats had a significantly lower expansion (0.22 mm) compared to the control animals. In the histological examination of the pressure sides of the PDL of the upper first molars, the mean value of osteoclasts per microns x 10(-3) increased non-significantly in the group of pregnant rats and decreased significantly among the NaF-supplied animals compared to the non-pregnant control rats. The present experiment in rats indicated that the velocity of orthodontic tooth movement is influenced by hormones as well as trace elements.

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The maximum bite force and position of the hyoid bone during natural and extended head posture were studied in 15 adults. All participants had normal occlusions and full dentitions. In addition, there were no signs or symptoms of craniomandibular disorders. The bite force was measured with a bite force sensor placed between the first molars. Six registrations of gradually increasing bite force up to a maximum were made with randomized natural and extended head postures. With one exception, the mean maximum bite force value was found to be higher for every subject with extended head posture compared to natural head posture. The sample mean was 271.6 Newton in natural head posture and 321.5 Newton with 20 degrees extension. With changed head posture, the cephalometric measurements pointed towards a changed position of the hyoid bone in relation to the mandible and pharyngeal airway. The cephalometric changes in the position of the hyoid bone could be due to a changed interplay between the elevator and depressor muscle groups. This was one factor which could have influenced the registered maximum bite force.