Parallel to earlier reports on different ethnic groups, the results of this study indicate that the permanent teeth of Tanzanian children erupt earlier in girls than in boys, and the mandibular teeth erupt earlier than the corresponding maxillary teeth. The difference between boys and girls was found in both the first and second transitional period. Permanent teeth in Tanzanian children clearly emerge earlier than in Caucasian children.

Objective:  To examine the expression of possible secular trend in timing of the emergence of permanent teeth in Finnish children over the past few decades, considering the differences between genders. Materials and Methods:  Two age groups of Finnish children, one born in 1976–1985 (group 1980) and the other born in 1999–2002 (group 2000), were examined. Group 2000 comprised 483 children (235 girls and 248 boys) aged 6.4 to 8.5 years at the time of the examination, and the same children were examined at the age of 9.0 to 11.8 years. Altogether 405 children could be recalled, 196 girls and 209 boys. For comparison, matching age groups were selected from the group 1980 data (n = 1579), resulting in a sample of 312 children (155 girls and 157 boys) aged 6.4 to 8.5 years and 393 children aged 9.0 to 11.8 years. The emergence stage of each permanent tooth was determined clinically (Grades 0–3), based on which the subjects were furthermore divided according to the emergence stage of the dentition. Results:  Linear regression models showed that the permanent teeth of the first phase of the mixed dentition erupted earlier in group 2000 than in group1980, but the teeth of the second phase of the mixed dentition erupted later in group 2000. Girls showed more advanced tooth eruption than boys. Conclusion:  The longer duration of mixed dentition in group 2000 than in group 1980 makes the duration of combined follow-up and active treatment longer, and should be considered in timing of efficient orthodontic treatment.

A cephalometric evaluation of the changes in the horizontal and vertical placement of the hyoid bone and of those in the position of the head over the cervical spine after surgical mandibular advancement was undertaken. Seven linear and one angular measurement were investigated in 60 patients, 17 males and 43 females, before and one year after surgical mandibular advancement. The hyoid bone moved forwards horizontally in 78 per cent of the subjects, backwards in 17 per cent, and in 5 per cent of patients it retained its pre-operative position. It moved vertically downwards in 32 per cent of subjects, and in 63 per cent it moved upwards and closer to the body of mandible. The amount of horizontal and vertical change of the hyoid bone was associated with the corresponding change of the mandible after surgery. The vertical change was more distinct in females compared with males. There was variation in the position of the head over the cervical spine; it showed extension in 26.7 per cent of the sample, flexion in 71.7 per cent, and remained the same in only 1.6 per cent after surgery. The results show that with surgical mandibular advancement the hyoid bone follows mainly the advancement of the mandible and moves closer to the body of the mandible. However, there are variations in the changes of hyoid bone and head position that are difficult to predict.