Secular trends affect timing of emergence of permanent teeth.

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.