Waiting on teeth to erupt? Evidence of a secular trend & clinical implications.

If treatment begins during the mixed dentition, a longer transitional dentition phase may lead to longer treatment time.

BY TATE H. JACKSON

STUDY SYNOPSIS
A recent study published in the Angle Orthodontist compared two cohorts of children in Finland in terms of the timing of eruption of permanent teeth. The historic group of children born from 1976-1980 included more than 1,500 children from rural parts of the country. The more recent group, born from 1999-2002, included 483 children who lived in a less rural environment and were followed longitudinally.
 
Permanent tooth eruption was observed clinically and graded using consistent criteria for both groups. Two age ranges were the focus of the study: 1) age 6-9 years, to include the early mixed-dentition transition and 2) age 9-12 years, to include the late transition to permanent dentition.
 
Compared to the 1980 group, the 2000 group showed more advanced permanent tooth eruption during the first age range (6-9 years). There was no difference, however, in permanent tooth eruption between the 1980 and 2000 groups when considering the second age range (9-12 years). So, although teeth began to erupt earlier in the 2000 group, the full transition to permanent dentition was completed no quicker than the group observed 20 years earlier.
 
Effectively, the 2000 group had a longer transitional phase from primary to permanent dentition.

WHAT THE PROFESSOR THINKS
The authors compared cross-sectional observations of eruption stage for a historic group to a modern group who were followed longitudinally. To help account for one of the evident drawbacks of this design, the statistical analysis appropriately accounted for differences in age distribution between the groups. Further, few studies include any good longitudinal data of this sort.
 
This report of a secular trend – that the emergence of permanent teeth is occurring at an earlier age compared to many years ago – is worth consideration by clinicians. Especially since this finding means that the transitional dentition phase is effectively longer.
 
Put in a clinical context, this study implies that the orthodontist who begins comprehensive treatment for children in the mixed dentition because they appear to be advanced dentally may find that they also have longer treatment times. Why? Because all of the permanent teeth did not finish erupting on the apparently accelerated pace that was initially observed.
 
It is unfortunate that the magnitude of the secular trend effect was not reported in a meaningful way in this study. So how should clinicians use these data?
 
These data find utility when combined with individual clinical experience. For the orthodontist who suspects that he or she is waiting on the eruption of permanent teeth longer today than a few years ago, this study provides some evidence to trust their clinical judgement – and not rush to start patients younger and thereby sacrifice treatment efficiency.

Article Reviewed: Eskeli, Losonen et al. Secular trends affect timing of emergence of permanent teeth. Angle Orthod. 86:53-58. 2016 (Jan.) 

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