Posted by R. Warotayanont
Do you know how much teeth move during development? In a series of 4 papers, Baume et al studied tooth migration in primary, mixed, and permanent dentitions as well as the biogenesis of overbite. This post will mention some keys (and keywords) in each dentition.
1. Primary dentition During 3-5.5 years old, everything (arch length, intercanine width, spacing) is largely unchanged. The only one factor that has reported to be increased during this age group is the vertical growth of alveolar process.
2. Accessional dentition (mainly about eruption of permanent first molars)
- In type I primary dentition, there is an early mesial shift of permanent first molars (both upper and lower) into the primate space*.
- In case of the closed primary dentition (type II, no spacing), early mesial shift cannot occur because of absence of primate space. However, late mesial shift of permanent first molars can still occur after lower second primary molars exfoliate. This late mesial shift can possibly adjust the end-to-end occlusion into class I.
- There is no change in A-P relationship of primary canine, meaning that there is no mesial shift of the mandible. Therefore, the cause of migration is the eruption and root formation of permanent first molars, not the mandible growth.
3. Successional dentition (mainly about eruption of permanent incisors)
- Secondary spacing of upper deciduous incisors occur after eruption of permanent lower incisors. I think this is a pretty interesting observation that eruption of lower teeth could account for increased arch width in the upper arch.
- The lateral growth of alveolar process is the key for proper alignment of permanent incisors. This lateral growth occur during formation of deciduous arch during lactation, eruption of permanent incisors, and eruption of permanent canines and premolars.
4. Degree of overbite. This has been shown to depend on (1) The sequence of permanent canine eruption (whether it is before or after premolar eruption) and (2) the degree of mandibular forward growth.
*Note: primate space is the space observed between tooth B and C in maxilla, and between tooth C and D in mandible.