8 So this rare discrepancy in the prediction of leeway space
can leads to slight crowding in the permanent dentition.
At approximately 11 years of age, the permanent first molars migrate forward to close up the ex- cess leeway space
provided by the difference in size between the primary molars and the suc- cedaneous premolars.
What would our orthodontic colleagues think of the recommendation of the wholesale removal of the leeway space
that nature has provided for the permanent dentition by allowing subsequent mesial drift?
The maximum leeway space that he measured from cases in his practice was 8 mm and the least was 0 mm.
Thanks to Steve Dugoni et al, (13) looking at Art Dugoni's records, we learned that leeway space could be successfully held to offset anterior crowding with excellent long-term results.
Apparently, Nance had been correct; we can use the full leeway space to our advantage.
Conclusion: For mixed dentition cases in which leeway space is favorable compared with anterior crowding, use a passive lingual arch.
Space loss occurred from tipping of the teeth adjacent to the infra-occluded primary molar with the space loss being greater than that normally lost by the leeway space [Becker et al.
The leeway space is mainly due to the difference in widths of the mandibular second primary molar versus the narrower underlying permanent second premolar.
One potential disadvantage of a PMC is the risk of over-sizing the retained primary molar and compromising the leeway space.