Leeway Space

This space can be maintained by preserving arch length with a lingual arch as the primary teeth begin to exfoliate unless conditions such as the premature loss of a primary canine require earlier intervention.
Leeway space. The difference in combined width between the primary canine first molar and second molar and their permanent successors the permanent canine and premolars. The leeway space provides adequate space to resolve crowding that is present in the mixed dentition in the majority of individuals. The leeway space is mainly due to the difference in widths of the mandibular second primary molar versus the narrower underlying permanent second premolar. Usually the sum of the primary tooth widths is greater than that of their permanent successors.
Leeway space is the size differential between the primary posterior teeth canine first and second molars labeled c d and e in the picture and the permanent canine and first and second premolar labeled 3 4 and 5. In caucasians it is greater in the primary dentition by about 1 1 5mm in the maxilla and 2 2 5mm in the mandible.