The effect of maxillary palatal expansion on the primary dental arch circumference.

Rapid palatal expansion was used to correct constricted maxillas on 29 subjects, 10 o[ whom had cle~t palates. Arch width, measured transversely at the primary canine and at the primary second molar, increased in all cases with a mean value o[ 4.0 mm. Arch perimeter (arch length) also increased approximately 4.0 mm. Correlations between change in transverse palatal dimension versus change in arch circum[erence were variable. Besides the known benefits of correcting posterior crossbite through rapid palatal expansion, the probable increase o~ arch perimeter due to rapid palatal expansion should be recognized.