[Arch perimeter changes on non-extraction correction of dental crowding with Damon appliance]

To clarify the arch perimeter changes and the mechanism of Damon technique on the correction of dental crowding with non-extraction approach in different dental stages.

24 patients with non-extraction Damon appliance treatment were reviewed. They had Class I skeletal pattern and upper arch crowding more than 5mm. They were divided into 2 groups according to the eruption of upper second molars, with 9 subjects in group G1 (second molar unerupted) and 15 subjects in group G2 (second molar erupted). The dental casts and cephalometric radiophotographs were analyzed before and after the upper arch crowding correction. The difference between the two groups was analyzed with SPSS15.0 software package.

Significant increase in upper arch length and arch width were noted after the correction of crowding, with no significantly difference between the two groups. Stepwise regression analysis indicated that the increase in arch length (X1) and inter-bicuspid arch width (X2) were predictive of the increase in arch perimeter (Y), with the equation of Y=1.35X1+0.63X2+1.77. Both molar distalization and incisor protrusion contributed to the increase in arch length, which were 2.4mm and 1.2mm in G1 group, and 0.9mm and 2.5mm in G2 group. The difference between two groups was statistically significant (P<0.05).

During the correction of upper arch crowding with non-extraction Damon technique, arch perimeter is gained by the increase in both arch length and inter-bicuspid arch width. In addition to the labial movement of incisors, space can be provided by the distal movement of the first molars before the eruption of second molars.