Validation of the Chick Embryotoxicity Screening Test (CHEST). A comparative study

The purpose of the present study was to compare the effects of Gjessing's canine retraction arch with a sectional arch including a reverse closing loop, which are both used for canine retraction in extraction cases. Our study involved both the maxilla and the mandible independently. After upper first premolar extractions and levelling of the teeth with 0.018-inch slot standard Edgewise appliances on 12 subjects, with a mean age of 15 years, the right maxillary canines were retracted by 0.016 x 0.022-inch sectional arches including a reverse closing loop, for a mean period of 7.75 months whereas the left maxillary canines were retracted by 0.016 x 0.022-inch Gjessing retraction arches for a mean period of 6.25 months. Following lower first premolar extractions and levelling of the teeth in eight subjects with a mean age of 13 years 7 months, the right mandibular canines were retracted by 0.016 x 0.022-inch sectional arches with reverse closing loop for a mean period of 7.75 months and the left mandibular canines were retracted by 0.016 x 0.022-inch Gjessing arches for a mean period of 6 months. The present study was carried out on 40 lateral cephalometric films of 20 subjects taken prior to and at the end of canine retraction. The differences between the mean changes of the sectional arch including reverse closing loop and Gjessing retraction arch groups were found to be statistically significant for the amount of upper canine crown retraction, mesial movement of upper first molar crown and duration and rate of upper canine distal movement.(ABSTRACT TRUNCATED AT 250 WORDS)