Comparative evaluation of interrupted and intermittent forces on canine retraction: an in vivo study

Introduction: Various force systems are used in orthodontics to move teeth, such as continuous, intermittent and interrupted. Teeth responds differently to these orthodontic forces. Aims: The aim of the study is to compare the rate of canine retraction with intermittent and interrupted forces. Materials and Methods: A split mouth study was carried among eighteen participants. One side of maxillary arch randomly received interrupted force with elastomeric powerchain while other received intermittent force with elastics with magnitude of 150-170g for canine retraction on each side. For 15 weeks, participants were asked to wear the elastics 8 hours a day whereas the elastomeric powerchains were replaced by operator every 5 weeks. The outcomes were assessed using scanned images of study models collected at the beginning (T0) and 15 weeks later (T3) as well on OPG. Linear and angular measurements were used to measure the distal movement, rotation as well tipping of canines and the results were statistically analysed using Independent t-test. Results: The distal movement of canine on the interrupted force side was 0.98mm/5weeks and on the intermittent force side was 1.06mm/5weeks. The distopalatal rotation on interrupted and intermittent force side was 8.38° and 5.72°. Tipping measured on OPG was 5.72° and 5.27° for interrupted and intermittent force. No statistically significant differences were found. Conclusion: The rate of canine retraction with interrupted force and intermittent force showed no statistically significant differences. Less canine rotation and tipping with intermittent force compared to interrupted force though not statistically significant.