DISCUSSION
reactivations decrease, incisors, pain, periodontium, tooth, orthodontic
BENDING, ROOT RESORPTION, DECAY
Studies have previously compared different methods of canine retraction. Most studies concluded that different techniques produce similar rates of movement.However, force decay of elastomeric chains is a disadvantage. Studies showed a significant decrease in the initial force during the first hour of activation. It was then relatively stable for the following four weeks, retaining 30-60% of the force.Studies reported canine retraction for up to 15The 2005 JCO surveyVarying the reactivation interval for canine retraction produced similar amounts of tooth movement. The difference between the highest and lowest amount was 2.35mm, which was statistically insignificant. This may be explained by the variation in the amount of canine retraction and the fact that tooth movement depends on the strain and tissue reaction produced in the periodontium, regardless of the reactivation rate.Although orthodontic appliances were activated every two weeksStudies that reactivated elastomeric chains every four weeks observed canine retraction comparable to the results of the present study. Mezomo et al.Mitra et alHeavy archwires are recommended for sliding mechanics, to prevent wire bending and binding with the brackets.Bypassing the four incisors avoided round-tripping the anterior teeth, and prevented these teeth to take up the extraction space in the cases with crowding. It also allowed the early retraction of the canines.It was expected that frequent activations would increase the canine tipping. However, the four groups showed similar tipping, probably due to the use of the power arms. Studies by Zeigler and Ingervall,Zeigler and IngervallThe studies employed different methods of outcome measurements. Three studies used innovative tools to measure the amount of canine retraction, without radiation exposureOrthodontic treatment produces mild to moderate root shortening. Frequent reactivations decrease the time for the resorbed cementum to recover. The maximum root resorption in all the groups was smaller than 2.7 mm, which is within the average amount reported for orthodontic apical root resorption. The results in this study were higher than those reported by Alkebsi et alIn the present study, the follow-up CBCTs were acquired after six months of retraction. This left a waiting period between the complete canine retraction and the acquisition of the second CBCT for the 27 canines, which may have allowed for the correction of root resorption, distal tipping and rotation, thus underestimating the true amounts of change. However, this does not seem to be the case in the present study, since the changes observed were similar to those reported in the above-mentioned studies.Similar to other studies,The results of the present study should be interpreted with caution. Limitations of the study, including the missing data reported in the eight-week group and the uneven number of quadrants across the groups, may affect the robustness of the analysis. Block randomization with each patient receiving the four interventions would have eliminated this problem. However, this was not possible since not all patients required four premolar extraction. The large variability for canine tipping, rotation, root resorption, and pain should be considered. Some image artifacts in the CBCTs prevented a clear localization of the mesial and distal crown convexities, which may have increased the error of measurements for canine rotation. Although the trial protocol was not pre-registered, the authors adhered to the protocol and have reported all relevant outcomes.Nineteen quadrants in seven patients had severe crowding. Although the anterior teeth were not leveled and aligned, they may have used up part of the extraction space. The inclusion of these cases may have underestimated the amount of canine retraction. There are some drawbacks regarding the generalizability of this study. The pain experience reported is different from most published trials, which may be attributed to ethnicity and culture. There was an unequal representation of males and females in the present study. Since this was the first prospective trial to evaluate the effect of reactivation intervals, further studies are required to elucidate the reliability of these results.This study was conducted to highlight the effect of different reactivation intervals on the canine retraction rate using conventional elastomeric chains. The present data may guide the methodology and sample size calculation of future studies.