Comparison of survival time of Hawley and Vacuum-formed retainers in orthhodontic patients– a randomized clinical trial

Background: Maintaining the results of orthodontic treatment and keeping the teeth in the corrected position is a great challenge in orthodontics. This study aimed to compare the survival time of three types of retainers including Hawley, 1-mm Vacuum-Formed (VF), and 1.5-mm VF within 6-month period. Methods: In this randomized clinical study, 152 patients were allocated into three groups to receive one type of the retainers. They were visited 1, 3, and 6 months after retainer delivery and checked for breakage, loss, local perforation, and discoloration from the patient's and clinician's point of view as indicators of failure. Chi-square and Fisher's exact tests were used as appropriated. Result: The results revealed that breakage was among the main reasons of failure of retainers within 6 months, which was statistically significantly different between Hawley and VF retainers, as well as between 1-mm and 1.5-mm VF retainers in the three intervals (p<0.05). Concerning the loss of retainer and discoloration from the clinician's point of view, there was no significant difference between the retainers in any interval (p>0.05). Assessing the discoloration from the patient's point of view revealed statistically significant differences between Hawley and VF retainers within the first month; however, the difference was not significant at the third and sixth months (p<0.05). The difference between the two thicknesses of VF retainer was not significant in any interval (p>0.05). By the end of the sixth month, some of the VF retainers had perforation; while, perforation was not observed in Hawley retainers. Conclusion: Considering the higher breakage rate of 1-mm VF, 1.5-mm VF seems the retainer if choice