ABSTRACT
INTRODUCTION: The rough surface of Hawley removable appliances provides an environment for plaque accumulation, leading to enamel demineralization. The aim of this study was to evaluate the effect of silver nanoparticles incorporated into acrylic baseplates of orthodontic retainers on Streptococcus mutans colony-forming units. METHODS: Sixty-six orthodontic patients at the debonding stage were randomly assigned to 2 sex-matched groups with stratified block randomization: group 1 received conventional removable retainers; group 2 received removable retainers containing silver nanoparticles (about 40 nm in size and 500 ppm in concentration). After comprehensive orthodontic treatment, patients who revealed no clinical evidence of dental caries, periodontal pockets, or systemic disease were considered eligible for this study. Swab samples were taken from the maxillary palatal side from the patient in the dental chair at retainer placement (T1, 1 week after debonding the fixed orthodontic appliance) and T2, 7 weeks later. The main outcome was to compare the number of S mutans colony-forming units between the 2 groups 7 weeks after retainer delivery. The results were analyzed by using analysis of covariance. The participants and the assessors were blinded to the allocation groups. RESULTS: Twenty-nine patients in the control group and 32 in the intervention group were analyzed. At T1, the intervention group had higher S mutans colony counts relative to the control group. The analysis of covariance test showed a significant reduction of colonies in the intervention group after 7 weeks. The mean difference of colony counts between the 2 groups was 40.31 (95% confidence interval, 24.83-55.79; P < 0.001). CONCLUSIONS: Adding silver nanoparticles to the acrylic plate of retainers had a strong antimicrobial effect against S mutans under clinical conditions. REGISTRATION: This study was registered as a clinical trial at the Iranian Clinical Trial Center under the code number IRCT201309239086N2. FUNDING: This trial was supported by Hamadan Dental Research Centre, Hamadan University of Medical Sciences, Hamadan, Iran.