title: Streptococcus mutans counts in patients wearing removable retainers with silver nanoparticles vs those wearing conventional retainers: A randomized clinical trial.
abstract: BACKGROUND
  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.
  
  
  BACKGROUND
  This study was registered as a clinical trial at the Iranian Clinical Trial Center under the code number IRCT201309239086N2.
  
  
  BACKGROUND
  This trial was supported by Hamadan Dental Research Centre, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.affiliation: Associate professor, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Nasrin
authors.initials: N
authors.lastname: Farhadian
authors.affiliation: Professor, Department of Microbiology, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Rasoul
authors.initials: R
authors.lastname: Usefi Mashoof
authors.affiliation: Postgraduate student, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Sajad
authors.initials: S
authors.lastname: Khanizadeh
authors.affiliation: Chemist, Department of Chemistry, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Esmaeil
authors.initials: E
authors.lastname: Ghaderi
authors.affiliation: Postgraduate student, Department of Biostatics, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Farhadian
authors.affiliation: Associate professor, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran. Electronic address: miresmaeili@umsha.ac.ir.
authors.forename: Amirfarhang
authors.initials: A
authors.lastname: Miresmaeili
mesh_terms: D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000627:therapeutic use*; D058491:Bacterial Load / Q000187:drug effects*; D016022:Case-Control Studies; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry; D003773:Dental Plaque / Q000382:microbiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry / Q000627:therapeutic use*; D020366:Methylmethacrylate / Q000737:chemistry; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers / Q000382:microbiology*; D010159:Palate / Q000382:microbiology; D012834:Silver / Q000737:chemistry / Q000627:therapeutic use*; D016037:Single-Blind Method; D013295:Streptococcus mutans / Q000187:drug effects*; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D020099:Coated Materials, Biocompatible; D003764:Dental Materials; D020366:Methylmethacrylate; D012834:Silver