title: Comparison of residual monomer loss from cold-cure orthodontic acrylic resins processed by different polymerization techniques.
abstract: BACKGROUND
  This investigation aimed to assess and compare the amount of residual monomer (RM) released from removable orthodontic appliances constructed by sprinkle-on and dough techniques.
  
  
  METHODS
  One hundred and twenty acrylic samples were prepared from orthodontic autopolymerized acrylic resins and divided into three groups, according to the processing method: sprinkle-on with polyclave, sprinkle-on without polyclave and dough technique. After polymerization, the specimens of each group were immersed in distilled water for 24 h, 48 h, 72 h and 1 week. High-performances liquid chromatography (HPLC) was utilized to measure residual monomer content.
  
  
  RESULTS
  Maximum observed RM was 1284·91±129·07 ppm measured for sprinkle-on technique without polyclave after 24 h of water immersion. At this time, the level of RM was significantly different among the three applied techniques (P<0·05). In all soaking time groups, sprinkle-on technique with polyclave released the least amount of RM. Within each group, the maximum monomer releasing was observed after the first 24 h and decreases were observed in subsequent time groups. The reduction over the time was not significant in the polyclave groups (P>0·05).
  
  
  CONCLUSIONS
  The sprinkle-on technique with polyclave and longer water immersion reduced residual monomer released from acrylic orthodontic appliances.
authors.affiliation: F. Aghajani Department of Dental Biomaterials, Faculty of Dentistry & Dental Research Center, Tehran University of Medical Sciences, Tehran, Iran. Farzaneh.aghajani@ymail.com.
authors.forename: Tahereh Hosseinzadeh
authors.initials: TH
authors.lastname: Nik
authors.forename: Atefe Saffar
authors.initials: AS
authors.lastname: Shahroudi
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Eraghihzadeh
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Aghajani
mesh_terms: D000180:Acrylic Resins / Q000138:chemical synthesis / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003764:Dental Materials / Q000138:chemical synthesis / Q000737:chemistry*; D006801:Humans; D007101:Immersion; D008768:Methylmethacrylates / Q000737:chemistry; D016382:Orthodontic Appliance Design; D009968:Orthodontic Appliances, Removable; D058105:Polymerization; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D003764:Dental Materials; D008768:Methylmethacrylates; C091936:Orthocryl; D014867:Water
keywords: Acrylic resins; cold-cure; polymerization technique; residual monomer