title: Study of shrinkage-strain and contraction rates of commercial and experimental compomers.
abstract: OBJECTIVE
  To asses the contraction rate and shrinkage-strain of a new experimental compomer in comparison with four commercial compomers and a flowable composite resin.
  
  
  METHODS
  Shrinkage-strain and contraction rate were calculated by measuring the deflection of a disc in a developed instrument using "bonded disk" method.
  
  
  RESULTS
  Both shrinkage-strain and contraction rate are reported. Total shrinkage-strain for compomer systems varies from 2.59 to 3.34%, whereas the flowable composite resin showed a value of 3.50%. The contraction rate for compomers varies from 81.60 to 109.80 microm/min, whereas the flowable composite resin obtained 141.6 microm/min. Commercial compomers show a lower contraction rate than the control group, whereas the experimental group only shows statistical differences with a commercial compomer (Dyract AP).
  
  
  CONCLUSIONS
  The shrinkage-strain and contraction rate results for the experimental compomer are as good as those obtained for a commercial flowable compomer and a flowable composite resin. The contraction rates of all compomers could be directly related to polymerization rates. The method used to measure shrinkage-strain and contraction rate is adequate because it simulates conditions in situ. It can be inferred that the contraction rate is directly related to shrinkage-strain.
authors.affiliation: Laboratorio de Investigación de Materiales Dentales, División de Estudios de Posgrado e Investigación, Facultad de Odontología, UNAM, Circuito de la Investigación Científica, Delegación Coyoacán, Ciudad Universitaria, 04510, México. amalteaom@hotmail.com
authors.forename: Mariana
authors.initials: M
authors.lastname: Latorre-García
authors.forename: Carlos
authors.initials: C
authors.lastname: Alvarez-Gayosso
authors.forename: Federico
authors.initials: F
authors.lastname: Barceló-Santana
authors.forename: Ricardo
authors.initials: R
authors.lastname: Vera-Graziano
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D020770:Compomers / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008422:Materials Testing / Q000379:methods; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: C105428:Compoglass; D020770:Compomers; D003188:Composite Resins; D003764:Dental Materials; C088486:Dyract; C118368:F2000 cement; C467913:Filtek Flow; D005899:Glass Ionomer Cements; D011108:Polymers; D011109:Polymethacrylic Acids; D017640:Silicates; C476992:compoglass flow; C111840:flowable hybrid composite; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate