title: Effect of light curing modes and light curing time on the microhardness of a hybrid composite resin.
abstract: OBJECTIVE
  The aim of this in vitro study was to evaluate the influence of light curing modes and curing time on the microhardness of a hybrid composite resin.
  
  
  METHODS
  Forty-five Z250 composite resin specimens (3M-ESPE Dental Products, St. Paul, MN, USA) were randomly divided into nine groups (n=5): three polymerization modes (conventional-550 mW/cm2; light-emitting diodes (LED)-360 mW/cm2, and high intensity-1160 mW/cm2) and three light curing times (once, twice, and three times the manufacturer's recommendations). All samples were polymerized with the light tip 8 mm from the specimen. Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample.
  
  
  RESULTS
  Conventional and LED polymerization modes resulted in higher hardness means and were statistically different from the high intensity mode in almost all experimental conditions. Tripling manufacturers' recommended light curing times resulted in higher hardness means; this was statistically different from the other times for all polymerization modes in the bottom surface of specimens. This was also true of the top surface of specimens cured using the high intensity mode but not of conventional and LED modes using any of the chosen curing times. Top surfaces showed higher hardness than bottom surfaces.
  
  
  CONCLUSIONS
  It is important to increase the light curing time and use appropriate light curing devices to polymerize resin composite in deep cavities to maximize the hardness of hybrid composite resins.
authors.affiliation: Department of Restorative Dentistry, Piracicaba School of Dentistry, Campinas State University, Sao Paulo, Brazil. aguiar@fop.unicamp.br
authors.forename: Flávio Henrique Baggio
authors.initials: FH
authors.lastname: Aguiar
authors.forename: Aline
authors.initials: A
authors.lastname: Braceiro
authors.forename: Débora Alves Nunes Leite
authors.initials: DA
authors.lastname: Lima
authors.forename: Gláucia Maria Bovi
authors.initials: GM
authors.lastname: Ambrosano
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Lovadino
mesh_terms: D003188:Composite Resins / Q000528:radiation effects*; D003748:Dental Equipment; D003793:Dental Restoration, Permanent; D006219:Halogens; D006244:Hardness / Q000528:radiation effects; D008027:Light; D044367:Phase Transition; D011897:Random Allocation; D012666:Semiconductors; D013674:Technology, Dental / Q000295:instrumentation; D013997:Time Factors
chemical_list: D003188:Composite Resins; C444701:Filtek Z250; D006219:Halogens