title: Hardness evaluation of a dental composite polymerized with experimental LED-based devices.
abstract: OBJECTIVE
  The main goal of this study was the hardness evaluation of a composite resin cured by five LED (Light Emitting Diodes) based devices and a comparison with a conventional curing unit. The hardness test was used to compare the efficacy of both types of light source.
  
  
  METHODS
  The LED-based devices were made employing an array of LEDs (Nichia Chem. Ind., Japan) emitting light peaked at 470nm. Composite resin (Z100, shade A3) was cured for 20, 40, 60, 120 and 180s with each LED-based device and for 40s with the halogen lamp. The composite samples were prepared with 0.35, 1.25 and 1.8mm of thickness. Five samples of each set of parameters were done. The hardness evaluation was performed at the non-illuminate surface with three indentations for each sample.
  
  
  RESULTS
  All the samples cured by the LED-based devices showed inferior hardness values when compared with the halogen lamp at the typical curing time (40s). The L6 (device composed of six LEDs) was the most efficient one of the LED-based devices. Its obtained irradiance was 79mW/cm(2), whereas the halogen lamp irradiance was of 475mW/cm(2). For the L6 device here presented, longer exposure times or a thinner resin layer are required to achieve reasonable hardness values.
  
  
  CONCLUSIONS
  Besides the difference of irradiance when compared with halogen lamps, LED-based devices show to be a promising alternative curing instrument. Further development in instrumentation may result in devices even more efficient than conventional lamps.
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, Caixa Postal 369, 13560-970, São Carlos, SP, Brazil. cristina@if.sc.usp.br
authors.forename: C
authors.initials: C
authors.lastname: Kurachi
authors.forename: A M
authors.initials: AM
authors.lastname: Tuboy
authors.forename: D V
authors.initials: DV
authors.lastname: Magalhães
authors.forename: V S
authors.initials: VS
authors.lastname: Bagnato
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D004581:Electronics / Q000295:instrumentation; D004867:Equipment Design; D006244:Hardness; D006801:Humans; D008027:Light; D008422:Materials Testing; D012822:Silicon Dioxide; D013499:Surface Properties; D013997:Time Factors; D015040:Zirconium
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium