title: In vitro study of surface microhardness of a resin composite exposed to a quartz-halogen lamp.
abstract: OBJECTIVE
  To determine the minimum exposure times consistent with optimized surface microhardness numbers (VHN) for the top and bottom surfaces, respectively, of a resin composite (1.5-mm depth) cured using a quartz-halogen activation lamp. Additionally, to determine the conditions appropriate to achieve optimized bottom/top hardness ratios.
  
  
  METHODS
  Disk specimens of a commercial resin composite restorative (Spectrum TPH) were exposed to a quartz-halogen lamp, and VHNs were measured for the top and bottom surfaces at elapsed times of 1 hour and 24 hours.
  
  
  RESULTS
  Data were dependent on exposure time, time elapsed after exposure, and the surface involved. Exposure time featured limiting values in excess of which no significant increase in microhardness took place. All microhardness data increased significantly over an elapsed time interval between 1 hour and 24 hours postexposure. Microhardness ratios (bottom/top) were dependent on exposure time only and were not influenced by time elapsed after exposure.
  
  
  CONCLUSIONS
  Minimum exposure time may be considered as the greater of the times to achieve optimized top hardness and optimized hardness ratio, respectively.
authors.affiliation: Department of Restorative Dentistry, National University of Ireland, Cork, Ireland.
authors.forename: Orla
authors.initials: O
authors.lastname: Coffey
authors.forename: Noel J
authors.initials: NJ
authors.lastname: Ray
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Lynch
authors.forename: Francis M
authors.initials: FM
authors.lastname: Burke
authors.forename: Ailish
authors.initials: A
authors.lastname: Hannigan
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003793:Dental Restoration, Permanent / Q000295:instrumentation; D004867:Equipment Design; D006219:Halogens; D006244:Hardness; D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D008422:Materials Testing; D011791:Quartz; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins; D006219:Halogens; C420128:Spectrum composite resin; C467914:TPH spectrum; D011791:Quartz