title: The effects of light intensity and method of exposure on the hardness of four light-cured dental restorative materials.
abstract: OBJECTIVE
  To determine the microhardness of several light-curing dental restorative materials at the top surface as well as at a depth of 2mm.
  
  
  METHODS
  Comparisons were made using different light sources. Four groups of five specimens each (3mm diameter, 2mm thick) of Z250 (composite), Filtek Flow (flowable composite), Dyract AP (compomer) and Dyract Flow (flowable compomer) were cured using different methods of exposure. The curing lights used were a Spectrum 800 halogen curing light at settings of 800 mW/cm2 and 400 mW/cm2 and an Optilux 501 ramping light. Vickers microhardness tests were performed at the top surface and at the bottom surface.
  
  
  RESULTS
  Significant differences in microhardness between the top and bottom surfaces were demonstrated for all materials and with all light sources (p<0.05). The different exposures also produced significant differences (p<0.05). The light source used had less of an effect on the hardness of the compomers than the composites.
  
  
  CONCLUSIONS
  Effective hardness ratios between the top and bottom surfaces were achieved with all three curing protocols. The effect of total energy application must be taken into account before assumptions can be made as to the effect on hardness using different exposure methods.
authors.affiliation: Department of Applied Oral Sciences, School for Oral Health Sciences, Stellenbosch, Republic of South Africa. tgo@sun.ac.za
authors.forename: Theunis G
authors.initials: TG
authors.lastname: Oberholzer
authors.forename: Sias R
authors.initials: SR
authors.lastname: Grobler
authors.forename: Cornelis H
authors.initials: CH
authors.lastname: Pameijer
authors.forename: Athol P G
authors.initials: AP
authors.lastname: Hudson
mesh_terms: D020770:Compomers / Q000528:radiation effects*; D003188:Composite Resins / Q000528:radiation effects*; D006244:Hardness / Q000528:radiation effects; D008027:Light; D008422:Materials Testing
chemical_list: D020770:Compomers; D003188:Composite Resins; C088486:Dyract; C467913:Filtek Flow; C444701:Filtek Z250; C476993:dyract flow