title: The initiating radical yields and the efficiency of polymerization for various dental photoinitiators excited by different light curing units.
abstract: OBJECTIVE
  To evaluate the efficiency of the photopolymerization of dental resins it is necessary to know to what extent the light emitted by the light curing units is absorbed by the photoinitiators. On the other hand, the efficiency of the absorbed photons to produce species that launch the polymerization process is also of paramount importance. Therefore, the previously determined PAE (photon absorption efficiency) is used in conjunction with the polymerization quantum yields for the photoinitiators, in order to be able to compare the total process on an equivalent basis. This parameter can be used to identify the best performance for the photochemical process with specific photoinitiators.
  
  
  METHODS
  The efficiency of LED (Ultrablue IS) and QTH (Optilux 401) lamps were tested comparing their performances with the photoinitiators camphorquinone (CQ); phenylpropanedione (PPD); monoacylphosphine oxide (Lucirin TPO); and bisacylphosphine oxide (Irgacure 819). The extent of photopolymerization per absorbed photon was determined from the polymerization quantum yields obtained by using the photoinitiators to polymerize methyl methacrylate, and afterwards combined with the previously determined PAEs.
  
  
  RESULTS
  Although CQ presents a rather low polymerization quantum yield, its photopolymerization efficiency is practically the highest when irradiated with the Ultrablue LED. On the other hand, Lucirin is much more efficient than the other photoinitiators when irradiated with a QTH lamp, due to its high quantum yield and the overlap between its absorption spectrum and the output of the visible lamp light.
  
  
  CONCLUSIONS
  Difference in photopolymerization efficiencies arise when combinations of photoinitiators are used, and when LED sources are used in preference to QTH. Mechanistic understanding is essential to optimal initiator formulation.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, Caixa Postal 780, 13560-970 São Carlos SP, Brazil. neumann@iqsc.usp.br
authors.forename: Miguel G
authors.initials: MG
authors.lastname: Neumann
authors.forename: Carla C
authors.initials: CC
authors.lastname: Schmitt
authors.forename: Giovana C
authors.initials: GC
authors.lastname: Ferreira
authors.forename: Ivo C
authors.initials: IC
authors.lastname: Corrêa
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry; D000042:Absorption; D047188:Chalcones / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008027:Light; D008029:Lighting / Q000295:instrumentation*; D008422:Materials Testing; D020366:Methylmethacrylate / Q000737:chemistry; D009636:Norbornanes / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry* / Q000528:radiation effects; D013729:Terpenes / Q000737:chemistry; D062366:para-Aminobenzoates
chemical_list: D047188:Chalcones; D003764:Dental Materials; D009636:Norbornanes; D010087:Oxides; D010720:Phosphines; D011108:Polymers; D012117:Resins, Synthetic; D013729:Terpenes; D062366:para-Aminobenzoates; D020366:Methylmethacrylate; C048339:camphoroquinone; D010129:4-Aminobenzoic Acid; C100349:1-phenyl-1,2-propanedione