title: Effect of LED-LCU light irradiance distribution on mechanical properties of resin based materials.
abstract: The objective of this study is to analyze the light power distribution along the tip end of the light guide of three LED-LCUs (Light Curing Units) and to evaluate its effect on the mechanical properties of a polymer based dental composite. Firstly, the light power distribution over the whole area of LED-LCU light guide surface was analyzed by three methods: visual projection observation, spectral measurement and optical spectral analysis (OSA). The light power distribution and the total irradiance were different for the three LEDs used, but the wavelength was within the camphorquinone absorption spectrum. The use of a blank sheet was quite on hand to make a qualitative analysis of a beam, and it is costless. Secondly, specimens of a hybrid composite with approximately 8mm diameter and 2mm thickness were produced and polymerized by 20s exposition time to each LED-LCU. Thirdly, the elastic modulus (E) and hardness (HV) were measured throughout the irradiated area by instrumented micro-indentation test (IIT), allowing to correlate localized power and mechanical properties. Both E and HV showed to be very sensitive to local power and wavelength dependent, but they followed the beam power profile. It was also shown that the mechanical properties could be directly correlated to the curing process. Very steep differences in mechanical properties over very short distances may impair the material performance, since residual stresses can easily be built over it.
authors.affiliation: Faculdade de Odontologia, Universidade Federal Fluminense, Rua São Paulo 28, CEP 24020-150 Niterói, Brazil; Engenharia Metalúrgica e de Materiais (COPPE), Universidade Federal do Rio de Janeiro, CP 68505, CEP: 21941-972 Rio de Janeiro, Brazil.
authors.forename: T R
authors.initials: TR
authors.lastname: Magalhães Filho
authors.affiliation: Faculdade de Odontologia, Universidade Federal Fluminense, Rua São Paulo 28, CEP 24020-150 Niterói, Brazil; Engenharia Metalúrgica e de Materiais (COPPE), Universidade Federal do Rio de Janeiro, CP 68505, CEP: 21941-972 Rio de Janeiro, Brazil.
authors.forename: K M
authors.initials: KM
authors.lastname: Weig
authors.affiliation: Engenharia Metalúrgica e de Materiais (COPPE), Universidade Federal do Rio de Janeiro, CP 68505, CEP: 21941-972 Rio de Janeiro, Brazil.
authors.forename: M F
authors.initials: MF
authors.lastname: Costa
authors.affiliation: Engenharia Elétrica (COPPE), Universidade Federal do Rio de Janeiro, CP 68504, CEP: 21941-972 Rio de Janeiro, Brazil.
authors.forename: M M
authors.initials: MM
authors.lastname: Werneck
authors.affiliation: Instituto de Física, Universidade Federal do Rio de Janeiro, CP 68528, CEP: 21941-972 Rio de Janeiro, Brazil.
authors.forename: R B
authors.initials: RB
authors.lastname: Barthem
authors.affiliation: Engenharia Metalúrgica e de Materiais (COPPE), Universidade Federal do Rio de Janeiro, CP 68505, CEP: 21941-972 Rio de Janeiro, Brazil. Electronic address: celio@metalmat.ufrj.br.
authors.forename: C A
authors.initials: CA
authors.lastname: Costa Neto
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D055119:Elastic Modulus; D006244:Hardness; D008027:Light; D058105:Polymerization
chemical_list: D003188:Composite Resins
keywords: Composite resin; Irradiance, photopolymerization; Light power; Mechanical properties