title: Knoop microhardness and FT-Raman spectroscopic evaluation of a resin-based dental material light-cured by an argon ion laser and halogen lamp: an in vitro study.
abstract: OBJECTIVE
  The purpose of this study was to evaluate in vitro the Knoop microhardness (Knoop hardness number [KHN]) and the degree of conversion using FT-Raman spectroscopy of a light-cured microhybrid resin composite (Z350-3M-ESPE) Vita shade A3 photopolymerized with a halogen lamp or an argon ion laser.
  
  
  BACKGROUND
  Optimal polymerization of resin-based dental materials is important for longevity of restorations in dentistry.
  
  
  METHODS
  Thirty specimens were prepared and inserted into a disc-shaped polytetrafluoroethylene mold that was 2.0 mm thick and 3 mm in diameter. The specimens were divided into three groups (n = 10 each). Group 1 (G1) was light-cured for 20 sec with an Optilux 501 halogen light with an intensity of 1000 mW/cm(2). Group 2 (G2) was photopolymerized with an argon laser with a power of 150 mW for 10 sec, and group 3 (G3) was photopolymerized with an argon laser at 200 mW of power for 10 sec. All specimens were stored in distilled water for 24 h at 37 degrees C and kept in lightproof containers. For the KHN test five indentations were made and a depth of 100 microm was maintained in each specimen. One hundred and fifty readings were obtained using a 25-g load for 45 sec. The degree of conversion values were measured by Raman spectroscopy. KHN and degree of conversion values were obtained on opposite sides of the irradiated surface. KHN and degree of conversion data were analyzed by one-way ANOVA and Tukey tests with statistical significance set at p < 0.05.
  
  
  RESULTS
  The results of KHN testing were G1 = 37.428 +/- 4.765; G2 = 23.588 +/- 6.269; and G3 = 21.652 +/- 4.393. The calculated degrees of conversion (DC%) were G1 = 48.57 +/- 2.11; G2 = 43.71 +/- 3 .93; and G3 = 44.19 +/- 2.71.
  
  
  CONCLUSIONS
  Polymerization with the halogen lamp (G1) attained higher microhardness values than polymerization with the argon laser at power levels of 150 and 200 mW; there was no difference in hardness between the two argon laser groups. The results showed no statistically significant different degrees of conversion for the polymerization of composite samples with the two light sources tested.
authors.affiliation: Department of Restorative Dentistry, Guarulhos University, Guarulhos, SP, Brazil. acassoni@prof.ung.br
authors.forename: Alessandra
authors.initials: A
authors.lastname: Cassoni
authors.forename: Juliana de Oliveira
authors.initials: Jde O
authors.lastname: Ferla
authors.forename: Jamil Awad
authors.initials: JA
authors.lastname: Shibli
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kawano
mesh_terms: D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental; D006244:Hardness; D066298:In Vitro Techniques; D054020:Lasers, Gas; D011108:Polymers; D012117:Resins, Synthetic / Q000737:chemistry / Q000528:radiation effects*; D013059:Spectrum Analysis, Raman
chemical_list: D003188:Composite Resins; D011108:Polymers; D012117:Resins, Synthetic