title: Impact of the distance of light curing on the degree of conversion and microhardness of a composite resin.
abstract: OBJECTIVE
  This study evaluated the impact of the distance between the light guide tip of the curing unit and material surface on the degree of conversion and Knoop microhardness of a composite resin.
  
  
  METHODS
  Circular samples were carried out of a methacrylate micro-hybrid resin-based composite and light cured at 0, 2 and 4 mm distance. Monomer conversion rate was measured using a Fourier-transform Raman spectrometer and Knoop hardness number was obtained using a microhardness tester on the top and bottom surfaces. Data were statistically analyzed by analysis of variance and Tukey's test (α=0.05).
  
  
  RESULTS
  Overall, the increase of curing distance reduced the microhardness (p≤0.05), but did not influence the carbon double bond conversion rate (p>0.05) of the composite resin tested; and the top surface showed better properties compared to the bottom (p≤0.05).
  
  
  CONCLUSIONS
  The light curing at distance can reduce mechanical properties and could affect long-term durability of the composite restorations. Thus, the use of a curing device with high irradiance is recommended.
authors: Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas , Piracicaba, SP , Brazil.
authors: Anderson
authors: A
authors: Catelan
authors: Larissa Sgarbosa Napoleão
authors: LS
authors: de Araújo
authors: Bruna Cilene Martins
authors: BC
authors: da Silveira
authors: Yoshio
authors: Y
authors: Kawano
authors: Gláucia Maria Bovi
authors: GM
authors: Ambrosano
authors: Giselle Maria
authors: GM
authors: Marchi
authors: Flávio Henrique Baggio
authors: FH
authors: Aguiar
mesh_terms: D002244:Carbon / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation / Q000379:methods*; D008689:Methacrylates / Q000737:chemistry; D058105:Polymerization; D011897:Random Allocation; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; D008689:Methacrylates; D002244:Carbon
keywords: dental materials; physical properties; polymerization