title: Effect of temperature, curing time, and filler composition on surface microhardness of composite resins.
abstract: OBJECTIVE
  The aim of this study was to evaluate the microhardness of two composite resins when subjected to three different temperatures and three different light-curing times.
  
  
  METHODS
  Two composites were used; Filtek Z250 and Grandio. Three different temperatures (23, 37, and 55(o)C) were used, utilizing a composite warmer. The heated samples were immediately injected into cylindrical molds (6 mm × 2 mm) and the top surface of the specimens was polymerized for 10, 20, and 40 sec, using a Quartz-Tungsten-Halogen light-curing unit (QTH LCU). Vickers microhardness measurements were performed from both the top and bottom surface of the specimens, following dry storage for 24 hours in the dark. Statistical analysis were performed using one-way analysis of variance (ANOVA) and Tukey post-hoc test at a level of significance of a = 0.05.
  
  
  RESULTS
  The results indicated that there was an increase in microhardness as the temperature of the composite was increased for either the top or the bottom surface (P < 0.05). Furthermore, there was a general increase in microhardness for both composites as curing time increased (P < 0.05). The type of composites did not influence the surface microhardness (P > 0.05).
  
  
  CONCLUSIONS
  Temperature of composites affects their surface microhardness. Also, light-curing time influence microhardness values of the composites tested.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Dionysopoulos
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Papadopoulos
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Koliniotou-Koumpia
keywords: Composite resins; light-curing time; microhardness; preheating
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