title: Composite pre-heating: effects on marginal adaptation, degree of conversion and mechanical properties.
abstract: OBJECTIVE
  This study evaluated the effect of composite pre-polymerization temperature and energy density on the marginal adaptation (MA), degree of conversion (DC), flexural strength (FS), and polymer cross-linking (PCL) of a resin composite (Filtek Z350, 3M/ESPE).
  
  
  METHODS
  For MA, class V cavities (4 mm x 2 mm x 2 mm) were prepared in 40 bovine incisors. The adhesive system Adper Single Bond 2 (3M/ESPE) was applied. Before being placed in the cavities, the resin composite was either kept at room-temperature (25 degrees C) or previously pre-heated to 68 degrees C in the Calset device (AdDent Inc., Danbury, CT, USA). The composite was then light polymerized for 20 or 40s at 600 mW/cm(2) (12 or 24 J/cm(2), respectively). The percentage of gaps was analyzed by scanning electron microscopy, after sectioning the restorations and preparing epoxy resin replicas. DC (n=3) was obtained by FT-Raman spectroscopy on irradiated and non-irradiated composite surfaces. FS (n=10) was measured by the three-point-bending test. KHN (n=6) was measured after 24 h dry storage and again after immersion in 100% ethanol solution for 24h, to calculate PCL density. Data were analyzed by appropriate statistical analyses.
  
  
  RESULTS
  The pre-heated composite showed better MA than the room-temperature groups. A higher number of gaps were observed in the room-temperature groups, irrespective of the energy density, mainly in the axial wall (p<0.05). Composite pre-heating and energy density did not affect the DC, FS and PCL (p>0.05).
  
  
  CONCLUSIONS
  Pre-heating the composite prior to light polymerization similar in a clinical situation did not alter the mechanical properties and monomer conversion of the composite, but provided enhanced composite adaptation to cavity walls.
authors.affiliation: Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Nívea Regina
authors.initials: NR
authors.lastname: Fróes-Salgado
authors.forename: Luciana Maria
authors.initials: LM
authors.lastname: Silva
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kawano
authors.forename: Carlos
authors.initials: C
authors.lastname: Francci
authors.forename: Alessandra
authors.initials: A
authors.lastname: Reis
authors.forename: Alessandro D
authors.initials: AD
authors.lastname: Loguercio
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D006244:Hardness; D006358:Hot Temperature; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D018583:Pliability; D058105:Polymerization; D011108:Polymers / Q000737:chemistry; D011897:Random Allocation
chemical_list: D003188:Composite Resins; D011108:Polymers; C533204:filtek Z350