title: Effect of polymerization under pressure on indirect tensile mechanical properties of light-polymerized composites.
abstract: BACKGROUND
  Flaws developed during polymerization of restorative materials cause a decrease in mechanical properties.
  
  
  OBJECTIVE
  The aim of this study was to determine the effect of polymerization under pressure on the indirect tensile mechanical properties (stiffness and diametral tensile strength) of several light-polymerized composites.
  
  
  METHODS
  Five light-polymerized composites were tested: Brilliant, Z100, TPH Spectrum, Prodigy, and Pertac Hybrid. A total of 80 cylindrical disk specimens (6 mm x 2 mm) were prepared for each material in a special mold that enabled polymerization under pressure (PUP). An equal number of specimens were polymerized under surface pressures of 0,.35,.71 and 1.06 MPa (n = 20). Stiffness (N/mm) and diametral tensile strength (DTS) (MPa) were analyzed while loading the specimen to failure with a loading machine. Two-way analysis of variance and Weibull analyses were applied (alpha=5%).
  
  
  RESULTS
  Material type had a statistically significant influence on both DTS and stiffness (P<.0001). Differences up to 33% in DTS and up to 70% in stiffness values were found among the tested materials. Loading (PUP) had a significant influence on stiffness (P<.03) and DTS (P<.0001). PUP caused an increase in DTS values for Brilliant, Z100, and Prodigy of about 20% (P<.001) and increased stiffness only for Brilliant (15%). However, the amount of pressure needed for the improvement was different between materials (interaction between materials and loadings) (P<.0005). Weibull statistics showed that PUP improved the chances for reducing flaws in a material.
  
  
  CONCLUSIONS
  Polymerizing material under pressure can improve its DTS and stiffness. However, the pressure needed for the procedure is material dependent.
authors.affiliation: The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel. t.brosh@post.tau.ac.il
authors.forename: Tamar
authors.initials: T
authors.lastname: Brosh
authors.forename: Nechama
authors.initials: N
authors.lastname: Ferstand
authors.forename: Harold
authors.initials: H
authors.lastname: Cardash
authors.forename: Haim
authors.initials: H
authors.lastname: Baharav
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000528:radiation effects; D003188:Composite Resins / Q000528:radiation effects*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D004548:Elasticity; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000528:radiation effects; D011312:Pressure; D012822:Silicon Dioxide / Q000528:radiation effects; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D013674:Technology, Dental / Q000379:methods*; D013718:Tensile Strength; D015040:Zirconium / Q000528:radiation effects
chemical_list: C472109:Brilliant hybrid composite; D003188:Composite Resins; C079764:Pertac hybrid; D011108:Polymers; C099128:Prodigy; C467914:TPH spectrum; C083568:Z100 composite resin; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium