title: Flexural strength of composites: influences of polyethylene fiber reinforcement and type of composite.
abstract: OBJECTIVE
  The microfill veneering of hybrid composite restorations has been indicated to improve esthetics. Also, polyethylene fiber reinforcement has been proposed for use in composite restorations in high-stress clinical situations. However, minimal information in the literature addresses the influence of such combinations on the resistance to fracture. The purpose of this study was to investigate the flexural strength of two composites, a microfill and a hybrid, the effect of their combination, and the influence of polyethylene fiber reinforcement.
  
  
  METHODS
  Twenty-eight specimens were prepared using a standard metallic mold (20x2x2 mm) and divided into groups of seven each: Filtek Z-250 (3M ESPE, St. Paul, Minn., USA) (group I), Filtek A-110 (3M ESPE) (group II), Filtek Z-250 combined with Filtek A-110 (group III), and Filtek Z-250 combined with polyethylene fiber (Ribbond, Seattle, Wash., USA) (group IV). The specimens were stress-loaded to fracture in a three-point bending device according to International Standardization Organization (ISO) 4049.
  
  
  RESULTS
  Data were analyzed using analysis of variance and Tukey's test at a 0.05 level of significance. No statistically significant differences were observed between groups I and IV. Group II, however, exhibited statistically lower resistance to fracture than the other groups. Group III presented intermediate results, showing statistically higher fracture resistance than group II but lower than group I.
  
  
  CONCLUSIONS
  With the methodology employed, microfill composite presented the lowest flexural strength, but its association with hybrid composite increased the resistance to fracture. The combination of polyethylene fiber and hybrid composite did not present higher flexural strength than hybrid composite alone.
authors.affiliation: Department of Restorative Dentistry, College of Dentistry, Federal University of Pelotas, 457 Gonçalves Chaves Street, Pelotas, RS, Brazil.
authors.forename: C L
authors.initials: CL
authors.lastname: Pereira
authors.forename: F F
authors.initials: FF
authors.lastname: Demarco
authors.forename: M S
authors.initials: MS
authors.lastname: Cenci
authors.forename: P W R
authors.initials: PW
authors.lastname: Osinaga
authors.forename: E M
authors.initials: EM
authors.lastname: Piovesan
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D020959:Polyethylene / Q000737:chemistry*; D011095:Polyethylenes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C452225:Filtek A110 composite resin; C444701:Filtek Z250; D011095:Polyethylenes; C084063:RIBBOND; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose; D020959:Polyethylene