title: Effects of glass fiber layering on the flexural strength of microfill and hybrid composites.
abstract: BACKGROUND
  In stress-bearing cavities, low fracture resistance adversely affects the longevity of the dental resin composite restorations.
  
  
  OBJECTIVE
  The aim of this in vitro study was to investigate the effect of glass fiber layering on the flexural strength of microfill and hybrid composites.
  
  
  METHODS
  Flexural test specimens (N = 75) were prepared according to International Organization for Standardization (ISO) 4049 specifications (25 x 2 x 2 mm) by using a standard metallic mold. Materials used and groups were as follows (N = 15): group 1: hybrid composite (Clearfil APX, Kuraray Co.Ltd, Osaka, Japan); group 2: microfill composite (Clearfil ST, Kuraray Co.Ltd.); group 3: hybrid + microfill composite; group 4: woven glass fiber (EverstickNet, StickTech Ltd, Turku, Finland) + hybrid composite; group 5: woven glass fiber + microfill composite. The specimens were stored in distilled water at 37 degrees C for 7 days. Afterward, they were loaded to fracture (1 mm/min) by using a universal testing machine (AG-50 kNG Shimadzu Co., Kyoto, Japan). Flexural strengths were expressed as maximum flexural load per cross-sectional area of the specimen. The results were statistically analyzed with Kruskall-Wallis and Mann-Whitney U tests (p < 0.01).
  
  
  RESULTS
  Significant increases in the flexural strength were found for both hybrid and microfill composites when fiber layering was used (group 1: 78 +/- 7 MPa; group 4: 93 +/- 4 MPa) (group 2: 42 +/- 5 MPa; group 5: 64 +/- 4 MPa) (p < 0.01). Flexural strength of fiber-reinforced hybrid composite was significantly higher than the other groups evaluated (p < 0.01). There were no significant differences in flexural strength between microfill/hybrid combination and fiber-reinforced microfill composite (p > 0.01).
  
  
  CONCLUSIONS
  Glass fiber layering of microfill and hybrid composites presented higher flexural strength, and veneering of hybrid composite with microfill composite increased the resistance of the restoration.
authors.affiliation: Professor, Department of Pediatric Dentistry, Ege University, School of Dentistry, Izmir, Turkey. nesrin.eronat@ege.edu.tr
authors.forename: Nesrin
authors.initials: N
authors.lastname: Eronat
authors.forename: Umit
authors.initials: U
authors.lastname: Candan
authors.forename: Murat
authors.initials: M
authors.lastname: Türkün
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D005898:Glass / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D055668:Photochemical Processes; D018583:Pliability; D011108:Polymers / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: C112828:Clearfil AP-X; C483502:Clearfil ST; D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D011108:Polymers; C496140:everStick; C009753:fiberglass; D014867:Water