title: Mechanical properties of contemporary composite resins and their interrelations.
abstract: OBJECTIVE
  To characterize a spectrum of mechanical properties of four representative types of modern dental resin composites and to investigate possible interrelations.
  
  
  METHODS
  Four composite resins were used, a microhybrid (Filtek Z-250), a nanofill (Filtek Ultimate), a nanohybrid (Majesty Posterior) and an ormocer (Admira). The mechanical properties investigated were Flexural Modulus and Flexural Strength (three point bending), Brinell Hardness, Impact Strength, mode I and mode II fracture toughness employing SENB and Brazilian tests and Work of Fracture. Fractographic analysis was carried out in an SEM to determine the origin of fracture for specimens subjected to SENB, Brazilian and Impact Strength testing. The results were statistically analyzed employing ANOVA and Tukey post hoc test (a=0.05) while Pearson correlation was applied among the mechanical properties.
  
  
  RESULTS
  Significant differences were found between the mechanical properties of materials tested apart from mode I fracture toughness measured by Brazilian test. The latter significantly underestimated the mode I fracture toughness due to analytical limitations and thus its validity is questionable. Fractography revealed that the origin of fracture is located at notches for fracture toughness tests and contact surface with pendulum for Impact Strength testing. Pearson analysis illustrated a strong correlation between modulus of elasticity and hardness (r=0.87) and a weak negative correlation between Work of Fracture and Flexural Modulus (r=-0.46) and Work of Fracture and Hardness (r=-0.44). Weak correlations were also allocated between Flexural Modulus and Flexural Strength (r=0.40), Flexural Strength and Hardness (r=0.39), and Impact Strength and Hardness (r=0.40).
  
  
  CONCLUSIONS
  Since the four types of dental resin composite tested exhibited large differences among their mechanical properties differences in their clinical performance is also anticipated.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, University of Athens, Greece.
authors.forename: Socratis
authors.initials: S
authors.lastname: Thomaidis
authors.forename: Afrodite
authors.initials: A
authors.lastname: Kakaboura
authors.forename: Wolf Dieter
authors.initials: WD
authors.lastname: Mueller
authors.forename: Spiros
authors.initials: S
authors.lastname: Zinelis
mesh_terms: D000465:Algorithms; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D008422:Materials Testing / Q000379:methods; D055595:Mechanical Phenomena; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D053761:Nanocomposites / Q000737:chemistry; D063225:Organically Modified Ceramics / Q000737:chemistry; D018583:Pliability; D016062:Porosity; D012833:Siloxanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C000590992:Filtek Supreme Ultra; C444701:Filtek Z250; D008689:Methacrylates; D063225:Organically Modified Ceramics; D012833:Siloxanes; C479084:admira; C541508:clearfil majesty
keywords: Brazilian test; Composite resin; Flexural Strength; Fractography; Fracture toughness; Hardness; IZOD impact test; Modulus; Resin-composites; SENB