title: The effect of proximal contour on marginal ridge fracture of Class II composite resin restorations.
abstract: OBJECTIVE
  To compare the marginal ridge fracture strength of Class II composite resin restorations placed with a straight or contoured matrix band using composite resins with different modulus of elasticity.
  
  
  METHODS
  In 60 artificial first molars standardized MO-preparations were ground. Two matrix systems were used: (1) A straight matrix (Standard Tofflemire Matrix, KerrHawe) in Tofflemire retainer (Produits Dentaire). (2) A contoured matrix (Standard matrix, Palodent, Dentsply). In both groups, a wooden wedge and separation ring (Composi-Tight Gold, GDS) were placed and the matrix was burnished against the adjacent tooth. Three composite resins together were used (Filtek Supreme: e-modulus 13.3 GPa (3M ESPE), Clearfil AP-X: 16.6 GPa (Kuraray) and Clearfil Majesty Posterior: 22.0 GPa (Kuraray)), resulting in six groups (n=10). Teeth were mounted into a MTS servo hydraulic testing machine (Mini Bionix II, MTS, USA) with stylus placed on the marginal ridge. Samples were loaded at a crosshead speed of 1.0mm/min until fracture occurred. Fracture resistance data were statistically analyzed using ANOVA and Scheffé's post hoc test for multiple comparison of groups (p<0.05).
  
  
  RESULTS
  Contoured proximal surfaces (365.5+/-87.6N) resulted in significant stronger marginal ridges compared to straight surfaces (290.5+/-64.2N) (p<0.001). Clearfil AP-X (378.1+/-94.63N) provided a higher resistance to fracture than Filtek Supreme (301.4+/-67.3N) (p=0.001) and Clearfil Majesty Posterior (304.5+/-70.6N) (p=0.002). No differences were found between Filtek Supreme and Clearfil Majesty Posterior (p=0.890).
  
  
  CONCLUSIONS
  Within the limitations of this in vitro study it was shown that use of a contoured matrix results in a stronger marginal ridge of a Class II composite resin restoration.
authors.affiliation: Department of Preventive and Restorative Dentistry, Radboud University Nijmegen Medical Centre, The Netherlands. b.loomans@dent.umcn.nl
authors.forename: B A C
authors.initials: BA
authors.lastname: Loomans
authors.forename: F J M
authors.initials: FJ
authors.lastname: Roeters
authors.forename: N J M
authors.initials: NJ
authors.lastname: Opdam
authors.forename: R H
authors.initials: RH
authors.lastname: Kuijs
mesh_terms: D000704:Analysis of Variance; D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation / Q000145:classification; D018772:Dental Marginal Adaptation; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000145:classification / Q000379:methods*; D003799:Dental Stress Analysis; D004548:Elasticity; D008434:Matrix Bands; D008953:Models, Anatomic; D010865:Pilot Projects
chemical_list: D003188:Composite Resins