The effect of proximal contour on marginal ridge fracture of Class II composite resin restorations

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.

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).

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).

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.