Mechanical Properties of Dual-cure, Ion-releasing Dental Composite and Glass-hybrid Restorative

Objectives: Following the Minimata convention, there is a growing interest in developing new materials to replace amalgam in stress-bearing Class II restorations. This study compared the flexural strength and fracture toughness of two such new materials, Cention N (Ivoclar-Vivadent), a dual cure ion-releasing composite and EQUIA Forte (GC America), a glass hybrid restorative (EQUIA Forte Fil glass-ionomer and EQUIA Forte Coat) to an in-house produced resin composite control.
Methods: A conventional composite was formulated containing BisGMA/TEGDMA/BisEMA and barium aluminium silicate glass (63%vol) as a control group. Cention N samples were prepared by mixing the powder/liquid at 1:1 ratio, mixture was then incrementally placed into the mould and light cured for 20s using BulePhase Style LED (1200mW/cm²) as per manufactures instructions. EQUIA Forte samples were prepared by mixing each capsule for 10s, material was then placed incrementally into the mould followed by application of EQUIA Forte coat which was light cured for 20s. Flexural strength (FS) and fracture toughness were determined using a universal testing machine (Instron 3365,USA) equipped with a three-point bending apparatus at 0.5 mm/min cross head speed. FS was conducted following the ISO4049 protocol and specimens were loaded on a support span with knife edge geometry. Fracture toughness (K_1C) was evaluated using the sharp single edge notch beam method following the ASTM (E399-83). Fractographic analysis was conducted using the SEM.
Statistical analysis was conducted using One-Way ANOVA and post hoc Tukey tests using SPSS 21.
Results: Cention N showed similar FS values (102MPa, SD=13) to the composite control (91MPa, SD=9) (p>0.05) and increased fracture toughness (1.9MPa.m^(1/2), SD=0.2) compared to both the control (1.3 MPa.m^(1/2), SD=0.1) and EQUIA Forte (0.5 MPa.m^(1/2),, SD=0.5) (p<0.05). EQUIA Forte showed lower FS and K_1C compared to the control (p<0.05)
Conclusions: Cention N exhibited similar FS and enhanced K_1C compared to a highly filled conventional resin composite and significantly higher FS and K_1C compared to a glass hybrid material. This shows promising results considering that K_1C and FS directly correlate to the clinical performance and longevity of restorations.