Polymerisation kinetics in a fibre reinforced resin-based composite

What is it about?

Objective: The study aimed to evaluate the potential of a commercial fiber reinforced resin composite (FRC) to be cured adequately also in increments larger than 2-mm.Material and methods: One FRC (EverX Posterior, GC) was investigated by assessing in real-time the degree of conversion (DC) and polymerisation kinetic at increasing depths (100-μm, 2-mm 4-mm and 6-mm). In addition, a battery of mechanical properties - flexural strength, flexural modulus, Vickers hardness, indentation modulus, creep – and the characteristics of the used curing light were determined. Results: One-way ANOVA revealed no significant difference in DC measured 300 s post-irradiation in a depth of 100-μm and 2-mm (p = 0.281). Similarly, no significant difference was identified between DC measured at 2-mm and 4-mm (p = 0.724), while the DC measured at 6-mm depth was significantly lowest (p<0.001). The polymerisation kinetic was well described (R²>0.95) by a double exponential sum function, distinguishing between the gel and the glass phase of the polymerisation process. It allowed identifying a slower start of polymerization in depth, associated with a lower maximal rate of C-C double bond conversion. The mechanical properties amounted (128.30±8.38) MPa (flexural strength), (8.38±0.87) GPa (flexural modulus), (92.00±15.86) N/mm² (Vickers hardness), (17.82±1.82) GPa (indentation modulus) and (3.35±0.84) % for creep.Conclusions: While DC recorded in 2-mm and 4-mm depths were statistically similar, there is evidence that the quality of curing in a depth of 4-mm is lower compared to the top of the specimen. The mechanical properties were within the range of high viscosity bulk-fill resin-composites.Keywords: fiber reinforced resin-based composite, degree of cure, polymerisation kinetics, bulk-fill, mechanical properties.

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