Polymerization Contraction and Degree of Conversion of Bulk-fill Composite-resins

Objectives: The aim of the present in vitro study was to evaluate the intensity of the forces generated during the polymerization contraction and the degree of conversion (DC) of bulk-fill composite-resins using two light-curing protocols (continuous pulse and pulse activation, with light-activation for 10s and 20s, respectively), with the same energy density (14Jcm²).
Methods: High-viscosity (Filtek Bulk-Fill Posterior Restorative) and low-viscosity (SureFill SDR Flow and Filtek Bulk-Fill Flowable) bulk-fill composite-resins were compared with standard composites (Z350XT and Z350XT Flow). The investigated materials were inserted in a single increment between two rectangular stainless plates (6x2mm) in a UTM (INSTRON 3342) with constant volume (12mm³), in a total of 10 groups (n=6). LED light-source (Dabi Atlante) with 1400mW/cm² was used for both modes of polymerization. The forces generated during the polymerization were recorded in intervals of 20, 65, 120 and 300s by the UTM software and the general means were calculated. For the DC tests, specimens were prepared and divided into 10 similar groups (n=5), using Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflectance (ATR). Data analysis was accomplished using two-way ANOVA with the post-hoc Tukey’s test (p<0.05).
Results: The results of polymerization contraction force and DC are shown in the Table.
Conclusions: Light-curing protocols did not influence the forces generated during the polymerization contraction for all composite-resins studied. Pulse activation increased the DC for the low-viscosity bulk-fill composites. Filtek and SDR bulk-fill flow presented the lowest polymerization contraction force.