engleski

Real-time light transmittance monitoring for determining polymerization completeness of conventional and bulk-fill dental composites

Objectives: To monitor the real-time changes in light transmittance during composite curing and to use transmittance data to determine curing times required for a complete polymerization. Methods: Three conventional and three bulk-fill composites were cured with two LED curing units at layer thicknesses of 2 mm and 4 mm. The real-time light transmittance data were collected by a uv-vis spectrometer in the wavelength range of 350-550 nm, plotted against time (t) and fitted to an exponential function f(t), whose first derivative ΔT(t)=df(t)/dt represented the rate of transmittance change. As the changing transmittance reflects structural changes that occur during polymerization, ΔT(t)>0 was considered to indicate an ongoing polymerization, whereas ΔT(t) values approaching zero suggested a complete polymerization. This principle was used to determine times required for a complete polymerization (tcomplete) for each material/thickness/curing unit combination. Results: Light transmittance was significantly influenced by the material type, sample thickness and curing unit, amounting to 2.9–27.0% for the bulk-fill and 0.7–16.7% for the conventional composites. The values of tcomplete amounted to 15.3–23.3 s for the bulk-fill composites at 2 mm, 20.2–33.3 s for the conventional composites at 2 mm, 26.9–42.1 s for the bulk-fill composites at 4 mm, and 40.1–59.8 s for the conventional composites at 4 mm. Additionally, an exponential relationship was discovered between the light transmittance and tcomplete. Conclusions: Some of the tcomplete values considerably exceeded the curing times recommended by the manufacturers. Clinical relevance: Short curing times of 10–20 s may be insufficient for an optimal polymerization, especially under the non-ideal clinical conditions.

Resin Composite ; Bulk-fill Composite ; Photopolymerization ; Light Transmittance ; Curing time

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