Ability of a novel primer to enhance the polymerization of a self-cured resin composite

This study evaluated the degree of conversion (DC), polymerization kinetics, and temperature of a new self-cure bulk-fill resin-based composite (Stela Automix, SDI).

The study was divided into seven groups: (1) Stela Primer, (2) Stela Automix, (3) Stela Automix exposed to light for 20 s after 100 s, (4) Stela Primer with Stela Automix, (5) Stela Primer with Stela Automix and exposed to light for 20 s after 100 s, (6) Scotchbond Universal with Stela Automix, and (7) Scotchbond Universal with Stela Automix and exposed to light for 20 s after 100 s. The real-time reaction rates and DC at the bottom of 2 mm thick specimens at ∼32 °C were measured at 720 s after insertion using a spectrometer with an Attenuated Total Reflectance detector. The temperature of Stela, Stela exposed to light, Stela Primer with Stela, and Stela Primer with Stela exposed to light were measured by an infrared thermal camera in human molar teeth with Class I cavities. The temperature was recorded in real-time every 0.03 s for 720 s. The results were compared with ANOVA and Tukey's multiple comparison test (α = 0.05).

The highest degree of conversion (DC) at the 2 mm depth was achieved when Stela Primer was combined with Stela (72.4 ± 3.5 % at 720 s). Stela could self-cure independently, but not as rapidly or effectively as when used with its Primer. The greatest temperature increase was for the light-cured Stela, followed by Stela Primer with Stela RBC exposed to light for 20 s. The Scotchbond Universal bonding system did not significantly increase the DC compared to Stela alone, except when exposed to light for 20 s, which slightly increased the final DC. Exposing Stela to light for 20 s did not improve the final DC of Stela as much as using the Stela Primer, but it did increase the temperature and prolonged the time taken to return to 37 °C.

The Stela primer accelerates the degree of conversion of Stela. The reaction occurred rapidly and achieved a higher DC at the bottom of the specimens where the Stela was in contact with the Stela primer. Exposing Stela to light for 20 s is not recommended. Instead, Stela should be used with Stela Primer.