Ethanol Softening of Alkasite as a Function of Curing Mechanism

Objectives: To investigate microhardness and ethanol-induced softening in light-cured and self-cured specimens of the “alkasite” material.
Methods: Cylindrical specimens of Cention (Ivoclar Vivadent, Schaan, Liechtenstein) were prepared in Teflon molds (d=6 mm, h=2 or 4 mm) and subjected to one of the following curing conditions: (I) immediate irradiation with 1100 mW/cm² for 20 s, (II) irradiation with 1100 mW/cm² for 20 s after an initial 5-min delay, and (III) self-curing without light exposure for 20 min. The cured specimens were stored in distilled water at 37 °C for 24 h in the dark. Vickers microhardness (load = 100 g, dwell time = 15 s) was measured on the specimen surfaces (0 mm), 2 mm, and 4 mm. Eight specimens per experimental group were used (n=8). Specimens were immersed in absolute ethanol for 7 days and Vickers microhardness was re-measured using the same parameters. The ratio of microhardness values after/before ethanol immersion was evaluated as an indicator of crosslinking density.
Results: For 0-mm and 2-mm depths, microhardness values before ethanol immersion were significantly lower in self-cured specimens (51.8-53.8 VHN) compared to the irradiated specimens (59.6-69.8 VHN), whereas at 4-mm depths statistically similar microhardness was obtained regardless of curing conditions (44.3-52.9 VHN). After ethanol immersion, microhardness values at 0-mm and 2-mm were statistically similar for all curing conditions (44.3-47.2 VHN), while at 4-mm the delayed curing produced significantly higher microhardness compared to immediate curing (42.9 vs. 35.0, respectively). The ratios after/before ethanol immersion were statistically similar within each tested depth regardless of the curing conditions and amounted to 67.8-82.2% for immediate light-curing, 75.0-77.1% for delayed light-curing, and 75.7-92.2% for self-curing.
Conclusions: Light-curing, either immediate or delayed, of the alkasite material Cention produced significantly higher microhardness than self-curing. However, no significant effect of curing conditions on susceptibility to ethanol softening was observed.