How does thermocycling affect the surface properties of ion-releasing bulk‑fill resin composites?

This in vitro study evaluated the effect of thermocycling on the surface properties of ion-releasing and non-ion-releasing bulk-fill resin composites. Disc-shaped samples were fabricated from three commonly used ion-releasing resin composites and one non-ion-releasing control (Filtek Bulk). The baseline readings were recorded for one-third of randomly selected samples, whereas the rest underwent thermocycling (5000 and 10,000 cycles between 5 and 55°C, 30 s dwell time, 10 s transfer). Surface morphology, topography, nanoindentation, contact angle, pH, and color changes were evaluated. Data were analyzed using one-way analysis of variance, followed by post hoc tests (p < 0.05). Thermocycling led to increased roughness, reduced hardness, and elastic modulus in ion-releasing groups. Filtek Bulk exhibited minimal changes, with roughness increasing slightly (0.64 ± 0.08 to 0.79 ± 0.08 µm) and nanohardness decreasing (0.67 to 0.58 GPa). Beautifil Bulk Restorative and Fill-Up! showed moderate degradation, whereas Cention Forte experienced the sharpest decline in tested properties. Filtek Bulk maintained the highest color stability, whereas Cention Forte showed pronounced discoloration. Thermocycling was pronounced in ion-releasing bulk-fill restorative resin composites compared to non-ion-releasing ones. These findings suggest that, alongside therapeutic benefits, surface integrity, mechanical stability, and long-term esthetics must be considered when selecting ion-releasing bulk-fill restorative composites.