Biodegradation of One-Shade Versus Multi-Shade Composites: a Gravimetrical Analysis

Objectives: Our lab has previously shown that the physical, optical, and mechanical behaviors of one-shade composites are more stable compared to a multi-shade composite. Expanding upon our previous findings, herein we report the effects of cholesterol esterase (CE) on the biodegradation of two one-shade composites (Omnichroma (OM), Tokuyama and Venus Pearl ONE (VP), Kulzer) versus one multi-shade composite (Tetric EvoCeram (TE), Ivoclar/Vivadent) as assessed by a gravimetrical approach.
Methods: Composite discs (n=5/group) were prepared using custom molds (15mm x 2mm) and photopolymerized for 40s (20s/side) using an LED-unit (VALO, Ultradent; irradiance>1.2W/cm²). Samples were dried for 72hrs in dark conditions. The baseline dry mass (b-dry-mass) of specimens was obtained using an analytical balance. Specimens were incubated at 37°C in 2mL PBS added, or not, with CE from pseudomonas sp. (20 units/mL) for 40 days. They were rinsed, blot-dried and measured for wet mass at incubation day-9 (9d-wet-mass) and day-40 (40d-wet mass). Specimens were dried for assessment of respective final dry mass (f-dry-mass). Samples’ water sorption (WS), solubility (SL) and mass variation (MV) across incubation were measured and compared by ANOVA and Tukey post-hoc tests (a=0.05).
Results: Differences in WS (mg/mm³) were significant for incubation time (p<0.05) but among composites. Conversely, difference in SL (mg/mm³) and MV (as % b-dry-mass) were significant for incubation time (p<0.05) and among composites. Overall, the one-shade composites VP and OM exhibited lower mean SL and MV than multi-shade composite TE for both incubation timepoints (p-values <0.01). Significant difference was found in SL values between VP and OM for 40-day incubation time (p=0.01), with OM>VP.
Conclusions: CE incubation significantly affected composites stability. Nonetheless, one-shade composites were confirmed to be more stable upon in vitro CE-biodegradation challenge than a multi-shade composite.