Bisacryl Resins: Optical Properties, Microhardness and Filler Particles Characterization

Objectives: This study evaluated the effect of polishing and artificial aging on surface roughness (Sa), specular gloss (Gs) and color alteration (ΔE₀₀) of bisacryl resins. Additionally, Knoop microhardness (Hv) and characterization of filler particles were investigated.
Methods: An acrylic resin, Alike/GC, was used as a control and six bisacryl resins, Luxatemp/DMG, Protemp/3M, Systemp/Ivoclar, Tempsmart/GC (self- and dual-cure modes), Structur/Voco, Yprov/Yller, were evaluated. Samples (10-mm diameter, 1-mm thickness) were either not polished (NP) or polished (PO) with SiC abrasives (600 to 2,000-grit), and polishing cloth with diamond paste (1 µm). Sa and Gs were measured for NP and PO samples at the baseline, and after 833 and 10,000 toothbrushing cycles (n=10). The ΔE₀₀ [CIEDE2000 (1:1:1)] of NP and PO samples was evaluated after 24 h and 12 days immersion in coffee (n=5). A set of PO samples was used to calculate ΔE₀₀ after UVB aging for 10 and 120 h (n=5), and another set for Hv test (n=10). Base and catalyst pastes of all resins were dissolved with organic solvents in order to characterize filler particles under SEM and EDS analyses. Data were analyzed by two- (ΔE₀₀/UVB) and three-way (Sa, Gs, ΔE₀₀/coffee) ANOVA, followed by Tukey’s test, and additional Dunnett’s analyses (Sa, Gs) (α=5%)
Results: For both color-aging protocols, ΔE₀₀ after 1-year was above the clinically acceptable threshold. Toothbrushing of PO samples resulted in lower values of Sa and higher values of Gs than NP samples, while Sa increased and Gs decreased with toothbrushing. Materials with low Hv and spherical nanometric fillers obtained the highest Gs.
Conclusions: The tested materials might not be indicated for long-term provisional use in esthetic zones, as their ΔE₀₀ was above the clinically acceptable. The use of PO materials with low Hv and small spherical fillers is indicated in order to reduce Sa, loss of Gs and ΔE₀₀ after aging.