Double-layered acrylic resin denture base with nanoparticle additions: An in vitro study

Statement of problem: Whether the addition of different antifungal nanoparticles to denture base materials may affect physical or esthetic properties of the resulting nanocomposite is unclear. Purpose: The purpose of this in vitro study was to determine how a new method of adding antifungal nanofiller affects the properties of the processed nanocomposite denture base material. Material and methods: Heat-polymerized acrylic resin specimens were prepared according to each test specification. Zirconium dioxide nanoparticles (ZrO₂NPs) and silver nanoparticles (AgNPs) were added in 0.5, 1.0, and 1.5% of acrylic resin powder. The specimens were divided into 2 groups according to the acrylic resin packing method: 1 layer packed conventionally in one step and 2 layers packed in 2 steps, first with unmodified acrylic resin and then by a thin layer of modified acrylic resin before the final closure. The control group was made of unaltered acrylic resin in 1 step. Flexural strength (FS), translucency, and surface roughness (R_a) were measured. A microbial assay was performed by using the direct culture and slide count methods. Three-way ANOVA and Tukey post hoc tests were used to identify statistical differences among groups (α=.05). Results: The addition of ZrO₂NPs and AgNPs in the 1- or 2-layer specimens reduced Candida albicans adhesion (P<.001). In the 1- and 2-layer specimens, FS significantly increased with ZrO₂NPs. AgNPs decreased FS only in the 1-layer specimen (P<.001). Surface roughness was not changed for the 1- and 2-layer specimens with ZrO₂NPs or the 1-layer specimen with 0.5% AgNPs (P>.05), while other AgNP groups exhibited increased surface roughness (P<.001). AgNPs significantly lowered translucency in the 1- and 2-layer specimens (P<.001), while ZrO₂NPs decreased translucency only in the 1-layer specimen (P<.001). Conclusions: The addition of ZrO₂NPs in the double-layer technique decreased Candida adhesion and improved FS without affecting surface roughness, while AgNPs decreased Candida adhesion and FS and increased surface roughness. Both nanofillers decreased the translucency except 0.5% ZrO₂NPs, which did not change translucency when applied in 2 layers.