Abstract
Purpose
To introduce a new technique, denture base layering, for the addition of titanium dioxide nanoparticles (TiO2NPs) to polymethylmethacrylate (PMMA) and to investigate the effects of the layering technique on Candida albicans (C. albicans) adhesion and on surface roughness, hardness, translucency, and flexural strength.
Materials & Methods
In total, 210 heat-polymerized acrylic resin specimens were prepared as discs (15 × 2 mm) for testing C. albicans adhesion (n = 70) and surface roughness, hardness, and translucency (n = 70); and as acrylic plates (65 × 10 × 2.5 mm) for testing flexural strength (n = 70). Specimens were divided into 4 groups: control (n = 30), one-layer (n = 60), double-layer (n = 60), and dotted-layer (n = 60) according to the packing and layering technique. Each group was divided according to the concentration of TiO2NPs 1% and 2.5% (n = 10). The control group comprised one layer of unmodified resin. The one-layer group comprised one layer of a mixture of PMMA/TiO2NPs packed conventionally. The double-layer group consisted of two different layers packed in two steps, as follows: unmodified resin first, followed by a continuous thin layer of the PMMA/TiO2NPs mixture. Similarly, the dotted-layer group consisted of two di fferent layers packed in two steps, as follows: unmodified resin first, followed by a thin layer of the PMMA/TiO2NPs. However, the second mixture was added in a dotted manner. The direct culture method for C. albicans adhesion before and after ultraviolet light activation, and surface roughness, hardness, translucency, and flexural strength were measured. An analysis of variance and Tukey's post hoc test were used for data analysis (α = 0.05).
Results
The addition of TiO2NPs reduced C. albicans adhesion (P ˂.001). However, no significant difference was found between both concentrations within the same group before and after ultraviolet light activation (P >0.05), except in the 1% dotted-layer (P = .022). Surface roughness and hardness were not affected by the additions of different concentrations of TiO2NPs (P = .905) and (P = .059), respectively. Translucency was significantly reduced in all the groups (P ˂.001) except in the 1% dotted-layer (P = .332). Flexural strength decreased as the TiO2NPs concentration increased, with the greatest reduction in strength observed in the one-layer group (P ˂.001).
Conclusions
The double and dotted layering techniques were effective in reducing C. albicans adhesion, without affecting surface roughness, hardness, or flexural strength. However, translucency was reduced in all the groups, except the 1% dotted-layer group.
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