Non-silicate nanoparticles for improved nanohybrid resin composites

Abstract

Objective: Zirconia and alumina nanoparticles were coated with a silica-rich layer (ALSI and ZRSI) and used to prepare experimental nanohybrid resin composites, which were characterized and compared to a control commercial resin composite (Filtek Z350 XT).

Methods: Silica nanoparticles with sizes compatible to ALSI (Aerosil 150) and ZRSI (Aerosil OX 50) were tested as references. The volume of nanoparticles was equivalent across the composites, which also had consistent content of glass microparticles. CC conversion, viscosity, depth of cure, surface topography, hardness, opacity, radio-opacity, and edge chipping resistance (ReA) were tested after 24 h. Flexural strength (σ_f) and fracture toughness (K_IC) were also tested after 15 K thermal cycles. Data were analyzed using one-way or two-way ANOVA and Tukey's test (α = 0.05).

Results: ALSI and ZRSI yielded resin composites with lower viscosity and more irregular nanoagglomerates compared to nanosilica-based composites. CC conversion and depth of cure were lower for ZRSI composite, which had higher opacity, radio-opacity, and hardness. ReA was higher for ALSI composite. Composites with ALSI and ZRSI showed stable σ_f after aging, whereas the control and Aerosil 150 resin composites showed significant degradation. The commercial and nanosilica-based composites showed up to 42% reduction in K_IC after aging, whereas resin composites with ZRSI and ALSI showed a more stable K_IC.

Significance: ALSI and ZRSI generated nanohybrid resin composites with improved and/or more stable physical properties compared with nanosilica-based and commercial composites. This study suggests that changing the composition of nanofillers is a simple method to enhance the performance of nanohybrid composites.

Keywords: Fillers; Mechanical stress; Methacrylates; Nanotechnology; Silica; Surface properties.

Figure 1.

Viscosity of the experimental resin composites (n=3). Note that Y-axis has a logarithmic scale. The resin composites showed a thixotropic behavior. ALSI and ZRSI nanoparticles yielded hybrid resin composites with lower viscosity compared with their silica nanoparticle references (Aerosil 150 and Aerosil OX 50, respectively).

Figure 2.

SEM images of the resin composite polished surfaces (field width: 100 μm). Nanoagglomerates were observed in all images (arrows), but were more clearly detected and appeared more closely bound for ALSI, ZRSI, and the commercial resin composite (Filtek Z350 XT). Composition of the agglomerates was confirmed in the EDS analysis. The agglomerates in the commercial material were round and uniformly dispersed in the polymer matrix, whereas those in ALSI and ZRSI were more irregular in shape and dispersion.

Figure 3.

Means + standard deviations for flexural strength (σ_f) at 24 h and after aging by 15K thermal cycles (n=10). Whereas ALSI and ZRSI showed stable σ_f after aging, Aerosil 150 and the commercial resin composite (Filtek Z350 XT) showed significant degradation.

Figure 4.

Means + standard deviations for fracture toughness (K_IC) at 24 h and after aging by 15K thermal cycles (n=15). Whereas the commercial resin composite (Filtek Z350 XT) and those formulated with silica nanoparticles (Aerosil 150 and Aerosil OX 50) showed remarkable degradation in K_IC after 15K thermal cycles, the resin composites prepared with ALSI and ZRSI showed less degradation.