Effects of whisker-to-silica ratio on the reinforcement of dental resin composites with silica-fused whiskers

ZnO–AlBw-reinforced dental resin composites: the effect of pH level on mechanical properties

Silanized ZnO–AlBws were synthesized and manually mixed by spatulation with a dental resin monomer consisting of UDMA, TEGDMA, CQ and DMAEMA. The paste was placed into a steel mold, and the specimens were cured by light at atmospheric pressure to make flexural specimens.

Polymer grafted hydroxyapatite whisker as a filler for dental composite resin with enhanced physical and mechanical properties

The objective of this study was to investigate the effect of surface graft polymerization of hydroxyapatite whisker (HW) on physical and mechanical properties of dental composite resin. Poly bisphenol A glycidyl methacrylate (Poly(Bis-GMA)) was grafted onto silanized hydroxyapatite whisker (SHW) via solution polymerization and the amount of the Poly(Bis-GMA) on the surface was effectively controlled by polymerization time. The obtained poly(Bis-GMA) grafted hydroxyapatite whisker (PGHW) with different polymer contents was filled into a resin matrix respectively, meanwhile the composites with HW and with SHW served as controls. Monomer conversion was characterized by Fourier transform infrared spectroscopy (FTIR) and volume shrinkage of the composite resin was measured with a density tester. Mechanical properties were tested with a universal testing machine. The results indicated that the composite filled with PGHW-1h (graft ratio of poly(Bis-GMA): 8.5 wt.%) showed lower shrinkage and better mechanical properties, improving flexural strength by 6.5% and 11.9% compared with SHW filled composite and HW filled composite, respectively. However, PGHW with higher graft ratios aggregated seriously and formed defects in the composite, leading to deterioration of mechanical properties. It was revealed that the poly(Bis-GMA) on the surface of PGHW acted as a functional transition layer and enhanced interfacial compatibility and interaction between whisker and resin matrix, which facilitated the dispersion of PGHW in the composite and decreased the composite shrinkage. Thus, the graft polymerization of Bis-GMA on the surface of filler might be a promising modification method for the fabrication of dental materials.

Effect of the addition of silanated silica on the mechanical properties of microwave heat-cured acrylic resin

OBJECTIVES

The purpose of this study was to evaluate the flexural strength and Vickers hardness of a microwave energy heat-cured acrylic resin by adding different concentrations of silane surface-treated nanoparticle silica.

METHODS

Acrylic resin specimens with dimensions of 65 × 10 × 2.5 mm were formed and divided into five experimental groups (n = 10) according to the silica concentration added to the acrylic resin mass (weight %) prior to polymerisation : G1, without silica; G2, 0.1% silica; G3, 0.5% silica; G4, 1.0% silica; and G5, 5.0% silica. The specimens were submitted to a three-point flexural strength test and to the Vickers hardness test (HVN). The data obtained were statistically analysed by anova and the Tukey test (α = 0.05).

RESULTS

Regarding flexural strength, G5 differed from the other experimental groups (G1, G2, G3 and G4) presenting the lowest mean, while G4 presented a significantly higher mean, with the exception of group G3. Regarding Vickers hardness, a decrease in values was observed, in which G1 presented the highest hardness compared with the other experimental groups.

CONCLUSION

Incorporating surface-treated silica resulted in direct benefits in the flexural strength of the acrylic resin activated by microwave energy; however, similar results were not achieved for hardness.

Effects of different whiskers on the reinforcement of dental resin composites

OBJECTIVE

Whiskers were recently used to reinforce dental composites to extend their use to large stress-bearing restorations. The aim of this study was to investigate the effects of different types of whiskers on composite properties.

METHODS

Silicon nitride and silicon carbide whiskers were each mixed with silica particles at whisker/silica mass ratios of 0:1, 1:5, 1:2, 1:1, 2:1, 5:1, and 1:0, and thermally treated. The composite was heat-cured at 140 degrees C. Strength and fracture toughness were measured in flexure, while elastic modulus and hardness were measured with nano-indentation.

RESULTS

Both whisker type and whisker/silica ratio had significant effects on composite properties (two-way ANOVA; p<0.001). Silicon nitride whiskers increased the composite strength and toughness more than did silicon carbide. Silicon carbide whiskers increased the modulus and hardness more than silicon nitride did. The silicon nitride whisker composite reached a strength (mean+/-SD; n=6) of 246+/-33 MPa at whisker/silica of 1:1, while the silicon carbide whisker composite reached 210+/-14 MPa at 5:1. Both were significantly higher than 114+/-18 MPa of a prosthetic control and 109+/-23 MPa of an inlay/onlay control (Tukey's multiple comparison test; family confidence coefficient=0.95). Fracture toughness and work-of-fracture were also increased by a factor of two. Higher whisker/silica ratio reduced the composite brittleness to 1/3 that of the inlay/onlay control.

SIGNIFICANCE

Whisker type and whisker/silica ratio are key microstructural parameters that determine the composite properties. Reinforcement with silica-fused whiskers results in novel dental composites that possess substantially higher strength and fracture toughness, and lower brittleness than the non-whisker control composites.

Long-term water-aging of whisker-reinforced polymer-matrix composites

Long-term water exposure may degrade polymer-matrix composites. This study investigated the water-aging of whisker composites. It was hypothesized that whiskers would provide stable and substantial reinforcement, and that whisker type would affect water-aging resistance. Silica-fused Si(3)N(4) and SiC whiskers were incorporated into a resin. The specimens were tested by three-point flexure and nano-indentation vs. water-aging for 1 to 730 days. After 730 days, SiC composite had a strength (mean +/- SD; n = 6) of 185 +/- 33 MPa, similar to 146 +/- 44 MPa for Si(3)N(4) composite (p = 0.064); both were significantly higher than 67 +/- 23 MPa for an inlay/onlay control (p < 0.001). Compared with 1 day, the strength of the SiC composite showed no decrease, while that of the Si(3)N(4) composite decreased. The decrease was due to whisker weakening rather than to resin degradation or interface breakdown. Whisker composites also had higher moduli than the controls. In conclusion, silica-fused whiskers bonded to polymer matrix and resisted long-term water attack, resulting in much stronger composites than the controls after water-aging.

Dental resin composites containing silica-fused whiskers--effects of whisker-to-silica ratio on fracture toughness and indentation properties

Dental resin composites need to be strengthened in order to improve their performance in large stress-bearing applications such as crowns and multiple-unit restorations. Recently, silica-fused ceramic whiskers were used to reinforce dental composites, and the whisker-to-silica ratio was found to be a key microstructural parameter that determined the composite strength. The aim of this study was to further investigate the effects of whisker-to-silica ratio on the fracture toughness, elastic modulus, hardness and brittleness of the composite. Silica particles and silicon carbide whiskers were mixed at whisker:silica mass ratios of 0:1, 1:5. 1:2, 1:1, 2:1, 5:1, and 1:0. Each mixture was thermally fused, silanized and combined with a dental resin at a filler mass percentage of 60%. Fracture toughness was measured with a single-edge notched beam method. Elastic modulus and hardness were measured with a nano-indentation system. Whisker:silica ratio had significant effects on composite properties. The composite toughness (mean+/-SD; n = 9) at whisker:silica = 2:1 was (2.47+/-0.28) MPa m(1/2), significantly higher than (1.02+/-0.23) at whisker:silica = 0:1, (1.13+/-0.19) of a prosthetic composite control, and (0.95+/-0.11) of an inlay/onlay composite control (Tukey's at family confidence coefficient = 0.95). Elastic modulus increased monotonically and hardness plateaued with increasing the whisker:silica ratio. Increasing the whisker:silica ratio also decreased the composite brittleness, which became about 1/3 of that of the inlay:onlay control. Electron microscopy revealed relatively flat fracture surfaces for the controls, but much rougher ones for the whisker composites, with fracture steps and whisker pullout contributing to toughness. The whiskers appeared to be well-bonded with the matrix, probably due to the fused silica producing rough whisker surfaces. Reinforcement with silica-fused whiskers resulted in novel dental composites that possessed fracture toughness two times higher than, and brittleness less than half of current dental composites.