Effects of resin formulation and nanofiller surface treatment on in vitro wear of experimental hybrid resin composite.

While adding nonbonded nanofillers and lowering the viscosity of the resin matrix have shown success in reducing deleterious polymerization stresses in dental composites, their effects on wear resistance is unknown. This study evaluated abrasion and attrition wear of experimental composites with varied resin viscosities [inherent to varied ratios of TEGDMA:UDMA:bis-GMA (47:33:16 wt%; 30:33:33 wt%; 12:33:51 wt%)] and nanofiller surface treatment (12.6 wt% silanated or unsilanated silica: OX-50; 0.04 microm). Specimens (n = 6) were light cured, aged in water at 37 degrees C for 7 days, and evaluated in the new OHSU oral wear simulator (100,000 cycles). Nonbonded nanofiller increased abrasion and attrition in the low and medium viscosity composites. Increase in resin viscosity increased abrasion and attrition in composites containing silanated nanofiller, with equivocal effects in composites containing unsilanated nanofiller. Nonbonded nanofiller can lower the overall wear resistance of some composite formulations. Increasing resin viscosity generally lowers the wear resistance, but had minimal effect on composites containing nonbonded nanofiller.

Effect of admixed high-density polyethylene (HDPE) spheres on contraction stress and properties of experimental composites.

Additives that provide stress relief may be incorporated into dental composites to reduce contraction stress (CS). This study attempted to test the hypothesis that conventional fillers could be replaced by high-density polyethylene (HDPE) spheres in hybrid and nanofill composites to reduce CS, but with minimal effect on mechanical properties. Nanofill and hybrid composites were made from a Bis-GMA/TEGDMA resin having either all silica nanofiller or 75 wt.% strontium glass + 5 wt.% silica and replacing some of the nanofiller or the glass with 0%, 5% (hybrid only), 10% or 20 wt.% HDPE. The surface of the HDPE was either left untreated or had a reactive gas surface treatment (RGST). Contraction stress (CS) was monitored for 10 min in a tensilometer (n = 5) after light curing for 60 s at 390 mW/cm(2). Other specimens (n = 5) were light cured 40 s from two sides in a light-curing unit and aged 1 d in water before testing fracture toughness (K(Ic)), flexure strength (FS), and modulus (E). Results were analyzed by ANOVA with Tukey's multiple comparison test at p < 0.05. There was no difference between composites with RGST and untreated HDPE except for FS-10% HDPE hybrid (RGST higher). An increased level of HDPE reduced contraction stress for both types of composites. Flexure strength, modulus (hybrid only), and fracture toughness were also reduced as the concentration of HDPE increased. SEM showed evidence for HDPE debonding and plastic deformation during fracture of the hybrid composites. In conclusion, the addition of HDPE spheres reduces contraction stress in composites, either through stress relief or a reduction in elastic modulus.