Effect of filler porosity on the abrasion resistance of nanoporous silica gel polymer composites

Objectives. This laboratory study was designed to investigate the effect of controlled nanoporosity on the wear resistance of polymeric composites rei nforced with silica gel powders and to determine the mechanisms controlling the abrasive wear properties of these unique nanostructured materials. Methods. Silica gels were prepared by hydrolysis and condensation of tetrae thylorthosilicate (TEOS) using four different catalysts to modify the porou s structure of the resulting polysilicate silanation, an organic monomer (T EGDMA) containing Various initiators was introduced into the gel powders to form a paste. The various pastes were then polymerized inside a glass mold . A pin-on-disk apparatus was then used to record the specimen length and n umber of revolutions. Abrasive wear rates were determined by regression ana lysis and statistical differences were determined by analysis of variance a nd multiple comparisons. BET was used to characterize the filler pore struc ture and scanning electron microscopy was used used to visually examine the abraded surfaces. Results. Significant differences (p < 0.05) in the wear rates of the experi mental composites were noted. Within the range of filler porosities examine d, wear resistance was found to be linearly dependent (R-2=0.983) on filler pore volume. The wear rates decreased with increasing filler porosity. HCI -catalyzed gels having low porosity produced composites having relatively l imited abrasion resistance. In contrast, high porosity HF-catalyzed gels pr oduced more wear-resistant composites. The abrasive wear resistance of thes e nanocomposites was not significantly affected by the level of silane coup ling used in these experiments. SEM evaluation suggested that better wear r esistance was associated with fine-scale plastic deformation of the wear su rface and the absence of filler particle pullout. Significance. Porous particles prepared via sol-gel show some promise as fi llers that improve the wear resistance of photopolymerized resins. The wear resistance of the fillers appears to be directly related to nanoporous str ucture of the gel particles. Unlike conventional dental composites, these m aterials rely primarily on nanomechanical coupling for improved wear resist ance. This new principle should benefit subsequent investigations. (C) 1998 Academy of Dental Materials. Published by Elsevier Science Ltd.