The Effect of Aging and Silanization on the Mechanical Properties of Fumed Silica-based Dental Composite

Abstract Statement of Problem: Mechanical strength and durability of dental composites are the main topics studied in this field of science today. This study examined fumed silica-based composite as a strong and durable restorative material through flexural and cycling test methods.    Objectives: The purpose of this study was to evaluate the effect of silanization, ageing, cycling and hybridizing on mechanical properties of fumed silica-based resin composite.Materials and Methods:  Composites were made of light-cured copolymer based on Bisphenol A glycolmethacrylate (Bis-GMA) and Triethylene glycoldimethacrylate (TEGDMA) at proportion of 50:50 which reinforced by fumed silica filler. For each composite sample, 5 specimen bars were made using Teflon mould (2 x 2 x 25 mm3). The samples with 12 wt% fumed silica (FS) were considered as a base line group. The samples were exposed to cyclic cold water (FS-CCW) and hot water (FS-CHW). The effect of silanization and adding more filler was studied together with samples containing 12 wt% (FS-S (12), 16 wt% (FS-S (16) and 20 wt% (FS-S (20) fumed silica filler. The filler was silanized with (γ-MPS). The degree of conversion was assessed with Fourier Transform Infra-Red spectroscopy. Flexural properties were evaluated with the Three-Point Bending test. Flexural data were analyzed with Excel software. Hardness was measured with an Atomic Force Microscope (AFM).Results: The degree of conversion of the resin reached 74% within 24 hrs. Salinization allowed more filler to be wetted by resin. Addition of silanized particles from sample FS-S (12) to sample FS-S (20) improved the mechanical strength. Hybridizing fumed silica with nano-silica (FS-N) had no significant effect on the strength, but nano-hardness improved greatly. Ageing and cycling had adverse effects on the strength of the sample FS. The flexural strength of FS-CHW was 72% less than FS sample.Conclusions: Sample FS-N with low diluent and filler percentage complied with the requirements of flexural strength was established by ISO 4049/2009 and may be cost benefit to be used as a dental composite for clinical application.Keywords: Flexural Strength, Flexural Modulus, Ageing, Cycling, Silanization, Hardness