Synthesis of Bis-GMA and UDMA Nanofibers for Reinforcing Experimental resin-composites: Influence on Degree of Conversion, Depth of Cure, Flexural Strength, Flexural Modulus and Fracture Toughness

Abstract

Objectives: To study the degree of conversion, depth of cure, flexural strength, flexural modulus and fracture toughness of experimental resin-composites reinforced with Bis-GMA and UDMA nanofibers synthesized by electrospinning technique.Materials and methods: Bis-GMA (Bis-GMA+TEGDMA+PEGDMA) and UDMA (UDMA+PEGDMA) nanofibers were synthesized by wet electrospinning technique and characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). After ball-milling to a nanoscale size (< 100 nm) in a ball-milling machine (Retsch – PM 400, Haan, Germany), these nanofibers were added to a prepared experimental resin-composite. According to the percent and type of added nanofibers, this study was divided into eight groups (n=10/group): one control group, three groups reinforced with 7, 11 and 15 wt% Bis-GMA nanofibers and four groups reinforced with 7, 11, 15 and 20 wt% UDMA nanofibers. For each of these groups, the degree of conversion (DC), depth of cure (DoC), flexural strength (FS), flexural modulus (Ef) and fracture toughness (FT) were studied. DC was studied using the FTIR method (FTIR, Model: EQUINO X55, Bruker, Germany). DoC was measured according to ISO 4049: 2009a. FS testing (and Ef calculation) was carried out according to ISO 4049:2009 by a three-point bending test. FT testing was conducted according to ISO/FDIS 6872:2007. Data were collected and submitted to One-way ANOVA and post-hoc Tukey test with the significance level set at (p ≤ 0.05).Results: Pure forms of Bis-GMA (70-100 nm) and UDMA (50-100 nm) nanofibers were confirmed by SEM and FTIR. One-way ANOVA revealed significant differences for flexural strength (p = 0.001), flexural modulus (p = 0.001) and fracture toughness (p = 0.001) but not for neither degree of conversion (p = 0.078) nor depth of cure (p = 0.879). For both types of nanofibers, compared to the control group, reinforced groups showed greater FS and FT and comparable DC and DoC results. For Ef, except the group reinforced with 7 wt% Bis-GMA,all groups exhibited lower values than that of the control group. Within the range of studied properties, Bis-GMA nanofibers exhibited more favourable results than UDMA nanofibers.Conclusions: Synthesis if Bis-GMA and UDMA nanofibers could be successfully accomplished by electrospinning to be used for resin-composite reinforcement. At a certain ratio (7 wt%), these fibers recorded improvement in FS and FT while keeping Ef, DC and DoC unchanged.