Effect of Synthesized Bis-GMA and UDMA Nanofibers on Cuspal Flexure, Microhardness, Wear, Surface Roughness and Color Stability of Experimental Resin-Composites

Objective: To study the cuspal flexure (CF), Vickers microhardness (HV), three-body wear (W), surface roughness (SR) and color stability (CS) 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 being ball-milled 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. This study was divided, according to the percent and type of added nanofibers, into eight groups (n=10/group except for color stability n=11): 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, CF, HV, W, SR and CS were studied. CF was studied by the digital image correlation method which analyzes the displacement of an object using a USB digital microscope with a built-in camera (COMET xS, Steinbichler Optotechnik GmbH, Neubeuern, Germany). HV was measured according to the ASTM E-384:1999 using a Digital Display Vickers Microhardness Tester (ZHVµ Micro Vickers Hardness Tester, Indentec Hardness Testing, Zwick Roell Co., Ltd. Atlanta, USA). W testing was carried out according to ISO/TS 14569:2001 using a custom-made cusp-on-disc sliding machine. Measurement of SR was performed according to ISO 25178-2:2012 and CS testing was carried out according to the regulations of ISO 4049; 2009 using a portable reflective spectrophotometer (X-Rite, model RM200QC, Neu-Isenburg, Germany). Data were collected and submitted to One-way ANOVA and post-hoc Tukey and Dunnett’s T3 tests 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 between studied groups for CF, HV, W and SR (p = 0.001) but not for CS (p = 0.068). For both types of nanofibers, compared to the control group, reinforced groups showed lower CF, HV and SR and greater W results. For CS, there was no consistent trend of results of experimental groups that were comparable to that of control group. Within the range of added nanofibers (7-20 wt%), Bis-GMA nanofibers exhibited more favourable HV and W results than UDMA nanofibers, while the reverse was the case for CF and SR. Both nanofibers exhibited comparable CS results.
Clinical Significance: A resin-composite reinforced with such nanofibers showing improved CF and unfavorably lower HV and more W should be used as a base layer and covered with a layer of another resin-composite with enhanced surface properties.