الفهرس 
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Abstract
The aim of this study was to evaluate resin composite restorative material after modification with two types of organo-modified MMT nanoclay; an experimentally prepared polymethyl-methacrylate modified MMT nanoclay (PMMA/MMT) and a commercially available dimethyl di-hydrogenated tallow quaternary ammonium modified MMT (Cloisite20A).
Three different concentrations (0.5wt%, 1wt% and 1.5wt%) of each organo-modified nanoclay were used and evaluated regarding their effect on degree of conversion (DC), microhardness, flexural properties and color change of resin composite.
The experimental MMT was synthesized by the sol-gel technique, then organo-modified by polymethyl methacrylate (PMMA) by graft polymerization. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS) and transmission electron microscope (TEM) were employed for phase identification, chemical characterization, particle size analysis and morphological characterization of unmodified MMT, PMMA/MMT and Cloisite20A nanoclays.
A total of 316 specimens were used in this study. Two hundred and forty modified resin composite specimens were prepared and divided into 6 groups according to the type and the concentration of nanoclay used for resin composite modification. Forty unmodified resin composite specimens were used as the control group. Moreover, for evaluation of nanoclay dispersion in resin composite matrix, 36 specimens of resin composite modified with PMMA/MMT and Cloisite20A in 0.5wt%, 1wt% and 1.5wt% concentrations were prepared.
The weighed nanoclay powder was mixed with flowable resin composite using an ultrasonicator device and evaluated for dispersion in resin matrix using XRD analysis and scanning electron microscope (SEM) equipped with elemental mapping analysis.
DC was assessed by FTIR analysis, microhardness was analyzed by Vickers microhardness tester, flexural strength and modulus were tested by three-point flexural test using universal testing machine and color change (ΔE00) was evaluated using reflective spectrophotometer.
Characterization results of XRD, FTIR, EDX, DLS and TEM confirmed the synthesis of MMT nanoclay and the organo-modification of MMT nanoclay by organic PMMA polymer. The results also suggested higher organic modifier loading for PMMA/MMT compared to Cloisite20A as indicated by XRD and DLS analysis.
XRD results, scanning electron microscope (SEM) imaging as well as elemental mapping analysis revealed exfoliation of both types of nanoclays (PMMA/MMT and Cloisite20A) in resin composite at 0.5wt% concentration whereas, aggregation at 1.5wt% concentration of both types was detected.
DC results showed that there was no significant difference on adding either types of nanoclays in resin composite up to 1wt% concentration whereas, adding 1.5wt% showed significant decrease in DC compared to the control group. Moreover, 1.5wt% PMMA/MMT showed significantly lower DC value than 1.5wt% Cloisite20A.
Results of microhardness testing revealed a significant increase in PMMA/MMT groups in all tested concentrations. However, all Cloisite20A modified groups revealed insignificant difference.
Flexural strength and modulus results showed that addition of 0.5wt% of PMMA/MMT significantly increased flexural properties. However, the addition of 1.5wt% of PMMA/MMT resulted in significant decrease. Weibull analysis was performed to analyze flexural strength data and the results showed that the addition of 0.5wt% of PMMA/MMT was associated with the highest characteristic strength and the lowest failure probability up to 140 MPa in contrast to addition of 1.5wt% of PMMA/MMT which showed the lowest characteristic strength with the highest failure probability.
Color change (ΔE00) results showed that the addition of 0.5wt% PMMA/MMT or Cloisite20A nanoclay resulted in clinically acceptable color change with lighter resin composite shades and less color saturation compared to other tested groups.