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      Effect of Preheating and Precooling on the Flexural Strength and Modulus of Elasticity of Nanohybrid and Silorane-based Composite

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          Abstract

          Statement of the Problem

          Composite resin may be used in different temperatures; it is crucial to determine the effect of temperature on mechanical properties of nanohybrid and silorane-based composite.

          Purpose

          This in vitro study compared the flexural strength and modulus of elasticity of nanohybrid and silorane-based resin composite, at 4˚C, room temperature (25˚C), and 45˚C.

          Materials and Method

          In this experimental study, 60 specimens were prepared in a metal split mold (2×2×25mm). Two different resin composites, Filtek Z250 XT (3M/ ESPE) and Filtek P90 (3M/ESPE), were evaluated. The material were inserted into split molds at room temperature, 4˚C or 45˚C and cured with LED (1200 mW/cm 2) for 20 seconds in four points (n=10). Then, a three-point bending test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min for measuring the flexural strength and flexural modulus of samples. The data were analyzed by the two-way ANOVA and Tukey test ( p< 0.05).

          Results

          The mean highest flexural strength was observed at 45˚C, showing statistically significant difference with flexural strength at 4˚C ( p= 0.0001) and 25˚C ( p= 0.003) regardless of the type of resin composite. The flexural modulus at 45˚C was highest, showing the statistically significant difference with flexural modulus at 4˚C ( p= 0.0001) and 25˚C ( p= 0.002). The flexural modulus was statistically different between nanohybrid and silorane-based resin composite ( p= 0.01) in 25˚C and 45˚C, but there were no statistically significant differences between flexural strength of Filtek Z250 XT and Filtek P90 regardless of the temperatures ( p= 0.062).

          Conclusion

          Preheating the resin composite at 45˚C improves flexural strength and modulus of nanohybrid and silorane-based resin composite. However, flexural strength and modulus of the tested materials were not affected by precooling. The flexural modulus of nanohybrid resin composite was significantly higher than silorane-based resin composite in 25˚C and 45˚C temperatures.

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          Most cited references31

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          The effect of filler loading and morphology on the mechanical properties of contemporary composites.

          Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness. The objectives of this study were to: (1) classify commercial composites according to filler morphology, (2) evaluate the influence of filler morphology on filler loading, and (3) evaluate the effect of filler morphology and loading on the hardness, flexural strength, flexural modulus, and fracture toughness of contemporary composites. Field emission scanning electron microscopy/energy dispersive spectroscopy was used to classify 3 specimens from each of 14 commercial composites into 4 groups according to filler morphology. The specimens (each 5 x 2.5 x 15 mm) were derived from the fractured remnants after the fracture toughness test. Filler weight content was determined by the standard ash method, and the volume content was calculated using the weight percentage and density of the filler and matrix components. Microhardness was measured with a Vickers hardness tester, and flexural strength and modulus were measured with a universal testing machine. A 3-point bending test (ASTM E-399) was used to determine the fracture toughness of each composite. Data were compared with analysis of variance followed by Duncan's multiple range test, both at the P<.05 level of significance. The composites were classified into 4 categories according to filler morphology: prepolymerized, irregular-shaped, both prepolymerized and irregular-shaped, and round particles. Filler loading was influenced by filler morphology. Composites containing prepolymerized filler particles had the lowest filler content (25% to 51% of filler volume), whereas composites containing round particles had the highest filler content (59% to 60% of filler volume). The mechanical properties of the composites were related to their filler content. Composites with the highest filler by volume exhibited the highest flexural strength (120 to 129 MPa), flexural modulus (12 to 15 GPa), and hardness (101 to 117 VHN). Fracture toughness was also affected by filler volume, but maximum toughness was found at a threshold level of approximately 55% filler volume. Within the limitations of this study, the commercial composites tested could be classified by their filler morphology. This property influenced filler loading. Both filler morphology and filler loading influenced flexural strength, flexural modulus, hardness, and fracture toughness.
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            Monomer conversion of pre-heated composite.

            The potential for maximizing conversion of room-temperature, photoactivated resin composite in the oral environment is limited. Pre-heating composite prior to light-curing is hypothesized to increase monomer conversion and reduce the duration of light exposure. Composite temperature was controlled at between 3 degrees C and 60 degrees C prior to exposure with a conventional quartz-tungsten-halogen curing unit: 5, 10, 20, or 40 sec. Monomer conversion was calculated from infrared spectra at 0 mm (top) and 2-mm-deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r(2) = 0.999, 2 mm r(2) = 0.998. Conversion ranged from 31.6% (3 degrees C) to 67.3% (60 degrees C). The duration of light exposure, reduced by 50 to 75% with pre-heated composite, yielded the same or significantly higher conversion (p = 0.001) than with control (22 degrees C, 20 sec). Both hypotheses were accepted: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light exposure than with room-temperature composite.
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              Characterization of nanofilled compared to universal and microfilled composites.

              The purpose of this study was to compare the inorganic fraction and the mechanical properties of three nanofilled composites with four universal hybrid and two microfilled composites. The degrees of conversion of the materials photopolymerized using halogen and LED units were also investigated. Three nanofilled (Supreme, Grandio and Grandio Flow), four universal hybrid (Point-4, Tetric Ceram, Venus, Z 100) and two microfilled (A 110, Durafill VS) composites were used in this study. Their filler weight content was measured by thermogravimetric analysis. The morphology of the filler particles was determined using scanning-electron microscopy (SEM). Mechanical properties were measured: dynamic and static elastic moduli, flexural strength and Vickers microhardness. The degree of conversion in relation with the depth of polymerization of every material tested was evaluated using Raman spectrophotometry. Nanofilled resin composites show higher elastic moduli than those of universal and microfilled composites, except for the Z-100. The microfilled composites exhibit by far the lowest mechanical properties. The flexural strength does not appear as a discriminating factor in this study. The degrees of polymerization obtained with the halogen lamp are higher than those obtained with the LED lamp. Nanofilled resin composites show mechanical properties at least as good as those of universal hybrids and could thus be used for the same clinical indications as well as for anterior restorations due to their high aesthetic properties.
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                Author and article information

                Journal
                J Dent (Shiraz)
                J Dent (Shiraz)
                JDS
                Journal of Dentistry
                Shiraz University of Medical Sciences (Shiraz, Iran )
                2345-6485
                2345-6418
                September 2015
                : 16
                : 3 Suppl
                : 224-229
                Affiliations
                [a ]Biomaterial Research Center, Dept. of Operative Dentistry, School of Dentistry, Shiraz University of Medical Science, Shiraz, Iran.
                [b ]Dept. of Operative Dentistry, School of Dentistry, Shiraz University of Medical Science, Shiraz, Iran.
                [c ]Post Graduate Student, Student Research Committee, Dept. of Operative Dentistry, School of Dentistry, Shiraz University of Medical Science, Shiraz, Iran.
                Author notes
                Correspondence: Motamedi M., Dept. of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. Tel: +98-71-36263193-4 Fax: +98-71-36263192 Email: mehran_motamedi@yahoo.com
                Article
                jds-16-224
                4623839
                08daf9e5-c1f2-4d6b-84e4-975384602e23
                © 2015: Journal of dentistry (Shiraz)

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License, ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : May 2014
                : June 2014
                : August 2014
                Categories
                Original Article

                nanohybrid resin composite,silorane-based resin composite,flexural strength,flexural modulus,preheating,precooling

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