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      Enhancing the Mechanical Properties of Glass-Ionomer Dental Cements: A Review

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          Abstract

          This paper reviews the strategies that have been reported in the literature to attempt to reinforce glass-ionomer dental cements, both conventional and resin-modified. These cements are widely used in current clinical practice, but their use is limited to regions where loading is not high. Reinforcement might extend these applications, particularly to the posterior dentition. A variety of strategies have been identified, including the use of fibres, nanoparticles, and larger particle additives. One problem revealed by the literature survey is the limited extent to which researchers have used International Standard test methods. This makes comparison of results very difficult. However, it does seem possible to draw conclusions from this substantial body of work and these are (1) that powders with conventional particle sizes do not reinforce glass-ionomer cements, (2) certain fibres and certain nanoparticles give distinct improvements in strength, and (3) in the case of the nanoparticles these improvements are associated with differences in the morphology of the cement matrix, in particular, a reduction in the porosity. Despite these improvements, none of the developments has yet been translated into clinical use.

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          Most cited references91

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          Review on fluoride-releasing restorative materials--fluoride release and uptake characteristics, antibacterial activity and influence on caries formation.

          The purpose of this article was to review the fluoride release and recharge capabilities, and antibacterial properties, of fluoride-releasing dental restoratives, and discuss the current status concerning the prevention or inhibition of caries development and progression. Information from original scientific full papers or reviews listed in PubMed (search term: fluoride release AND (restorative OR glass-ionomer OR compomer OR polyacid-modified composite resin OR composite OR amalgam)), published from 1980 to 2004, was included in the review. Papers dealing with endodontic or orthodontic topics were not taken into consideration. Clinical studies concerning secondary caries development were only included when performed in split-mouth design with an observation period of at least three years. Fluoride-containing dental materials show clear differences in the fluoride release and uptake characteristics. Short- and long-term fluoride releases from restoratives are related to their matrices, setting mechanisms and fluoride content and depend on several environmental conditions. Fluoride-releasing materials may act as a fluoride reservoir and may increase the fluoride level in saliva, plaque and dental hard tissues. However, clinical studies exhibited conflicting data as to whether or not these materials significantly prevent or inhibit secondary caries and affect the growth of caries-associated bacteria compared to non-fluoridated restoratives. Fluoride release and uptake characteristics depend on the matrices, fillers and fluoride content as well as on the setting mechanisms and environmental conditions of the restoratives. Fluoride-releasing materials, predominantly glass-ionomers and compomers, did show cariostatic properties and may affect bacterial metabolism under simulated cariogenic conditions in vitro. However, it is not proven by prospective clinical studies whether the incidence of secondary caries can be significantly reduced by the fluoride release of restorative materials.
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            Nanoindentation mapping of the mechanical properties of human molar tooth enamel.

            The mechanical behavior of dental enamel has been the subject of many investigations. Initial studies assumed that it was a more or less homogeneous material with uniform mechanical properties. Now it is generally recognized that the mechanical response of enamel depends upon location, chemical composition, and prism orientation. This study used nanoindentation to map out the properties of dental enamel over the axial cross-section of a maxillary second molar (M(2)). Local variations in mechanical characteristics were correlated with changes in chemical content and microstructure across the entire depth and span of a sample. Microprobe techniques were used to examine changes in chemical composition and scanning electron microscopy was used to examine the microstructure. The range of hardness (H) and Young's modulus (E) observed over an individual tooth was found to be far greater than previously reported. At the enamel surface H>6GPa and E>115GPa, while at the enamel-dentine junction H<3GPa and E<70GPa. These variations corresponded to the changes in chemistry, microstructure, and prism alignment but showed the strongest correlations with changes in the average chemistry of enamel. For example, the concentrations of the constituents of hydroxyapatite (P(2)O(5) and CaO) were highest at the hard occlusal surface and decreased on moving toward the softer enamel-dentine junction. Na(2)O and MgO showed the opposite trend. The mechanical properties of the enamel were also found to differ from the lingual to the buccal side of the molar. At the occlusal surface the enamel was harder and stiffer on the lingual side than on the buccal side. The interior enamel, however, was softer and more compliant on the lingual than on the buccal side, a variation that also correlated with differences in average chemistry and might be related to differences in function.
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              Titanium dioxide nanoparticles addition to a conventional glass-ionomer restorative: influence on physical and antibacterial properties.

              The aim of this study was to evaluate the addition of titanium dioxide (TiO(2)) nanoparticles to a conventional glass-ionomer (GI) on physical and antibacterial properties. TiO(2) nanoparticles were incorporated into the powder component of Kavitan(®) Plus (SpofaDental, Czech Republic) at 3%, 5% and 7% (w/w). Unblended powder was used as control. Fracture toughness, compressive strength, flexural strength and microtensile bond strength were evaluated using a universal testing machine. Surface microhardness was measured using Vickers microhardness tester. Setting time was determined as specified in the ISO standard. The antibacterial activity was evaluated using direct contact test against Streptococcus mutans. Fluoride release and SEM analysis were carried out. Data were analysed using ANOVA and Tukey's test. GI-containing 3% and 5% (w/w) TiO(2) nanoparticles improved the fracture toughness, flexural strength and compressive strength compared to the unmodified GI. However, a decrease in the mechanical properties was found for GI-containing 7% (w/w) TiO(2) nanoparticles. GI-containing 5% and 7% (w/w) TiO(2) nanoparticles compromised the surface microhardness. Setting time of GI-containing TiO(2) nanoparticles decreased but the values remained within ISO limits. The addition of TiO(2) nanoparticles to the conventional GI did not compromise its bond strength with dentine or fluoride release of the GI. GI-containing TiO(2) nanoparticles possessed a potent antibacterial effect. GI-containing 3% (w/w) TiO(2) nanoparticles is a promising restorative material with improved mechanical and antibacterial properties. This novel experimental GI may be potentially used for higher stress-bearing site restorations such as Class I and II. Copyright © 2011 Elsevier Ltd. All rights reserved.
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                Author and article information

                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                31 May 2020
                June 2020
                : 13
                : 11
                : 2510
                Affiliations
                [1 ]Dental Materials Unit, Bart’s and the London Institute of Dentistry, Queen Mary University of London, Mile End Road, London E1 4NS, UK
                [2 ]Bluefield Centre for Biomaterials, 67-68 Hatton Garden, London EC1N 8JY, UK
                [3 ]Centre for Oral Bioengineering, Institute of Dentistry, Bart’s & The London School of Medicine and Dentistry, Queen Mary University of London, Turner Street, London E1 2AD, UK; s.k.sidhu@ 123456qmul.ac.uk
                [4 ]Department of Biomaterials and Experimental Dentistry, Poznań University of Medical Sciences, ul. Bukowska 70, 60-812 Poznań, Poland; czarnecka@ 123456ump.edu.pl
                Author notes
                Author information
                https://orcid.org/0000-0002-2438-8770
                https://orcid.org/0000-0001-8362-385X
                https://orcid.org/0000-0003-2541-312X
                Article
                materials-13-02510
                10.3390/ma13112510
                7321445
                32486416
                5fea4dee-7ba6-437d-ba7b-9375f00c81aa
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 11 April 2020
                : 26 May 2020
                Categories
                Review

                glass-ionomer cements,resin-modified,fibre,reinforcement,nanoparticles,testing,strength

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