Glass ionomer cements (GICs), while being beneficial source of fluoride ions, suffer from inferior mechanical properties. The mechanical properties of these cements are significantly influenced by the characteristics of the Sr-Aluminosilicate glass used in the fabrication of these cements. This study investigates the changes in glass properties when Zn2+ ions are substituted for Sr2+ ions at different concentrations of 1, 3, and 5 wt% This substitution was under taken based on the similarity of zinc ion valence electrons and the same time its greater ionic field strength with respect to strontium ions. It is demonstrated that the ability of ZnO to provide crosslinks with polyacrylic chains during cement setting stage is lower in comparison to SrO, a fact with detrimental effect on the setting time of cements. Nevertheless, our findings suggest that the effect of ZnO on the mechanical properties of cement depends on the specific composition of the glass. ZnO has the ability compete with Al2O3 in network forming process, which lead to the creation of AlOx species with a higher coordination number. It was determined that parameters such as stronger bonding of Zn-O and the presence of AlOx species with higher coordination numbers played a crucial role in enhancing the compressive strength of cement from 43.8 f 2.1 up to 90.3 f 3.5 MPa. Moreover, the presence of zinc cations enhanced the strength of non-bridging oxygen bonds, reducing the viscous flow during the application of load through deformation. This reduction in viscous flow is considered to play a significant factor in the increase of the microhardness values of the samples from 90.3 f 3.5 to 265 f 1.5 HV.

This article reviews the topic of stannous fluoride as an anti-caries additive in toothpastes. It is based on a literature survey carried out using Science Direct, supplemented by information from PubMed. The keywords used were stannous fluoride, toothpaste, clinical effects, caries, hypersensitivity, gingival health, structure and aqueous solutions. The initial searches covered the period 2015–2024 and identified 57 references. Older references cited in these papers, and also papers already known to the author, were also included. The information thus obtained shows that stannous fluoride has three main effects, namely, reduction in the viability of the oral biofilm, increase in remineralisation of the hydroxyapatite tooth mineral and occlusion of dentinal tubules leading to reduced hypersensitivity. Stannous fluoride was shown to be the most effective of all the fluoride additives used in toothpastes. In much of the dental literature, this is attributed to the effects of Sn2+ ions. However, as has been shown extensively in the wider scientific literature, free Sn2+ ions do not occur in aqueous systems. Rather, the initial products of the dissolution of SnF2 is undissociated, hydrated SnF2 and SnF+ ions. These gradually exchange fluoride to form Sn(OH)2 and Sn(OH)+. Their likely mechanism of action based on their toxicity towards oral micro-organisms and their interaction with hydroxyapatite is discussed.

Glass-ionomer cements (GICs) are used in various applications in clinical restorative dentistry. In this study the effect of CaF2 content of the glasses on microstructure, thermal and mechanical behaviors of the synthesized glass ionomer cements was investigated. The results showed that by adding CaF2 at expense of SrF2 the first exothermic temperature (TE) of the glass was reduced from 735 to 704°C and the compressive strength was increased from 42.0±1.29 MPa to 60.3±1.5 MPa as well. These substitutions led to extending of liquid-liquid phase separation in the glass. The enhancement of mechanical properties demonstrated through the process of annealing glass powder at temperatures below half of the glass transition temperature. This technique contributes to the improvement of mechanical properties by decreasing the residual stress and fostering the separation of amorphous phases. The formation of phase separation appears to be a significant factor in improving the mechanical properties of the oxyfluoride cements.

Objectives: This paper reviews the chemical behaviour of glass polyalkenoate (glass-ionomer) dental cements, both conventional and resin-modified, in contact with natural tissues, with the aim of determining whether these materials can be considered to be bioactive. Data: Relevant papers describing the behaviour of bioactive glasses and ceramics, and glass-ionomer (glass polyalkenoate) cements have been identified using PubMed and Science Direct. This has allowed a comparison to be made between the behaviour of glass-ionomers and the speciality glasses and ceramics that are widely classified as bioactive, a designation considered valid for over fifty years. More recent papers concerning bioactive metals and polymers have also been studied and both in vitro and in vivo studies are included. Sources: Have included general papers on the chemistry and biological behaviour of bioactive glasses and ceramics, as well as papers on glass-ionomers dealing with (i) ion release, (ii) bonding to the surface of teeth, (iii) influence on surrounding pH and (iv) interaction with bone. Conclusion: The literature shows that glass-ionomers (glass polyalkenoates) have three types of behaviour that are similar to those of bioactive glasses as follows: Formation of direct bonds to living tissue (teeth and bones) without fibrous capsule; release of biologically beneficial ions; and change of the local pH. However, in in vitro tests, they do not cause calcium phosphate to precipitate from solutions of simulated body fluid, SBF. Despite this, studies show that, in patients, glass-ionomers interact chemically with hard tissues and this suggests that may indeed be considered bioactive.

The topic of fluoride release and uptake by glass-ionomer (glass polyalkenoate) dental cements is reviewed. The study was based on a literature search carried out using PubMed. The main key words used were glass-ionomer and fluoride, and further refinements were made by adding the keywords anti-microbial, anti-caries and remineralization. Papers were selected from the initial search, which concentrated on fundamental aspects of fluoride release, including kinetics and the influence of the cement composition, and resulting clinical performance against caries. Other relevant papers were cited where they added useful and relevant data. From these published papers, it was possible to explain the detailed mechanism of fluoride release by glass-ionomer cements and also its uptake. Fluoride release has been shown to be a two-step process. In neutral solutions, the steps can be divided into early wash-out and long-term diffusion. In acid conditions, the early wash-out remains, though with greater amounts of fluoride released, and the long-term release becomes one of slow dissolution. The effect of fluoride on the viability of oral micro-organisms has been described, and glass-ionomers have been shown to release sufficient fluoride to reduce the size and viability of adjacent populations of oral bacteria. The effect of low levels of fluoride on the remineralization of tooth tissue has been considered. Levels needed to increase remineralization are much lower than those needed to adversely affect oral bacteria, from which we conclude that glass-ionomers release sufficient fluoride to promote remineralization. Despite this, there remains uncertainty about their overall contribution to sound oral health, given the widespread use of other sources of fluoride, such as toothpastes.

This paper sets out the current position with respect to the replacement of dental amalgam as a restorative material. The environmental impact and the question of possible adverse effects of mercury on human health, including that of dental personnel, are reviewed. The literature has been surveyed using Pub Med with the following key words employed: dental amalgam; environmental; disposal; alternative materials. This identified a large number of papers, and more recent ones were selected for inclusion, particularly where they summarised the earlier literature. The findings of this process are that dental amalgam remains a popular and widely used material which, with appropriate hygiene measures, does not pose a threat to human health. However, environmental concerns with the mining, transport and technical uses of mercury led to the Minamata Convention in 2013, one consequence of which is that mining of mercury will cease from the year 2032. This means that dental amalgam will no longer be available for use. This article considers alternative materials. Results from the literature show that neither of the main possibilities, namely composite resins of glass-ionomer cements, compares with amalgam in terms of strength or durability. The impact of this on the dental profession is discussed briefly.

Zinc phosphate cement is used in dentistry to lute crowns and bridges. So far, its biocompatibility for other applications has not been studied. This paper reports the biocompatibility of zinc phosphate towards MG63 cells, testing both the material (discs; 3 mm diameter × 1 mm thick) and leachate from the cement. Cell viability was determined using an MTT assay, and cytotoxicity from the effects of leachate, studied in triplicate. Microscopy (optical and scanning electron) determined the morphology and proliferation of cells attached to zinc phosphate. ICP-OES measured element release into leachate, and anti-microbial behaviour was determined against Streptococcus pyrogenes cultured on a Brain Heart Infusion agar using cement discs (3 mm diameter × 1 mm thick). Zones of inhibition were measured after 72 h. MG63 cells proliferated on zinc phosphate surfaces and retained their morphology. The cells were healthy and viable as shown by an MTT assay, both on cement and in leachate. High levels of phosphorus but low levels of zinc were released into leachate. The cement showed minimal antimicrobial activity against S. pyogenes, probably due to the long maturation times used. Zinc phosphate cement was found to be biocompatible towards MG63 cells, which indicates that it may be capable of use in bone contact applications.

(1) Background: The compound ytterbium trifluoride is used as a component of several dental materials, and this is reviewed in the current article. (2) Methods: Published articles on this substance were identified initially from PubMed, and then from Science Direct and Google Scholar. The publications identified in this way showed that ytterbium trifluoride has been included in a variety of dental restorative materials, including composite resins, glass polyalkenoate cements, and calcium trisilicate cements. (3) Results: Ytterbium trifluoride is reported to be insoluble in water. Despite this, its presence is associated with fluoride release from dental materials. There is evidence that it reacts with the components of calcium trisilicate cements to form small amounts of a variety of compounds, including ytterbium oxide, Yb2O3, and calcium–ytterbium fluoride, CaYbF5. In nanoparticulate form, it has been shown to reinforce glass polyalkenoates and it also provides high contrast in X-ray images. (4) Conclusions: Ytterbium trifluoride is a useful component of dental materials, though some of the published findings suggest that there are aspects of its chemistry which are poorly understood.

The following paper is a review essay of Daniel Larsen’s Plotting for Peace. It begins with a brief overview of the book, which highlights its seminal insights on the financial quandaries of the Anglo-American international trade relationship during the First World War, and their galvanising effect on British strategy and American peace mediation symbolised by the House-Grey memorandum. It then traces the wide-ranging historiographical significance of Larsen’s placement of British strategy in the context of the balance of payments. Finally, the review offers some general criticisms of the book. In particular, the shortcomings of its American diplomatic and political history.

This paper reviews the use of bioactive glasses as materials for periodontal repair. Periodontal disease causes bone loss, resulting in tooth loosening and eventual tooth loss. However, it can be reversed using bioactive glass, typically the original 45S5 formulation (Bioglass®) at the defect site. This is done either by plcing bioactive glass granules or a bioactive glass putty at the defect. This stimulates bone repair and causes the defect to disappear. Another use of bioactive glass in periodontics is to repair so-called furcation defects, i.e., bone loss due to infection at the intersection of the roots in multi-rooted teeth. This treatment also gives good clinical outcomes. Finally, bioactive glass has been used to improve outcomes with metallic implants. This involves either placing bioactive glass granules into the defect prior to inserting the metal implant, or coating the implant with bioactive glass to improve the likelihood of osseointegration. This needs the glass to be formulated so that it does not crack or debond from the metal. This approach has been very successful, and bioactive glass coatings perform better than those made from hydroxyapatite.

The complex role of water in glass ionomer cement (polyalkenoate) dental restorative materials has been studied, but much of the present understanding concerning water balance within these materials is based on very early studies and short-term experiments. This study evaluated the nature of the water species of six conventional and four resin modified glass ionomer restorative materials over 3 years using thermogravimetric analysis techniques. Materials were prepared, placed in crucibles, and stored in physiologic phosphate buffered saline and evaluated at 24 h, 1 week, and then at 1, 3, 6, 9, 12, 18, 24, 30 and 36 months. All materials demonstrated a significant increase in unbound water percentage content but except for the resin modified materials, the enthalpy required to remove the unbound water species did not significantly change over 36 months. Also, bound water content percentage and removal enthalpy was established at 24 h, as no significant increase was noted in both bound water content and removal enthalpy over the course of this evaluation. This study suggests that unbound water species may increase with time and is loosely held except for the resin modified materials. Protective coatings placement and re-evaluation are prudent to prevent unbound water loss.

Background: The effect of the antimicrobial agents benzalkonium chloride (BC) and cetylpyridinium chloride (CPC) on the restorative glass ionomer tooth cement (GIC) Fuji IX was investigated. Aim of the study: The aim of the study was to determine whether the addition of antimicrobial compounds impairs the physical and mechanical properties of the commercial GIC Fuji IX. Materials and Methods: The concentrations of 1%, 2% and 3% of antimicrobial agentsBC and CPC, by weight of the cement, were added during the mixing phase and different effects were studied. In most samples, there was a slight change in setting time. Samples with 4 mm diameter and 6 mm height were used to measure compressive strength and release. The release of antimicrobial compounds was analysed by UV-visible spectrophotometry at a wavelength of 259 nm for CPC and 214 nm for BC, in deionized water. Results: The obtained results showed that the release takes place through the diffusion mechanism in the first 2-3 hours, and the diffusion coefficients vary depending on the concentration. The values range is from 1.97 x 10-14 -1.78 x 10-12 m2 s-1. Release of antimicrobial compound had ceased after seven days, with total release representing between 2.15 and 4.84% of the initial additive loading. Conclusion: Both compounds have minor effect on the setting time of the GIC. The reduction of compressive strength is not statistically significant. CPC containing cements (1 and 2%), were statistically significantly weaker, than those containing BC (p<0.05).Both antimicrobial compounds have shown constant release from the GIC with values which are directly proportional both to the time and to the concentration.

This study examined the possible buffering effect of acid-base glass-ionomer cements. Commercial capsulated materials were used, namely: Riva Self Cure, Ketac Molar, Equia Forte and Chemfil Rock. Cements were prepared by vibratory mixing then cylinders (4 mm diameter, 6 mm height) prepared from them using metal moulds. They were cured in the moulds at 37 °C for one hour, then placed in 8 ml deionised water at 22 °C and stored for 24 h or 4 weeks. Then they were crushed to powders with a pestle and mortar. Ten samples per powder (0.05 g) were placed in individual 10 ml volumes of deionised water. For two sets of ten (24 h or 4 weeks old), 1.0 ml of 0.01 M HCl was added, equilibrated and the pH measured by calibrated electrode. For another two sets of ten (24 h or 4 weeks old), 1.0 ml of 0.01 M NaOH was added, equilibrated, and the pH measured. The pH of a control set of solutions (no cement powder) was also measured. Data were tested using 1-way ANOVA and Tukey HSD test. The original acid solution pH was 3.2, which rose to 4.4–5.5 depending on brand and age of cement. The original alkali solution pH was 11.3, which fell to 6.7–8.3 depending on the details of the cement. Differences from initial pH had Tukey HSD p values of 0.001 in all cases. It was concluded that acid-base glass-ionomers can act as solid-state buffers, a finding attributed to the carboxylic acid/carboxylate conjugate pairs within them.

The literature on composite resins has been surveyed, with particular emphasis on recent publications, to build up a picture of the current state of the art concerning their use in dentistry.They are shown to be versatile materials, capable of being formulated for a variety of clinical applications.A major current division is into packable (high viscosity) and flowable (low viscosity) types that between then can be used to repair full cavities, including in posterior teeth, as well as provide repairs for abfraction (Class V) lesions and for fractured incisors.Current trends in material composition, including varying filler loadings and use of new photo-initiators, are described.Recent clinical findings show good outcomes with these materials and are described in appropriate detail.

Four brands of glass-ionomer cement (Fuji IX GP, Riva, Ketac Molar and Chemfil Superior) have been stored in aqueous media comprising distilled water, or phosphate buffer solutions at pH 5.42, 6.91 and 8.13 at 37°C for 7 days. Cements differed widely in their response. All took up small amounts of water in distilled water, and had high compressive strengths. Ketac Molar showed no differences in any of the buffer solutions, but gained small amounts in mass, and showed high compressive strength in all storage media. Conversely Chemfil Superior was adversely affected by all three buffers, and Fuji IX and Riva were adversely affected by the buffers at pH 6.91 and 8.31. The reasons for these differences were not clear, but the fact that the buffer closest to neutral (pH 6.91) caused significant damage to three of the cements studied shows that this is not a simple effect of pH.

Objective. The aim of the present study was to determine the chemical species formed inside glass ionomer cements after fluoride uptake and to investigate the depth of penetration of fluoride ions within the cement matrix. Methods. An experimental fluoride-free glass with composition 2SiO(2)-AlO3-CaO was produced. The glass powder was mixed with aqueous poly(acrylic acid) (PAA), and allowed to set. The resulting specimens were stored in 20 ml KF solution with 1000 ppm fluorine for 24 hand then placed into the same amount of water as for 24 h. A fluoride selective electrode was used to give the F concentration of the respective solutions. F-19 MAS-NMR spectra were recorded on powdered cement specimens using a Bruker AVANCE-NEO 600 spectrometer. In addition, SEM observation and EDX chemical analysis were conducted on the cross-section of a carefully fractured specimen. Results. Fluoride was shown to be mainly present in the surface layers of the specimen after placement in the KF solution, and only a small fraction was re-released into water. F-19 NMR spectroscopy showed that AlF complexes were formed within the cement. Significance. The fluoride taken up by a free-fluoride glass ionomer cement mostly occupies surface layers and is retained because it bonds to aluminum within the matrix. This finding explains why the majority of fluoride taken up by conventional glass ionomer cements is retained. (C) 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Objectives: To evaluate the effect of preheating glass-ionomer cement (GIC) restorative materials on stabilization time (ST) of their metal carboxylate bonds and on microhardness. Methods and Materials: Two conventional high-viscosity GICs, Ketac Universal (3M ESPE) and Equia Forte (GC), were evaluated. The thermographic camera was used to measure the temperature inside the glass-ionomer cement capsules before and after heating. The preheating of capsules was performed at 54 degrees C for 30 seconds in a commercial device. Characterization of ST in the GICs was determined by Fourier Transform Infrared (FTIR) spectroscopy. For this, 10 samples of each material were prepared, five in the non-preheated group (control) and five with preheating. FTIR spectra were obtained 10 minutes after mixing (control group) or after heating and then every 10 minutes for 120 minutes. For the microhardness test, 20 cylindrical specimens (3 mm height x 6 mm diameter) were prepared for each material (10 preheated, 10 control). The microhardness was determined at three time intervals: 10 minutes after mixing, after the ST as detected through the FTIR part of the study, and after one week. Knoop microhardness was assessed using a diamond indenter with a 25 g load and 15 seconds dwell time. Results: Ketac Universal showed an increase in temperatures of 15.7 degrees C for powder and 3.6 degrees C for liquid, while Equia Forte showed 16.4 degrees C for powder and 8.5 degrees C for liquid. FTIR spectra indicated that preheating reduced the ST for Equia Forte but increased it for Ketac Universal. Preheating increased the initial microhardness (T-1) of Equia Forte. With maturation over one week, it was observed that preheating significantly improved the microhardness of both materials compared with the control specimens. Conclusion: Preheating influenced the ST and the microhardness of Ketac Universal and Equia Forte. The ST and microhardness of Ketac Universal increased after seven days, whereas Equia Forte showed a reduced ST and increased microhardness from the outset.