Ion processes in glass ionomer cements

Comparison of remineralization ability of tricalcium silicate and of glass ionomer cement on residual dentin: an in vitro study

OBJECTIVE

This study aimed to compare the remineralization effects of a calcium silicate-based cement (Biodentine) and of a glass ionomer cement (GIC: Fuji IX) on artificially demineralized dentin.

METHODS

Four standard cavities were prepared in dentin discs prepared from 34 extracted sound human third molars. In each disc, one cavity was covered with an acid-resistant varnish before demineralization (Group 1). The specimens were soaked in a chemical demineralization solution for 96 h to induce artificial carious lesions. Thereafter, one cavity each was filled with Biodentine (Group 2) and GIC (Group 3), respectively, and one carious lesion was left unrestored as a negative control (Group 4). Next, specimens were immersed in simulated body fluid (SBF) for 21 days. After cross-sectioning the specimens, the Ca/P ratio was calculated in each specimen by using scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). Finally, data were analyzed using repeated-measures ANOVA with post-hoc Bonferroni correction.

RESULTS

Both cement types induced dentin remineralization as compared to Group 4. The Ca/P ratio was significantly higher in Group 2 than in Group 3 (p < 0.05).

CONCLUSION

The dentin lesion remineralization capability of Biodentine is higher than that of GIC, suggesting the usefulness of the former as a bioactive dentin replacement material.

CLINICAL RELEVANCE

Biodentine has a higher remineralization ability than that of GIC for carious dentin, and its interfacial properties make it a promising bioactive dentin restorative material.

Changes in enamel hardness, wear resistance, surface texture, and surface crystal structure with glass ionomer cement containing BioUnion fillers

This study investigated the potential of BioUnion filler containing glass ionomer cement (GIC) to enhance the properties of enamel surrounding restorations, with a specific focus on the effect on hardness. The hardness of the bovine enamel immersed in the cement was measured using Vickers hardness numbers. Following sliding and impact wear simulations, the enamel facets were examined using confocal-laser-scanning microscopy and scanning-electron microscopy. Surface properties were further analyzed using energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD). A significant increase in Vickers hardness numbers was observed in the BioUnion filler GIC after 2 days. Furthermore, the mean depth of enamel facets treated with BioUnion filler GIC was significantly less than that of untreated facets. Characteristic XRD peaks indicating the presence of hydroxyapatite were also observed. Our findings imply that GIC with BioUnion fillers enhances the mechanical properties of the tooth surface adjacent to the cement.

Fluoride Release and Rechargeability of Poly(lactic acid) Composites with Glass Ionomer Cement

This study investigates the fluoride release, rechargeability and degradation behaviors of newly developed anticariogenic poly(lactic acid) (PLA) composites. The PLA composite with various concentrations (0%, 5%, 10%, 15% and 20% by weight) of glass ionomer cement (GIC) and sodium fluoride (NaF) were prepared using solvent casting method. The fluoride release, fluoride rechargeability and degradation behavior were evaluated. All experimental groups demonstrated fluoride-releasing ability. The highest level of fluoride ions released was found in PLA composite with sodium fluoride (PLA/NaF). Following the 28-day period, both groups showed a gradual reduction in fluoride ion released, ranging between 0.03 ± 0.01 and 0.53 ± 0.06 ppm, although remaining within the effective range for tooth remineralization. However, the rechargeability was only observed in PLA composite with GIC (PLA/GIC). Following an eight-week in vitro degradation test, all PLA/NaF groups displayed a significantly higher percentage of weight change and water absorption compared to the PLA/GIC and the control group. In SEM analysis, the formation of surface porosities was clearly noticed in all PLA/NaF. All specimens retained their structural integrity throughout the study. In conclusion, the newly developed PLA/GIC displays promising possibilities as an anticariogenic material. Furthermore, the rechargeability of these ions are repeatable, ensuring their long-term utility.

Long-Term Effect of Modified Glass Ionomer Cement with Mimicked Biological Property of Recombinant Translationally Controlled Protein

This study modified glass ionomer cement (GIC) by adding mimicked biological molecules to reduce cell death. GIC was modified to BIOGIC by adding chitosan and bovine serum albumin for enhancing protein release. The BIOGIC was supplemented with tricalcium phosphate (TCP) and recombinant translationally controlled tumor protein (TCTP) to improve its biological properties. Four groups of materials, GIC, BIOGIC, BIOGIC+TCP, and BIOGIC + TCP + TCTP, were examined by XRD and SEM-EDX. TCTP released from the specimens was determined by an ELISA method. Human dental pulp stem cells (hDPSCs) were harvested and analyzed by MTT assay, apoptosis, gene expression, and cell differentiation. All groups had the same crystallization characteristic peaks of La2O3. The elemental compositions composed of La, Si, and Al are the main inorganic components. The results show that BIOGIC + TCP + TCTP presented significantly higher percentages of cell viability than other groups on day 1 to day 23 (p < 0.05), but were not different after day 24 to day 41 and had reduced cell apoptosis including BAX, TPT1, BCL-2, and Caspase-3. The BIOGIC + TCP + TCTP demonstrated higher odontoblast mineralization and differentiation markers including ALP activity, DSPP, DMP-1, ALP, BMP-2, and OPN. It enhanced cell proliferation and differentiation as well as mineralization with down-regulation of genes related to apoptosis compared with other groups.

Determination of chemical species of fluoride during uptake mechanism of glass-ionomer cements with NMR spectroscopy

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 2SiO₂-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 20ml KF solution with 1000ppm fluorine for 24h and then placed into the same amount of water as for 24h. A fluoride selective electrode was used to give the F concentration of the respective solutions. ¹⁹F 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. ¹⁹F 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.

Surface roughness and chemical composition changes of resin-modified glass ionomer immersed in 0.2% sodium fluoride solution

BACKGROUND/PURPOSE

Glass ionomers undergo degradation when exposed to fluoride, which changes the physico-chemical characteristics of the materials. The purpose of this study was to evaluate the surface changes of resin-modified glass ionomer (RMGI) when immersed in a sodium fluoride (NaF) solution according to pH and time.

MATERIALS AND METHODS

120 RMGI specimens were prepared, and 30 specimens were placed in four types of storage solutions for four weeks; pH 7 artificial saliva with or without 0.2% NaF (As7 and NaF7), pH 5 artificial saliva with or without 0.2% NaF (As5 and NaF5). Interferometry and microscopy were performed to evaluate the surface roughness and topography, while spectroscopy was used to analyze the chemical composition changes.

RESULTS

Rougher topography and increased roughness was exhibited in NaF groups, owing to the disintegration of the polysalt matrix. Reduced Sr and F was exhibited in all groups, whereas NaF group showed a decrease in Al and inorganic components.

CONCLUSION

This study suggest that excessive use of fluoride therapy could lead to severe degradation of RMGI.

Protective Effects of GIC and S-PRG Filler Restoratives on Demineralization of Bovine Enamel in Lactic Acid Solution

This study was aimed at investigating the protective effects of glass ionomer cement (GIC) and surface pre-reacted glass ionomer (S-PRG) fillers used as dental restorative materials on demineralization of bovine enamel. GlasIonomer FX ULTRA (FXU), Fuji IX GP Extra (FIXE), CAREDYNE RESTORE (CDR) were used as GICs. PRG Barrier Coat (BC) was used as the S-PRG filler. They were incubated in a lactic acid solution (pH = 4.0) for six days at a temperature of 37 °C. The mineral was etched from the enamel surface, and a large number of Ca and P ions were detected in solution. The Al, F, Na, Sr, and Sr ions were released in GICs and S-RPG fillers. The Zn ion was released only in CDR and the B ion was released only in BC. The presence of apparent enamel prism peripheries was observed after six days of treatment for the group containing only enamel blocks. pH values for the FXU, FIXE, CDR, BC, and enamel block groups after six days were 6.5, 6.6, 6.7, 5.9, and 5.1, respectively. Therefore, the observed pH neutralization effect suppressed progression of caries due to the release of several ions from the restoratives.

The effect of temperature and ionic solutes on the fluoride release and recharge of glass-ionomer cements

OBJECTIVE

To determine the effect of storage temperature and the presence of sodium chloride in solution on the fluoride uptake and release of glass-ionomer cements.

METHODS

Several commercial brands were used, and stored at either room temperature (21-23°C) or 37°C, in KF solution at a concentration of 1000ppm F^- with and without 0.9% NaCl present. Fluoride levels in the storage solutions after 24h were measured using a fluoride-ion selective electrode. Specimens were then stored in water, and fluoride release after 24h was determined. Studies were also carried out to determine chloride levels when specimens were stored in 0.9% NaCl, with or without 1000 ppm fluoride, again using an ion selective electrode.

RESULTS

All glass-ionomer specimens took up fluoride, and most of the fluoride was retained over the next 24 h when the specimens were stored in water. There was a slight variation in the amount of fluoride taken up with storage temperature and with the presence of sodium chloride. All specimens also took up chloride, with greater uptake at higher temperatures, but little or no effect when KF was also present in solution.

SIGNIFICANCE

The substantial retention of fluoride after 24h in deionised water confirms previous findings and suggests that an insoluble species, possibly SrF₂, forms in situ. Chloride uptake has not been reported previously, and its significance requires further investigation. Fluoride and chloride uptake were apparently independent of each other, which suggests that the ions are taken up at different sites in the cement. This may relate to differences in the respective sizes and hydration states of F^- and Cl^- ions.

New Pre-reacted Glass Containing Dental Composites (giomers) with Improved Fluoride Release and Biocompatibility

The aim of the present work was to prepare a series of novel restorative giomers and investigate the morphology, the physico-chemical properties (residual monomer, fluoride release), and the cytotoxicity of the new materials. The experimental giomers were prepared as light-cured pastes by blending different resin matrices comprising aromatic/aliphatic/urethane (di) methacrylates, with hybrid fillers containing pre-reacted glasses (PRGs), a radiopaque glass, and nano fluorhydroxyapatite. Polyalkenoic acids based on acrylic acid/itaconic acid/N-acryloyl -L-leucine modified or not with methacrylic groups, together with a superficially active glass, were used to prepare the PRGs. The fluoride ion release of the experimental giomers was investigated within a period of 60 days of storage in bidistilled water while using a fluoride ion selective electrode. Beautifil II commercial product was used as a reference. Cell cytotoxicity tests were done in vitro, in accordance with ISO 10993-122012 proceedings. Human dermal fibroblasts and umbilical endothelial vein cultures were used. The values that were obtained for cumulative fluoride release for all experimental giomers were higher than for the Beautifil II product, being more than twice the ones that were obtained for the commercial product after 60 days of storage in bidistilled water. The experimental biomaterials showed similar and/or better results when compared to the commercial one; this effect was maintained in all tested conditions.

Investigating the effect of germanium on the structure of SiO2-ZnO-CaO-SrO-P2O5 glasses and the subsequent influence on glass polyalkenoate cement formation, solubility and bioactivity

A series of germanium (Ge)-containing glasses were synthesized based on a starting glass composition of SiO₂-ZnO-CaO-SrO-P₂O₅. Additions of GeO₂ (6 and 12 mol%) were incorporated at the expense of SiO_2, which retained the amorphous character, and each glass was processed to present similar particle size and surface area. Glass characterization using x-ray photoelectron spectroscopy (XPS) and magic angle spinning nuclear magnetic resonance (MAS-NMR) determined that the addition of GeO₂ increased the fraction of lower Q-speciation and subsequently the concentration of non-bridging oxygens (NBO). Glass Polyalkenoate Cements (GPC) were formulated from each glass with 40, 50 and 60 wt% PAA, and presented time dependent solubility profiles (1, 10, 100, 1000 h) for the release of Si⁴⁺ (4-140 mg/l), Ca²⁺ (1-8 mg/l), Zn²⁺ (<6 mg/l), Sr²⁺ (2-37 mg/l), PO₄^3- (2-43 mg/l) and Ge⁴⁺ (20-911 mg/l) and attained pH values close to 7.5 after 1000 h. Ge-GPCs containing 40 wt% polyacrylic acid (PAA) presented appropriate working time (T_w) and setting times (T_s), and the corresponding compressive strengths ranged from (14-30 MPa). The Ge-GPCs (40, 50 wt%) presented a linear increase (R²-0.99) with respect to time. Simulated Body Fluid (SBF) testing resulted in the Ge-GPCs encouraging the precipitation of crystalline hydroxyapatite on the GPC surface, more evidently after 100 and 1000 h incubation.

Ion release of chitosan and nanodiamond modified glass ionomer restorative cements

Purpose

Ion release from glass ionomer restorative cements (GICs) plays an important role in GICs. The ion release from chitosan and nanodiamond-modified glass ionomers was assessed.

Materials and methods

Three GICs (Fuji IX, Ketac Universal and Riva Self Cure) were modified in the powder phase per weight by adding 5% or 10% of a commercially available chitosan powder (CH) or nanodiamond (ND) powder to the GICs. The specimens with dimensions 4 mm diameter and 6 mm height manufactured from the 15 GIC formulations were allowed to set for 1 hr and subsequently placed in neutral de-ionised water. The released ions were assessed using inductively coupled plasma-mass spectrometer (ICP-MS) to determine the elemental release. Additionally, three different disc-shaped specimens (3 mm in diameter and 1 mm thick) were constructed from each material for scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (SEM-EDS) microanalysis to establish an ion weight percentage.

Results

There were no significant differences in the ion release between the control materials for aluminium, silicon and strontium. The ion release from CH and most ND-modified GICs were significantly (p<0.00001) increased compared to the control materials. CH modifications significantly increased the ion release of aluminium, sodium, silicon and strontium for all three control materials (with the exception of the strontium release from Ketac Universal that was modified with 5% chitosan).

Conclusion

Ion release can be advantageous to tooth structure due to the interaction of chitosan with the GIC chemistry and moisture during maturation. Ion release up to five times greater than the control was noted for some ions.

Combination of ions promotes cell migration via extracellular signal‑regulated kinase 1/2 signaling pathway in human gingival fibroblasts

Wound healing is a dynamic process that involves highly coordinated cellular events, including proliferation and migration. Oral gingival fibroblasts serve a central role in maintaining oral mucosa homeostasis, and their functions include the coordination of physiological tissue repair. Recently, surface pre‑reacted glass‑ionomer (S‑PRG) fillers have been widely applied in the field of dental materials for the prevention of dental caries, due to an excellent ability to release fluoride (F). In addition to F, S‑PRG fillers are known to release several types of ions, including aluminum (Al), boron (B), sodium (Na), silicon (Si) and strontium (Sr). However, the influence of these ions on gingival fibroblasts remains unknown. The aim of the present study was to examine the effect of various concentrations of an S‑PRG filler eluate on the growth and migration of gingival fibroblasts. The human gingival fibroblast cell line HGF‑1 was treated with various dilutions of an eluent solution of S‑PRG, which contained 32.0 ppm Al, 1,488.6 ppm B, 505.0 ppm Na, 12.9 ppm Si, 156.5 ppm Sr and 136.5 ppm F. Treatment with eluate at a dilution of 1:10,000 was observed to significantly promote the migration of HGF‑1 cells. In addition, the current study evaluated the mechanism underlying the mediated cell migration by the S‑PRG solution and revealed that it activated the phosphorylation of extracellular signal‑regulated kinase 1/2 (ERK1/2), but not of p38. Furthermore, treatment with a MEK inhibitor blocked the cell migration induced by the solution. Taken together, these results suggest that S‑PRG fillers can stimulate HGF‑1 cell migration via the ERK1/2 signaling pathway, indicating that a dental material containing this type of filler is useful for oral mucosa homeostasis and wound healing.

Fluoride release and uptake in enhanced bioactivity glass ionomer cement ("glass carbomer™") compared with conventional and resin-modified glass ionomer cements

Objectives

To study the fluoride uptake and release properties of glass carbomer dental cements and compare them with those of conventional and resin-modified glass ionomers.

Materials and Methods

Three materials were used, as follows: glass carbomer (Glass Fill), conventional glass ionomer (Chemfil Rock) and resin-modified glass ionomer (Fuji II LC). For all materials, specimens (sets of six) were matured at room temperature for time intervals of 10 minutes, 1 hour and 6 weeks, then exposed to either deionized water or sodium fluoride solution (1000 ppm in fluoride) for 24 hours. Following this, all specimens were placed in deionized water for additional 24 hours and fluoride release was measured.

Results

Storage in water led to increase in mass in all cases due to water uptake, with uptake varying with maturing time and material type. Storage in aqueous NaF led to variable results. Glass carbomer showed mass losses at all maturing times, whereas the conventional glass ionomer gained mass for some maturing times, and the resin-modified glass ionomer gained mass for all maturing times. All materials released fluoride into deionized water, with glass carbomer showing the highest release. For both types of glass ionomer, uptake of fluoride led to enhanced fluoride release into deionized water. In contrast, uptake by glass carbomer did not lead to increased fluoride release, although it was substantially higher than the uptake by both types of glass ionomer.

Conclusions

Glass carbomer resembles glass ionomer cements in its fluoride uptake behavior but differs when considering that its fluoride uptake does not lead to increased fluoride release.

Evaluation of Ion Release from Four Dental Sealants

The purpose of this study was to determine the ion release from four commercially available pit-and-fissure sealants [3M Clinpro, 3M Concise™, BeautiSealant (BS), and GI FX-II)]. With each brand, 18 specimens were prepared. Their fluoride release in de-ionized water was measured by fluoride electrode, while the release of silicate (Si), aluminum (Al), sodium (Na), calcium (Ca), strontium (Sr), and phosphorus (P) was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) on days 1, 3, 7, 14, 21, and 28. The result showed that fluoride was not released from 3M Concise™. GI FX-II displayed the largest fluoride release, which, however, dropped rapidly on day 3. 3M Clinpro exhibited less fluoride release than GI FX-II and BS did. At any time during the 28-day experimental period, GI FX-II released more Na than the other sealants (P<0.001). BS ranked the second in Na release, and a small amount of Na ions was released from the 3M Clinpro and 3M Concise™ samples. Al ions were only detected from BS and GI FX-II, but not from the 3M Clinpro and 3M Concise™. Additionally GI FX-II had the largest Si release among the four brands at any time during the experimental period (P<0.001). Ca ions were detected from 3M Clinpro and 3M Concise™, but not from GI FX-II. BS released more Sr than the other sealants at any time during the experimental period (P<0.001). All the samples released similar amounts of P continuously during these 28 days. In conclusion, based on the type and the amount of ion release, BS is the best pit-and-fissure sealant among the four brands.

Sol-gel methods for synthesis of aluminosilicates for dental applications

INTRODUCTION

Amorphous aluminosilicates glasses containing fluorine, phosphorus and calcium are used as a component of the glass ionomer dental cement. This cement is used as a restorative, basis or filling material, but presents lower mechanical resistance than resin-modified materials. The Sol-Gel method is a possible route for preparation of glasses with lower temperature and energy consumption, with higher homogeneity and with uniform and nanometric particles, compared to the industrial methods Glass ionomer cements with uniform, homogeneous and nanometric particles can present higher mechanical resistance than commercial ionomers.

OBJECTIVES

The aim of this work was to adapt the Sol-Gel methods to produce new aluminosilicate glass particles by non-hydrolytic, hydrolytic acid and hydrolytic basic routes, to improve glass ionomer cements characteristics. Three materials were synthesized with the same composition, to evaluate the properties of the glasses produced from the different methods, because multicomponent oxides are difficult to prepare with homogeneity. The objective was to develop a new route to produce new glass particles for ionomer cements with possible higher resistance.

CHARACTERIZATION METHODS

The particles were characterized by thermal analysis (TG, DTA, DSC), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The glasses were tested with polyacrylic acid to form the glass ionomer cement by the setting reaction.

CONCLUSIONS

It was possible to produce distinct materials for dental applications and a sample presented superior characteristics (homogeneity, nanometric particles, and homogenous elemental distribution) than commercial glasses for ionomer cements. The new route for glass production can possible improve the mechanical resistance of the ionomer cements.

Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO

Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved.

How mobile are protons in the structure of dental glass ionomer cements?

The development of dental materials with improved properties and increased longevity can save costs and minimize discomfort for patients. Due to their good biocompatibility, glass ionomer cements are an interesting restorative option. However, these cements have limited mechanical strength to survive in the challenging oral environment. Therefore, a better understanding of the structure and hydration process of these cements can bring the necessary understanding to further developments. Neutrons and X-rays have been used to investigate the highly complex pore structure, as well as to assess the hydrogen mobility within these cements. Our findings suggest that the lower mechanical strength in glass ionomer cements results not only from the presence of pores, but also from the increased hydrogen mobility within the material. The relationship between microstructure, hydrogen mobility and strength brings insights into the material's durability, also demonstrating the need and opening the possibility for further research in these dental cements.

Chemical and structural characterization of glass ionomer cements indicated for atraumatic restorative treatment

Glass ionomer cements (GICs) are restorative materials, which clinical use has increased significantly during the last decade. The aim of the present study was to analyze the chemical constitution and surface morphology of four glass ionomer cements: Maxxion R, VitroFill, Vidrion R and Vitremer. Twelve polyethylene tubes with an internal diameter of 3 and 3 mm in length were prepared, filled and then transferred to a chamber with 95% relative humidity and a temperature of 37°C. The surface morphology of the tested materials was examined by scanning electron microscopy (SEM) and main components were investigated by energy-dispersive X-ray microanalysis (EDX). Scanning electron microscopy revealed irregular and rough external surface. Cracking was not observed. The main constituents were found to be aluminum, silicon, calcium, sodium and fluoride. Phosphorus, sulfur and barium were only observed in Vidrion R, while chlorine were only observed in Maxxion R. Elemental mapping of the outer surface revealed high concentration of aluminum and silicon. Significant irregularities on the surface of the tested materials were observed. The chemical constitution of all GIC was similar.

Development of a novel antimicrobial-releasing glass ionomer cement functionalized with chlorhexidine hexametaphosphate nanoparticles

Background

Glass ionomer cements (GICs) are a class of dental biomaterials. They have a wide range of uses including permanent restorations (fillings), cavity linings, fissure sealants and adhesives. One of the most common reasons for replacing a dental restoration is recurrent bacterial tooth decay around the margins of the biomaterial. Therefore, a dental biomaterial which creates a sustained antimicrobial environment around the restoration would be of considerable clinical benefit. In this manuscript, the formulation of a GIC containing novel antimicrobial nanoparticles composed of chlorhexidine hexametaphosphate at 1, 2, 5, 10 and 20% powder substitution by mass is reported. The aim is to create GICs which contain chlorhexidine-hexametaphosphate nanoparticles and characterize the nanoparticle size, morphology and charge and the release of chlorhexidine and fluoride, tensile strength and morphology of the GICs.

Results

The GICs released chlorhexidine, which is a broad spectrum antimicrobial agent effective against a wide range of oral bacteria, over the duration of the experiment in a dose-dependent manner. This was not at the expense of other properties; fluoride release was not significantly affected by the substitution of antimicrobial nanoparticles in most formulations and internal structure appeared unaffected up to and including 10% substitution. Diametral tensile strength decreased numerically with substitutions of 10 and 20% nanoparticles but this difference was not statistically significant.

Conclusion

A series of GICs functionalized with chlorhexidine-hexametaphosphate nanoparticles were created for the first time. These released chlorhexidine in a dose-dependent manner. These materials may find application in the development of a new generation of antimicrobial dental nanomaterials.

Glass ionomer cements: effect of strontium substitution on esthetics, radiopacity and fluoride release

OBJECTIVE

SrO and SrF2 are widely used to replace CaO and CaF2 in ionomer glasses to produce radiopaque glass ionomer cements (GIC). The purpose of this study was to evaluate the effects of this substitution on release of ions from GIC as well as its effect on esthetics (translucency) and radiopacity.

MATERIALS AND METHODS

Cements were produced from ionomer glasses with varying content of Sr, Ca and F. The cements were stored in dilute acetic acid (pH 4.0) for up to 7 days at 37°C. Thereafter, the cements were removed and the solution was tested for F(-), Sr(2+), Ca(2+), and Al(3+) release. Radiopacity and translucency were measured according to BS EN ISO 9917-1:2003.

RESULTS

Ion release was linear to t(1/2) suggesting that this is a diffusion controlled mechanism rather than dissolution. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium. Radiopacity shows a strong linear correlation with Sr content. All cements were more opaque than the C0.70 0.55 standard but less opaque than the C0.70 0.90 standard which is the limit for the ISO requirement for acceptance.

SIGNIFICANCE

This study shows that the replacement of calcium by strontium in a glass ionomer glass produces the expected increase in radiopacity of the cement without adverse effects on visual properties of the cement. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium.

Present and future of glass-ionomers and calcium-silicate cements as bioactive materials in dentistry: biophotonics-based interfacial analyses in health and disease

Objective

Since their introduction, calcium silicate cements have primarily found use as endodontic sealers, due to long setting times. While similar in chemistry, recent variations such as constituent proportions, purities and manufacturing processes mandate a critical understanding of service behavior differences of the new coronal restorative material variants. Of particular relevance to minimally invasive philosophies is the potential for ion supply, from initial hydration to mature set in dental cements. They may be capable of supporting repair and remineralization of dentin left after decay and cavity preparation, following the concepts of ion exchange from glass ionomers.

Methods

This paper reviews the underlying chemistry and interactions of glass ionomer and calcium silicate cements, with dental tissues, concentrating on dentin–restoration interface reactions. We additionally demonstrate a new optical technique, based around high resolution deep tissue, two-photon fluorescence and lifetime imaging, which allows monitoring of undisturbed cement–dentin interface samples behavior over time.

Results

The local bioactivity of the calcium-silicate based materials has been shown to produce mineralization within the subjacent dentin substrate, extending deep within the tissues. This suggests that the local ion-rich alkaline environment may be more favorable to mineral repair and re-construction, compared with the acidic environs of comparable glass ionomer based materials.

Significance

The advantages of this potential re-mineralization phenomenon for minimally invasive management of carious dentin are self-evident. There is a clear need to improve the bioactivity of restorative dental materials and these calcium silicate cement systems offer exciting possibilities in realizing this goal.

Drug-eluting cements for hard tissue repair: a comparative study using vancomycin and RNPA1000 to inhibit growth of Staphylococcus aureus

Bone cement used in orthopaedic applications can become colonized with bacterial biofilms, resulting in severe medical complications. Consequently, bone cements are often loaded with antibiotics in an effort to prevent bacterial colonization. However, current formulations may not release antibiotics into the environment at sufficient and sustained concentrations required to impede bacterial growth or may be incompatible with antibiotics that are effective against the colonizing organism. Thus, new cement formulation options are needed. This report describes the performance of a novel SiO2-TiO2-ZnO-CaO-SrO-based glass polyalkenoate cement as a carrier of antimicrobials active against Staphylococcus aureus, the predominant cause of orthopaedic biofilm-associated infections. The antibiotic vancomycin and a novel Staphylococcus aureus RnpA inhibitor under pre-clinical development, RNPA1000, were included in these studies. Rheological testing characterized the workability of the glass polyalkenoate cement over a range of powder-to-liquid ratios and polyacrylic acid concentrations and revealed that the most suitable powder-to-liquid ratio was 2/1.25 with 40 wt% polyacrylic acid. Loading glass polyalkenoate cement with either 20-30% RNPA1000 or vancomycin prevented bacterial growth. However, longer incubations allowed for Staphylococcus aureus colonies to form near the vancomycin-infused cement, indicating that vancomycin may not be suitable for long-term biofilm inhibition in comparison to RNPA1000. Scanning electron microscopy and energy-dispersive X-ray analyses confirmed successful incorporation RNPA1000 into the cement matrix and were indicative of its slow release. These studies establish a drug-eluting formulation of glass polyalkenoate cement with great potential in orthopaedic implants that incorporates known antibiotics as well as RNPA1000 to prevent growth of the dangerous pathogen Staphylococcus aureus.

Gallium containing glass polyalkenoate anti-cancerous bone cements: glass characterization and physical properties

A gallium (Ga) glass series (0.48SiO(2)-0.40ZnO-0.12CaO, with 0.08 mol% substitution for ZnO) was developed to formulate a Ga-containing Glass Polyalkenoate Cement (GPC) series. Network connectivity (NC) and X-ray Photoelectron Spectroscopy (XPS) was employed to investigate the role of Ga(3+) in the glass, where it is assumed to act as a network modifier. Ga-GPC series was formulated with E9 and E11 polyacrylic acid (PAA) at 50, 55 and 60 wt% additions. E11 working times (T(w)) ranged from 68 to 96 s (Lcon.) and 106 s for the Ga-GPCs (LGa-1 and LGa-2). Setting times (T(s)) ranged from 104 to 226 s (Lcon.) and 211 s for LGa-1 and LGa-2. Compression (σc) and biaxial flexural (σf) testing were conducted where Lcon. increased from 62 to 68 MPa, LGa-1 from 14 to 42 MPa and LGa-2 from 20 to 47 MPa in σc over 1-30 days. σf testing revealed that Lcon. increased from 29 to 42 MPa, LGa-1 from 7 to 32 MPa and LGa-2 from 12 to 36 MPa over 1-30 days.

In vitro study of the effects of fluoride-releasing dental materials on remineralization in an enamel erosion model

OBJECTIVES

This study was conducted to compare the remineralization effects of five regimens on the loss of fluorescence intensity, surface microhardness, roughness and microstructure of bovine enamel after remineralization. We hope that these results can provide some basis for the clinical application of these materials.

METHODS

One hundred bovine incisors were prepared and divided into the following five groups, which were treated with distinct dental materials: (1) Clinpro™ XT varnish (CV), (2) F-varnish (FV), (3) Tooth Mousse (TM), (4) Fuji III LC(®) light-cured glass ionomer pit and fissure sealant (FJ) and (5) Base Cement(®) glass polyalkenoate cement (BC). Subsequently, they were detected using four different methods: quantitative light-induced fluorescence, microhardness, surface 3D topography and scanning electron microscopy (SEM).

RESULTS

The loss of fluorescence intensity of CV, BC and FJ groups showed significant decreases after remineralization (p<0.05). The microhardness values of the BC group were significantly higher than those of the other groups (p<0.05) after 6 weeks of remineralization. The CV group's surface roughness was significantly lower than those of the other groups after 6 weeks of remineralization (p<0.05). Regarding microstructure values, the FV group showed many round particles deposited in the bovine enamel after remineralization. However, the other four groups mainly showed needle-like crystals.

CONCLUSIONS

Glass ionomer cement (GIC)-based dental materials can promote more remineralization of the artificial enamel lesions than can NaF-based dental materials. Resin-modified GIC materials (e.g., CV and FJ) have the potential for more controlled and sustained release of remineralized agents. The effect of TM requires further study.

Maturation affects fluoride uptake by glass-ionomer dental cements

OBJECTIVES

Four commercial glass-ionomer cements have been studied for their ability to take up fluoride from aqueous solution following variable maturation times in the dry at 37°C.

METHODS

Sets of five specimens of four different materials were cured for times of 10 min, 24 h and 1 month, then transferred to a neutral solution of NaF at approximately 1000 ppm in fluoride. Fluoride concentration was then measured at regular time intervals up to 1 month using a fluoride ion selective electrode.

RESULTS

Specimens cured for 1 month showed little or no uptake over 24 h, specimens cured for 24 h showed fluctuating uptake over time, and specimens cured for 10 min showed the greatest fluoride uptake. For the latter specimens, simple kinetic models were found to apply in two cases (pseudo-first order and pseudo-second order for Chemflex and Ketac Molar Quick respectively).

SIGNIFICANCE

The ability to take up fluoride has been shown to decline with age of cement which suggests that in clinical use glass-ionomers may become less effective at undergoing fluoride recharge than has been previously assumed.

The effect of ultrasound on the uptake of fluoride by glass ionomer cements

Ultrasound has been shown to improve the set of glass ionomer cements (GICs) and also other cement properties. In particular, the release of fluoride is enhanced. These cements also can take up fluoride ion from liquids. The aim of this study is to investigate the effect of ultrasound on this cement property. Two commercial dental restorative GICs were used together with a modified commercial material and an experimental material based on a F-free glass. All three commercial materials came in capsules which were mixed as makers directed, the experimental material was mixed as in previous papers. Mixed cement was placed polyethylene moulds to create 3 × 2 mm thick discs. These were either allowed to standard set for 6 min or set with ultrasound for 55 s. 18 samples were made for each material/set. Three samples were placed in 4 ml of 0.2% NaF solution for 24 h at 37°C. The cylinders were removed and the F concentration of the solutions measured by ISE using TISAB decomplexant. F uptake was determined by difference from the original NaF concentration. The two conventional GICs showed reductions of 17.4 and 8.5% for ultrasound compared to standard set whereas the modified material increased by 32.3% and the experimental one by 20.6%. It is suggested that the effect of ultrasound may increase the surface area of the residual glass particles in the GIC which would increase F uptake. In GICs where considerable F ion is released into the cement matrix by the enhanced reaction caused by ultrasound this may be sufficient to reverse the former effect producing the reduced uptake observed.

Detection of ions released from S-PRG fillers and their modulation effect

The purpose of this study was to analyze the ions released from a surface pre-reacted glass ionomer (S-PRG) filler in distilled water or lactic acid solution. S-PRG filler was mixed with either solution at 1000:1, 100:1, 10:1, and 1:1 ratios by weight. By means of inductively coupled plasma atomic emission spectroscopy and a fluoride electrode, elements released from S-PRG filler were identified to be Al, B, Na, Si, Sr, and F. To investigate the effect of solution pH on ion release, the pH values of the solutions before mixing and after 24 hours' mixing with S-PRG were measured. After 24 hours' mixing, the pH values of solutions at all ratios became more neutral or weakly alkaline regardless of their initial pH levels before mixing. In conclusion, results showed that S-PRG filler released several types of ions, and that ion release was influenced by the mixing ratio of the solution rather than the initial pH of the solution.

Preparation and evaluation of an experimental luting glass ionomer cement to be used in dentistry

The aim of this paper is to compare the fluoride-releasing and mechanical properties of an experimental luting glass ionomer cement, which has a modified composition and a commercial luting cement. The experimental powder was obtained by sol-gel process and then, it was used to prepare the experimental cements. The properties of cement pastes, such as setting time and working time, microhardness and diametral tensile strength were determined. Fluoride release from GICs was evaluated at time intervals of 1, 7, 14, 21 and 28 days in deionized water. Atomic force microscopy (AFM) analyses showed that the surface of the experimental cements is more homogeneous than commercial GICs. The mechanical properties and the measure of liberation of fluoride of the two cements were influenced by ratio powder:liquid and chemical composition of the precursor powders. Experimental cements released less fluoride than commercial cements. However, this liberation was more constant during the analyzed period. Thus, the results obtained in this study indicated that the composition of the experimental powder modified by the niobium can lead the formation of the polysalt matrix with good mechanical properties. In other words, we can say that experimental powder offered considerable promise for exploitation in dental field.

The interaction of zinc oxide-based dental cements with aqueous solutions of potassium fluoride

The ability of zinc oxide-based dental cements (zinc phosphate and zinc polycarboxylate) to take up fluoride from aqueous solution has been studied. Only zinc phosphate cement was found to take up any measurable fluoride after 5 h exposure to the solutions. The zinc oxide filler of the zinc phosphate also failed to take up fluoride from solution. The key interaction for this uptake was thus shown to involve the phosphate groups of the set cement. However, whether this took the form of phosphate/fluoride exchange, or the formation of oxyfluoro-phosphate groups was not clear. Fluoride uptake followed radicaltime kinetics for about 2 h in some cases, but was generally better modelled by the Elovich equation, dq(t)/dt = alpha exp(-betaq(t)). Values for alpha varied from 3.80 to 2.48 x 10(4), and for beta from 7.19 x 10(-3) to 0.1946, though only beta showed any sort of trend, becoming smaller with increasing fluoride concentration. Fluoride was released from the zinc phosphate cements in processes that were diffusion based up to M(t)/M(infinity) of about 0.4. No further release occurred when specimens were placed in fresh volumes of deionised water. Only a fraction of the fluoride taken up was re-released, demonstrating that most of the fluoride taken up becomes irreversibly bound within the cement.

Fluoride at non-toxic dose affects odontoblast gene expression in vitro

Elevated fluoride intake may lead to local tissue disturbances, known as fluorosis. Towards an understanding of this effect, fluoride-induced molecular responses were analyzed in MO6-G3 cultured odontoblasts cells. NaF at 1mM changed expression of genes implicated in tissue formation and growth, without affecting cell proliferation or inducing stress factor RNAs. Up to 1mM NaF, DNA accumulation was not inhibited, whereas at 3mM, cells detached from their support and did not proliferate. Intracellular structures, characterized by EM, were normal up to 1mM, but at 3mM, necrotic features were evident. No sign of apoptotic transformation appeared at any NaF concentration. Fluoride-sensitive genes were identified by microarray analysis; expression levels of selected RNAs were determined by conventional and real-time RT-PCR. At 1mM fluoride, RNAs encoding the extracellular matrix proteins asporin and fibromodulin, and the cell membrane associated proteins periostin and IMT2A were 10-fold reduced. RNA coding for signaling factor TNF-receptor 9 was diminished to one-third, whereas that for the chemokine Scya-5 was enhanced 2.5-fold. These RNAs are present in vivo in tooth forming cells. This was demonstrated by in situ hybridization and RT-PCR on RNA from dissected tissue samples; for the presence and functioning of fibromodulin in dentin matrix, a more comprehensive study has earlier been performed by others [Goldberg, M., Septier, D., Oldberg, A., Young, M.F., Ameye, L.G., 2006. Fibromodulin deficient mice display impaired collagen fibrillogenesis in predentin as well as altered dentin mineralization and enamel formation. J. Histochem. Cytochem. 54, 525-537]. Expression of most other RNA species, in particular of stress factor coding RNAs, was not altered. It was concluded that fluoride could influence the transcription pattern without inducing cell stress or apoptosis. In odontoblasts in vivo, aberrant expression of these fluoride-sensitive genes may impair the formation of the extracellular matrix and influence cell communication, with the possible consequence of fluorotic patterns of normal and deviant dentin.