The effect of ytterbium fluoride and barium sulphate nanoparticles on the reactivity and strength of a glass-ionomer cement

doi:10.1016/j.dental.2005.11.001

Dental Materials

Volume 22, Issue 8, August 2006, Pages 746-751

https://doi.org/10.1016/j.dental.2005.11.001 Get rights and content

Abstract

Objectives

While clinical advantages of glass-ionomers include fluoride release and radiopacity, disadvantages include low strength, slow initial setting times and opacity. The addition of nanoparticles, in particular those containing fluoride and cross-linkable ions, may mitigate the disadvantages while further improving the advantages. This investigation evaluated the effects of the addition of ytterbium fluoride (YbF₃) and barium sulphate (BaSO₄) on the strength and reactivity of a commercial glass-ionomer cement.

Methods

YbF₃ and BaSO₄ nanoparticles were incorporated into the powder component of Riva SC (SDI Ltd., Bayswater, Australia) at 1, 2, 5, 10, 15, and 25% by weight. Capsules were assembled at a powder:liquid ratio of 2.9:1, activated and mixed, and the resultant pastes evaluated for working time, initial setting time, 24-h surface hardness and 24-h compressive strength.

Results

Working and initial setting times were reduced with the addition of YbF₃. Addition of BaSO₄ at low concentrations reduced working and initial setting times, but further addition delayed the setting reaction. Compressive strength decreased with the addition of either YbF₃ or BaSO₄, while surface hardness was slightly but insignificantly higher at 1–2% nanoparticles and then decreased with increasing nanoparticle concentrations.

Significance

Nanoparticles modified the setting characteristics, strength and surface hardness of a commercial glass-ionomer cement, and may be useful for refining the handling characteristics of these materials. Further improvements in powder blending may result in more significant improvements in mechanical properties.

Introduction

The use of nanoparticles, generally defined as particles smaller than 0.1 μm, or 100 nm, has become a significant area of research in dentistry. In resin composite systems, nanoparticles have been shown to improve strength and other mechanical properties [1], [2]. There have been numerous publications on the topic and several manufacturers now claim to produce various “nanoparticle” materials including new resin composites that claim to be “nanocomposites.”

However, research into the effect of nanoparticles in conventional glass-ionomer cements has not yet been published. Salt- or oxide-based nanoparticles, as opposed to the silica-based materials commonly used in resin composites, may react with the polyacid in a glass-ionomer system, or, due to their significantly smaller size than GIC glass fillers, take up interstitial sites, thereby strengthening the set cement. Xie et al. [3] demonstrated an inverse size-strength relationship for GIC fillers, and also commented that the nature of the matrix interaction—in particular the bond between the filler and the matrix—was a key contributor to overall mechanical properties. Viscosity restrictions, and the need for reasonable powder–liquid ratios to obtain sufficient strength, generally limit the use of small particle sizes [4], although nanoparticles have not yet been tested in these systems. Some resin-modified GICs contain nanoparticulate or “fumed” silica, often silane-treated, which is also used in resin composites. However, fumed silica is only reactive with the resin system, and only after surface treatment with a silane coupling agent.

A further rationale is that while radiopacity is an important property in restorative materials, radiopaque GICs are often less translucent than non-radiopaque GICs. The addition of radiopaque nanoparticles, translucent to visible light in solution, may provide more aesthetic GICs. Barium sulphate particles have previously been examined as radiopacifiers in therapeutic biomedical applications [5].

The addition of various components, by admixture, into glass-ionomer powders is a common experimental technique, and has been used for a wide range of reactive and inert fillers [6], as well as soluble species. These have included alloy powders [7], a tannin-fluoride preparation [8], borax [9], a modified polymer [10], sodium fluoride [11], glass fibres [12], hydroxyapatite/zirconia [13], [14], spherical fillers [15], and chlorhexidine [16]. Replacement of water in the glass-ionomer liquid with potassium fluoride has also been investigated [17].

This study aimed to investigate the effects of the addition of radiopaque nanoparticles on the setting time, 24-h compressive strength, and 24-h surface hardness of a commercial conventional GIC. The null hypothesis was that the addition of BaSO₄ or YbF₃ nanoparticles has no effect on setting time, 24-compressive strength or surface hardness of the GIC.

Section snippets

Materials and methods

A commercial glass-ionomer powder (Riva SC; SDI Ltd., Bayswater, Australia) was blended in various proportions with either YbF₃ or BaSO₄ nanoparticles. Fig. 1 shows a TEM (transmission electron micrograph) of the BaSO₄ particles. Lot numbers and mean sizes are given in Table 1. Powders were made with 1, 2, 5, 10, 15, and 25% (w/w) nanoparticles with the glass-ionomer powder, and mixed by hand in 30 g lots with three 1/2 in. ceramic balls for 10 min. Unblended powder was used as the control for all

Working time and initial setting time

The addition of BaSO₄ or YbF₃ nanoparticles at concentrations of 2 and 1%, respectively, resulted in working times and initial setting times significantly shorter than the control (Table 2).

For cements containing BaSO₄, both the working and setting times initially decreased with increasing concentration. However, the effect was reversed at higher concentrations; working time was shortest with cements containing 2–5% BaSO₄, and initial setting time was shortest for cements containing 10% BaSO₄ (

Working and setting times

Because of the reduced powder:liquid ratio, working time and initial setting time were expected to be longer, and strength data weaker, for the control than those quoted by the manufacturer [19].

The significant decrease in working and setting time of cements caused by the incorporation of YbF₃ nanoparticles indicates a significant interaction of the nanoparticles with the glass-ionomer matrix. The working time with 0.5% YbF₃ was almost half, and initial setting time about three-quarters, of the

Conclusion

The null hypothesis was rejected: the incorporation of ytterbium fluoride and barium sulphate nanoparticle into a glass-ionomer cement significantly reduced 24-h compressive strength and surface hardness. YbF₃ accelerated the glass-ionomer curing reaction, as did low concentrations of BaSO₄, but higher concentrations of BaSO₄ led to slower materials.

Acknowledgement

The authors wish to acknowledge the support of SDI Ltd. (Bayswater, Australia) in the supply of materials and use of experimental equipment.

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The effect of ytterbium fluoride and barium sulphate nanoparticles on the reactivity and strength of a glass-ionomer cement

Abstract

Objectives

Methods

Results

Significance

Introduction

Section snippets

Materials and methods

Working time and initial setting time

Working and setting times

Conclusion

Acknowledgement

J Am Dent Assoc

Dent Mater

Dent Mater

Biomaterials

Dent Mater

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Dent Mater

J Dent

Dent Mater

Direct applications of a nanocomposite resin system. Part 1. The evolution of contemporary composite materials

Pract Proc Aesthet Dent