Reinforced glass-ionomer cements--a review of properties and clinical use

Concept of a Novel Glass Ionomer Restorative Material with Improved Mechanical Properties

The objective of this study was to transfer the concept of ductile particle reinforcement to restorative dentistry and to introduce an innovative glass ionomer material that is based on the dispersion of PEG-PU micelles. It was hypothesized that reinforcing a conventional glass ionomer in this way increases the flexural strength and fracture toughness of the material. Flexural strength and fracture toughness tests were performed with the novel reinforced and a control glass ionomer material (DMG, Hamburg, Germany) to investigate the influence of the dispersed micelles on the mechanical performance. Transmission electron microscopy was used to identify the dispersed micelles. Fracture toughness and flexural strength were measured in a 3-point-bending setup using a universal testing machine. Before performing both tests, the specimens were stored in water at 37 °C for 23 h. The fracture toughness (MPa∙m0.5) of the novel glass ionomer material (median: 0.92, IQR: 0.89-0.94) was significantly higher than that of the control material (0.77, 0.75-0.86, p = 0.0078). Significant differences were also found in the flexural strength (MPa) between the reinforced (49.7, 45.2-57.8) and control material (41.8, 40.6-43.5, p = 0.0011). Reinforcing a conventional glass ionomer with PEG-PU micelles improved the mechanical properties and may expand clinical applicability of this material class in restorative dentistry.

Leaching components and initial biocompatibility of novel bioactive restorative materials

OBJECTIVES

Bioactive restorative materials were developed on the premise that direct restorations should not only serve the purpose of reconstructing dental hard tissue defects but also exhibit biological features that prevent secondary caries development, without having adverse effects on the host cells. This study focuses on assessing the in vitro biocompatibility of two novel bioactive restorative materials.

METHODS

Specimens of the bioactive restorative materials, Cention Forte (CF) and ACTIVA BioACTIVE RESTORATIVE (AB), a glass ionomer cement/glass hybrid (EQUIA Forte HT, EF) and an established nanohybrid composite (Venus Diamond, VD) were produced and finished. The specimens were eluted in water and methanol and the resulting eluates were analyzed via gas chromatography-mass spectrometry. hGF-1 cells were exposed to eluates prepared in cell culture medium. Cellular ATP levels, oxidized glutathione concentration, caspase-3/7 activity and the inflammatory response (IL-6 and PGE₂ levels) were determined. Microscopic images were taken to examine the cell morphology.

RESULTS

Methyl methacrylate and 2-Hydroxyethyl methacrylate were the main monomers detected in CF and AB eluates. All materials inhibited cell proliferation and led to significantly reduced ATP-levels. The cells exhibited a healthy morphology in the presence of CF and AB. Cells exposed to VD showed increased oxidized glutathione levels. Only EF led to enhanced caspase-3/7 activity. CF and AB caused IL-6 levels to increase, while EF and AB led to enhanced PGE₂ levels.

SIGNIFICANCE

CF and AB are promising materials from a biological point of view and seem to have improved bioactive properties compared to glass ionomer cements.

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

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.

The Clinical Repair of Teeth Using Direct Filling Materials: Engineering Considerations

This paper reviews the way in which teeth damaged by caries may be repaired clinically. The mechanical effects of caries are described, as are the materials available to repair the damage caused by this disease. Studies are reported which have shown that caries reduces the compressive strength of the tooth to less than 50 per cent of its original value and that, by use of appropriate materials and placement techniques, this can be restored to some 80 per cent of this value. However, very few studies have been carried out which view tooth repair from an engineering perspective. Instead, emphasis is placed on determining clinical durability of repairs. This is related to repair strength but brings in other factors, such as the oral hygiene of the patient. Despite this complication, durability studies show that modern restorative materials perform well under clinical conditions, from which it may be concluded that the repair process allows a structure to be fabricated that is essentially sound from an engineering view-point, even if inferior to the original tooth structure provided by nature.

Mechanical properties of direct core build-up materials

OBJECTIVE

This work was undertaken to measure mechanical properties of a diverse group of materials used for direct core build-ups, including a high copper amalgam, a silver cermet cement, a VLC resin composite and two composites specifically developed for this application.

METHODS

Compressive strength, elastic modulus, diametral tensile strength and flexural strength and modulus were measured for each material as a function of time up to 3 months, using standard specification tests designed for the materials.

RESULTS

All the materials were found to meet the minimum specification requirements except in terms of flexural strength for the amalgam after 1 h and the silver cermet at all time intervals.

SIGNIFICANCE

There proved to be no obvious superior material in all respects for core build-ups, and the need exists for a specification to be established specifically for this application.

Glass-ionomers in medicine and dentistry

This paper describes the current uses and future prospects for glass-ionomer cements in dentistry and medicine. Glass-ionomers divide into two chemical types, one is known as self-hardening and sets entirely by a neutralization reaction to give relatively brittle materials, the other is known as resin-modified and sets partly by polymerization and partly by neutralization to give slightly tougher materials. Compared with the self-hardening cements, these latter materials have improved aesthetics and easier clinical handling. Both types bond well to enamel and dentine, and release clinically useful amounts of fluoride. They have been used in a variety of applications in dentistry, including as liners/bases, luting cements for stainless steel crowns, and in various restorative procedures for both permanent and primary teeth. The resin-modified glass-ionomers are particularly promising for these latter uses, though it is too soon to be sure how durable they will prove to be over the longer term. Self-hardened glass-ionomers have been shown to have much better biocompatibility than resin-modified glass-ionomers in a variety of situations and consequently they have been used for various non-dental applications, such as ear, nose and throat surgery and craniofacial reconstruction.