An FTIR study of the effects of artificial saliva on the physical characteristics of the glass ionomer cements used for art

The influence of hydrothermal fatigue on the clinically relevant functional properties of conventional glass-ionomer cements

During their everyday service, the restorative dental materials are subjected to temperature changes which can be viewed as intensive in the context of the highest allowed temperatures for these materials. In this work, the effect of hydrothermal fatigue on the in vitro tribological performance, compression strength, microhardness, and surface roughness of glass-ionomer cements was studied. Samples of 3 commercially available cements were divided into the reference (aged 14 days) and thermocycled (20,000 cycles; 5-55 °C) groups. The results obtained show that functional properties of the specimens subjected to thermal fatigue significantly differ from the literature data on the cements aged at constant temperatures. The effect of hydrothermal fatigue on the functional properties of cements is discussed in the context of processes induced by exposure to variable temperatures.

Effect of resin coating on highly viscous glass ionomer cements: A dynamic analysis

OBJECTIVES

This study determined the effects of self-adhesive resin coatings on viscoelastic properties of highly viscous glass ionomer cements (HVGICs) using dynamic mechanical analysis.

MATERIALS AND METHODS

The HVGICs evaluated were Zirconomer [ZR] (Shofu), Equia Forte [EQ] (GC) and Riva [RV] (SDI). Sixty specimens (12mm x 2mm x 2mm) of each material were fabricated using customized Teflon molds. After initial set, the specimens were removed from their molds, finished, measured and randomly divided into 3 groups of 20. Half the specimens in each group were left uncoated while the remaining half was covered with the respective manufacturers' resin coating. The specimens were subsequently conditioned in distilled water, artificial saliva or citric acid at 37°C for 7 days. The uncoated and coated specimens (n=10) were then subjected to dynamic mechanical testing in flexure mode at 37°C with a frequency of 0.1 to 10Hz. Storage modulus, loss modulus and loss tangent data were subjected to normality testing and statistical analysis using one-way ANOVA/Scheffe's post-hoc test and Ttest at significance level p<0.05.

RESULTS

Mean storage modulus ranged from 1.39 ± 0.36 to 10.80 ± 0.86 GPa while mean loss modulus varied from 0.13 ± 0.03 to 0.70 ± 0.14 GPa after conditioning in the different mediums. Values for loss tangent ranged from 39.4 ± 7.75 to 213.2 ± 20.11 (x10 -3 ). Significant differences in visco-elastic properties were observed between mediums and materials. When conditioned in distilled water and artificial saliva,storage modulus was significantly improved when ZR, EQ and RV were uncoated. Significantly higher values were, however, observed with resin coating when the materials were exposed to citric acid.

CONCLUSION

The visco-elastic properties of HVGICs were influenced by both resin coating and chemical environment.

Avaliação da rugosidade superficial e análise morfológica de cimentos de ionômero de vidro: influência do armazenamento em saliva artificial

Resumo Introdução O desenvolvimento dos cimentos de ionômero de vidro (CIVs) proporcionou vantagens aos procedimentos restauradores diretos devido a suas propriedades, como adesão química à estrutura dentária e liberação de flúor. No entanto, o ambiente bucal pode promover condições capazes de alterar a superfície deste material. Objetivo Avaliar a rugosidade superficial e a morfologia de superfície de quatro cimentos de ionômero de vidro (Ketac Molar Easy Mix, Vitremer, Vitro Molar e Maxxion), quando imersos em diferentes soluções de saliva artificial. Material e método Dez amostras de cada material foram confeccionadas e a rugosidade superficial foi avaliada antes e após imersão em saliva artificial ácida e neutra, durante 28 dias, por meio de um rugosímetro (Surftest SJ - 40), e a análise morfológica deu-se através de microscopia eletrônica de varredura. Os valores médios de rugosidade foram submetidos aos testes de Kruskal-Wallis e de Wilcoxon, além do teste de Mann Whitney, com nível de significância de 5%. Resultado Os valores de rugosidade foram maiores estatisticamente após a imersão em saliva ácida e neutra para todos os materiais, exceto o Vitromolar, que não apresentou diferença estatística entre as médias de rugosidade antes e após imersão em saliva neutra. O Maxxion R apresentou estatisticamente maiores valores de rugosidade quando comparado aos outros materiais após imersão em saliva neutra e ácida. Conclusão A rugosidade superficial dos cimentos de ionômero de vidro aumentou após imersão em saliva neutra e ácida para a maioria dos cimentos estudados. A solução de armazenagem ácida promoveu aumento da rugosidade superficial para o Maxxion R e o Vitro Molar.

Protection Offered by Root-surface Restorative Materials against Biofilm Challenge

The prevalence of root-surface caries is increasing. We hypothesized that some restorative materials are protective against cariogenic challenge on root surfaces. Our goal was to study the effects of different restorative materials on root surfaces incubated with an oral biofilm generated in an artificial mouth. A biofilm of Streptococcus mutans, Streptococcus sobrinus, Lactobacillus rhamnosus, and Actinomyces naeslundii was co-cultured for 21 days on 24 glass-ionomer cement, resin-modified glass-ionomer cement, or resin-composite-restored root surfaces. These surfaces were then examined with Fourier transform infrared spectroscopy and scanning electron energy-dispersive spectroscopy. Only glass-ionomer restorations showed a significant increase in log calcium-to-phosphorus ratio (P < 0.01), and a significantly lower log amide I-to-hydrogen phosphate ratio on the root surface after incubation in the artificial mouth. Glass-ionomer restoratives conferred a preventive effect on the root surfaces against initial cariogenic challenge with a mixed-species oral biofilm without therapeutic intervention.

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.

Effects of nanocrystalline calcium deficient hydroxyapatite incorporation in glass ionomer cements

Glass ionomer cements (GICs) are clinically attractive filling materials often employed in the field of dentistry as restorative and luting materials. The present work aims to formulate bioactive nanocrystalline calcium deficient hydroxyapatite (nCDHA)-GIC composite cements with improved mechanical and resorption properties of the set cement than GICs. The nCDHA was synthesized via an accelerated microwave process and characterized by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) methods. The synthesized nCDHA was mixed with GIC in different compositions (5, 10 and 15 wt%) maintaining the powder to liquid ratio. Cylinders of dimensions 8 mm height and 4 mm diameter were formed using a Teflon mold following a conventional cement forming technique. The XRD and FT-IR of the cylinders showed increased intensity and characteristic bands of CDHA with increase in nCDHA content. The surface cracks and the elemental composition of the set cements were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Decreased surface hardness was observed for composite cements with increase in nCDHA addition. The cement cylinders were tested for ionic release in Millipore water (pH=7) via inductive coupled plasma (ICP) spectroscopy and in demineralization solution of pH=5 to find out the weight loss in an acidic environment at 37 °C performed periodically for 5 weeks. The ionic release percentage, weight loss and compressive strength were observed to increase with an increase in nCDHA addition.