Hertzian load-bearing capacity of a ceramic-reinforced glass ionomer cement stored wet and dry

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.

Does Modification of Amalgomer with Propolis Alter Its Physicomechanical Properties? An In Vitro Study

Objective

To assess if incorporating ethanolic extract of propolis into ceramic-reinforced glass ionomer (Amalgomer CR) might have an influence on its physicomechanical properties.

Materials and Methods

Three groups were assessed; group I: Amalgomer CR (control) and two experimental groups (II and III) of propolis added to the liquid of Amalgomer CR with 25 and 50 v/v %, respectively. Evaluation parameters were color stability, compressive strength, microhardness, and surface roughness. Representative specimens of each group were analyzed by Fourier-transform infrared spectroscopy, energy-dispersive X-ray, X-ray diffraction, and scanning electron microscopy. Analysis of variance (ANOVA) was used to compare the results, followed by a Tukey post hoc test (p < 0.05).

Results

Nonsignificant color change for both groups of modified Amalgomer CR. Meanwhile, the two experimental groups exhibited a significant increase in both compressive strength and microhardness. Simultaneously, there was a significant difference in roughness values among groups with the lowest roughness values exhibited by the 50 v/v % propolis concentration.

Conclusions

Modification of Amalgomer CR with 50 v/v % propolis may increase its mechanical properties without compromising its esthetic. Clinical Significance. Modification of Amalgomer CR by 50 v/v % propolis is supposed to be a hopeful restorative material with favorable characteristics.

A comparative evaluation of compressive strength and antimicrobial efficacy of Fuji IX and Amalgomer CR: An in vitro study

Purpose

To evaluate and compare the compressive strength and antimicrobial efficacy of Amalgomer CR and Fuji IX.

Method

40 restorative pellets were taken for evaluating compressive strength and 40 blood agar petridishes for antimicrobial efficacy. 40 restorative pellets were fabricated from the tested materials according to manufacturer intructions. Then the pellets were subjected to compressive strength testing using Instron Universal Testing machine. Antibacterial activity of Amalgomer CR and Fuji IX was assessed using the agar diffusion test. The powder and liquid of each test material was mixed and inserted in the punched wells (6 mm × 2 mm) in agar petridishes. An empty well was taken as control to authenticate the results. The agar plates were incubated at 37 °C for 24 h for Streptococcus mutans growth and then size of the inhibition zones was measured using vernier caliper.

Results

Amalgomer CR had shown significantly higher Compressive Strength but comparable antimicrobial efficay to GIC Fuji IX.

Conclusion

Amalgomer CR can be recommended as a permanent restorative material based on its better compressive strength and comparable antimicrobial efficacy to GIC Fuji IX.

Hertzian indentation testing of glass-ionomer restoratives: A reliable and clinically relevant testing approach

OBJECTIVES

To investigate the load to failure of encapsulated posterior glass-ionomer (GI) restoratives tested under Hertzian indentation and to explore the validity and reproducibility of the test results achieved for consideration of inclusion as an ISO testing protocol.

METHODS

Groups of 20 disc-shaped specimens (10.0±0.1mm diameter, 3.10±0.03mm thickness) were prepared (in batches of four) from three encapsulated posterior GI restoratives. Discs were tested while resting freely on a dentine analogue material at 24h under Hertzian indentation at a rate of 1mm/min delivered through a 20mm diameter hard steel ball. The failure mode and fracture origin of the GI specimens was assessed by fractography. Statistical analyses of the load to failure data were conducted using SPSS software (p<0.05) with the normality and homogeneity of variance of the load to failure data assessed using the Shapiro-Wilk and Levene's test, respectively. Data was also analysed using regression analyses to identify trends within the load to failure data sets.

RESULTS

The load to failure data for the GI restorative groups investigated were normally distributed (p>0.05), homogenous (p>0.05) and not significantly influenced by batch (p>0.780) or specimen number (p>0.447) although significant differences (p<0.05) between the GI restorative materials were evident. Fractographic analysis identified smooth fracture surfaces parallel to the loading axis where the failure mode was bottom initiated radial cracking. The mean coefficient of variation (CoV) for the GI restorative load to failure data sets achieved using Hertzian indentation testing was 7%.

SIGNIFICANCE

The failure mode and fracture origin of the GI restoratives tested using Hertzian indentation is representative of the clinical situation in vivo. The reliability of the load to failure data sets produced were improved compared with routinely employed mechanical testing approaches suggesting the possibility of inclusion as an ISO testing protocol.

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.