Finished surface texture, abrasion resistance, and porosity of Aspa glass-ionomer cement

Estudo comparativo in vitro da resistência ao desgaste entre o cimento de ionômero de vidro pó/líquido e o encapsulado

Resumo Introdução Os cimentos de ionômero de vidro possuem limitações devido à sua baixa resistência mecânica, a qual está diretamente relacionada com a proporção pó/líquido e a sua manipulação. Com o intuito de padronizar o proporcionamento e a manipulação, surgiram os cimentos de ionômero de vidro encapsulados, os quais possuem proporção pré-estabelecida e manipulação mecânica. Objetivo Comparar, in vitro, a resistência ao desgaste entre os cimentos de ionômero de vidro pó/líquido (Riva self cure e Riva light cure) e os encapsulados (Riva self cure e Riva light cure). Material e método As amostras foram divididas em quatro grupos, tendo sido confeccionados 48 corpos de prova (n=12), sendo 12 para cada grupo, com as seguintes dimensões: 7 mm de diâmetro e 4 mm de espessura. O desgaste foi avaliado de acordo com a massa perdida no processo de escovação (10.000 ciclos). Os valores obtidos na diferença entre a massa inicial e a massa final foram submetidos à análise de variância ANOVA e Teste de Tamhane (p<0,05). Resultado Segundo os resultados obtidos, todas as amostras sofreram perda de massa estatisticamente significativa e, em ordem crescente de desgaste, temos os cimentos de ionômero de vidro modificado por resina ‒ para os quais não houve diferença significativa entre o sistema pó/líquido (ΔM=11,62 mg e p=0,001) e o encapsulado (ΔM=12,96 mg e p=0,003) (p>0,05) ‒ seguidos pelo convencional pó/líquido (ΔM=20,68 mg e p=0,014) e o convencional encapsulado (ΔM=47,95 mg e p=0,002). Conclusão Pode-se conseguir uma resistência ao desgaste semelhante e até melhor no sistema pó/líquido.

Incorporation of CPP-ACP into Luting and Lining GIC: Influence on Wear Rate (in the Presence of Artificial Saliva) and Compressive Strength

The improvement of mechanical and antibacterial properties of glass ionomer cements (GICs) is an important goal in dental research. In this way, modification of GIC with caries preventive and remineralizing materials such as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is a new strategy to enhance its anticariogenic properties and the remineralization of teeth. However, one main concern is that adding CPP-ACP may have negative effects on the mechanical properties of GIC. This study investigated the influence of adding CPP-ACP on the wear rate (in the presence of artificial saliva) and compressive strength of luting and lining glass ionomer cement. CPP-ACP was incorporated into a luting and lining glass ionomer cement at different percentages (1, 1.56, and 2%). Wear rate and compressive strength were measured for each group using Pin-on-Disk tribometer device (in artificial saliva condition) and universal testing machine, respectively. The wear test was carried out in the presence of artificial saliva for better simulation of the oral environment. Our results demonstrated that increasing the percentage of CPP-ACP from 0 up to 1.56% (w/w), caused a decrease of 19% in the wear rate. However, at 2% (w/w) CPP-ACP, the wear rate increased. Compressive strength was improved by 31% when the CPP-ACP concentration was increased to 1.56% (w/w), but decreased when the concentration was raised to 2% (w/w). In conclusion, adding 1.56% CPP-ACP into luting and lining glass ionomer cement appears to provide an acceptable combination of two important mechanical properties, compressive strength and wear rate.

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.

Are encapsulated anterior glass-ionomer restoratives better than their hand-mixed equivalents?

OBJECTIVES

The performance of encapsulated anterior GI restoratives were compared with their hand-mixed equivalents for the range of powder to liquid mixing ratios routinely encountered clinically. The clinically induced variability of powder to liquid mixing variations of an anhydrous GI restorative formulation was also compared with conventional GI restorative formulations that contained a polyalkenoic acidic liquid.

METHODS

Mean compressive fracture strengths, mean elastic moduli and mean total volumetric wear were determined for the encapsulated anterior GI restoratives mechanically mixed in a Capmix or Rotomix machine and the hand-mixed GI restoratives prepared with powder contents reduced from that recommended by the manufacturer (100%) in 10% increments to 50% for a constant weight of liquid. Multiple comparisons of the group means were made using a one-way analysis of variance (ANOVA) and Tukey's multiple range tests employed at P<0.05.

RESULTS

For the encapsulated GI restoratives, the mean compressive fracture strength, mean elastic modulus and in-vitro wear resistance were significantly increased compared with their hand-mixed equivalents prepared with powder contents below that recommended by the manufacturers. The conventional GI restoratives resulted in a linear deterioration (R2>0.95) of the mean compressive fracture strength and mean elastic modulus with powder content compared with the bi-modal deterioration for the anhydrous GI restorative.

CONCLUSIONS

Encapsulated anterior GI restoratives outperform their hand-mixed equivalents for the range of powder to liquid mixing ratios routinely encountered clinically such that they are advocated for use in clinical practice. Anhydrous GI restorative formulations are more susceptible to clinically induced variability on mixing compared with conventional GI restorative formulations that contained a polyalkenoic acidic liquid.

Mechanical properties and microstructures of glass-ionomer cements

OBJECTIVE

The objective of this study was to determine the flexural strength (FS), compressive strength (CS), diametral tensile strength (DTS), Knoop hardness (KHN) and wear resistance of ten commercial glass-ionomer cements (GICs). The fracture surfaces of these cements were examined using scanning electron microscopic (SEM) techniques to ascertain relationships between the mechanical properties and microstructures of these cements.

METHODS

Specimens were fabricated according to the instructions from each manufacturer. The FS, CS, DTS, KHN and wear rate were measured after conditioning the specimens for 7 d in distilled water at 37 degrees C. One-way analysis of variance with the post hoc Tukey-Kramer multiple range test was used to determine which specimen groups were significantly different for each test. The fracture surface of one representative specimen of each GIC from the FS tests was examined using a scanning electron microscope.

RESULTS

The resin-modified GICs (RM GICs) exhibited much higher FS and DTS, not generally higher CS, often lower Knoop hardness and generally lower wear resistance, compared to the conventional GICs (C GICs). Vitremer (3M) had the highest values of FS and DTS; Fuji II LC (GC International) and Ketac-Molar (ESPE) had the highest CS; Ketac-Fil (ESPE) had the highest KHN. Ketac-Bond (ESPE) had the lowest FS; alpha-Silver (DMG-Hamburg) had the lowest CS. Four GICs (alpha-Fil (DMG-Hamburg), alpha-Silver, Ketac-Bond and Fuji II) had the lowest values of DTS, which were not significantly different from each other; alpha-Silver and Ketac-Silver had the lowest values of KHN. The highest wear resistance was exhibited by alpha-Silver and Ketac-Fil; F2LC had the lowest wear resistance. The C GICs exhibited brittle behavior, whereas the RM GICs underwent substantial plastic deformation in compression. The more integrated the microstructure, the higher were the FS and DTS. Higher CS was correlated with smaller glass particles, and higher KHN was found where there was a combination of smaller glass particles and lower porosity. Larger glass particle sizes and a more integrated microstructure contributed to a higher wear resistance.

SIGNIFICANCE

The mechanical properties of GICs were closely related to their microstructures. Factors such as the integrity of the interface between the glass particles and the polymer matrix, the particle size, and the number and size of voids have important roles in determining the mechanical properties.

Comparison of the porosity of hand-mixed and capsulated glass-ionomer luting cements

The strength of dental glass-ionomer cements will be influenced by defects present within its structure. This study measured the surface area porosity, percentage surface area porosity, and mean surface area of small bubbles (<0.01 mm2) and the surface area porosity, percentage surface area porosity and diameter of large bubbles within 40-microm-thick layers of four cements, using image analysis software. Two hand-mixed cements (Fuji I and KetacCem) and two capsulated cements (Fuji Cap I and KetacCem Maxicap) were viewed under transmitted light at x117.6 magnification. For each selected area (64.75 mm2) of each cement sample, five independent measurements were made of each of these parameters. Analysis of variance (ANOVA) indicated that there were no significant differences between the four cements in the small bubble parameters measured, whilst there were significant differences in the surface area porosity, percentage surface area porosity and diameter of the large bubbles. It was concluded that the hand-mixed cements tested had a greater number of larger diameter bubbles compared with the capsulated cements.

The effect of various base/core materials on the setting of a polyvinyl siloxane impression material

Five resin-modified glass ionomers and amalgam, used as a base or core buildup material, were clinically evaluated for whether they effected polymerization of a low viscosity (light body) regular set polyvinyl siloxane impression material. A total of 20 samples per group was prepared according to the manufacturer's recommendations. Ten samples from each group were handled with latex gloves during mixing and the other 10 were handled with vinyl gloves. Five of the 10 samples had the outer surface prepared with a round diamond wheel. Impressions were made of all the samples. The impression materials were visually scored inhibited or noninhibited. Inhibited impression materials met at least one following criterion: (1) an oily substance on the surface of the impression readily collected on a sterile explorer tine as it was moved across the impression surface; (2) a rippled appearance on the surface of the impression material; or (3) unpolymerized impression material adherent to the prepared sample surface. If none of the criteria were observed, the impression was scored noninhibited. The data were analyzed with the chi square analysis (level of significance p = 0.05). Total chi square analysis revealed a significant difference between brands (p = 0.0001) and between prepared and non-prepared samples (p = 0.001). Interrater reliability data were analyzed with the kappa correlation analysis. Raters were in complete agreement (kappa = +1). The prepared samples of Vitrebond material had an inhibitory effect on the polymerization of Express impression material.

Dental composites/glass ionomers: the materials

Most commercial dental composites contain liquid dimethacrylate monomers (including BIS-GMA or variations of it) and silica-containing compositions as inorganic reinforcing filler particles coated with methacrylate-functional silane coupling agents to bond the resin to the filler. They also contain initiators, accelerators, photo-initiators, photosensitizers, polymerization inhibitors, and UV absorbers. Durability is a major problem with posterior composites. The typical life-span of posterior composites is from three to 10 years, with large fillings usually fewer than five years. Polymerization shrinkage and inadequate adhesion to cavity walls are remaining problems. Some pulp irritation can occur if deep restorations are not placed over a protective film. Some have advocated the use of glass-ionomer cement as a lining under resin composite restorations in dentin. The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970's. Current GICs may contain poly(acrylic acid) or a copolymer. Higher-molecular-weight copolymers may also be used to improve the physical properties of some GICs. Stronger and less-brittle hybrid materials have been produced by the addition of water-soluble compatible polymers to form light-curing GIC formulations. The ion-leachable aluminosilicate glass powder, in an aqueous solution of a polymer or copolymer of acrylic acid, is attacked by the hydrated protons of the acid, causing the release of aluminum and calcium ions. Salt bridges are formed, and a gel matrix surrounds the unreacted glass particles. The matrix is adhesive to mineralized tissues. Provisions must be made for maintenance of the water balance of restorations for the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Glass ionomer bond strength and treatment of dentin with polyacrylic acid

This investigation compared the effect of smear layer removal using various treatments with polyacrylic acid on the shear bond strength of glass ionomer restorative materials to dentin. Three brands of glass ionomer were applied to prepared dentin surfaces of extracted human molars, after one of four treatments with polyacrylic acid. Samples using dentin surfaces with the smear layer left intact served as controls. Comparison of mean shear bond strength values for all possible combinations of restorative material and polyacrylic acid treatment indicated that samples produced using 25% polyacrylic acid had lower (p less than 0.05) values in some instances. No other significant differences were found when test values were compared with each other or with control values. The authors concluded that removal of the smear layer does not enhance the dentin-glass ionomer restorative bond strength, as has been suggested by other investigators. Scanning electron photomicrographs indicate that treatment with higher concentrations of polyacrylic acid produces higher degrees of dentinal tubular orifice patency.

In vitro abrasion resistance and hardness of glass-ionomer cements

The aim of this study was to compare the abrasion resistance and surface hardness of four glass-ionomer cements. The effects of hydration and dehydration on wear resistance were also studied. A composite material, enamel, and dentin were used as controls. For wear testing, the specimens were abraded on abrasion discs under water. All glass ionomers showed greater wear than composite and enamel, but less wear than dentin. Ketac-Fil showed the highest and Ketac-Silver the lowest wear resistance. Hydration or dehydration of the specimens did not significantly influence the wear rate of conventional glass ionomers, but the wear resistance of Ketac-Silver was increased due to dehydration. Ketac-Fil had the highest and Ketac-Silver the lowest hardness rating of the glass ionomers. The cement material did not show abrasion resistance better than that of the conventional glass ionomers, as has previously been suggested.

Wear of materials used in dentistry: a review of the literature

This is a review of the literature concerning wear related to the following materials used in dentistry: dental amalgam, composite resins, and glass-ionomer cements, as well as natural tooth substance. Discussions are included on both in vivo and in vitro studies in which various methods were used to help determine wear resistance.

Etched glass ionomer liners: surface properties and interfacial profile with composite resins

The purpose of this study was to assess the surface alterations induced by acid etching on two glass ionomer lining cements (Ketac Bond, G-C lining cement) and to evaluate their interface with a composite resin (Herculite XR) following various surface treatments. The changes in the surface composition and topography of the etched liners were studied by electron microprobe and ESCA analyses. The interfacial treatments performed on the ionomer surfaces were: (i) application of a bonding resin; (ii) 20-s acid etching and application of a bonding resin; (iii) application of a dental adhesive based on a chlorophosphate ester of BisGMA (Scotch-bond LC), without acid etching. The interfacial sealing efficiency of these treatments was studied by the silver nitrate microleakage technique combined with optical and electron microscopy. According to the results the etched surfaces of both the liners present excessive porosity with glass and matrix dissolution. Significant changes in the surface chemistry of the liners were detected indicating severe degradation. The microleakage study revealed interfacial gaps and fractures in the etched samples. The best results were obtained from the non-etched ionomer liners which were subjected to the adhesive treatment. The efficiency of acid etching as a necessary step in the 'layered' technique is seriously questioned.