Influence of environmental calcium/phosphate and pH on glass ionomers

Effect of the incorporation of hydroxyapatite on the diametral tensile strength of conventional and hybrid glass ionomer cements

The objective was to evaluate the effect of the incorporation of calcium hydroxyapatite particles (HAp) in the diametral tensile strength of a conventional type II glass ionomer (GC Gold Label 2) and a resin-modified glass ionomer cement (GC Gold Label 2 LC R). Two experimental HAp (E1HAp or E2HAp) were synthesized and characterized using X-ray diffraction and Confocal Raman spectroscopy. Both HAp were added into the powder of a conventional or resin-modified glass ionomer cement at 5 or 10 wt.%. A commercial HAp (CHAp) was used as reference material. For each glass ionomer cement, a group without the incorporation of HAp was used as a control. A universal testing machine was used for the mechanical test. The results were analyzed through a two-way ANOVA test followed by a complementary Tukey test. For all analyzes, the level of significance was set at α = 0.05. The average particle size for E1Hap was 15 µm, E2HAp was 35 μm and for CHAp was 1 µm. For conventional GIC, the addition of 10% E1HAp and 5% CHAp significantly increased the diametral tensile strength values (p ≤ 0.005). On the other hand, for the resin-modified GIC, except for the 5% E2HAp group, all experimental groups significantly reduced the values of diametral tensile strength (p ≤ 0.007). The addition of HAp improved the mechanical properties only for the conventional glass ionomer cement.

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.

An in vitro study on the maturation of conventional glass ionomer cements and their interface to dentin

The objective of the study was to investigate the influence of long-term storage (up to 1 year) and coating on the variation of micro-mechanical properties of four conventional restorative glass ionomer cements (GICs) within 3.5 mm deep class I cavities. Four commercially available GICs (Riva Self Cure (SDI), ChemFil Rock (Dentsply), Fuji IX Fast and Fuji IX GP Extra/Equia (GC)) were applied to 100 teeth. In each tooth, two similar 3.5 mm deep class I cavities were prepared and filled with the GICs, with and without resin coating. The samples were stored in artificial saliva at 37 °C for 1 week, 1 month, 3 months, 6 months and 1 year. The variation in mechanical properties (indentation modulus (E) and Vickers hardness (HV)) were determined in 100 μm steps starting from the filling surface, through the intermediate layer in between dentine and GIC, and ending 100 μm in dentin. HV and E were strongly influenced by the material (P<0.05, partial eta-squared ηP(2) = 0.31 and 0.23) but less by aging duration (P<0.05, ηP(2) = 0.02 and 0.12) and resin coating (P<0.05, ηP(2) = 0.02 and 0.03). The depth of measurement (0-2 mm) has no influence on HV (P = 0.789). HV shows a gentle increase over the 1 year storage period (P = 0.002). A ∼300 μm GIC zone at the areas close to dentin with weaker properties as those measured in dentin or GIC was identified in all fillings, irrespective of the presence of coating, and at all storage periods. The thickness of this zone is more strongly influenced by storage (P<0.05, ηP(2) = 0.081) than by material type (P<0.05, ηP(2) = 0.056), while coating showed no influence (P = 0.869). Filler morphology and dimension were similar to upper parts of the GIC filling; however, the amount of low cations was higher. We concluded that the development of an intermediate layer in between dentine and GIC with lower mechanical properties might be responsible for the bond quality of GIC to dentine. Moreover, class I GIC restorations are unlikely to feature constant mechanical properties throughout the cavity, regardless of conditions such as aging and coating.

Microhardness and chemical analysis of high-viscous glass-ionomer cement after 10 years of clinical service as ART restorations

OBJECTIVES

The aim of this study was to evaluate the Knoop microhardness (KHN) and chemical composition of high-viscous glass-ionomer cement (HVGIC) after 10 years of clinical service.

METHODS

Six HVGIC samples were cut from 10-year ART restorations. The sections were embedded in acrylic moulds with their longitudinal profile exposed. KHN was determined by performing three sequences of five indentations at 10, 30, 50, 70 and 90 μm of HVGIC outer surface. For the control group (n=6), HVGIC specimens were stored in distilled water for 24 months. Hardness measurements were taken at days 7, 30, 60, 120, 180, 360, and 720. For chemical analysis using SEM-EDX, 10-year and control specimens were dehydrated and coated with carbon. Data were analysed using T-test and ANOVA/Tukey's test (p<0.05).

RESULTS

A significant KHN increase was observed in the control group up to the 180-day period. From this point the values stabilized and no more significant differences were found between the 10-year and the control KHN values. No statistical differences were observed amongst the KHN from inner distances compared to the outer surface of the 10-year HVGIC specimens. In one 10-year specimen, SEM-images identified the transformation of HVGIC in an altered layer with no glass filler particles detectable, and raised Ca, K and P contents.

CONCLUSIONS

KHN values of ten-year HVGIC specimens were similar to the control group values at 180-day storage period. Except for one 10-year specimen in that an altered layer could be seen, chemical composition was similar amongst the depths evaluated.

Ten-year survival of ART restorations in permanent posterior teeth

This study evaluated the 10-year clinical performance of high-viscosity glass-ionomer cement placed in posterior permanent teeth by means of the Atraumatic Restorative Treatment (ART) approach. One operator placed 167 single- and 107 multiple-surface restorations in 43 high-risk caries pregnant women (mean decayed teeth = 9.8 ± 5.5). Examinations were performed at 1-, 2-, and 10-year intervals according to ART criteria. In the last evaluation, the US Public Health Service (USPHS) criteria were also used. After 10 years, 129 restorations (47.1%) were evaluated and achieved a cumulative survival rate of 49.0% (SE 7.2%). The 10-year survival of single- and multiple-surface ART restorations assessed using the ART criteria were 65.2% (SE 7.3%) and 30.6% (SE 9.9%), respectively. This difference was significant (jackknife SE of difference; p < 0.05). Using the USPHS criteria, the 10-year survival of single- and multiple-surface ART restorations were 86.5% and 57.6%, respectively. The primary causes of failure were total loss (9.3%) and marginal defects (5.4%). The survival rates observed, especially for the single-surface restorations, confirm the potential of the ART approach for restoring and saving posterior permanent teeth.