H. Ngo

Glass-ionomer cements as restorative and preventive materials

This article focuses on glass-ionomer cement (GIC) and its role in the clinical management of caries. It begins with a brief description of GIC, the mechanism of fluoride release and ion exchange, the interaction between GIC and the external environment, and finally the ion exchange between GIC and the tooth at the internal interface. The importance of GIC, as a tool, in caries management, in minimal intervention dentistry (MI), and Caries Management by Risk Assessment (CAMBRA) also will be highlighted.

The influence of resin coating on the shear punch strength of a high strength auto-cure glass ionomer

OBJECTIVES The aim of this study is to examine the influence of early water contact on the shear punch strength of a modern, high strength, auto-cure glass ionomer (Fuji IX GP). METHODS Specimens, 8.0mm in diameter and approximately 1.25mm thick, were prepared in metal washers, and allowed to remain covered by polyester strips for 7min, to ensure completion of the initial set. A minimum of 32 specimens was prepared for each set of experiments and they were divided into two equal groups. Following removal of the strips, the surfaces of the specimens in Group 1 were immediately coated on both sides with Fuji Coat LC and light cured for 10s. In Group 2 the specimens were left uncoated. All specimens were then placed in distilled water at 37 degrees C, and stored for periods of 24h, 1, 2, 5, or 8 weeks. The strength of the specimens was measured at each time interval in the shear mode by a punch test in a universal testing machine. RESULTS The mean strength of the coated specimens in Group 1, which had been protected against exposure to water, increased significantly on ageing from 67.1 (24h) to 78.0MPa (1 week), with no further significant change in strength. The mean strength of the specimens in Group 2 increased significantly from 75.7 (24h) to 83.3 (1 week) and 91.9MPa (2 weeks), with no further significant change in strength. Uncoated specimens were stronger at all points of time. The difference was statistically significant at 24h, 2, 5, and 8 weeks (P<0.05), but not at 1 week (P=0.061). Significance. The results suggest that, contrary to the usual instructions for placement of glass ionomer, early access to water will positively influence the shear punch strength of Fuji IX GP.

An in vitro model for the study of chemical exchange between glass ionomer restorations and partially demineralized dentin using a minimally invasive restorative technique

OBJECTIVES This study was designed to validate an in vitro model of the Atraumatic Restorative Technique (ART). This model allowed in depth analyses of the migration of apatite forming Sr and F, from a glass-ionomer, Fuji IXGP (GC Corporation, Tokyo, Japan), into partly demineralized dentine. The second objective was to study the effects of the levels of mineral loss on such ionic exchange. METHODS Artificial lesions were created in thirty third molars, which were divided into three groups based on time of exposure to the demineralizing solution (7, 14 and 21 days). These were restored with Fuji IXGP and left for 21 days. The method of analysis was electron probe microanalysis (EPMA) with wavelength dispersive spectrometry (WDS). This combination can yield both qualitative identification of elements as well as quantitative compositional information, with a minimum detection limit of 0.01%. RESULTS The results indicated that there was no significant difference in the levels of Ca and P from the control and test sides for all three groups of demineralized dentine. The differences in the depth of penetration and the amount of Sr and F between control and test were significant. CONCLUSIONS The validity of the in vitro model was confirmed. There was migration of both strontium and fluorine to the artificially demineralized dentine in a pattern consistent with remineralization and similar to what was observed in a previous in vivo study.

Effect of early water exposure on the strength of glass ionomer restoratives

This study examined the effect of early water exposure on the shear strength of a spectrum of glass ionomer restoratives. The materials evaluated included conventional auto-cured (Fuji II [FT], GC), resin-modified light-cured (Fuji II LC [FL]) and, recently introduced, high strength auto-cured (Fuji IX GP Fast [FN], GC; Ketac Molar Quick [KQ], 3M-ESPE; Ketac Molar [KM], 3M-ESPE) cements. Sixteen specimens (8.7-mm in diameter and 1-mm thick) of each material were prepared in metal washers and randomly divided into 2 groups. The specimens were allowed to set for 6 minutes between polyester strips, to ensure completion of the initial set. The strips were subsequently removed, and the surfaces of Group 1 specimens were coated on both sides with resin (Fuji Coat LC, GC) and light cured for 10 seconds. Group 2 specimens were left uncoated. All specimens were then conditioned in distilled water at 37 degrees C for 4 weeks. After conditioning, the specimens were restrained with a torque of 2.5 Nm and subjected to shear punch testing using a 2-mm diameter punch at a crosshead speed of 0.5-mm/minute. The mean shear strengths of the materials were computed and subjected to Independent Samples t-test and ANOVA/Scheffes tests at significance level 0.05. Mean strength ranged from 78.34 to 99.36 MPa and 79.88 to 95.78 MPa for Groups 1 and 2, respectively. No significant difference in shear strength was observed between the 2 groups. For both groups, KM and KQ were significantly stronger than FT. Contrary to current teaching, early exposure to water did not weaken glass ionomer restoratives. A marginal increase in strength was actually observed for some materials.