Maturation of restorative glass ionomers with simplified application procedure

Recent developments in glass ionomers (GI), including improved mechanical properties, allow the application of a filling without using a varnish to protect the initial setting reaction. Thus, this study aims to monitor the mechanical behavior of these new developments in comparison to traditional and clinically established GIs within one year of maturation by using generally accepted testing methodology along with a new test for determining chipping resistance.

Four GIs were characterized by assessing the variation in edge strength (ES), compressive strength (CS), Vickers hardness (HV) and indentation modulus (Y_HU). A special jig was constructed to examine ES, allowing a standardized positioning of the specimen during measurement to simulate clinical chipping, which is a commonly observed failure in brittle restoratives.

The properties analyzed herein progressively enhanced with maturation, but each properties followed different patterns. All applied tests were able to discriminate between different GI products and maturation stages. Depth-sensing indentation was evidenced as the most discriminatory testing methodology. Differences in chemical composition were better reflected by Y_HU, while the effect of maturation by HV. HV correlates moderate with CS (0.669) and ES (0.468). The correlation of Y_HU with the same parameters was lower (0.550 and 0.369). A very good correlation was identified between HV and Y_HU (0.843).

The new developed test was identified as reliable, sensitive to changes in the chemical composition of GIs and during maturation, easy-to-implement and may be used for ascertaining chipping resistance. The claimed improvement in mechanical properties in the absence of a protective varnish was generally confirmed.