الفهرس 
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Abstract
This research was performed to evaluate the effect of aging and surface coating on surface microhardness of conventional and resin-modified glass-ionomer cements.
A total of 150 specimens were constructed from two different types of glass ionomer cement (Medifil conventional glass-ionomer cement and Photac™ Fil resin modified glass ionomer cement). Two surface coating materials used in this study were Copal varnish with fluoride and Prime & Bond 2.1 adhesive system.
specimens were constructed in Teflon mold with (5 mm in diameter, 2mm in thickness). The surface coating materials were applied on the exposed surfaces of the specimens after setting once or twice (except for uncoated specimens). The specimens were stored in a normal saline at room temperature (23±2°С) for three aging periods; 24 h, one and three months.
Each experimental group was sub-divided into 3 subgroups; each of which consisting of 25 specimens according to the aging period (24 h, one month and three months).
Each subgroup was further divided into (5) smaller divisions; each one had five specimens according to the protocol of the surface protection that was followed, where the first group was uncoated, the second was coated with one layer of copal varnish, the third group was coated with two layers of copal varnish, the fourth group was coated with one layer of Prime &Bond 2.1 while the last group was coated with two layers of Prime &Bond 2.1.
All specimens were subjected to surface hardness testing in Vickers hardness units (VH) using digital microhardness tester (HMV-2 series, Shimadzu)
The results were recorded, tabulated statistically analyzed using Graph pad Prism-4 statistics software for Windows. One way analysis of variance ANOVA followed by Newman-Keuls post-hoc tests to examine effects of aging and surface coating. Student t-test was done to evaluate significance between both cements.
The obtained results of surface microhardness measurements showed that there was statistically significant difference in Vickers microhardness mean values between conventional and resin-modified glass-ionomer cements. Also there was statistically significant difference in Vickers microhardness mean values between un/coated specimens of both cements. On other hand, the difference in Vickers microhardness mean values between one layer and two layers coat was statistically non-significant.
In view of the results obtained in this research, it can infer that the copal varnish was the best agent for surface protection, presented the best mean microhardness values for GICs when compared with the adhesive system tested