الفهرس 
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Abstract
This study was designed to investigate, in vitro, the degree of weight changes, the degree of selective fluoride emission in various levels of hydrogen ion concentration (pH 2, 3, and 4) of lactic and citric acids of resin-modified glass-ionomer (photac-fil) (RMGI) and polyacid-modified resin composite (F2000) (PMRC), and electron microscopic evaluation of the surface morphological changes of the selected materials before and after immersion in the specified solutions,
A total number of 210 specimens were prepared as discs from each of the former materials according to manufacturer instructions using the specially designed and fabricated Teflon mould. Specimens were divided into two equal groups, 105 each, according to the different materials used (RMGI) and (PMRC).
Each group was sub-divided into seven equal sub-groups, 15 each, according to the immersion media used [saline (control group), lactic acid (pH 2, 3, 4) and citric acid (pH 2, 3, 4)].
Then each sub-group was further sub-divided into three equal sub-groups, five each, according to the period of immersion in the media used [one day, one week, and two months].
The specimens were weighted before and after immersion for time intervals of one day, one week, and two months in different test solutions: saline (control group), lactic acid (pH 2, 3, 4) and citric acid (pH 2, 3, 4), using electronic sensitive balance “six digits sensitivity” to determine the degree of weight changes and to test the amount of fluoride ion released from different restorative materials, after each prescribed immersion period, each solution into which the specimens were placed, was subjected to testing by using a fluoride ion-selective electrode connected to a pH ion-selective electrode meter in mg/L., and then specimens were analyzed for the determination of topographic changes by environmental scanning electron microscopy at a fixed magnification (x1000).
The results of this study showed that (RMGI) showed higher weight gain than (PMRC), in different test solutions, for different immersion periods, which is affected by immersion time but not affected by different test solutions and different pH values.
(PMRC) showed higher fluoride release than (RMGI), in different test solutions, for different immersion periods, which is affected by immersion time, as well as different test solutions and different pH values.
(RMGI) showed more surface destruction than (PMRC) in terms of surface cracks, voids and punched out filler particles. Also the more the acidity of the immersion media and the immersion period, the larger, more numerous, and deeper surface erosion and cracks.
So under the limitations of this study, several conclusions could be detected:
(1) The plateau of fluoride release is directly affected by time; 24 hour intial emitting.
(2) The fluoride release was affected by the PH of the solution.
(3) The change of the fluoride formulation seems to affect the ion release profile.
(4) There is a direct relation between acidity, voids and crack propagation as a function of time.