الفهرس 
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Abstract
This in-vitro study was carried out to evaluate time-dependent ionrelease and antibacterial activity of three self- adhesive resin cements. 60 cement discs of the three tested self-adhesive resin cements were fabricated according to the manufacturer’s instructions in a plastic transparent mould, their dimensions were 6 mm in diameter and 2 mm in height. They were divided into three main experimental groups according to the selfadhesive resin cement type (20 each) as the following: group (A): Thera-Cem (n=20) group (B): G-Cem capsules (n=20) group (C): RelyX Unicem 2 (n=20) Then, each main group was further subdivided into subgroup 1 (n=10) for antibacterial assessment and subgroup 2 (n=10) for ion-release assessment For the antibacterial activity assessment, the tested microbial strain was Streptococcus mutans, Direct Contact Test (DCT) was used to monitor the bacterial outgrowth, where 10 cement specimens of each group were embedded in microtiter plate and 10μl of bacterial suspension (1x106 cells /ml) was directly placed over them, One set of 3 wells in the same microtiter plate served as negative control group in which streptococcus mutans were allowed to grow without testing dental cements. Bacterial outgrowth of each group was recorded by a temperaturecontrolled spectrophotometer in optical density (OP) units and readings were taken after 1 hour, 24 hours and 1 week. For the ion-release assessment, 10 cement specimens of each group were placed in 30 ml of deionized distilled water in a jar and incubated at 37°C for 7 days. Deionized distilled water was changed on a daily basis; fluoride and calcium ions release were measured by using ion chromatography and an atomic absorption spectrometer respectively. Measurements were recorded after 1 hour, 24 hours and 1 week. Conclusion: Based on the results of this in-vitro study and within its limitations, it can be concluded that: 1) All the evaluated cements exhibited antibacterial effects against Streptococcus mutans. 2) Fluoride and calcium were released by all the three cements in varying concentrations. 3) The antibacterial effect seems to be a consequence of the synergistic action of fluoride and calcium released in certain amounts. 4) G-Cem has the highest antibacterial effect among tested cements and a sustained fluoride release, Thera-Cem showed the least antibacterial effect, a sustained fluoride and calcium release, while RelyX Unicem 2 occupied the middle rank of antibacterial activity with sustained fluoride and calcium release. Clinical significance: Self-adhesive resin cements can be considered promising for many clinicians with a special interest for G-Cem to be used especially in patients with high caries index and low compliance with prophylactic measures. Recommendations: Since the available data were obtained from studies that assessed only a limited number of these cements currently available; 1) Further studies are required to investigate the long-lasting antibacterial effectiveness and anti-cariogenic effects of these materials with other influencing factors as saliva and pH which illustrate the actual condition of the oral cavity. 2) Further studies are required to investigate the antibacterial effect against other species responsible for caries rather than S.mutans.