الفهرس 
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Abstract
The aim of this study was to evaluate the effect of modifying a tricalcium silicate-based cement (Rootdent MTA) with three different concentrations (1, 3, and 5 wt.%) of nano graphene oxide (GO) compared to Biodentine on the setting time, compressive strength, alkalizing potential, calcium ion release in deionized water at different time intervals (1, 7, 14, and 28 days), as well as its antibacterial activity.
GO powder was prepared and added to the MTA powder and divided into 4 groups (M0, M1, M3, and M5) according to the concentration of GO; 1, 3, and 5 wt.% by weight which is equivalent to 0.0025gm, 0.0075 gm and 0.0125 gm of GO respectively, where M0 represented the unmodified control MTA group in addition to B0 which represented the unmodified Biodentine group. A total of 145 specimens were prepared; 29 specimens for each group. All the experimental groups in addition to the raw GO powder were characterized using ESEM with EDX, XRD, Raman, and FTIR spectroscopy.
Both initial and final setting time were evaluated according to the ISO standard (6867:2012) 49 for root canal sealing materials and ISO standard (9917-1:2007) 159 for water-based cements in dentistry, respectively using Gilmore needle. For compressive strength testing, the tested groups were evaluated based on the ISO standard (9917-1:2007) 159 for water-based cements in dentistry using a universal testing machine.
For the pH and calcium ion release evaluation, the prepared discs were immersed in deionized water and stored in the incubator at 37◦C. The deionized water was collected and renewed at the predetermined time intervals (1, 7, 14, and 28 days). The pH was measured using pH meter and calcium ion release was evaluated using ICP-Mass spectroscopy. For evaluation of the antibacterial activity, the experimental groups were assessed using a direct contact test against Streptococcus mutans.
The results of this study revealed that the addition of GO to MTA showed significantly reduced initial setting time compared to M0. However, it was still significantly longer than that of B0. Regarding final setting time, M3 and M5 showed shorter setting time compared to M0 and M1. However, they still presented longer final setting time compared to B0.
The addition of 1 wt.% GO to MTA (M1 group) showed the highest mean compressive strength values among all MTA groups, however it was significantly lower compared to B0. All groups showed an alkaline pH that extended up to the 28 days interval. B0 group showed the least pH value at day one while M0 group showed the least pH value at 28 days. The amount of the leached calcium ions significantly decreased with time. The successive increase in the concentration of GO to MTA showed increased calcium ion release at each tested time interval. B0 group maintained the highest level of calcium ion release after 28 days. The overall cumulative calcium ion release showed the least significant values in M0 group.
Regarding the evaluation of antibacterial activity, the successive increase in the concentration of GO added to MTA resulted in a significant decrease in the bacterial count across the experimental groups. M0 presented better antibacterial activity compared to B0.