الفهرس 
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Abstract
The aim of this study was to evaluate the effect of modifying Biodentine with three different concentrations (2.5%, 5% and 7.5%) of Ytterbium tri-fluoride (YbF3) on radiopacity, compressive strength, setting time of Biodentine. Moreover, in vitro bioactivity was assessed at 3 different time intervals (1, 7 and 28 days) in terms of; apatite formation in a body simulating fluid, pH changes as well as ion leaching.
YbF3 was added to Biodentine powder and divided into 4 groups (X0, X1, X2 and X3) according to the concentration of YbF3; 0%, 2.5%, 5% and 7.5% by weight which is equivalent to 0.017gm, 0.03 gm and 0.052 gm of YbF3 respectively. Specimens were prepared for each experimental condition with a total of 40 specimens for each test (n=10 per group). All the experimental groups were characterized using ESEM with EDX and XRD.
Radiopacity was evaluated according to the ISO standard (6867:2012) for root canal sealing materials. It was determined using the equivalence in millimeters of aluminum (mm Al) from digital radiographs. The grey levels of the digital images were analyzed using image J software program.
Setting time was evaluated according to the ISO (6867-2012) for root canal sealers108. Both initial and final setting times were measured using Gilmore needle. For compressive strength testing, the tested groups were evaluated following the ISO (9917-1) for water based cements using a universal testing machine.
For in-vitro bioactivity assessment, the prepared discs of the different tested groups were stored in HBSS at 37◦ C in an incubator. The discs were collected at different time intervals (1, 7 and 28 days), their surfaces were scanned using ESEM in conjunction with EDX elemental analysis. Afterwards, the same discs were re-immersed in fresh HBSS to be assessed in the next intended time interval. After the final evaluation (28 days), the discs were crushed into powder for XRD analysis of the crystalline phases formed.
For the pH as well as Ca++, F- and Yb ion leaching evaluation, the prepared discs were immersed in deionized water and stored in the incubator at 37◦ C. The deionized water was collected and the pH was measured using pH meter. Calcium, ytterbium and fluoride leaching were evaluated using both ICP mass spectrometry and ion chromatography.
The results of this study revealed a significantly higher radiopacity in the modified Biodentine groups (Biodentine with 2.5%, 5% and 7.5% YbF3) compared to unmodified Biodentine. The highest significant mean compressive strength value was recorded by unmodified Biodentine group compared to all other groups. Regarding the initial setting time, there was no significant difference between different groups. The addition of YbF3 to Biodentine has extended the final setting time for all groups except for the 2.5% YbF3 group which showed no significant difference compared to the control.
All groups showed an alkaline pH that extends up to 28 days. X3 group showed the lowest pH mean value after 28 days. The amount of the released calcium ion significantly decreased with time. X1 group maintained the highest level of calcium ion leaching after 28 days. The overall cumulative calcium ion leaching showed the least significant amount in X3 group. The amount of leached fluoride and ytterbium ions was very small and slightly increased with increasing the YbF3 concentration with the highest amount in X3 group.
ESEM coupled with EDX analysis showed globular precipitates formed on the surface which probably indicates the development of CaP deposits which are the precursers for the assumed apatite layer. X1 group (2.5%YbF3) showed the most homogenous and dense surface layer of all groups. XRD analysis of the disc specimens of the different groups after 28 days revealed peaks of calcium silicate, calcium hydroxide, calcium carbonate in addition to calcium ytterbium fluoride in X1 and X2 groups denoting continuation of the hydration process.
Conclusions
Within the limitations of this study, it could be concluded that:
1. The addition of 2.5% YbF3 is a promising approach for improving Biodentine radiopacity without altering its setting time and bioactive potential as well as keeping compressive strength at acceptable level as indicated by the ISO standards.
2. Although the addition of 5% and 7.5% YbF3 to Biodentine improved its radiopacity, it had a negative impact on its setting time, compressive strength and bioactive potential.