الفهرس 
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Abstract
This current study was conducted to compare the resin modified calcium silicate cement as a modification of MTA with mineral trioxide aggregate cement .Our study was divided into two phases. The in vivo phase conducted to evaluate the histopathological effect on dog’s pulp and the ability to hard tissue barrier formation where four male dogs (16 teeth for each sub-groupe) were used and after 4 weeks & 6 weeks we extracted the pulp capped teeth, and then prepared to histopathological study and stained H&E stain. After statistical analysis; the inflammatory cell response of MTA was less than resin modified calcium silicate cement in all periods and hard tissue barrier formation of MTA was no significant difference with resin modified calcium silicate cement in all periods.
The in vitro phase was conducted to evaluate the compressive strength, diametral tensile strength and water solubility and sorption of resin modified calcium silicate cement, two types of MTA and Portland cement. For compressive strength test; 10 samples from each material were prepared and after 24 hrs. the samples were compressed till fracture in the universal testing machine and the compressive strength was calculated using the following equation:
K=4 F/π d2; where F is maximum applied load in Newton’s and d is the diameter of the test specimen in millimeters.
For the diametral tensile strength test 10 samples from each material were prepared after 24 hrs. the samples were diametrically compressed till fractured into two halves and then diametral tensile strength was calculated from the following equation:
δt= 2l/πd.h; where L is the maximum applied load, h is the height of specimen and d is the diameter of specimen.
For the water solubility and sorption test 10 samples were prepared and then the samples were weighed before immersion (M1) then they were immersed in distilled water for 24 hrs. the samples were weighed directly after removed from water (M2) and then were dessicated and weighed (M3). The water solubility and sorption were calculated from the following equation:
Water sorption= (M2-M1/M1) ×100
Water solubility= (M1-M3/M1) ×100
After statistical analysis, the results of compressive strength were variable between the two types of MTA and Portland cement; this may be due to the difference in production, particle size and conditions of test. While resin modified calcium silicate cement exhibited the highest compressive strength.
The results of diametral tensile strength were variable as compressive strength; this variation was explained as compressive strength. While resin modified calcium silicate cement exhibited the highest of diametral tensile strength.
For water solubility and sorption the resin modified calcium silicate cement exhibited the highest water sorption but it has the lowest solubility. While the results of water solubility and sorption of two types of MTA and Portland cement were variable this may be due to the difference in production, particle size and conditions of test.
Conclusions:
Within the limitations of this study we can conclude that:
The resin modified calcium silicate cement (Theracal l.c) showed more inflammatory reaction than mineral trioxide aggregate (MTA cem).
There was no significant difference in dentin bridge formation between the resin modified calcium silicate cement mineral and trioxide aggregate (MTA).
The resin modified calcium silicate cement (Theracal l.c) showed higher compressive strength & diametral tensile strength than two types MTA and Portland cement.
Regarding the water solubility and sorption the resin modified calcium silicate cement has lowest solubility but highest water sorption.
There were differences in the results of compressive strength, diametral tensile strength and water solubility and sorption between two types of MTA and Portland cement.
The MTA cem has the lowest mechanical and physical properties.