الفهرس 
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Abstract
Summary and conclusions
The purpose of the present study was to develop a new material for pulp capping by mixing calcium hydroxide and bismuth oxide into the powder of Portland cement and to evaluate the physical and biological properties of the new pulp capping material and compare all the materials with MTA.
Part I: Laboratory study
1- Formation of the new material: by adding 20% bismuth oxide, and calcium hydroxide with the concentrations of 10% and 25%. 2- Determination of powder/water ratio of the experimental cements. 3- Setting time evaluation of the experimental cements. 4- pH evaluation of the experimental cements. 5- Testing the strength properties of the experimental cements, such as a. Compressive strength. b. Diametral tensile strength. c. Push-out bond strength. The experimental cement which showed the best mechanical and adhesive properties (PortCal I) was included in the second part of the study (animal study) to be compared with MTA and Portland cement+bismuth oxide.
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Part II: Animal study
A total of four male mongrel dogs were selected for this study. Four teeth in each quadrant of each of the 4 dogs were included in the study. Pulp capping was performed by deepening of the pulpal floor till the appearance of pulpal shadow then exposure was done using endodontic probe. Dogs were classified into two main groups according to the evaluation period as follow:
group A: after 3 weeks (2 dogs/24 teeth).
group B: after 3 months (2dogs/24 teeth).
Each of these main groups were subdivided into three subgroups according to the capping material used:
Subgroup A1: MTA (8 teeth).
Subgroup A2: Port Cal I (8 teeth).
Subgroup A3: Portland cement + bismuth oxide (8 teeth).
Subgroup B1: MTA (8teeth).
Subgroup B2: Port Cal I (8 teeth)
Subgroup B3: Portland cement + bismuth oxide (8 teeth).
After the examination period dogs were sacrificed and the mandible and maxilla were removed for sectioning blocks of bone containing the experimental tooth.
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Teeth were then decalcified and serial sections were selected for histological evaluation.
Histologic analysis was performed for the following assessments
A) Inflammatory cell evaluation B) Dentin bridge formation C) Pulp calcification. Under the experimental conditions tested
1. MTA showed a significantly shorter setting time among the experimental materials. 2. pH of all materials was not significantly different. 3. Compressive strength at 24 hours and 21 days was significantly higher in MTA and Portland cement followed by PortCal I followed by PortCal II. 4. Diametral tensile strength at 24 hours was significantly higher in Portland cement+bismuth oxide followed by MTA followed by PortCal I followed by PortCal II. However, in 21 days MTA and Portland cement+bismuth oxide showed no significant difference. 5. Push out bond strength was statistically significantly higher with Portland cement+bismuth oxide followed by PortCal I followed by MTA and then PortCal II. 6. Mean inflammatory cell count at 3 weeks and 3 months was highly significant in MTA followed by PortCal I then Portland cement+bismuth oxide. 7. Dentin bridge formation in 3 weeks 25% of the pulps with MTA recorded partial dentin bridge while Portland cement+bismuth oxide showed 12.5% only. No dentin bridge in PortCal I. In 3
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months period MTA was significantly higher followed by Portland cement+bismuth oxide then came PortCal I. 8. No pulp stone formation at 3 weeks period was recorded with any of the materials. While in 3 months MTA showed no pulp stones, while Port Cal I and Portland cement+ bismuth oxide showed pulp stone formation.
Conclusions:
Within the conditions of the present study, the following could be concluded:
Addition of calcium hydroxide to Portland cement reduces its strength properties and push out bond strength, though it does not significantly affect its setting time and pH. Addition of calcium hydroxide to Portland cement in a ratio of 10% produces a new material with acceptable physical and adhesive properties. As for the biological properties the addition of calcium hydroxide improves the inflammatory reaction towards Portland cement, though it does not show the best dentin bridge formation. MTA shows the least inflammatory response and the greatest percentage of complete dentin bridge formation.