الفهرس 
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Abstract
The aim of this study was to synthesize and characterize nano-sized hydroxyapatite, prepare different mixtures of nano-hydroxyapatite and white Portland cement, and evaluate their workability, and to evaluate their efficacy as direct pulp capping materials in experimental animals.
Nano-sized hydroxyapatite was prepared using sol gel technique, with phosphoric acid and calcium nitrate tetrahydrate as precursors. characterization was done using XRD, FTIR, SEM, TEM, DSC and TGA to confirm the powder composition, powder size, crystallinity and thermal behaviour. The powder was then added in different concentrations to white Portland cement, which are: 25%, 50% and 75% by weight. The produced powders were then tested following the ISO standard 6876-2001 and ANSI/ADA specification number 57 for endodontic sealing materials, where water/powder ratios were established and adjusted to achieve required flow and film thickness, and setting time was determined.
For in vitro bioactivity, ion leaching and pH of the experimental materials (pure white Portland cement, pure nano hydroxyapatite, white Portland cement filled with 25, 50, 75% of nano hydroxyapatite by weight) as well as calcium hydroxide were measure at different time intervals (one hour, twenty four hours, one week, two weeks and 4 weeks).
For in vivo bioactivity, the materials were then used as direct pulp capping materials in dogs. where 60 dogs teeth were used (10 teeth for each material). After 8 weeks, the dogs were sacrificed and teeth were decalcified and histological sections were prepared.
The results of this study showed that high purity, nano sized, amorphous hydroxyapatite powder was produced. When used as a filler in white Portland cement, it increased the setting time, while when used as a pulp capping material it increased its bioactivity when used in 25% and 50% concentrations, where dentine bridge thickness increased and the incidence of pulp calcification decreased. Ion release results showed that the addition of 25% and 50% nanohydroxyapatite resulted in significant decrease in Aluminium ion release, increased pH value, the Calcium ion release increased compared to nano hydroxyapatite, yet it was less than that released by pure white Portland cement, similarly with Silica ions.
Conclusions:
Within the limitations of this study the following can be concluded:
• Sol gel technique can be a cheap and easily applicable method to produce nano hydroxyapatite of high purity and suitable for medical use.
• White Portland cement can be a cheap effective pulp capping material.
• Addition of nano hydroxyapatite to white Portland cement can enhance its bioactivity.
• Addition of less concentrations of nano hydroxyapatite to white Portland cement lead to better improvement in its bioactivity than higher concentrations.
• Addition of nano hydroxyapatite to white Portland cement can improve the thickness of produced dentine bridge when used for direct pulp capping.
• Further studies are needed to improve the setting time and radiopacity of the produced test material, while preserving its bioactivity