الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The key to re-establishing the functional microanatomical architecture of the resected root end is the regeneration of the periodontium . The Periodontium contains a combination of complex tissues that include alveolar bone, periodontal ligament and cementum (74, 93, 94, 97). The ultimate success of the periapical surgery depends on the regeneration of a functional periodontal attachment apparatus. Regeneration has been defined as the replacement of tissue components in their appropriate location in the correct amounts and the correct relationship to each other (84).
Among various types of endodontic surgery, retrograde filling aims to seal the root canal system using a material with adequate physical, chemical, and biological properties, preventing egression of infectious content of root canal toward the surrounding tissues (94). The ideal root-end filling material must present certain characteristics, i.e, biocompatibility, adequate marginal sealing ability, dimensionally stable, has osteogenic potential, antibacterial effect, radiopaque, nontoxic, noncorrosive, noncarcinogenic and ease of placement and manipulation. (80, 81, 85)
Ideally, after periradicular surgery, mesenchymal cells take part in healing process by differentiating into mature cells such as fibroblasts, osteoblasts, or cementoblasts (10, 11). Healing process includes osseous regeneration (medullary and cortical bone) and apical attachment healing. Cementum deposition over the resected area and root-end filling is essential for apical attachment regeneration (80, 81,85).
Endodontic surgery is performed in case of a persistant chronic periapical infection, which still symptomatic after orthograde retreatment (94).
The technique and type of root-end filling materials used are of great importance in this treatment; using an optimum root-end filling material has a critical effect on the success of endodontic surgery (94).
Mineral trioxide aggregate (MTA) was available in the late 1990’s. It was reported as a biocompatible material that induces osteogenesis and odontogensis, when MTA directly contacts fibroblasts, cementoblasts and osteoblasts cells of the periodontal ligament, making it ideal material for root-end filling for endodontic microsurgery (71, 84). The main constituents of this material are tricalcium silicate (CaSiO4), Bismuth oxide (Bi2O3), dicalcium silicate (2CaOSiO4), calcium sulphate (CaSO4), tricalcium aluminate (3CaOAl2O3), tetracalcium aluminoferrate (4CaOAl2O3FeO3) and amorphous structure consisting of 33% Calcium, 49% Phosphate, 2% carbon, 3% Chloride and 6% Silica (1, 3, 71).
MTA was developed to seal communication between the tooth and the external surfaces(76, 77). MTA was chosen because of its superior sealing ability, osteoinductive ability and its potential for hard tissue formation (71, 74). Recently, MTA is considered a gold standard repair material for various clinical applications. It is a unique material that is not influenced by moisture or blood contamination; the presence or absence of blood appears not to influence the sealing capacity of the material (94, 104).
MTA has some known drawbacks such as a long setting time, high cost, poor handling properties due to its sandy consistency providing difficulty during its placement and potential of discoloration. Hydroxyapatite crystals form over MTA when it comes in contact with tissue synthetic fluid. This can act as a nidus for the formation of calcified structures after the use of this material in endodontic treatments (9, 79, 94).
Hyaluronic acid (HA) was chosen due to its beneficial effect in previous periodontal studies. HA is a key element in the soft periodontal tissues, gingiva, and periodontal ligament, and in the hard tissue, such as alveolar bone and cementum. It has many structural and physiological functions within these tissues.(30, 31)
It can play a regulatory role in inflammatory response: the high-molecular-weight HA synthesized by hyaluronan synthase enzymes in the periodontal tissues, undergoes extensive degradation to lower molecular weight molecules in chronically inflamed tissue, such as gingival tissue inflammation (30).
High-molecular-weight HA is fragmented under the influence of reactive oxygen species (ROS) radicals, that are generated by infiltrating polymorphonuclear leukocytes and other inflammatory cells phagocytosis (31). Low-molecular-weight fragments play a role in signaling tissue damage and mobilizing immune cells, while the high-molecular-weight HA suppresses the immune response preventing excessive exacerbations of inflammation (30).
HA is one of the most hygroscopic molecules known in nature. When HA is incorporated into an aqueous solution, this feature allows HA to maintain conformational stiffness and to retain water. HA also presents important viscoelastic properties reducing the penetration of viruses and bacteria into the tissue, which also plays a role in the wound-healing process in both mineralized and non-mineralized tissues (30).
Hyaluronan has been the center of various studies, from early tissue development as an active bone matrix in mesenchymal cells’ differentiation, migration and adhesion to hydroxyapatite formation and has been used as a vehicle for growth factors. The hydrophilic nature of hyaluronan creates an environment for cellular migration, in addition to promoting many blood cells’ functions especially in the inflammatory response, e.g., phagocytosis and chemotaxis (31).
In this study, its effect on the healing of the periapical lesions and its ability to accelerate the healing and reformation of the periapical bone was assessed.
The new formulation of (MTA+Hyaluronic acid) was conducted and developed, this requires the characterization of the new mix in order to be eligible to be used as a root-end filling material.
The physicochemical characteristics of MTA are influenced by several factors: particle size, temperature and humidity during application, amount of air trapped in the mixture, the mixing procedure itself, and the liquid-powder ratio (12).
Due to the lack of specific standards to test the physical properties of retrofilling materials, studies conducted in this field have used the ANSI/ADA specification no.57 as reference for endodontic sealing materials (108).
Sealing ability testing have become some of the most popular, but at the same time most controversial laboratory tests for the clinical performance of root filling materials. Most endodontic failures occur as a result of leakage of irritants from pathologically involved root canals into the periradicular tissues (111).
The apical leakage of the root-end filling material has been measured by several methods: degree of penetration of dye (52, 53, 55 59), radioisotope penetration, bacterial penetration (33, 36), electrochemical means (113), scanning electron microscopy (96) and fluid filtration method (49, 50, 59).
In this study, the apical leakage of the root-end filling material was measured by fluid filtration method that overcomes the disadvantages of previous methods. Samples are not destroyed, and it is possible to obtain measurements of microleakage at intervals over extended time periods. it’s