الفهرس 
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Abstract
The present study was conducted to evaluate histologically the effect of platelet rich fibrin (PRF) combined with biphasic calcium phosphate as a bone graft on bone regeneration in surgically created bony defects.
Six healthy adult dogs (18-24 months old and weighing10-15kg) were used in this study. They were obtained from and kept in the animal house, Physiology Department, Faculty of Medicine, Alexandria University. They were kept under the same environmental conditions, and fed the same balanced diet throughout the whole period of the study.
Under thiopentone sodium general anaesthesia, mucoperiosteal flaps were reflected at the premolars area on both sides of the mandible. Artificial bony defects of 5mm diameter and 5mm depth were created buccally at the premolars area of both sides by a trephine bur mounted in a low speed straight handpiece. The experimental defects were divided into two groups, those of the right side (group A) were filled with PRF with biphasic calcium phosphate while, those of the left side (group B) filled with biphasic calcium phosphate alone. Mucoperiosteal flaps were repositioned and sutured with 3-0 polyglygolic acid suture.
All animals received the same course of antibiotic; Ampicillin 25mg/kg body weight by intravenous injection just after the operation. Amoxicillin 500mg was given every 24 hours for 5 days. Non-steroidal anti-inflammatory and analgesic drugs were given in the form of diclofenac potassium 25mg every 24 hours for 3 days. They were sacrified by an overdose of Thiopentone Sodium. Two dogs were sacrified 2, 6 and 12 weeks after surgery.The jaws were dissected out, and segments containing the operating defects were cut then fixed in 10 % neutral buffered formalin, decalcified in 8 % trichloro-acetic acid, then processed to obtain longitudinal mesio-distal serial 5 microns sections which were stained with Hematoxylin and Eosin (H&E) and Trichrome stains. Finally they were examined with the light microscope.
Clinical Results
All animals survived well, and remained active and alert all over the course of the experiment. During the first week the animals did not exhibit any clinical signs of infection. In the second post-operative week; the clinical observation revealed that the wound showed no difference in healing features for both groups.
Six weeks post operatively; there were no sign of graft rejection, also no depressions were noted in the level of bone facially on either side.
Twelve weeks post operatively; the continuity of the bone of the body of the mandible at the surgical sites was the same in both sides.
Histological Results
First observation period (after two weeks from the start of the experiment)
In both groups, in some sections inflammatory reactions were observed, with some areas of resorption of the boundary of the native bone. Other sections exhibited features of new bone formation and new vascularization which were more in association with group A (PRF+Osteon) than in group B (Osteon alone).
Second observation period (6 weeks after the start of the experiment)
Resolution of inflammation in the healing tissues was noted in both groups together with formation of more amounts of new bone and vascularization than in the first observation period. They were both more pronounced in group A than in group B. The blood supply to the healing mass was very outstanding in group A which also exhibited better figures of osteoblastic activity and osteocyte incorporation in the forming bone. Also, in group A the newly formed bone appeared more organized than in group B.
Third observation period (12 weeks after the start of the experiment)
In contrary to the variations of the histological features in the previous two experimental periods, the healing outcome here appeared consistent and bone formation was greater filling almost the whole of the created cavity in group A and the greater part of that cavity in group B with the same superior blood supply in group A than that in group B reflecting great neoangiogenesis. In both groups the formed mass of the new bone exhibited striking appearance of osteointegration with the native bone.
The better positive results obtained in association with group A in all of the experimental periods suggest a superior effect of PRF when used in association with BCP as a bone graft than if used alone.