الفهرس 
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Abstract
Post-extraction defect that resulted from tooth removal become partially restored. There are both bone growth into the socket, along with resorption of the alveolar ridges leading to significant changes in its dimensions (Couso‐Queiruga et al., 2020). Several materials are used for bone regeneration including nanomaterials which possess superior properties compared to their micron-structured counterparts (Boey et al., 2011). Hydroxy apatite crystal (HA) has been used to fill a wide range of bony defects in orthopedic and maxillofacial surgeries and dentistry (Habibah and Salisbury, 2019).
Theobromine is used as an effective remineralizing agent and as a possible alternative to fluorides (Amaechi et al., 2013). It has the capacity to improve the formation of HA during tooth development, suggesting that it may also enhance skeletal development (Clough et al., 2017). Yet not many studies were done to grade THB effect in bone healing in comparison with n-HA crystals. Thus, we aimed to compare between n-HA and THB in the efficacy on healing of extraction sockets in Albino rats.
Materials and methods:
Thirty-eight male Albino rats were used in this study. The mandibular molar was extracted in all rats. The rats were equally divided into the following groups (each contained 14 rats) except
control group contained (10 rats). Each group was subdivided into 2 subgroups according to the time of rat sacrificed. Summary of the groups and their divisions:
group name group code Sample size Treatment Subgroups
Control 1 10 No treatment 1A: Rats were killed week after extraction 1
1B: Rats were killed weeks after extraction 2
n-HA 2 14 Topical application of n-HA gel 2A: Rats were killed week after extraction 1
2B: Rats were killed weeks after extraction 2
THB 3 14 Topical application of THB gel 3A: Rats were killed week after extraction 1
3B: Rats were killed weeks after extraction 2
At the end of each specified period, the rats of the corresponding subgroups were sacrificed, and their heads were immediately dissected to obtain the mandibular molar area. Specimens were processed for routine histological, histochemical (Masson Trichrome) and immuno-histochemical (Beta-catenin) examination under light microscope.
Results:
Hematoxylin and Eosin stain n-HA group:
after one week: fibrous connective tissue surrounding the socket bone margins with a decrease in the number of inflammatory cells. Evident new bone development.
after two weeks: apparent new woven bone trabeculae radiating from the socket fundus to the socket center was seen. The newly formed bone was bordered by numerous active osteoblasts as well as new round plump osteocytes. This new bone was connected to the old bone containing blood capillaries in addition to the presence of n-HA remnants this proved that n-HA material is better in induction new bone formation than the control group which was no evident of bone formation after the first week and less amount of new bone formation seen after two weeks.
THB group:
after one week: new woven bone formation with irregular bone trabeculae was seen. new blood vessels formation was evident. Trabeculae of woven bone also showed numerous plump osteocytes in wide lacunae in addition to the presence of developing blood vessels. Moreover, granulation tissue was also found separating the newly formed woven bone from the socket old bone
with evidence of new blood vessels formation. Comparing this group with n-HA group it was evident that THB group developed more bone.
After two weeks: newly formed lamellate compact bone in the extraction space was found. This new bone contains numerous spindle shaped osteocytes present in wide lacunae which surround circumferentially the developing osteons and marrow space that are lined by active elongated osteoblast. An area of incomplete healing was seen containing dense fibrous connective tissue with little inflammatory cells presence. The newly formed bone was separated from the old bone by reversal line.
Masson trichrome stain:
n-HA group:
After one week: fibrous connective tissue with a less predominance of inflammatory cells. trabeculae of new woven bone were observed with wide osteocyte lacunae.
After two weeks: new woven bone trabeculae in the socket center surrounded by fibrous connective tissue which consist of newly formed collagen fibers and cellular aggregations of fibroblasts and inflammatory cells.
THB group:
After one week: hyalinazed areas of developing bone matrix and mature collagen fibers were seen. Apparent inflammatory cells, fibroblasts, mature collagen fibers andhylanized matrix were seen
After two weeks: newly formed lamellated compact bone in the extraction space connected old mature compact bone.
Beta-Catenin stain:
n-HA group:
After one week: it showed negative reaction in the cells.
After two weeks: it showed positive immunohistochemical reaction in some cells lining the bone.
THB group:
After one week: it showed negative reaction in the cells.
After two weeks: it showed occasional positive reaction in the newly entrapped osteocytes.