الفهرس 
Introduction .Only 14 pages are availabe for public view
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Abstract
T
ooth extraction is one of the most widely performed procedures in dentistry. It has been historically well-documented that this may induce significant dimensional changes in the alveolar ridge (Horowitz et al., 2012).
A significant dimensional change occurs during the healing phase of extracted sockets. The walls of the socket shrink, and the changes are more apparent in the buccal walls than in the lingual/palatal walls. Following tooth extraction, the ridge width decreases to about 50% in 12 months. Two-thirds of this change occurs in the first 3 months after tooth extraction. The final position of the socket walls is determined by the bone surface of adjacent teeth (Darby et al., 2009; Thoma et al., 2009; Farmer and Darby, 2014).
To reduce the loss of alveolar bone to an acceptable level, several ARP techniques’ procedures have been proposed. These have included the atraumatic extraction of a tooth, followed by immediate grafting of the extraction sockets using particulate bone grafts or substitutes, guided bone regeneration (GBR) with or without bone grafts or substitutes and a socket seal technique using different tissue graft materials (Mardas et al. 2010; Araujo et al. 2015).
The use of grafting materials as an adjunct to GBR or socket seal techniques are based on the assumption that this material may be useful not only in prohibiting membrane or soft tissue graft collapse into the socket area but also in enhancing new bone formation through osteoinduction and osteoconduction (Horvath et al., 2013).
Direct grafting and augmentation of the extraction socket has been proposed using autogenous bone, demineralized freeze-dried bone allograft, mineralized freeze-dried bone allograft, deproteinized bovine bone, alloplastic polymers, bioactive glasses, and composite ceramic materials (Froum et al., 2002; Frank et al., 2003; Mardas et al., 2010).
HA exhibits biophysical properties of high viscosity, elasticity, and highly negative charge. It also shows bacteriostatic, fungistatic, anti-inflammatory, anti-edematous, osteoinductive, and pro-angiogenetic characteristics. Moreover, HA participates in several important biological procedures, such as the mediation of cellular signaling, regulation of cell adhesion and proliferation, and manipulation of cell differentiation.In addition, HA is involved in embryonic development, suggesting materials including HA may provide favorable conditions for tissue growth and regeneration ( de Brito et al., 2010; Kang et al., 2011; Raines et al., 2011; Dahiya and Kamal, 2013).
The aim of the present study was to compare three months post-extraction augmented ridge with HA 1% covered by resorbable collagen membrane versus an empty socket covered by collagen membrane only.
The study was conducted on twenty patients, Patients were divided into two groups: group I included 10 patients who underwent alveolar ridge preservation with HA 1% gel plus collagen membrane, and group II included 10 patients who underwent alveolar ridge preservation with collagen membrane alone.
This comparison was done clinically, radiographically, and histologically. Clinical parameters included; bone width that was recorded at baseline before extraction and three months after extraction. Radiographic parameters included superimposition of baseline CBCT before extraction and another one done three months after extraction with subsequent measurement of bone height, bone width, and bone density. Moreover, histomorphometric parameters included; the area fraction of osteoid and mature bone measured three months after extraction by histomorphometric analysis. Implant placement was also done three months after tooth extraction.
In the present study, we found that mean bone width decreased by more percent in the HA gel group than in the collagen membrane group without a significant difference between both groups after 3 months.
Radiographically, CBCT superimposition revealed that a more percent decrease in bone width had occurred in the HA gel group than collagen membrane group without a significant difference between both groups, regarding bone height less percent decrease in the collagen membrane group than in the HA gel group without a significant difference between both groups after three months.
Regarding, bone density showed less increase in the HA gel group than the bone density of the collagen membrane group with a significant difference between both groups after 3 months.
Histologically, HA 1% group showed trabeculae of woven bone with dilated osteocytes lacunae. Smaller areas of matured bone with less dilated osteocytes lacunae can also be observed, while the collagen membrane group showed more trabeculae of matured bone with less dilated osteocytes lacunae than in the HA group. More fibrous bone marrow can be observed than in group HA 1%.
Finally, by histomorphometric analysis, a higher mean surface area of osteoid bone was found in the HA gel group than in the collagen membrane group with a significant difference between both groups with a higher mean value of newly formed mature bone in the collagen membrane group with a significant difference between groups.