## 4 Discussion  
The enigma of periodontal regeneration is yet to unravel itself. For a long time, there has been an ongoing attempt to regenerate the components of the periodontitis [14,15]. Although radiographic bone fill is achieved routinely, the ultimate goal of regenerative therapy is to obtain new cementum, periodontal ligament and alveolar bone as a total composite unit [16,17]. The human eggshell is a ubiquitous source of hydroxyapatite, and nanotechnology has made it possible to elicit a veritable biomaterial in the form of Eggshell-derived nano Hydroxyapatite (EnHA). Under SEM analysis (scanning electron microscopy) the individual hydroxyapatite crystals were spherical/semi-spherical with a porosity of 1.87-4.81 um and particle size 200-700 um [18, 19, 20]. The MTT assay for cell viability and proliferation  
Figure 4: Comparison of Mean Density at different visits between the study groups. Figure 3: Comparison of Mean Radiographic measurements among the study groups at baseline and 6 months. portrayed that the graft sample was amendable for the growth of osteoblasts and fibroblasts, the key players for bone regeneration. The periosteum is an elixir of osteoprogenitor cells and is the inherent component of the mucoperiosteal flap [21]. In the last decade, microsurgery has found its way to the periodontal armamentarium and has now assumed the key spot for enhanced surgical results [22; 23]. Thus, in the present study, a combination of periosteal membrane and EnHA is used for the regeneration of intrabony defects under surgical loupes for accentuated outcome. The superiority of results of the pedicle group (group A) could be attributed to the intrinsic property of the periosteum. As we know, the periosteum has two component layers, an outer fibrous and inner cambial. The cambial layer contains undifferentiated mesenchymal cells and osteoprogenitor cells which help in bone formation ([PERSON] CA 1990). Under ideal situations, the periosteal cells have been said to secrete extracellular matrix and form a membranous structure ([PERSON] H 2006) [24]. When evaluating or classifying the density of the bone, Grey Values (GVs) obtained from 3D CT images are quantified as Hounsfield units. This implies that for every image voxel, a Hounsfield unit value based on the material inside that voxel needs to be determined during image reconstruction. Hounsfield units are defined as linear transformations of measured X-ray attenuation coefficients of a material with reference to water. Hounsfield units can be calculated for any material using the formula:  
\[\mathrm{HU}_{\mathrm{material}}=1000\times(\mu_{\mathrm{material}}-\mu_{ \mathrm{water}})/\mu_{\mathrm{water}}\]  
where in \(\mu_{\mathrm{material}}\) and \(\mu_{\mathrm{water}}\) are the linear attenuation coefficients for the material and water, respectively. The Hounsfield unit scale is based on two fixed values, which are 0 HU for water and \(-1000\) HU for air (\(\mu_{\mathrm{air}}=0\)). Materials or tissues that absorb more X-rays, such as bone, have a higher Hounsfield unit value. Although Hounsfield unit values are not absolute measurements of material density, they can be used for clinical purposes to quantify bone material density (BMD) [25; 26]  
[PERSON] et al. investigated bony changes in periapical lesions before and 2 years after treatment on 16 patients. They found a significant increase in GVs after treatment, using GVs in a relative way rather than trying to calculate actual bone density. Pre- and post-treatment comparison of CBCT GV is feasible when scanning patients under the same exposure conditions [27]  
At baseline, bone density values for control group was 760.86 \(\pm\) 110.99 HU, 924.43 \(\pm\) 69.33 HU in test group A and 865.86 \(\pm\) 70.90 HU in test group B. At 6 months, in control group was 853.14 \(\pm\) 110.89 HU, 1144.29 \(\pm\) 82.64 HU in test group A and 1065.57 \(\pm\) 60.48 HU in test group B.