Nano-hydroxyapatite particles were prepared using sol gel chemical precipitation method. The sol was thermally aged at low temperature at 50 °C for 2 h. Upon drying the sol particles agglomerated into a dry gel through van der Waals forces composed of 10–14-nm particles. A crystalline apatite is achieved after sintering at 450 °C resulting in a gained structure of 25–55 nm in diameter. Twenty-five weight percent suspension of nano-hydroxyapatite particles were added to 80% ethyl alcohol and stirred to achieve a homogenous suspension, and the right scaffold of each dog was immersed in the prepared suspension for 15 min under vacuum to insure adequate filling of all pores. Scaffolds were dried at 120 °C for 180 min and the process was repeated two times. Finally, the coated scaffolds were heated at 900 °C for 30 min to ensure proper drying of the particles without changing the chemistry of the particles or the supporting scaffold.

Mercury porosimetery was performed for evaluate pore size and distribution and to measure the total porosity percent of the scaffolds. Pore sizer (Porosimeter, Micromeritics 9320, USA) was used for testing the produced porosity on the nanoscale covering pore diameter in range from 360 to 0.006 μm.

Energy dispersive X-ray analysis (EDX) (INCA Penta FETX3, OXFORD Instruments, Model 6583, England) and X-ray diffraction analysis (XRD) (PANalytical, X Pert PRO, The Netherlands) with Cu target (λ = 1.54 Å), 45 kV, 40 mA, and 2Ɵ (10°–80°) were used to analyze elemental surface composition and crystal structure of the scaffolds. Density of the prepared scaffolds was compared to theoretical density of fully sintered zirconia.

Twelve weeks after healing of the resected ridges, the animals were exposed to the second stage surgery where the created defect size was exposed using the same procedures described previously and each scaffold was seated in its final position. Resorbable collagen membrane (Biomend, Zimmer Inc, CA, USA) was used to cover the exposed surface of the scaffold and soft tissue was gently expanded and sutured to secure proper wound closure using resorbable suture material (Vicryl Rapide 5; Ethicon Inc., Somerville, NY). To increase primary retention, the scaffolds were fixed using resorbable polylactic acid fixation screws (Rapidsorb, Deput Synthes, PA, USA).