Zirconia powder (50 μm, 3 mol YTZP, E grade, Tosoh, Japan) was mixed with 50 wt.% resin beads (50 μm polymethyl methacrylate powder) added to create microscopic pore sizes. Thirty weight percent coarse sodium chloride particles (500–700 μm) were added to the mix to create large interconnected pores. The powder was mixed in a rotating cylinder for 24 h to insure homogenous powder distribution. A binder material (1 wt.% polyvinyl glycol) was added to the mix, and the powder was isostatically pressed into cylinders (40 mm in diameter and 80 mm in length) to create the required dimensions of the CAD/CAM milling blocks. The blocks were partially sintered at 1250 ^○C for 30 min then soaked in deionizer water for 24 h to dissolve the salt particles.

The ethics committee of Alexandria University approved the working protocol used in this study (STDF reintegration grant 489) according to the university code of conduct regarding using animals in scientific studies. After approval of the ethics committee on publishing parts of the obtained data, 2-year-old healthy male Beagle dogs (weighing 10–12 kg) were generally anesthetized by administration of subcutaneous injection of atropine (0.05 mg/kg; Kwangmyung Pharmaceutical, Seoul, Korea) and an intravenous injection of a mixed xylazine (Rompun, Bayer Korea, Seoul, Korea) and zoletil (Virbac, Carros, France) and maintained by inhalation anesthesia (Gerolan, Choongwae Pharmaceutical, Seoul, Korea). Surgical flap was reflected to expose the premolar-molar region of the lower jaw with minimum amount of trauma, afterwards the involved teeth were removed and a surgical block 2 cm long × 2 cm deep was cut using a surgical guide to demarcate the wound boundaries. Finally, the surgical flap was repositioned and sutured and the dogs received an antibiotic (20 mg/kg of cefazoline sodium, intramuscularly; Yuhan, Seoul, Korea) for 3 days, given soft diet, and the surgical site was sprayed with topical 0.2% chlorhexidine solution. After 3-month healing time, three-dimensional images of the boney defect was performed using cone beam CT radiographic imaging (I cat, Imaging science international, Hatfield, PA). The images were transferred to an open access CAD/CAM software (CAMworks, Geometric Americas INC, Scottsdale, AZ) and the design of the required zirconia scaffold was reconstructed to accurately fit the modeled boney defect putting in account the expected sintering shrinkage of the material (25 vol.% shrinkage). The scaffold was designed to restore normal contour of the resected ridge. Five axes dry milling unit (DWX-51D 5, Roland, Parkway, Irvin, Cal) was used to mill the prepared blocks into the required shape and the scaffold was sintered at 1350 ^○C for 4 h.