The objective of this study was to evaluate the biological responses of three different mixtures of a bone substitute material placed in tooth extraction sites to determine which mixture best enhances bone formation. Under general anesthesia three adult mongrel canine had bilateral extractions of the second and fourth premolar bicuspids. Each site was modeled into 3-wall defect with box-like dimensions and having the window on the buccal (outer) side of the mandible. A synthetic hydroxyapatite bone cement (HAC) was prepared three different ways: 1) 2.5 gms HAC + 0.75 cc sterile water (W); 2) 2.5 gms HAC + 0.75 cc 2% Hydroxypropylmethylcellulose in sterile water (HPMC); 3) 2.5 gms HAC + 0.75 cc Sodium Phosphate [45mM/15mL Phosphate + 60 MEq/15mL Sodium] (SP). Each mixture was syringe injected into a different extraction site and the fourth site received no cement to serve as a control site, and after sites were filled, a periodontal flap closure was accomplished with a 4-0 VICRYL suture.