Ahmed M.Zaen El Din ¹, HamdiH.Hemdan², Mohamed A.Abo El Elaa³, Salah H. Mahmoud ^{4 1}Demonstrator, Department of Conservative dentistry, Faculty of Oral and Dental Medicine, Delta University for Science and Technology, ²Lecturer of Operative dentistry, Faculty of Dentistry, Mansoura University, ³Professor of Microbiology and Immunology, Faculty of Medicine, Mansoura University, ⁴Professor of Operative dentistry, Faculty of Dentistry, Mansoura University. Abstract: Background and objectives:Vital pulp therapy (direct pulp capping) aims to treat reversible pulpal injury whenever the pulp is exposed by caries, trauma, or restorative procedures. Preserving the pulp vitality, function and formation of reparative dentine are the ultimate goals of treatment. The Pulpal response is expressed by deposition of reparative dentine that seals the defect and compensates for the lost hard tissue, pulpal cells and provide protection against different stimuli. Materials and Methods: Eight non-specific race healthy dogs aged about 2-3 years, free of any systematic disease were selected for the study. The dogs were randomly assigned into four groups according to the materials used in this study calcium hydroxide group, mineral trioxide group, tricalcium silicate-based cement, and hydroxyapatite nano crystals. Each group is subdivided into two sub groups according to the time intervals of the animals sacrifice 7 days sub group, and 65 days subgroup. Results:MTA and Biodentine showed higher results followed by hydroxyapatite and Dycal respectively. Conclusion: All the used materials had calcific bridge formed, but with variations in terms of number of specimens in which the dentine was formed, and the properties of the formed dentinal bridge.  This study was done on healthy vital pulp under controlled conditions, so more studies involving the response of infected and inflamed pulps are needed to be done to avoid the need of devitalizing dental pulps.