Abstract: This histological study was performed to assess the different histologic reactions in dentin-pulp organs in the pulp of mongrel dogs after stimulation with Low-Level Laser (LLL), mineral trioxide aggregate (MTA), and TheraCal light-cured (LC) and compare it with the conventional calcium hydroxide (Ca(OH)). Materials and Methods: Eight male mongrel dogs 12-18 months old were chosen for this study. The pulp exposure was done via the preparation of a class V cavity on the buccal surface of the premolar teeth. In each doge, the premolar teeth were assigned to four different groups (group 1: LLL; group 2: MTA; group 3: TheraCal LC; and group 4; Ca(OH). The histological reactions recorded at 3 different follow-up periods (7, 14, and 42 days). Results: The histological finding showed formation of a partial or complete calcified dentine bridge in Laser, and MTA therapies after 42 days, and the pulp returned to its normal condition. Additionally, TheraCal LC, and Ca(OH) showed the formation of granulation tissues. Conclusion: MTA specimens form a complete dentine bridge after the end of the follow-up period. However, Laser specimens from incomplete dentine bridge after the end 42 days. TheraCal has a comparable result when compared with Ca(OH). Keywords: Dentin-Pulp Organ, Histologic Reactions, Laser, MTA, TheraCal