A therapeutic gum irrigator is provided for subgingival periodontal irrigation with a chemotherapeutic fluid. The irrigator includes a housing surrounding at least a portion of the irrigator, a reservoir connected to the housing to retain the fluid, and a cannula configured for subgingival periodontic insertion in fluid communication with the reservoir. The irrigator further includes a neck connected to the housing and separating the reservoir from the cannula. A pump in fluid communication with the reservoir and the cannula includes a displacing element movable between first and second positions and a biasing element that biases the displacing element to the first position. A lever connected to the housing can mechanically move the displacing element to the second position, expelling a predefined volume of the fluid through the cannula. The biasing element causes the displacing element to return to the first position upon release of the thumb lever by the user.