Abstract: An oral irrigator device is formed of an adapter mountable in interposed relation between a supply pipe of treatment liquid, generally water, and a shower head, a user-graspable handpiece, and a flexible liquid-communicating hose connecting the adapter and handpiece. A rotatable turbine within the adapter generates, from the continuous-flow stream of treatment liquid from the supply pipe, a pulsating stream of the liquid for delivery to the handpiece through a normalizing flow regulator and the flexible connecting hose. In the handpiece, the pulsating stream is separated into a primary stream for discharge through an appliance head carried on the handpiece and a secondary stream that is directed into an expansion chamber partially bounded by an elastic diaphragm which separates the chamber from a storage reservoir for a flowable medicament.