Dental powder-jet device having - a container for an abrasive powder, - a nozzle, - a first line arrangement which extends from a connection of the powder-jet device, through the container, to the nozzle and is configured to conduct to the nozzle a mixture formed from the powder and a first fluid made available to the powder-jet device, - a second line arrangement which extends from the connection of the powder-jet device and is configured to introduce into the first line arrangement, at a point situated downstream of the container for the abrasive powder, a second fluid made available to the powder-jet device that is of the same type as the first fluid, wherein the powder-jet device is designed as a handheld device which has a grip part and, at the front end region, a cannula which contains the nozzle, and wherein the point where the second line arrangement opens out into the first line arrangement is formed in a transition region between the grip part and the cannula, characterized in that a valve for opening up and for blocking the second line arrangement is arranged at the point where the second line arrangement opens out into the first line arrangement, wherein the valve is designed in such a way that the second line arrangement for the second fluid is connected in a conducting manner to the first line arrangement if a greater pressure prevails in the second line arrangement than in the first line arrangement, and in that the second line arrangement for the second fluid is not connected in a conducting manner to the first line arrangement if a lower pressure prevails in the second line arrangement than in the first line arrangement. - a container for an abrasive powder, - a nozzle, - a first line arrangement which extends from a connection of the powder-jet device, through the container, to the nozzle and is configured to conduct to the nozzle a mixture formed from the powder and a first fluid made available to the powder-jet device, - a second line arrangement which extends from the connection of the powder-jet device and is configured to introduce into the first line arrangement, at a point situated downstream of the container for the abrasive powder, a second fluid made available to the powder-jet device that is of the same type as the first fluid, wherein the powder-jet device is designed as a handheld device which has a grip part and, at the front end region, a cannula which contains the nozzle, and wherein the point where the second line arrangement opens out into the first line arrangement is formed in a transition region between the grip part and the cannula, characterized in that a valve for opening up and for blocking the second line arrangement is arranged at the point where the second line arrangement opens out into the first line arrangement, wherein the valve is designed in such a way that the second line arrangement for the second fluid is connected in a conducting manner to the first line arrangement if a greater pressure prevails in the second line arrangement than in the first line arrangement, and in that the second line arrangement for the second fluid is not connected in a conducting manner to the first line arrangement if a lower pressure prevails in the second line arrangement than in the first line arrangement.