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 . <EOS>