Tool for creating a perforation or cavity in a bone or bone structure (OS) in contact with a sinus membrane (MS), said tool comprising a drill (22, 24) having a free end and a channel (21) for supplying a liquid under pressure at said free end, said drill having at least one free end opening (37) for supplying said liquid to said perforation or cavity, said tool further comprising an insert (41) to be inserted into said channel (21) of said drill and to be connected to a source of said pressurized liquid, to thereby supply said liquid to said channel (21), and thus define a first flow path so that said liquid (33) flows through said insert (41 ) to said channel (21), wherein an external diameter of said insert is smaller than an internal diameter of said channel, thereby creating an open space (M) between said insert and said channel, thus defining a second flow path for a counterflow (35) of said liquid, which flows in a direction opposite to a direction of a flow of said liquid (33) flowing through said insert, and wherein said insert (41) and said end free to define a third flow path for said liquid (34) to flow from said insert (41) to said extremolibre； said first, said second and said third flow paths are configured so that dicholiquid (33) flowing through said first flow path can be divided into a dividing site in said liquid (35) flowing through said second flow path and said liquid (34) flowing through said third flow path, characterized in that said first, said second and said third flow paths are configured such that, at said dividing site, said liquid (33) flowing through said first flow path flow is flowing in a first direction, said liquid (35) flowing through said second flow path is flowing in a second direction opposite to said first direction and said liquid (34) flowing through said third flow path is flowing in said first direction, to automatically regulate the dicholiquid pressure supplied at said free end, so that said second flow of d said li
