A surgical tool assembly for forming holes in bone at precise locations and to controlled depths. The drilling tool has a leading apical tip and a shank. The shank includes an annular groove at a predetermined distance from the apical tip. An adjustable stop gauge is coupled to the shank. The stop gauge includes an indexing adapter which telescopically supports a tubular collar. The collar includes an integrated impeller that accentuates irrigation of the treatment site during surgical procedures. The adjustable stop gauge may be used in combination with a guided surgery jig. The jig includes a guide bushing having a generally semi-cylindrical alignment valley adapted to receive the spinning collar of the stop gauge. The alignment valley includes an elevated internal abutment step having a semi-annular surface adapted to engage the collar when the apical tip reaches a predetermined penetration depth in the bone.
