example the first height h 1 is 9 mm the axial movement allowed by the spring means 15 is 15 mm and the axial length l 5 of the guide sleeve 4 is 8 mm to adjust conveniently the axial position of the guide sleeve 4 the practitioner mounts the drill bit 5 and the centering and guiding device of the second embodiment of the invention on the dental handpiece 6 the rack of the support rod 19 is immobilized in the receiving sleeve 20 so that when the spring means 15 are compressed guide sleeve 4 in high position the proximal end 4 a of the guide sleeve is at a distance from the distal end 5 b of the drill bit 5 equal to the sum of the first height h 1 and the required depth of the hole 8 mm in this example that is to say 17 mm here in the low position the proximal end 4 a of the guide sleeve 4 is therefore offset from the distal end 5 b of the drill bit 5 by 2 mm in the direction of the proximal end 5 a of the drill bit 5 in the low position the distal end 5 b of the drill bit 5 is therefore inside the guide sleeve 4 adjustment of the device of the second embodiment to drill a hole 15 mm deep in the jaw of the patient in this example the first.