The dental handpiece of a center-injection type has a bur sleeve (8, 9) having an axial through hole capable of receiving and detachably holding therein a cutting bur having an axial through hole, upper and lower bearings (10, 11) for rotatably supporting the bur sleeve (8, 9), and an injection nozzle (5) capable of being inserted into the axial through hole of the cutting bur from its proximal end for injecting cooling water through the other end. The dental handpiece (1) further has an upper seal means (17) arranged to seal the space between the upper region of the bur sleeve (8, 9) and the upper bearing (10), and a lower seal means (17′9 arranged to seal the space between the lower region of the bur sleeve (8, 9) and the lower bearing (11).
