The ornamental design for a dentalhandpiece, as shown and described.
FIG. 1 is a front elevation of a dental handpiece showing my new design;
FIG. 2 is a rear elevation thereof;
FIG. 3 is a right side elevation thereof with broken lines showing environmental structure that form no part of the claim:
FIG. 4 is a left side elevation thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan thereof;
FIG. 7 is a rear perspective view thereof shown on a slightly reduced scale with broken lines showing environmental structure that form no part of the claim; and,
FIG. 8 is another side elevation thereof that includes broken lines to illustrate environment that forms no part of the claim.