The ornamental design for a dentalhandpiece, as shown and described.
FIG. 1 is an isometric view of a dental handpiece;
FIG. 2 is a first side view thereof;
FIG. 3 is a second side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a frontal view of the handpiece; and,
FIG. 7 is a rear view of the dental handpiece.
The broken lines shown in the figures are included for the purpose of illustrating portions of the dental handpiece and form no part of the claimed design.