The ornamental design for a dentalstick, as shown and described.
FIG. 1 is a perspective view of a dental stick;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a side view thereof; and,
FIG. 5 is a bottom plan view thereof.
The break lines shown in the middle portion of the dental stick in FIGS. 1 and 3-5 indicate that the appearance of any portion of the article between the break lines forms no part of the claimed design.