The ornamental design for a toothbrush, as shown and described.
FIG. 1 illustrates a top plan view of a toothbrush showing the new design;
FIG. 2 illustrates a bottom plan view thereof;
FIG. 3 illustrates a front elevation view thereof;
FIG. 4 illustrates a back elevation view thereof;
FIG. 5 illustrates a side elevation view thereof, the opposite side elevation view being a mirror image thereof; and,
FIG. 6 illustrates a perspective side view thereof.
The ovals shown on the vertical surfaces of the toothbrush in FIGS. 3, 5 and 6 (three on each side portion and three on the portion with the handle), are openings. The ovals shown on the floor surfaces of the toothbrush in FIGS. 1 and 2 (2 on each side and one directly in front of the handle) are also openings.