The ornamental design for a toothbrush, as shown and described.
FIG. 1 is a front elevational view of a toothbrush showing our new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a side elevational view thereof, the opposite side being a mirror
image; and,
FIG. 4 is an enlarged top plan view thereof.
The environmental broken lines on the rear of the toothbrush are for
illustrative purposes only and form no part of the claimed design. The
broken lines defining the bounds of the claimed design form no part
thereof.