FIG. 1 is a perspective view of my ornamental design for a toothbrush;

FIG. 2 is a side elevational view thereof the opposite side being a mirror image of that shown;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a rear view thereof;

FIG. 7 is a perspective view of an alternative embodiment of my ornamental design for a toothbrush;

FIG. 8 is a side elevational view of the embodiment of FIG. 7, the oposing side being alike;

FIG. 9 is a plan, top view of the embodiment of FIG. 7;

FIG. 10 is a plan, bottom view of the embodiment of FIG. 7;

FIG. 11 is a front view of the embodiment of FIG. 7; and,

FIG. 12 is a rear view of the embodiment of FIG. 7.