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

FIG. 2 is a side elevational view thereof, the opposing side being alike;

FIG. 3 is a plan, top view thereof;

FIG. 4 is a plan, bottom view thereof;

FIG. 5 is a front view thereof; and,

FIG. 6 is a rear view thereof.