We claim the ornamental design for a toothbrush handle, as shown and described.
FIG. 1 is a front isometric view of a toothbrush handle.
FIG. 2 is a front elevation view thereof.
FIG. 3 is a rear elevation view thereof.
FIG. 4 is a right side elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the drawings illustrate portions of the toothbrush handle that form no part of the claimed design. The dot-dash-dot line shown in FIG. 7 is to show boundary and forms no part of the claimed design.