The ornamental design for a toothbrushhead, as shown and described.
FIG. 1 is a perspective view of our toothbrush head as seen from the top, front and right sides.
FIG. 2 is a left side view of our toothbrush head.
FIG. 3 is a front view of our toothbrush head.
FIG. 4 is a right side view of our toothbrush head.
FIG. 5 is a rear view of our toothbrush head.
FIG. 6 is a top view of our toothbrush head; and,
FIG. 7 is a bottom view of our toothbrush head.
The broken line showing of a handle, brushing means, and the rear of the head are included for the purpose of illustrating environmental structure or portions of the article that form no part of the claimed design.