The ornamental design for an electrictoothbrushhead, as shown and described.
FIG. 1 is a perspective view of my design;
FIG. 2 is an enlarged perspective view of FIG. 1;
FIG. 3 is a front elevational view of FIG. 1;
FIG. 4 is a rear elevational view of FIG. 1;
FIG. 5 is a left side elevational view of FIG. 1;
FIG. 6 is a right side elevational view of FIG. 1;
FIG. 7 is a top plan view of FIG. 1; and,
FIG. 8 is a bottom plan view of FIG. 1.
The broken lines showing a handle in FIGS. 1-8 illustrate environmental structure of the electric toothbrush head that forms no part of the claimed design.