The ornamental design for an electrictoothbrush, as shown and described.
FIG. 1 is a front, top and right side perspective view of an electric toothbrush showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a back elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The circular area of solid black shading shown on the front surface of the electric toothbrush illustrates the color black.
The features shown in broken lines in the drawings illustrate portions of the electric toothbrush in which the design is embodied that form no part of the claimed design.