The design consists of the features of shape and ornament of the toothbrush head component shown in the drawings. The head portion of the toothbrush including an oval platform having a connecting surface facing the neck portion and a supporting surface supporting a cylindrical projection standing near a center portion of the platform, a plurality of bristles arranged in spaced cylindrical columns encircling the cylindrical projection, a plurality of additional bristles arranged in spaced elongated columns near a distal end of the head portion away from the neck portion, and a plurality of further bristles arranged in spaced elongated columns near a proximal end of the head portion closer to the neck portion. The cylindrical projection is provided with a plurality of spaced, radially inwardly extending fins.In the design shown in Figures 1-6, the elongated columns of bristles near the distal end and the proximal end of the head portion are taller than the cylindrical columns of bristles next to the elongated columns of bristles, which, in turn, are taller than the remaining cylindrical columns of bristles, which are taller than the cylindrical projection.In the variant shown in Figures 7-12, the elongated columns of bristles near the distal end are taller than the cylindrical columns of bristles next to the elongated columns of bristles near the distal end, which, in turn, are taller than the remaining cylindrical columns of bristles and the elongated columns of bristles opposite the free end, which are taller than the cylindrical projection.Drawings of the design are included, in which:Figure 1 is a perspective view of a toothbrush head component as seen from the top, front and left sides wherein the stippled lines illustrate part of the article but do not form part of the claimed design;Figure 2 is a top plan view thereof;Figure 3 is a left side elevational view thereof, the right side elevational view being a mirror image;Figure 4 is a bottom plan view thereof;Figure 5 is a front elevational view thereof;Figure 6 is a rear elevational view thereof;Figure 7 is a perspective view of a variant of the toothbrush head component as shown in Figure 1 as seen from the top, front and left sides wherein the stippled lines illustrate part of the article but do not form part of the claimed design;Figure 8 is a top plan view thereof;Figure 9 is a left side elevational view thereof, the right side elevational view being a mirror image;Figure 10 is a bottom plan view thereof;Figure 11 is a front elevational view thereof; andFigure 12 is a rear elevational view thereof.