The ornamental design for a refillhead for an oral care implement, as shown and described.
FIG. 1 is a front right perspective view of a refill head for an oral care implement according to the new design;
FIG. 2 is a rear left perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof,
FIG. 6 is a left side view thereof;
FIG. 7 is an enlarged top view thereof; and,
FIG. 8 is an enlarged bottom view thereof.
The broken lines formed by even length segments illustrate portions of the refill head for an oral care implement that form no part of the claimed design. The broken lines formed by dash-dot-dash segments define a boundary of the claimed design.