A molding element for a mold for vulcanizing a tread of a tire, comprising a base able to mold part of the tread surface of the tread and a bar able to mold a groove in the tread, the bar comprising two lateral faces extending along its length and projecting from the base and an upper face connecting the lateral faces. The molding element comprises a contact edge formed by the base and the bar, intended to come into contact with another molding element to form all or part of the vulcanizing mold, and further comprising at least one recess in the bar, which opens onto one of the lateral faces and onto the contact edge, but does not open onto the upper face of the bar.