A delivery system for use in the oral cavity, the system comprising a carrier for a bioactive substance. The carrier has a surface comprising oxygen-binding sites (X), and at least one link comprising a pentose group and one or more additional sugar groups, the pentose group being bonded to one of said oxygen binding sites (X) and wherein one or more bioactive molecules (R) are bonded directly to one of the sugar groups of the at least one link or to one or more substituents on one or more sugar groups in the at least one link.