A direct retainer is any unit of a removable dental prothesis that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissues.There are two basic types of direct retainers,one is the intracoronal retainer,which engages vertical walls built into the crown of the abutment tooth to create frictional resistance to removal.The other type is the extracoronal retainer,like clasp-type retainer.It engages an external surface of the abutment tooth in an area cervical to the greatest convexity or in a depression created for that purpose.A flexible arm is forced to deform,or a spring device is compressed,thereby generating to removal.

    Clasp are flexible elements of partial denture,one part of which engeges the undercut portion of a tooth.There are two main types:occlusally approaching,where the clasp approaches the undercut from an occlusal direction and gingivally approaching,where the clasp approaches the undercut from a gingival diraction.