Direct versus Indirect Retainers
Posted on 11/29/2011
Before we begin our discussion of various retentive arm designs, there is one important categorical distinction that has not been properly addressed hitherto: the definition of direct retainer versus indirect retainer.
Direct Retainer: We will refer to the direct retainer as a clasp assembly; that is a retentive element that includes a rest, a clasp and perhaps a guide plates but that touches any abutment tooth at three distinct points.
Indirect Retainers: Conversely, an indirect retainer is simply a rest that protrudes from the major connector. Examples of indirect retainers are cingulum rests or occlusal rests. The purpose of the indirect retainer is to provide for additional support in preventing dislodgement. Generally, the indirect retainer is placed anterior to the direct retainer. Anterior placement offers numerous advantages including:
1) Aiding greater efficiency of the direct retainer
2) Acting as vertical stops for the anterior portion of the framework and thereby preventing food from causing the major connector to place pressure on soft tissues.
There are some specific constraints to utilizing direct retainers - chiefly occlusal clearance concerns. As such, indirect retainers are typically placed in the mesio-occlusal fossa of the premolars or the cingula of the canines.
Direct Retainer: We will refer to the direct retainer as a clasp assembly; that is a retentive element that includes a rest, a clasp and perhaps a guide plates but that touches any abutment tooth at three distinct points.
Indirect Retainers: Conversely, an indirect retainer is simply a rest that protrudes from the major connector. Examples of indirect retainers are cingulum rests or occlusal rests. The purpose of the indirect retainer is to provide for additional support in preventing dislodgement. Generally, the indirect retainer is placed anterior to the direct retainer. Anterior placement offers numerous advantages including:
1) Aiding greater efficiency of the direct retainer
2) Acting as vertical stops for the anterior portion of the framework and thereby preventing food from causing the major connector to place pressure on soft tissues.
There are some specific constraints to utilizing direct retainers - chiefly occlusal clearance concerns. As such, indirect retainers are typically placed in the mesio-occlusal fossa of the premolars or the cingula of the canines.