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>     3. Resist anterior-posterior stress.
     4. Splint natural teeth.
     5. Act as an indirect retainer.
     DIRECT RETAINERS
     Direct retention is effected by precision attachments or by clasps.
     Clasps
     A clasp is a metal component of a partial denture, which fits against the vertical enamel surface of a standing tooth, aiding in the bracing end retention of the appliance. Although it is necessary to retain partial dentures this is not the only factor to be considered in designing appliances intended to conserve the remaining mouth structures. The control of lateral load is of paramount importance and its distribution between standing teeth and ridges by means of clasp arms is one of the most successful methods of preserving the alveolar bone and the remaining teeth.
     PRECISION ANTACHMENTS
     These attachments are normally supplied to the 'dentist prefabricated by a manufacturer. They consist of two parts, commonly designated male and female, that are matched to interlock together. One of these parts is attached to the abutment tooth and the other to the saddle of the denture. Their function is to provide positive direct retention for a partial denture. In this respect they may prove more deficient than clasps, but the clinical situations in which they are used require careful assessment, and, although in all cases the patient' s standard of oral hygiene must be good, this factor is of even greater importance to the success for a precision attachment partial denture.
     Preskel has sensibly classified the type of precision attachments as follows:
     l. intracoronal
     2. extracoronal
     3. stud
     4. bar
     INDIRECT RETAINERS
     Although other factors participate, direct and indirect retainers largely effect resistance to the displacement of partial dentures. The principle of indirect retention can be discussed in relation to a Class I lower denture, having clasps and rests on the first premolars and the saddle connected by a lingual bar. When a displacing force acts on one of the saddles of this denture, either through the action of a sticky bolus 01 food or through muscular action at the periphery of the saddle when the mouth is widely opened, the denture tends to rotate about an axis in the vicinity of the clasped teeth. Consequently, ad the saddles rotate away from the ridge, the lingual bar moves downwards towards the floor of the mouth, If, however, resistance is offered to this downward movement of the lingual bar, a more stable appliance results and the principle of indirect retention is used.
     Indirect retention, therefore, resists occlusally displacing forces' acting' on the saddle of a denture by creating a resistance on the opposite side of the fulcrum axis to that on which the displacing force is applied. If a continuous clasp is incorporated in the design, when an occlusally displacing force acts on the saddles, the lingual bar can not rotate towards the floor of the mouth since the continuous clasp rests on the cingula of the standing teeth. Rotation is therefore prevented by a reaction is all t