Direct Retainers

Direct Retainer

Any unit of a removable dental prosthesis that engages an abutment tooth or implant to resist displacement of the prosthesis away from the basal seat tissue. 

Circumferential/Suprabulge Direct Retainers (Akers Clasp) - Vertical Projection / Bar Type / Infrabulge Retainers (Roach Clasp)

2 Basic Categories of Retentive Clasp Assemblies.

Rest

Provides vertical support for the prostheses.

Rest

Transmits functional forces parallel to the long axis of the abutment. 

Retentive Arm

Contacts the surface of the abutment apical to the height of contour.

Suprabulge Clasp Arm - Infrabulge Clasp Arm

2 types of retentive arm.

Retention

Resists forces that act to dislodge the components AWAY from the supporting tissues.

Terminus

Only the clasp ________ of the retentive arm must engage the prescribed undercut.

Increases

Clasp flexibility increases as clasp length _________. 

Decreases

Clasp flexibility increases as cross sectional dimensions _________.

Omnidirectional - Bidirectional

A circular cross-sectional clasp form impacts ________________ flexure, while a half-round form allows only _____________ flexure. 

Reduces

Curvature of a clasp in more than one spatial plane ______ the clasp's flexibility.

Support

Quality of clasp assembly that resists displacement of a prosthesis in an apical direction. 

Stability

Quality of a clasp assembly that resists displacement of a prosthesis in a horizontal direction.

Reciprocation

Quality of clasp assembly that counteracts lateral displacement of an abutment when the retentive clasp terminus passes over the height of contour.

Encirclement

Prevents movement of the abutment away from the clasp assembly. 

Passivity

Prevents transmission of adverse forces to the abutment when prosthesis is completely seated. 

Cast Circumferential Clasp

Design of choice for tooth-supported RPD. 

Simple Circlet Design

(Design) From proximal surface of abutment adjacent to the edentulous area. 

Simple Circlet Design

Retentive arm terminus engages an undercut remote from the edentulous space. 

Reverse Circlet Design

May be used when the available undercut is at the facial or lingual line angle adjacent to the edentulous space.

Reverse Circlet Design

May help control stresses transmitted to an abutment during the functional movement of prosthesis in Kennedy Class I and II cases.

Embrasure Clasp Design

Two simple circlets joined at the bodies.

Embrasure Clasp Design

(Design) Requires adequate preparation of the marginal ridges and adjacent facial inclines. 

Ring Clasp Design

(Design) Indicated for tipped mandibular molar. 

Wrought Wire Circumferential Clasp

(Design) Beneficial for caries prone individuals.

Wrought Wire Circumferential Design

(Design) May be used for maxillary canine and premolar abutments for a more esthetic result. 

Apically

(Infrabulge) Clasp terminus must be located as far _______ on the abutment as is practical.

T-Clasp

Used in Kennedy Class I and II when an undercut is located adjacent to the edentulous area. 

I-clasp Design

(Design) Gradual, uniform taper throughout its length. Used in conjunction with a mesial rest. 

Mesial

The most posterior rests are placed on the ______ surfaces of the abutment. 

Mesial

Mesial rests direct tipping forces toward the ______. This provides a "buttressing" effect.

Proximal Plate

Guiding planes. From the marginal ridge to the junction of middle and gingival thirds of the abutment.