Possible movements of an RPD

By Dr.Swathi Pai on Saturday, January 17, 2009 with 0 comments

  1. Rotation about an axis through the most posterior abutments

-the axis, known as the fulcrum line, is the center of rotation as the distal extension base moves toward the supporting tissues when an occlusal load is applied.

-the axis of rotation shifts to anteriorly placed elements, occlusal or incisal to the height of contour of the abutment, as the base moves away from the supporting tissues when vertical dislodging forces become effective.

-we would rather see rotation vice displacement of the RPD.

-movement of the base in the opposite direction is resisted by the action of the retentive clasp arms on terminal abutments in conjunction with seated, vertical support elements of the framework anterior to the terminal abutments acting as indirect retainers.

-this movement is non-existent in a tooth-borne partial

  1. The second movement is rotation about a longitudinal axis as the distal extension base moves in a rotary direction about the residual ridge.

-this movement is resisted by the rigidity of the major connector and its ability to resist torque.

  1. A third movement is rotation about an imaginary vertical axis located near the center of the dental arch.

Stabilizing components, such as reciprocal clasp arms and minor connectors, which are in contact with vertical tooth surfaces, resists this.

So, in a tooth-borne partial, movement of the base toward the edentulous ridge is prevented primarily by rests on the abutment teeth and to some degree by any rigid portion of the framework located occlusal to the height of contour. Movement away from the edentulous ridge is prevented by the action of direct retainers on the abutments, situated at each end of each edentulous space.

Category: Prosthodontics Notes



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