This document discusses the biomechanics of removable partial dentures. It explains that biomechanics is the study of internal and external forces on living bodies, including dentures. Removable partial dentures are subject to internal forces like retention, muscle movement, and saliva, as well as external forces such as gravity. The document discusses how different types of partial dentures resist various movements like horizontal, vertical, and rotational forces. Factors that determine whether supporting tissues can resist applied forces are also outlined.

1. Dr Muhammad Shakeel Akram
Khawaja

2. BIOMECHANICS
Study of internal and external forces on the living body

3. Biomechanics of rpd
 Study of internal and external forces on dentures
 How the prosthesis reacts under such forces
 How to counter them

4.  Inetrnal forces:
 Retention by peripheral seal
 Muscle movement
 Salivary action
 External forces:
 Gravity

5. A tooth is better able to tolerate vertically
directed forces than non-vertical, torquing, or horizontal
forces.

6. In the tooth-supported denture, the only movements of
any significance are horizontal, and these may be resisted
by the stabilizing effects of components i.e. retainers
placed on the axial surfaces of the abutments.

7. In contrast, all Class I and Class II partial dentures,
which have one or more distal extension bases, are not
totally tooth supported

8.  Movement is a factor in distal extension bases

9. Whether the supporting structures
are capable of resisting the applied forces depends on
(1)what typical forces require resistance
(2) what duration and intensity these forces have
(3) what capacity the teeth and/or mucosa have to resist
these forces,
(4) how material use and application influence this teeth-
tissue resistance
(5)whether resistance changes over time

17. Possible Movements of
Partial Dentures (relative to diff.
planes)

18. Concept of stress distribution,
Cross arch stabilization
 Effort arm vs Resistance arm
 Archimedes statement:???

21. For a prosthesis that is capable of movement in three
planes,occlusal rests should provide occlusal support
only to resist tissue-ward movement. All other
movements of the partial denture should be resisted by
specific individual components other than occlusal rests.

24. VERTICAL/ TISSUE-WARD MOVEMENT of the
denture base is resisted by :
1)the tissue of the residual ridge in proportion to the
supporting quality of that tissue
2)the accuracy of the fit of the denture
base
3)the total amount of occlusal load applied.

25. HORIZONTAL MOVEMENT occurring in the partial
denture therefore depends on the magnitude of the
lateral forces that are applied and on the effectiveness of
the stabilizing components.

26. ROTATION about a longitudinal axis Frontal plane is
resisted by The rigidity of the major and minor
connectors and their ability to resist torque.
If the connectors are not
rigid, or if a stress-breaker exists between the distal
extension base and the major connector, this rotation
about a longitudinal axis applies undue stress to the sides
of the supporting ridge or causes horizontal shifting of
the denture base

28. ROTATION ABOUT AN IMAGINARY VERTICAL AXIS
located near the center of the dental arch:
This movement occurs under function because diagonal
and horizontal occlusal forces are brought to bear on the
partial denture.
It is resisted by stabilizing components, such as
reciprocal clasp arms and minor connectors that are in
contact with vertical tooth surfaces.
Such stabilizing components are essential to any partial
denture design, regardless of the manner of support and
the type of direct retention employed.
Stabilizing components on one side of the arch act to
stabilize the partial denture against horizontal forces
applied from the opposite side. It is obvious that rigid
connectors must be used to make this effect possible.

30. Impact of Implants on Movements of
Partial Dentures
 The purpose of using implants or mini implants is to
minimize rotational effects in long span saddle cases
and to convert such a scenario into fixed case i.e. tooth
supported case
 Implant supported “OVER DENTURE” OR Tooth-
Implant supported “bridge”

31. Tissue supported prosthesis