The document discusses biomechanical considerations in removable partial denture design. It notes that the primary goal is to control potentially damaging forces applied to the supporting structures, including bone and soft tissues. It describes the three classes of levers that a partial denture can act as when subjected to intraoral forces. Class I levers are most efficient while Class III are least efficient. Factors like extension base length can generate greater damaging loads. Removable partial dentures that are tooth-supported transmit forces axially like fixed bridges, while tissue-supported designs can result in non-axial loading and greater potential for damage over time. Control of forces is important through factors like tissue health and component positioning.

1. BIOMECHANICAL
CONSIDERATIONS IN
REMOVABLE PARTIAL
DENTURE DESIGN
Presented by: Pooja Chaturvedi

2.  The ability of living things to tolerate force is
largely dependent upon the magnitude or intensity
of the force.
 The control of potentially damaging forces is the
primary goal of removable partial denture design.
 It is the bone that provides support for a
removable partial denture(i.e., the alveolar bone
by way of periodontal ligament and the residual
ridge bone through its soft tissues)
 If potentially destructive forces can be minimized
then the physiologic tolerance of the supporting
structures are not exceeded and pathologic
changes do not occur.

3. Principles Of Lever
 When subjected to intraoral forces, a
removable partial denture can perform the
actions of lever.
 A lever consists of a rigid bar, a fulcrum, an
object to be moved and an applied force.
 There are 3 classes of lever:

4. Most efficient type
First class lever

5. Less efficient
Second class lever

6. Least efficient
Third class lever

7. As a rule, the longer the extension base, the
greater the potential for damaging loads to be
generated on the opposite side of the fulcrum
line
L
E

8. Entirely Tooth Supported
Prosthesis
As the teeth occlude, the teeth are subjected
primarily to axial loading.
Support is gained entirely from the periodontal
ligaments of indivisual teeth.
Like a conventional fixed partial denture, a
class III RPD is entirely tooth supported.
As a result, forces are directed within the long
axes of the abutments and are transmitted to
the associated periodontal tissues.

10. Compared with an FPD, an RPD does not
connect its abutments as rigidly to one
another.
Therefore limited movement is possible, and
this movement can result in non-axial
loading of the abutment teeth during
function.

11. Combined Tooth-Tissue-
Supported Prosthesis
Classes I, II and IV
They are not completely tooth supported but
derive a varying degree of support from the
tissues of the residual ridge.

13. De van determined that the mucoperiosteum of
the residual ridge offers only 0.4% of the support
provided by the periodontal ligament, i.e, the soft
tissues are 250 times more diplaceable than the
adjacent teeth.

14. Although initial forces may be oriented
in the long axes of the abutments,
differences in the tooth and soft tissue
support eventually result in non-axial
loading.
This occurs as the prosthesis pivots on
the abutment closest to the extension
base.
This can result in potentially damaging
forces to the teeth and tissues anterior
to the posterior abutment teeth.

15. Therefore these forces must be controlled
through optimal tissue health, maximum
coverage of soft tissues, proper use of
direct retainers and placement of all
components in their most advantageous
position.