a short presentation on the biomechanics in Removable Partial Denture.... a very important topic to be understood completely for easy designing of cast framework and also to know the problems in already treated conditions

1. Biomechanics of
Removable partial
denture

2. INTRODUCTION

Biomechanics basically deals with application of
mechanical principles to biological tissues. In the oral
cavity one would find a number of sources of stress
generation, the human body is built in such a manner
that it learns to adapt to any stressful situation.
However when we try to create an artificial
replacement of that natural component which is lost,
we are at a loss in making it fully functional and
adaptable.

3. 
Biomechanics (GPT 7):

1: the application of mechanical laws to living
structures, specifically the locomotor systems of the
body.

2: the study of biology from the functional viewpoint.

3: An application of the principles of engineering
design as implemented in living organisms.

4. Mechanical principles applicable in Removable
Prosthodontics
− Lever principle
− Inclined plane
− Snowshoe principle

5. Lever: A simple machine consisting of a rigid
bar pivoted on a fixed point and used to
transmit force, as in raising or moving a
weight at one end by pushing down on the
other.

6. Lever
Class I

7. Class II

8. Class III

9. Inclined plane

Inclined plane
Forces against an inclined
plane may result in
deflection of that which is
applying the forces or may
result in movement to the
inclined plane, neither of
these is desirable.

10. Snowshoe principle
 This principle is based on distribution of forces to as large an area as
possible. Like in a snow shoe which is designed to distribute forces on
the entire base area of the shoe, a partial denture should cover
maximum area possible within the physiologic limits so as to
distribute the forces over a larger area.

11. Stress consideration in a
partial denture

The stresses can be divided as:
− Vertical
1.Displacing stresses
2. Dislodging stresses
− Horizontal
− Torsional

12. Displacing stress
− Those forces which are the result of stresses along the long
axis of the teeth in a crown to apex direction and the
relatively vertical stresses on the ridge mucosa. These are
the least harmful and are born well if within physiologic
limits.

13. Dislodging stress
− These are the forces which tend to lift the partial denture from its
rest position. Reciprocal dislodging action occurs when wide
edentulous spaces are interrupted by few teeth thus inviting an
antero-posterior or lateral tilt of prosthesis.

14. Horizontal stress
− They originate as a component of rhythmic chewing
stroke. These forces are effective in mesio-distal and
buccolingual direction. These lateral stresses are most
damaging.

15. Torsional stress
− It is a twisting rotational type of force. It’s a combination of
vertical and horizontal force. Torsion is noted most frequently
where a long segment acts upon the first abutment it engages.
Where the ridge mucosa has higher resiliency torque is higher.
Torque applies rotation about a fixed point.

16. Biomechanical consideration
of individual component
“Perpetual preservation of
what is remaining is more
important than meticulous
replacement of what is lost”
De Van

17. Major connector
− Connects parts of prosthesis located on one side
of the arch with those on the opposite side
− Should be rigid:
− Distribution of force
− Effectiveness of other components
− If flexible forces concentrated on individual teeth or
ridge damaging.

18. Direct retainer

20. Rest
Relation between rest and
abutment should be such
that forces should be
directed apically down
along the long axis of the
tooth Stress absorbed by
fibers of PDL without
getting damaged.

21. Indirect retainer
To prevent the DEB from
moving away from its seat
because of cheek and
tongue forces, sticky food.
It uses mechanical
advantage of leverage by
moving the fulcrum line
farther from the force.

22. Contributes to support and
stability of the partial denture
counteracts horizontal forces
applied to the denture. Long
span mandibular lingual bar
major connector (even if
tooth supported), IR provides
additional support and rigidity
for lingual bar. Prevents
impingement of the lingual
bar on the mucosa during
function.

23. Factors influencing
magnitude of stress

24. Length of span

25. Quality of ridge

26. Type of mucosa

27. Clasp type

28. Clasp design

29. Amount of tooth contact

30. Occlusion

31. Control stress by design
consideration

32. 1. Retention as a means of stress control
A) forces of adhesion and cohesion
B) atmospheric pressure
C) Frictional contact
D) Neuromuscular control

33. 
Strategic clasp positioning
a) Quadrilateral configuration
b) Tripod configuration
c) Bilateral configuration

34. 
Clasp design
a) circumferential clasp
b) bar clasp
c) combination clasp

35. 4 Indirect retention
5 Functional basing
6 occlusion
a) harmonious occlusion
b) size of food table
c) occlusal pattern of posterior teeth

36. 7 Denture base
a) Size & configuration
b) accuracy of adaptation of base to
the tissues

37. Removable partial dentures by design are intended
to be removed from and replaced into the mouth.
Because of this, they are not rigidly connected to
the teeth or tissues, which means that they are
subjected to movement in response to functional
loads. These movement can cause generation of
stresses which if not controlled , can damage the
remaining teeth and supporting bone.Efforts must
be always directed towards minimizing the
harmful forces on the remaining teeth by proper
designing of the RPD.

38. THANK YOU