1. FORCES ACTING ON REMOVABLE PARTIAL DENTURES

1. 1- FORCES ACTING ON1- FORCES ACTING ON
REMOVABLE PARTIAL DENTURESREMOVABLE PARTIAL DENTURES

3. FORCES ACTING ON REMOVABLEFORCES ACTING ON REMOVABLE
PARTIAL DENTURESPARTIAL DENTURES
Dr. Amal Fathy KaddahDr. Amal Fathy Kaddah
Professor of Prosthodontic,Professor of Prosthodontic,
Faculty of Oral &DentalFaculty of Oral &Dental
Medicine, Cairo UniversityMedicine, Cairo University

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take immediate steps to correct it.

5. Consequences of loss of teeth andConsequences of loss of teeth and
distribution of forces in the oral cavitydistribution of forces in the oral cavity
Drifting, overeruption and inclination of the
teeth
disturbed occlusion and loss of vertical
dimension.
Disabilities associated with appearance.
Speech disabilities.
Reduction of masticatory efficiency.
Temporomandibular joint disorders.
Deviation of the mandible.

7. Tissue Supported
RPD
Tooth and Tissue Supported
RPD
Tooth Supported
RPD
The replacement
of missing teeth
and supporting
tissues with
prosthesis
designed to be
removed by the
wearer
Removable prosthodontics

8. Class ?????????Class ?????????
The third molar is missing and not to be
replaced.

9. Retention
Reciprocation
Support
Indirect Retention (Stabilization)
RPDRPD
REQUIREMENTSREQUIREMENTS
Bracing and Stabilization
A properly constructed partial denture must
achieve
All should be within the
physiological limits of the tissues
involved

11. • Forces acting on RPD and factors
that influence the magnitude of
stresses transmitted to the tissues.
Is the Planning of the form and extent
of RPD, after studying all the factors
involved
• Controlling the stresses by RPD
• Design concepts
Removable Partial Denture DesignRemovable Partial Denture Design
• Biomechanical aspect of RPD
design

12. * Mechanical ----- related to forces and
its application to object----- looseness
of teeth , bon resorption……etc
Removable Partial Denture DesignRemovable Partial Denture Design
• Biomechanical aspect of RPD design
* Bio ------ pertaining to
living systems-----
inflammation, Caries,
b. resorption….etc

13. FORCES ACTING ON
REMOVABLE
PARTIAL DENTURES

14. The magnitude and
intensity
The duration
The direction
The frequency
of these
forces
The Ability Of living tissues
To Tolerate Forces Is Largely Dependent Upon
Maxfield

15. Fibers of periodontal ligament are
arranged such that their resistance to
vertical forces is much greater
than that to horizontal
Tissues are adapted toTissues are adapted to
receive and absorb forcesreceive and absorb forces
within their physiologicalwithin their physiological
tolerancetolerance

16. Horizont
al or
lateral
forces
E

17. Class I Lever:
fulcrum: between E and R R X d1= E X d2
Direction of lever arm: E opposite R
Class I Lever:

18. Class II Lever: fulcrum at one end, Resistance R: More than E
Class II Lever:

19. Class I Lever:
fulcrum: between E and R
R
Free end
saddle
partial
denture
without
indirect
retention
1-
E

20. Class I Lever: fulcrum (F): between Effort (E)
and Resistance (R)
R X d1= E X d2
Direction of lever arm: E opposite R

21. Prevent
rotation of
the free
end saddle
around the
fulcrum
line
INDIRECT RETAINERSINDIRECT RETAINERS
Z
Class II Lever

22. Class II Lever: fulcrum at one end
Resistance R: More than E (force)
Direction of lever arm: the same at E and R

23. a beam supported
only at one end,
when force is
directed against
unsupported end
of beam
cantilever can act
as first class
2-

24. Aker Clasp

25. a- when force is directed against
unsupported end of beam
cantilever can act as first class
lever Torque on the
abutment tooth
F
b- A cantilever design allowsb- A cantilever design allows
excessive vertical movementexcessive vertical movement
toward the residual ridgetoward the residual ridge
a
b

26. Reverse Aker Clasp
F
Class ? Lever

27. Fencepost is more readily
removed by application of force
near its top than by applying
same force nearer ground level
in B- abutment has been contoured to
allow rather favorable location of
retentive and reciprocal arms.
A
B
3-

28. Class III Lever: fulcrum at one end
Resistance: less than E
Class III Lever:

29. Schematic diagram showing the
TMJ as a third –class lever

30. Class III Lever: fulcrum at one end
Sticky
food
X
F
R

31. POSSIBLE
MOVEMENTS OF THE
PARTIAL DENTURE

32. I- Tissue-ward movementsI- Tissue-ward movements
II- Tissue-away movementsII- Tissue-away movements
III- Horizontal movements:III- Horizontal movements:
A) Lateral movementsA) Lateral movements
B) Antero-posteriorB) Antero-posterior
movements.movements.
At least four possible
movements of the partial
dentures exist

33. I- Type of movementI- Type of movement
II- CausesII- Causes
III-III- Function of the partial denture
that resist this movement
IV- Components of PD that provideIV- Components of PD that provide
this functionthis function
Four possible movements of
PD

34. Vertical forces acting in
gingival direction tending to
move the denture towards
I- Tissue-ward movementsI- Tissue-ward movements
Control direction of force

35. • Mastication, swallowing and
aimless tooth contact, biting
forces.
They occur during
• P.D. should be designed to resist
this movement by providing
adequate supporting components
•This function of the partial denture is
called “Support”

36. • The Resistance to
Tissue Ward
Movement
Support
• Adequate Distribution of Forces Over the Supporting
Structure
• Transferring Occlusal
Stresses to the
Supporting Oral
Structures and
decrease forces / unit
area

37. • Adequate Distribution of Forces Over the
Supporting Sttructure
• Decrease forces/unit area
• The Resistance to Tissue Ward Movement

38. This Function Is Mainly Provided By:
Properly designed supporting
rests placed in rest seats,
which are prepared on the
abutment teeth,
Broad accurately fitting
denture bases in distal
extension partial dentures.
Rigid major
connectors that are
neither relieved from the
tissues nor placed on inclined
planes also provide support

39. Distribute the Forces Over the
Supporting Structure

40. Is the MMC play a role in support of
PD ????

41. LingualLingual
plateplate ????????????????????
Relieved?????
Inclined plane???????

42. II- Tissue-away movementsII- Tissue-away movements
Vertical forces acting in an occlusal direction
tending to displace and lift the denture from
its position

43. Tissue-away forces occur
due to
•This function of the partial denture is called
“Retention”
The action ofThe action of musclesmuscles acting along theacting along the
periphery of the dentureperiphery of the denture
GravityGravity acting on upper dentures or byacting on upper dentures or by
sticky foodsticky food adhering to the artificialadhering to the artificial
teeth or to the denture base.teeth or to the denture base.

44. Resistance to
movement of the
denture away from
its tissue
foundation
(resistance of a
denture to
dislodgment)
Retention

45. 1-Adhesion
2-Cohesion
3-Interfacial
s.t.
4-At. pressure
MechanicalMechanical
Retention
PhysiologicalPhysiologicalPhysica
l
-The physiologic
molding of the
tissues around
the polished
surfaces
- neuromuscular
• Direct retainers
• Indirect R.
• Frictional fit
• Parts of the
denture engaging
tooth and tissue
undercuts.

46. • Frictional
fit
Mechanical means ofMechanical means of
RetentionRetention
Indirect R.
Direct
retainers
Parts of the denture
engaging tooth and
tissue undercuts.
• Clasps
• Attachment
s

47. 1. Have less surface area.
2. Are bathed in saliva.
Lower major connectors are
relieved. contrary to upper m. c.
that are well adapted and their
borders are beaded against the
underlying tissues.
The effect of physical forces is less
applicable to lower dentures than upper
because:

48. This Function Is Mainly Provided By:
1-Mechanical Direct Retainers, Which
Engage Undercuts On Abutment Teeth
Attachment
s
2- physiologic forces on
polished surfaces of denture
bases
3- physical forces on fitting
surfaces of denture

49. RETENTIO
N
From:
• Direct Retainers
•Active I-Bars
• Indirect Retainers
•Rests on the other side of the
axis of rotation from the
extension base
Axis of Rotation
Axis of Rotation
Indirect retainer (rest)Indirect retainer (rest)
Extension BaseExtension Base
???

50. Horizontal movementsHorizontal movements
A) Lateral movementsA) Lateral movements
Horizontal forces developed when the
mandible moves from side to side during
function while the teeth are in contact
Lateral movements
have a destructive
effect on teeth leading
to tilting, breakdown of
the periodontal ligament
and looseness of
abutment teeth.

51. Bracing
Resistance
to Lateral
Movement
of the
Partial
Denture

52. This Function Is Mainly Provided By:
 Bracing clasp arms placed
at or above the survey line
of the tooth
 Minor connectors in contact
with axial (vertical) surfaces
of abutment teeth
 Proximal plates
 Adequate extension of the
flanges

55. Lateral movementLateral movement is resisted by:is resisted by:
Maximum extension and coverage of theMaximum extension and coverage of the
sides of the residual ridge with the denturesides of the residual ridge with the denture
base within the physiological limit.base within the physiological limit.
Rigid bracing clasp arms.Rigid bracing clasp arms.
Use of a continuous bar resting on theUse of a continuous bar resting on the
lingual surfaces of natural standing teethlingual surfaces of natural standing teeth
(Kennedy bar).(Kennedy bar).
Rigid major and minor connectorsRigid major and minor connectors
Reduction of cusp angle inclination of theReduction of cusp angle inclination of the
artificial teeth and balanced occlusion.artificial teeth and balanced occlusion.
Providing balanced occlusal contacts freeProviding balanced occlusal contacts free
of lateral interference
Bracing

56. HorizontalHorizontal
movementsmovements
B) Antero-posterior movementsB) Antero-posterior movements
Horizontal forces which occur
during forward and backward
movement of the mandible during
function while the teeth are in
contact
There is natural tendency for the
upper denture to move forward and

57. Forward movement of the upper denture could be resisted by:
Anterior natural teeth.
Palatal slope.
Maxillary tuberosity.
The natural teeth bounding the edentulous space.
The backward movement of the lower denture could be
resisted by:
The slope of the retromolar pad.
The natural teeth bounding the saddle area.
Proximal plates.
HorizontalHorizontal
movementsmovements
B) Antero-posterior movementsB) Antero-posterior movements

58. From:From:
• Guide platesGuide plates
• Bracing clasp armsBracing clasp arms
• Lingual platesLingual plates
• RestsRests
• Denture basesDenture bases
Active I-barActive I-bar
ReciprocationReciprocation
I-barI-bar
BRACING AND STABILITYBRACING AND STABILITY

60. Anterior-
posterior
movements
Side to side
movements

61. ReciprocationReciprocation
Nullifying the effect of pressure on one sideNullifying the effect of pressure on one side
of the teeth by application of pressure, equalof the teeth by application of pressure, equal
in amount, but in an opposite direction, on thein amount, but in an opposite direction, on the
opposite side of the teethopposite side of the teeth..
Retention
Palatal view
Proximal view
?

62. RECIPROCATIONRECIPROCATION can be achieved bycan be achieved by::
Reciprocal clasp arms contacting theReciprocal clasp arms contacting the
tooth prior to or at the same time thetooth prior to or at the same time the
retentive tip crosses the survey line of theretentive tip crosses the survey line of the
tooth.tooth.
Parts of the major connectors……..?????Parts of the major connectors……..?????
Proximal plates.Proximal plates.
Cross arch reciprocation should also beCross arch reciprocation should also be
provided.provided.
ReciprocationReciprocation

63. IV- Rotational movementsIV- Rotational movements
Rotational movements are due to
the variation in compressibility
of supporting structures, absence of
distal abutment at one end or more
ends of denture bases, and /or
absence of occlusal rests or
clasps beyond the fulcrum line.

64. 1-Rotation of the extension
denture base around transverse
fulcrum axis:
A) Rotation of the denture base
towards the ridge around the
fulcrum axis joining the two main
occlusal rests
B) Rotation of the denture base
away from the ridge around the
fulcrum axis joining the two main
occlusal rests

65. A) Rotation of the denture base
towards the ridge around the
fulcrum axis joining the two main
occlusal rests
?

66. B) Rotation of the denture base away
from the ridge around the fulcrum
axis joining the two main occlusal
rests

67. Components of
RPD That Are
Used to Reduces
the Tendency the
Denture to Rotate
in an Occlusal
Direction About
the Fulcrum Axis
Indirect Retention

68. 2-Rotation of all bases around a
longitudinal axis parallel to the crest of
the residual ridge

69. F
3-Rotation about an imaginary
perpendicular axis

70. Stabilization
Is the Resistance of Partial Denture to Tipping
(Rocking torsional forcestorsional forces)

72. This movement is
counteracted by:
 Providing adequate bracing
 A rigid major connector
 Broad base coverage
 Balanced contact between upper and
lower teeth and reduction of cusp slope..
 The use of additional rests on teeth otherThe use of additional rests on teeth other
than the abutment tooth serves as,than the abutment tooth serves as,
indirect retainers.indirect retainers.
 Coverage of the sloping part of the palateCoverage of the sloping part of the palate
ant. (rugea area) acts as an indirect ret.ant. (rugea area) acts as an indirect ret.

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