This document discusses the biomechanics of removable partial dentures. It begins by defining biomechanics in prosthodontics as the application of mechanical principles to biological tissues to design a stable prosthesis. It then discusses various types of stresses acting on partial dentures, including vertical, horizontal, and torsional stresses. Key biomechanical considerations for partial denture design are the length of the edentulous span, quality of ridge support, clasp design, and occlusal harmony. The document also covers biomechanical principles such as the snowshoe principle, L-beam effect, and concepts of levers, inclined planes, and rotation. The goal is to understand how to distribute forces across tissues to maximize prosthesis stability

1. BIOMECHANICS OF REMOVABLE
PARTIAL DENTURES
Presented by
Dr R Padmini Rani
P.G trainee
Dept. of Prosthodontics

2. INTRODUCTION

3. • 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.
• GREAT CAUTION AND RESERVE ARE ESSENTIAL WHENEVER AN
ATTEMPT IS MADE TO INTERPRET BIOLOGICAL PHENOMENON BY
MATHEMATICAL COMPUTATION.
3

4. WHAT IS BIOMECHANICS IN PROSTHODONTICS?
• APPLICATION OF MECHANICAL PRINCIPLES ON BIOLOGICAL TISSUES WHILE
STUDYING THE BIOLOGY FROM A FUNCTIONAL VIEWPOINT AND THEN USING
THESE PRINCIPLES TO DESIGN A STABLE PROSTHESIS.
• AN APPLICATION OF THE PRINCIPLES OF ENGINEERING DESIGN AS
IMPLEMENTED IN LIVING ORGANISM –GPT 9

5. • OUR GOAL…
• PROVISION OF USEFUL, FUNCTIONAL RPD BY UNDERSTANDING HOW TO
MAXIMIZE EVERY OPPORTUNITY FOR PROVIDING AND MAINTAINING A STABLE
PROSTHESIS.
• IMPORTANT THAT THE STRESS DOESN’T EXCEED THE PHYSIOLOGICAL
TOLERANCE

6. BIOMECHANICS AND DESIGN SOLUTIONS
• DESIGNING A REMOVABLE PARTIAL DENTURE CAN BE CONSIDERED AS A
MULTIFACETED DESIGN PROBLEM IN CONVENTIONAL ENGINEERING, WHICH IS
CHARACTERIZED BY BEING OPEN ENDED AND ILL STRUCTURED.
Problems typically
have more than
one solution
Solutions are not the
result of standard
mathematical
formulas used in
some structured
manner.

7. IDENTIFYING A NEED
DEFINING THE PROBLEM
SETTING DESIGN OBJECTIVES
SEARCHING FOR BACKGROUND DATA
DEVELOPING DESIGN RATIONALE
EVALUATING ALTERNATIVE SOLUTIONS
PROVIDING SOLUTION

8. BIOMECHANICAL CONSIDERATIONS
• THE SUPPORTING STRUCTURES FOR REMOVABLE PARTIAL DENTURES
(ABUTMENT TEETH AND RESIDUAL RIDGES) ARE SUBJECTED TO FORCES AND
THEIR CAPABILITY TO RESISTANCE DEPENDS UPON
1. DIRECTION, DURATION, MAGNITUDE AND FREQUENCY OF THE STRESS
(FORCE) BEING APPLIED ONTO THE DENTURE AND DENTURE BEARING
AREAS
2. CAPACITY OF THESE AREAS TO RESIST THESE FORCES/STRESS
3. CHANGES DUE TO RESISTANCE OVER TIME
4. THE TYPE OF RESISTANCE GENERATED:
Tooth based
Tooth and Tissue
based

9. • CONSIDERATION OF THE FORCES INHERENT IN THE ORAL CAVITY IS CRITICAL!!
• THIS INCLUDES THE DIRECTION, DURATION, FREQUENCY, AND MAGNITUDE OF
THE FORCE.
• IN THE FINAL ANALYSIS, IT IS BONE THAT PROVIDES THE SUPPORT FOR A
REMOVABLE PROSTHESIS (I.E., THE ALVEOLAR BONE BY WAY OF THE
PERIODONTAL LIGAMENT AND THE RESIDUAL RIDGE BONE THROUGH ITS SOFT
TISSUE COVERING)
An appropriate design includes the selection and location
of components in conjunction with a harmonious occlusion

10. TYPES OF STRESS (FORCE) ACTING ON AN RPD WITHIN THE
ORAL CAVITY:
• THESE STRESSES CAN BE CLASSIFIED INTO:
• 1. VERTICAL –
• A) DISPLACING FORCE
• B) DISLODGING FORCE
• 2. HORIZONTAL
• 3. TORSION

12. DISPLACING
STRESSES :
• MOVEMENT OF THE SADDLE TOWARD THE TISSUES
PERIODONTAL LIGAMENT IS BETTER ABLE TO RESIST
MASTICATORY FORCES AS COMPARED TO RESIDUAL
RIDGE.
• THEREFORE, LATTER LIKELY TO GET THE LARGER
BRUNT OF LOAD THAN TOOTH. GRADUALLY WITH
PASSAGE OF TIME, RESORPTION OCCURS, ESPECIALLY
AT THE DISTAL END.
• THERE IS SINKING OF THE SADDLE AT THE DISTAL END,
WHICH MAY ULTIMATELY CONTRIBUTE TOWARDS
ROTATIONAL ACTION ALONG TRANSVERSE AXIS
These are the least
harmful and well
tolerated if within
physiologic limits

13. DISLODGING STRESSES
• THIS MEANS TOTAL LIFTING OF THE
SADDLE AWAY FROM THE BASE
RATHER THAN LIFT AT ONE END .
• THIS MAY BE THE CASE IN ANY TYPE
OF SADDLE.
• FUNDAMENTAL PRINCIPLE OF
PLACING THE RETAINING ELEMENT
NEARER TO THE SADDLE WILL RESIST
SUCH FORCES

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. • RESISTANCE TO STRESS CAN BE DIVIDED INTO:
• A) TOOTH BASED RESISTANCE CONTRIBUTES MAINLY TO RESISTING
HORIZONTAL STRESS (DIRECT RETAINERS)
• B) TOOTH-TISSUE BASED RESISTANCE CONTRIBUTES TO RESISTING VERTICAL
STRESS AND TORSION (MAJOR CONNECTORS AND INDIRECT RETAINERS)

16. FACTORS CONTRIBUTING TO THE AMOUNT OF STRESS
ON THE RPD: (STEWART’S CLINICAL REMOVABLE PROSTHODONTICS 4TH EDITION)
1. THE LENGTH OF EDENTULOUS SPAN
2. QUALITY OF RIDGE SUPPORT
3. QUALITY OF ORAL MUCOSA
4. CLASP DESIGN
5. OCCLUSAL HARMONY

17. LENGTH OF SPAN
• LONGER EDENTULOUS SPAN
• LONGER DENTURE BASE
• GREATER FORCE TRANSMITTED TO ABUTMENT TEETH
Every effort be made to retain a posterior abutment to avoid
class I and class II situation.

18. QUALITY OF SUPPORT OF RIDGE
• BETTER SUPPORT BY RIDGE LESS STRESS ON ABUTMENT
TEETH
• LARGE WELL FORMED RIDGES ABSORB GREATER
STRESS. LESS STRESS ON ABUTMENT
• BROAD RIDGES WITH PARALLEL SIDES LONGER FLANGES
ON THE DENTURE BASE STABILIZE THE DENTURE AGAINST
LATERAL FORCES.

19. TYPE OF MUCOSA
• INFLUENCES MAGNITUDE OF STRESSES TRANSMITTED TO ABUTMENT TEETH
.
• HEALTHY MUCOSA IS CAPABLE OF BEARING GREATER FUNCTIONAL LOADS
THAN THIN ATROPHIC MUCOSA
• SOFT, FLABBY, DISPLACEABLE MUCOSA CONTRIBUTE LITTLE TO VERTICAL
SUPPORT OF DENTURE ALLOWS EXCESSIVE MOVEMENT OF DENTURE
AND MORE STRESS TRANSMITTED TO ABUTMENT TEETH

20. CLASP AS A FACTOR IN STRESS
• MORE FLEXIBLE THE RETENTIVE ARM OF CLASP. LESS STRESS TO ABUTMENT
TOOTH
• BUT, FLEXIBLE CLASP ARM. PROVIDES LESS STABILITY AGAINST HORIZONTAL
FORCES. INCREASE STRESS ON RESIDUAL RIDGE.
• DECISION SHOULD BE MADE WHETHER ABUTMENT OR RIDGE REQUIRES MORE
PROTECTION

21. • IN EXAMINATION PHASE DECIDE WHETHER RIDGE OR ABUTMENT TOOTH
REQUIRE MORE PROTECTION
if periodontal support weak use
more flexible clasp like
combination clasp
If periodontal support good less
flexible clasp like vertical
projection clasp

22. TYPE ABUTMENT TOOTH SURFACE
• GOLD CROWN OFFERS MORE FRICTIONAL RESISTANCE TO CLASP ARM
MOVEMENT THAN DOES ENAMEL SURFACE OF TOOTH.
• GREATER STRESS EXERTED ON TOOTH RESTORED WITH CROWN THAN WITH
INTACT ENAMEL.

23. AMOUNT OF CLASP SURFACE IN CONTACT
WITH TOOTH
• GREATER THE AREA OF TOOTH TO METAL CONTACT BETWEEN CLASP AND
TOOTH
• MORE WILL BE STRESS EXERTED ON THE TOOTH.

24. OCCLUSION AS A FACTOR
DISHARMONIOUS OCCLUSION
GENERATE HORIZONTAL STRESSES
WHEN MAGNIFIED BY FACTOR OF LEVERAGE
CAN TRANSMIT DESTRUCTIVE FORCES TO BOTH ABUTMENT TEETH AND
RESIDUAL RIDGE.

25. TYPE OF OPPOSING OCCLUSION
• PLAY IMPORTANT ROLE IN DETERMINING AMOUNT OF STRESS GENERATED BY
OCCLUSION
NATURAL TEETH CAN EXERT CLOSING FORCE UPTO 300 POUNDS/INCH SQUARE,
WHEREAS, COMPLETE DENTURE UPTO 30 POUNDS/INCH SQUARE.
• THEREFORE RPD CONSTRUCTED AGAINST REMOVABLE PROSTHESIS IS
SUBJECTED TO MUCH LESS OCCLUSAL STRESS THAN ONE OPPOSED BY
NATURAL DENTITION.

26. AREA OF DENTURE BASE TO WHICH LOAD IS
APPLIED
• LESS MOVEMENT OF BASE IF LOAD APPLIED ADJACENT TO THE ABUTMENT
TOOTH THAN IF IT IS APPLIED TO THE DISTAL END OF THE BASE.
• MOVEMENT MAY BE 4 TIMES GREATER AT DISTAL END OF BASE THAN NEXT TO
THE CLASP.

27. SNOWSHOE PRINCIPLE
This principle is based
on distribution of
forces to as large an
area as possible.
Like in a snowshoe
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.

28. L BEAM EFFECT : THIS PRINCIPLE IS APPLICABLE TO THE ANTERO-
POSTERIOR PALATAL BAR OR STRAP MAJOR CONNECTOR.
• IN THIS COMPONENT THERE ARE TWO BARS /STRAP LYING PERPENDICULAR
TO EACH
OTHER. THE ANTERIOR AND
POSTERIOR BARS ARE JOINED
BY FLAT LONGITUDINAL ELEMENTS
ON EACH SIDE OF THE LATERAL
SLOPES OF THE PALATE.
THE TWO BARS LYING IN TWO DIFFERENT PLANES PRODUCE A STRUCTURALLY
STRONG L BEAM EFFECT THAT GIVES EXCELLENT RIGIDITY TO THE
PROSTHESIS.

29. • A TOOTH IS APPARENTLY BETTER ABLE TO TOLERATE VERTICALLY
DIRECTED FORCES THAN NONVERTICAL, TORQUEING OR HORIZONTAL
FORCES.
• AN ABUTMENT TOOTH WILL BETTER TOLERATE THESE NON-VERTICAL
FORCES , IF THE FORCES ARE APPLIED AS NEAR AS POSSIBLE TO THE
HORIZONTAL AXIS OF ROTATION OF THE ABUTMENT.
31

30. UNDERSTANDING OF SIMPLE MACHINES

31. • THROUGH UNDERSTANDING IF APPLIED TO THE DESIGN OF
REMOVABLE PARTIAL DENTURES HELPS TO ACCOMPLISH
THE OBJECTIVE OF PRESERVATION OF ORAL
STRUCTURES.
• MACHINES CAN BE CLASSIFIED AS
SIMPLE
COMPLEX

33. • MECHANICAL FORCE PRINCIPLES TO BE CONSIDERED WITHIN THE ORAL
CAVITY:
• 1. LEVER PRINCIPLE (FURTHER DIVIDED INTO ORDERS I, II AND III)
• 2. INCLINED PLANE PRINCIPLE
• 3. WHEEL AND AXLE (ROTATION)

36. LEVER
• A LEVER IS A RIGID BAR
SUPPORTED SOMEWHERE ALONG
ITS LENGTH
• IT MAY REST ON THE SUPPORT, OR
MAY BE SUPPORTED FROM ABOVE.
• THE SUPPORT POINT OF THE LEVER
IS CALLED THE FULCRUM, AND THE
LEVER CAN MOVE AROUND THE
FULCRUM.

37. • TYPES OF LEVER ACTION:
• THERE ARE 3 TYPES OF MECHANICAL LEVER
ACTION BASED ON:
1. THE POSITION OF THE FULCRUM
2. THE LOCATION OF THE LOAD ALONG THE
FULCRUM LINE.
3. THE AREA FROM WHICH THE EFFORT TO
DISPLACE IS EXERTED

39. • EXAMPLE OF 1ST ORDER LEVER ACTION IN
CANTILEVER TYPE OF REMOVABLE
PARTIAL DENTURE WHERE THERE IS
DISTAL EXTENSION.
• IF THERE IS BONE RESORPTION OF THE
RESIDUAL ALVEOLAR RIDGE UNDER THE
DISTAL EXTENSION, IT WILL RESULT IN AN
EFFORT LEADING TO FIRST ORDER LEVER
MOVEMENT ALONG THE FULCRUM LINE.

42. • EXAMPLE OF THIRD ORDER LEVER ACTION:
• USUALLY SEEN IN THE TOOTH SUPPORTED RPD.
• UPON CONSUMING STICKY FOOD, THE FOOD EXERTS PULLING EFFORT ON
THE PROSTHETIC TEETH WHILE THE NATURAL TEETH AND RETAINERS EXERT
COUNTERACTING FORCES FROM BOTH SIDES.

43. • INCLINED PLANE
FORCES AGAINST THE INCLINED
PLANE MAY RESULT IN DEFLECTION
OF THAT WHICH IS APPLYING THE
FORCE OR MAY RESULT IN
MOVEMENT TO THE INCLINED
PLANE, NEITHER OF THESE
RESULTS ARE DESIRABLE.
Inclined planes are not a factor when the
partial denture is tooth supported.

44. BIOMECHANICS OF
INCLINED PLANES:
• THE REST WILL ‘SLIP OFF’
THE INCLINED REST SEAT
• HOWEVER, FLATTENING
THE REST SEAT WILL AID IN
THE RETENTION OF THE
DIRECT RETAINER ON THE
TOOTH SURFACE AND
RESIST HORIZONTAL
FORCES

45. WHEEL AND AXLE
PRINCIPLE: (ROTATION)
THE PARTIAL DENTURE CAN ROTATE
ALONG ONE OF 3 PLANES:
A. THE SAGITTAL PLANE
B. THE FRONTAL PLANE
C. THE HORIZONTAL PLANE
AND ALONG ONE OF 3 AXES:
1. SAGITTAL AXIS
2. VERTICAL AXIS
3. HORIZONTAL AXIS.

47. • SAGITTAL PLANE:
• ROTATION AROUND THE
FULCRUM LINE PASSING
THROUGH THE MOST POSTERIOR
ABUTMENTS WHEN THE DENTURE
BASE MOVES VERTICALLY
TOWARD OR AWAY FROM THE
SUPPORTING RESIDUAL RIDGE
Rotational movement around
this fulcrum line or axis is of
the greatest magnitude of
that among the three
fulcrums but not necessarily
the most damaging

48. (GREATEST VECTOR IN APICAL
DIRECTION)
Force on abutment
mesio-apical or disto-apical

49. • COUNTERACTED BY:
• RIGIDITY OF MAJOR AND MINOR
CONNECTOR AND THEIR ABILITY
TO RESIST TORQUE.
• CLOSE ADAPTATION OF THE
DENTURE BASE ALONG THE
LATERAL SLOPES AND THE
BUCCAL SLOPES OF THE PALATE
AND RIDGE.
• DIRECT RETAINER DESIGN

50. a) DENTURE BASE MOVES AWAY FROM
SUPPORTING TISSUES:
Counteracted by:
direct retainer and indirect retainer

51. b) Denture base moves towards the
supporting tissues:
Counteracted by:
Occlusal rest
Tissues of supporting
ridge

52. • FRONTAL PLANE:
• ROTATION AROUND A
LONGITUDINAL AXIS FORMED BY
THE CREST OF THE RIDGE
• IT EXTENDS THROUGH THE
OCCLUSAL REST ON THE TERMINAL
ABUTMENT AND THE CREST OF
THE RESIDUAL RIDGE ON ONE SIDE
OF THE ARCH.

53. • IN A CLASS I SITUATION THERE WILL BE 2 OF THESE FULCRUMS,
ONE ON EACH SIDE OF THE ARCH.
• THIS FULCRUM CONTROLS ROTATIONAL MOVEMENTS OF THE
DENTURE- ROCKING, SIDE- TO- SIDE MOVEMENTS OVER THE
CREST OF THE RIDGE

54. • HORIZONTAL PLANE
ROTATION AROUND A VERTICAL
AXIS LOCATED NEAR THE
CENTER OF THE ARCH.
THE FULCRUM IS LOCATED IN
THE VICINITY OF THE MIDLINE
JUST LINGUAL TO THE ANTERIOR
TEETH. THIS FULCRUM LINE IS
VERTICAL, AND IT CONTROLS
THE ROTATIONAL MOVEMENT OF
THE DENTURE IN THE
HORIZONTAL PLANE OR THE FLAT
CIRCULAR MOVEMENTS OF THE
DENTURE

55. • STABILIZING COMPONENTS ON ONE SIDE OF THE
ARCH ACT TO STABILIZE THE PARTIAL DENTURE
AGAINST HORIZONTAL FORCES APPLIED FROM
THE OPPOSITE SIDE
It is resisted by stabilizing components, such as reciprocal clasp
arms and minor connectors that are in contact with vertical tooth
surfaces.

56. • HORIZONTAL FORCES ALWAYS WILL EXIST TO SOME DEGREE BECAUSE OF
LATERAL STRESSES OCCURRING DURING MASTICATION AND BRUXISM.
• THESE FORCES ARE ACCENTUATED BY THE FAILURE TO CONSIDER THE
ORIENTATION OF THE OCCLUSAL PLANE, THE INFLUENCE OF
MALPOSITIONED TEETH AND EFFECT OF ABNORMAL JAW RELATIONSHIPS.
• THE AMOUNT OF HORIZONTAL SHIFT OCCURRING IN THE PARTIAL DENTURE
WILL THEREFORE DEPEND ON THE MAGNITUDE OF LATERAL FORCES
APPLIED AND EFFECTIVENESS OF STABILIZING COMPONENTS.

57. BASIC PRINCIPLES OF RPD
CONSTRUCTION
FIRST EXPOUNDED BY A H SCHMIDT IN 1956
1. THE DENTIST MUST HAVE A THOROUGH KNOWLEDGE
OF BOTH THE MECHANICAL AND BIOLOGICAL
FACTORS INVOLVED IN RPD DESIGN
2. TREATMENT PLAN MUST BE BASED ON COMPLETE
EXAMINATION AND DIAGNOSIS OF THE INDIVIDUAL
PATIENT

58. 3. THE DENTIST MUST CORRELATE THE PERTINENT
FACTORS AND DETERMINE A PROPER PLAN OF
TREATMENT – HE ALONE CAN MODIFY THE
CONDITIONS IN THE MOUTH TO ENHANCE THE
SUCCESS OF THE TREATMENT
4. THE RPD SHOULD RESTORE THE FORM AND
FUNCTION WITHOUT INJURY TO THE REMAINING
ORAL STRUCTURE
5. “A REMOVABLE PARTIAL DENTURE IS A FORM OF
TREATMENT AND NOT A CURE”

59. PHILOSOPHY OF DESIGN
• THEY ARE IDEAS OF DENTISTS WHO BY EXTENSIVE CLINICAL
EXPERIENCE HAVE FORMULATED RULES BY WHICH THEY
PRODUCE A DESIGN.
• THE CHALLENGE IN DESIGN LIES PRIMARILY IN CLASS 1 AND 2
ARCHES AND TO SOME EXTENT IN THE CLASS 4 ARCHES.

60. • WHEN VERTICAL FORCES ARE APPLIED, ANY COMPRESSION THAT
OCCURS IS UNIFORM OVER THE ENTIRE SEAT.
• DIFFERENCE IN TRANSMISSION OF LOAD IS DUE TO DIFFERENCE IN
RESILIENCY OF PERIODONTAL LIGAMENT AND DENTURE BEARING
MUCOSA.
• THIS PROBLEM CAN BE TACKLED WITH
• STRESS EQUALIZATION
• PHYSIOLOGIC BASING
• BROAD STRESS DISTRIBUTION

61. ADVANTAGES
1. MINIMAL DIRECT RETENTION IS REQUIRED- AS DENTURE
BASE ACTS MORE INDEPENDENTLY.
2. HAS THE MASSAGING OR STIMULATING EFFECT ON THE
UNDERLYING BONE AND SOFT TISSUE, WHICH MINIMIZES
TISSUE CHANGE AND RESULTING REBASING
PROCEDURES.

62. DISADVANTAGES.
1. CONSTRUCTION OF STRESS DIRECTOR IS COMPLEX
AND COSTLY.
2. CONSTANT MAINTENANCE REQUIRED.
3. DIFFICULT OR IMPOSSIBLE TO REPAIR.
4. LATERAL MOVEMENTS OF BASE CAN LEAD TO RAPID
RESORPTION OF THE RIDGES.

63. PHYSIOLOGIC BASING
STRESS EQUALIZATION CAN BE BEST ACHIEVED BY EITHER
• DISPLACING OR DEPRESSING THE RIDGE MUCOSA
DURING THE IMPRESSION MAKING PROCEDURE
• OR BY RELINING THE DENTURE BASE AFTER IT HAS
BEEN CONSTRUCTED

64. STRESS EQUALIZATION
• RESILIENCY OF THE TOOTH SECURED
BY THE PERIODONTAL LIGAMENT IN
AN APICAL DIRECTION IS NOT
COMPARABLE TO THE GREATER
RESILIENCY AND DISPLACEABILITY OF
THE MUCOSA COVERING THE
EDENTULOUS RIDGE.

65.  THEREFORE , IT IS BELIEVED THAT A TYPE OF STRESS
EQUALIZER IS NEEDED TO REPLACE THE RIGID
CONNECTION BETWEEN DENTURE BASE AND DIRECT
RETAINER.
 MOST COMMON TYPE IS A HINGE DEVICE WHICH PERMITS
VERTICAL MOVEMENT OF THE DENTURE BASE, WHICH CAN
BE ADJUSTED TO CONTROL THE AMOUNT OF VERTICAL
MOVEMENT.

66. • THE TISSUE SURFACE IS RECORDED IN FUNCTIONAL FORM
AND NOT ANATOMIC FORM.
• RPD CONSTRUCTED FROM TISSUE DISPLACING IMPRESSION
WILL BE ABOVE THE PLANE OF OCCLUSION WHEN THE
DENTURE IS NOT IN FUNCTION.
• TO PERMIT VERTICAL MOVEMENT FROM REST POSITION TO
FUNCTIONAL POSITION THE RETENTIVE CLASPS HAVE TO HAVE
MINIMUM RETENTION AND ALSO THEIR NUMBER HAS TO BE
LESS.

67. BROAD STRESS DISTRIBUTION
• EXCESSIVE TRAUMA TO THE REMAINING TEETH AND
RESIDUAL RIDGE CAN BE PREVENTED BY DISTRIBUTING
THE FORCES OF OCCLUSION OVER AS MANY TEETH AND
AS MUCH OF THE AVAILABLE SOFT TISSUE AREA AS
POSSIBLE.
• ACHIEVED BY MEANS OF ADDITIONAL RESTS , INDIRECT
RETAINERS, CLASPS AND BROAD COVERAGE DENTURE
BASES.

68. STRATEGIC CLASP POSITIONING AS A MEANS OF STRESS CONTROL
• LEVERAGES CAN BE CONTROLLED TO A LARGE EXTENT BY MEANS OF CLASPS, IF
THERE ARE SUFFICIENT ABUTMENT TEETH AND THEY ARE STRATEGICALLY
DISTRIBUTED IN THE DENTAL ARCH.
IF NUMBER AND LOCATION OF POTENTIAL ABUTMENTS IS LESS THAN IDEAL
HARMFUL EFFECTS CAN BE DECREASED BY STRATEGIC PLACEMENT OF CLASPS.

69. • USE OF MESIAL RESTS INSTEAD OF DISTAL
RESTS, WHICH PERMITS MORE EVEN
DISTRIBUTION OF LOAD AND LESS STRESS
ON ABUTMENT TEETH.
• WITH THE USE OF A MO REST THERE IS AN
INCREASE IN LENGTH OF LEVER ARM,
WHICH MAKES ROTATIONAL ACTION MORE
VERTICAL IN GINGIVAL AREA OF ABUTMENT
TOOTH
• RPI SYSTEM IS ONE SUCH SYSTEM
DESIGNED
• TO INCORPORATE MO REST AND ALLOWS
VERTICAL ROTATION OF SADDLE TOWARDS
MUCOSA WITHOUT DAMAGING THE
SUPPORTING STRUCTURES OF ABUTMENT
TOOTH.

70. A) QUADRILATERAL CONFIGURATION
• WHEN 4 ABUTMENT TEETH
AVAILABLE FOR CLASPING
AND PARTIAL DENTURE
CONFINED WITHIN 4 CLASPS
 ALL LEVERAGES NEUTRALIZED.
• IDEAL (FOR SUPPORT AND LEVERAGE CONTROL)
• INDICATED MOST OFTEN IN
CLASS III ARCHES
(WITH MODIFICATION
SPACE ON OPPOSITE SIDE)

71. B) TRIPOD CONFIGURATION
CLASS II SITUATIONS
• DISTAL ABUTMENT ON ONE SIDE
OF ARCH MISSING
LEVERAGE CONTROLLED TO
SOME EXTENT BY CREATING
TRIPOD CONFIGURATION OF
CLASP PLACEMENT.

72. CLASS II WITH NO MODIFICATION SPACE
Separating two abutments on dentulous side as far as possible
largest possible area of denture will be enclosed in a triangle formed by
retentive clasps.

73. BILATERAL CONFIGURATION
For class I situations
• Not considered ideal,
but best option available
• Stress must be controlled
by other means.

74. STRESS BREAKERS/ STRESS DIRECTORS
GPT 9- A DEVICE OR SYSTEM THAT RELIEVES
SPECIFIC DENTAL STRUCTURES OF PART OR ALL OF
THE OCCLUSAL FORCES AND REDIRECTS THOSE
FORCES TO OTHER BEARING STRUCTURES OR
REGIONS.

75. IN DISTAL EXTENSION SITUATION
Rigid connection
between denture base
and retainers
stress on abutment
reduced by using
functional basing, broad
coverage, harmonious
occlusion and correct
choice of direct retainers
stress breaking
Allows independent movement
of the denture base and the
direct retainers.
Separates the action of the
retaining elements from the
movement of the denture base

76. • THE NEED FOR STRESS BREAKERS ON FREE END RPDS HAS BEEN
RECOGNIZED ON THE BASIS THAT THE RESILIENCY OR
DISPLACEABILITY OF THE MUCOSAL TISSUE RANGES BETWEEN 0.4
MM TO 2MM, WHILE THE VERTICAL RESILIENCY OF A NORMAL
HEALTHY TOOTH IN ITS SOCKET
IS APPROX. 0.1MM.
• THIS TISSUE RESILIENCY
DIFFERENTIAL OF 20 TO 40
TIMES THE AXIAL
DISPLACEABILITY OF A
NORMAL TOOTH IN ITS
SOCKET DICTATES THE NECESSITY FOR SOME FORM OF STRESS
DIRECTION IN THE PARTIAL DENTURE DESIGN.

77. TWO TYPES OF DESIGNS:
1) HINGE DESIGN:
BASE IS PERMITTED TO MOVE IN A VERTICAL PLANE ONLY. THE
HINGE TYPE DEVICE SPARES THE TOOTH VIRTUALLY ALL OF
THE STRESS WHICH RESULTS FROM VERTICAL MOVEMENT
OF THE BASE, BUT IT IS STILL SUBJECTED TO ALL THE
LATERAL LOADS AND TORSIONAL STRESS.
• EG: GERBER HINGE, DE HINGE TYPE.

78. 2) ROTATIONAL TYPE:
WORKS ON THE BALL AND SOCKET PRINCIPLE, MOVEMENTS OF THE BASE IS
ALLOWED IN ALL PLANES, AND THE TOOTH IS RELIEVED OF VIRTUALLY ALL
STRESSES.
• EG: CRISMANI, DALBO

79. INDICATION FOR THE USE OF STRESS BREAKER
Because the stress breaker does, in far relieve the
abutment tooth of the forces generated by the masticatory
load, the stress is then borne by the residual ridge.
Therefore a prime indication for the application of this
principle would be the mouth where in an abutment tooth
is inherently weak.

80. CONCLUSION

81. • WHEN PLANNING TREATMENT FOR PARTIALLY EDENTULOUS PATIENTS, THE
DENTIST IS CONFRONTED WITH MYRIAD COMBINATIONS OF EDENTULOUS
SPACES AND REMAINING TEETH.
• IT IS UP TO THE DENTIST TO UNDERSTAND THE FUNCTIONS OF PARTS AND TO
SELECT THE ONES THAT WILL COUNTER VARIOUS FORCES GENERATED
AROUND FULCRUM LINES BY LEVERS OR INCLINED PLANES.
• WHEN A PATIENT COMES, VIEW THE DIAGNOSTIC MODELS, OUTLINE THE
SADDLE AND TRY TO IMAGINE THE FORCES TO WHICH IT CAN BE SUBJECTED
AND MOVEMENTS IT CAN MAKE.
• AFTER THIS MAKE JUDICIOUS USE OF VARIOUS COMPONENTS WITHOUT
COMPLICATING THE DESIGN.

82. • JUST REMEMBER, YOU ARE TO PRESCRIBE AND LAB IS TO EXECUTE AND NOT
THE OPPOSITE.
• RPD IS A TERTIARY PREVENTION AID.
• WITHOUT MECHANICAL AND BIOLOGICAL CONSIDERATION, AN RPD CAN BE
AND OFTEN IS UNKNOWINGLY DESIGNED AS A DESTRUCTIVE MACHINE.

83. REFERENCES
• 1) MCCRACKEN’S REMOVABLE PARTIAL PROSTHODONTICS 11TH EDITION.
• 2) STEWART’S REMOVABLE PARTIAL PROSTHODONTICS 4TH EDITION.
• 3) REMOVABLE PARTIAL DENTURE DESIGN: A REVIEW AND A CHALLENGE
POTTER, ROBERT B. ET AL. JOURNAL OF PROSTHETIC DENTISTRY , VOLUME 17 ,
ISSUE 1 , 63 – 68
• 4) SINGLA S G, LAL J. REMOVABLE PARTIAL DENTURES DESIGNING: FORCES AS
PRIMARY CONCERN. J INDIAN PROSTHODONT SOC 2006;6:179-84
• 5) CONTEMPORARY PARTIAL DENTURE DESIGN MCCRACKEN, WILLIAM L.
JOURNAL OF PROSTHETIC DENTISTRY , VOLUME 92 , ISSUE 5 , 409 - 417