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GOOD MORNING
Principles of Removable Partial
Dentures with special emphasis on
support and periodontal
consideration of remaining teeth...
CONTENTS
1) Introduction
2) Principles of desining
3) Stress considerations
4) Forces influencing the magnitude of stress
...
• INTRODUCTION
INDICATION FOR REMOVABLE PARTIAL
DENTURES
Stewart’s Clinical removable partial Prosthodontics 4th edition pg-8
1.Long stan...
INDICATION FOR REMOVABLE PARTIAL
DENTURES continued
Stewart’s Clinical removable partail prosthodontics 4th edition pg-8
5...
INDICATION FOR REMOVABLE PARTIAL
DENTURES continued
8) Immediate need to
replace extracted teeth
9) Patient desire
10)Unfa...
PRINCIPLES OF DESIGN
• 1953,Dr.A.H.Schmidt gave the basic principles
of designing
1.Dentist should have thorough knowledge...
3.Dentist must correlate the pertinent factors and
determine a proper treatment plan
4.RPD should restore the function wit...
STRESS CONSIDERATION IN A PARTIAL
DENTURE
The stresses can be divided as:
 Vertical
 Horizontal
 Torsional
Displacing s...
VERTICAL STRESS
Displacing stresses :
These are the least harmful and are borne well if within
physiologic limits
DISLODGING STRESSES :
These are the forces which tend to lift the partial denture
from it’s rest position
HORIZONTAL STRESS
They originate as a component of rhythmic chewing
stroke. These forces are effective in mesio-distal
and...
TORSIONAL STRESS
It is a twisting rotational type of force. It’s a
combination of vertical and horizontal force
FORCES ACTING ON
PARTIAL DENTURE
McCracken’s Removable Partial Prosthodontics 11th edition
Is a rigid bar supported
somewhere along its
length..
The point ...
CLASS I LEVER
Fulcrum lies in the centre,
Resistance is at one
end and force at the other.
McCracken’s Removable Partial P...
CLASS II LEVER
Fulcrum is at one end effort
at the opposite end and
resistance in the centre.
McCracken’s Removable Partia...
CLASS III LEVER
Fulcrum is at one end,
resistance at opposite
end and effort is in the centre.
McCracken’s Removable Parti...
INCLINED PLANE
• Forces against an inclined plane may result in
deflection of that which is applying the forces or
may res...
FULCRUM ON HORIZONTAL PLANE:
• Extends through the rest of principle abutments.
• Rotational movement of the denture in th...
DENTURE BASE MOVES AWAY FROM
SUPPORTING TISSUES:
Counteracted by:
Direct retainer
and
Indirect retainer
McCracken’s Remova...
DENTURE BASE MOVES TOWARDS THE
SUPPORTING TISSUES:
Counteracted by:
1) Occlusal rest.
2) Tissues of
supporting
ridge
McCra...
FULCRUM ON THE SAGITTAL PLANE
Extends through the occlusal rest on the terminal
abutment and along the crest of the ridge....
Counteracted by:
• Rigidity of major and
minor connector and
their ability to resist
torque.
• Close adaptation of the
den...
FULCRUM LOCATED IN MIDLINE JUST
LINGUAL TO THE ANTERIOR TEETH
(FULCRUM IS VERTICAL)
Rotational movement of denture in hori...
Counteracted by :
• Stabilizing components
(reciprocal arm and
minor connector)
• Rigid major connector
• Close adaptation...
FACTORS INFLUENCING MAGNITUDE
OF STRESSES TRANSMITTED TO
ABUTMENT TEETH
1. Quality of support of ridge
Form of residual ri...
4. Occlusion
Type of teeth
Harmony of occlusion
5. Areas of the base to which load is applied
Stewart’s clinical Removable...
1. QUALITY OF SUPPORT OF RIDGE
• Better support by ridge less stress on abutment
teeth
• Large well formed ridges absorb...
b. TYPE OF MUCOSA
• Influences magnitude of stresses transmitted to abutment
teeth.
• Healthy mucosa capable
of bearing g...
2. LENGTH OF SPAN
• Longer edentulous span
longer denture base
greater force transmitted to
abutment teeth
• Every effort ...
3. CLASPAS A FACTOR IN STRESS
• More flexible the retentive arm of claspless
stress to abutment tooth
• But, flexible cla...
In examination phase decide whether ridge or abutment
tooth require more protection
If periodontal
support good
less flexi...
TYPE ABUTMENT TOOTH SURFACE
• Surface if gold crown offers more frictional
resistance to clasp arm movement than does
enam...
AMOUNT OF CLASP SURFACE IN CONTACT
WITH TOOTH
Greater the area of tooth to metal contact between
clasp and tooth
more will...
OCCLUSION AS A FACTOR
Disharmonious occlusion
generate horizontal stresses
when magnified by factor of leverage
can transm...
TYPE OF OPPOSING OCCLUSION
• Play important role in determining amount of stress
generated by occlusion
• Natural teeth c...
• AREA OF DENTURE BASE TO WHICH LOAD
IS APPLIED
• Less movement of base if load applied adjacent to the
abutment tooth tha...
BIOMECHANICAL
CONSIDERATION OF
INDIVIDUAL COMPONENT
REST
Two basic
types
Primary rest
Secondary rest
DIFERENT TYPES OF RESTS
1) Occlusal rest
2) Extended occlusal rest
3) Inc...
REST
FUNCTIONS
• Provide vertical support for the partial denture.
• Maintains components in planned positions.
• Maintain...
OCCLUSAL REST
McCracken’s Removable Partial Prosthodontics 11th edition
If angle greater than 90 degrees
Forces not along long axis
but will create an inclined
plane effect
Slippage of prosthesi...
CINGULUM REST VS INCISAL REST
Cingulum rest nearer to center
of rotation
less tipping of tooth
Incisal rest
Longer minor c...
MESIAL REST or DISTAL REST FOR DEB
RPD???
Kratochvil et al (JPD 1963:13;114)
• Suggested using mesial occlusal rest so that the force
delivered to the mesial aspect...
John W. Mc Cartney (JPD 1980;43:15)
Did a study on the effect of location of occlusal rest
on abutment tooth movement and ...
A major connector is the
component of the partial
denture that connects the
parts of the prosthesis
located on one side o...
DESIRABLE CHARACTERISTICS OF MAJOR
CONNECTORS
1.Should be rigid
2.Provide vertical support and protect the soft tissue.
3....
MINOR CONNECTOR
1.Primary function is to join
other units of the prosthesis
such as clasp,rests,indirect
retainers and den...
DESIGN CONSIDERATIONS
1.Should have sufficient bulk to be rigid
2. Should be made thick buccolingually and thin
mesiodista...
Any unit of
removable dental
prosthesis that engages
an abutment tooth in
such a manner as to
resist displacement of
the p...
• Prothero Cone theory as basis
of clasp retention
• Described shape of crowns of
premolar and molar teeth as 2
cones sha...
• Height of contour of tooth changes as the vertical
position of tooth changes.
• Surface is retentive if it is cervical t...
• Clasp tip in infrabulge area resist the
movement in occlusal direction because to
release from tooth  it has to underg...
STRATEGIC CLASP POSITIONING AS A
MEANS OF STRESS CONTROL
• Leverages can be controlled to a large extent
by means of clasp...
• Indicated most often in class III arches (with
modification space on opposite side)
QUADRILATERAL CONFIGURATION
McCracke...
TRIPOD CONFIGURATION
Class II situations
Distal abutment on one
side of arch missing
leverage controlled to
some extent b...
BILATERAL CONFIGURATION
For class I situations
Not considered ideal, but best
option available
Stress must be controlled b...
REQUIREMENTS OF CLASP
DESIGN
:
• Retention:provided by retentive terminal
• Support:mainly by rest
• Stability:all the com...
CLASP DESIGNS:
• Combination clasp
• Reverse circlet clasp
• Bar clasp
• T Clasp
• Modified T Clasp
• Y clasp
• I clasp
• RPI system
INDIRECT RETAINER
Function: 1. to prevent the DEB
from moving away from its seat
because of cheek and tongue
forces, sticky food.
It uses me...
2. Contributes to support and stability of the partial
denture counteracts horizontal forces applied to the
denture.
Effectiveness of indirect retainer depends
upon:
1) Its distance from the fulcrum line
greater the distance between fulcru...
2) Effectiveness of direct retainer
Direct retainer must be effective if the
indirect retainer is to function when the
den...
Frank and Nicholls (JPD 1977:38;494)11
-did a study on the effectiveness of indirect retainer and
concluded that use of a ...
Frechette et al (JPD 1956;6:195-212)
demonstrated that removal of the indirect retainers
from a RPD results in the applica...
PHILOSOPHIES OF DESIGN
• There are three basic design philosophies:
• Stress Equalization
• Physiologic Basing
• Broad str...
ESSENTIALS OF PARTIAL DENTURE
DESIGN
• Should be systematically developed on the
diagnostic cast based on the following.
1...
WHERE IS THE PROSTHESIS SUPPORTED.
Tooth supported
Tooth - tissue supported:
TOOTH SUPPORTED
1) The most ideal support units are the RESTS.
2) The abutment selected for the support has to be
evaluate...
TOOTH- TISSUE SUPPORTED
Depends on 6 factors:-
1) Quality of residual ridge
2) The extent to which the ridge will be cover...
STRESS EQUALIZATION
• The resiliency of the tooth supported by periodontal ligament in
an apical direction is not comparab...
• Thus some form of stress director or stress equalizer is
essential to protect the abutment teeth.
• The most commonly us...
PHYSIOLOGIC BASING
 The belief is that the equalization can best and most simply
be accomplished by some form of physiolo...
 Displacing the mucosa during the impression procedure
records it in its functioning and not the anatomic form.
 This de...
BROAD STRESS DISTRIBUTION
distributing the forces of
occlusion over as many teeth
and as much of the available
soft tissue...
STEP BY STEP DESIGNING
Diagnostic cast area of recontouring
Black-mark survey lines desired undercut is measured
Desired rest seat-red desired denture base-blue
Major connector-brown
Retentive elements completed –rt side
Left side occlusal
• CONCLUSION
REFERENCES
1) McCracken’s removable partial Prosthodontics 11th
edition.
2) Stewart’s Removable partial Prosthodontics 4th...
5) Kratochvil et al influence of occlusal rest position and
clasp design on movement of abutment teeth J Prosthet
Dent 196...
9) Frank and Nicholis an investigation of effectiveness
of indirect retainer J Prosthet dent 1977:38;494
10)Frechette et a...
THANK
YOU
2. principles of designing rpd with special emphsis on support and perio
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2. principles of designing rpd with special emphsis on support and perio

  1. 1. GOOD MORNING
  2. 2. Principles of Removable Partial Dentures with special emphasis on support and periodontal consideration of remaining teeth By Dr ZARIR RUTTONJI
  3. 3. CONTENTS 1) Introduction 2) Principles of desining 3) Stress considerations 4) Forces influencing the magnitude of stress 5) Biomechanical consideration of individual component 6) Philosophies of designs 7) Essentials of designing 8) Procedure of designing 9) Conclusion 10)References
  4. 4. • INTRODUCTION
  5. 5. INDICATION FOR REMOVABLE PARTIAL DENTURES Stewart’s Clinical removable partial Prosthodontics 4th edition pg-8 1.Long standing edentulous area 2.No abutment tooth posterior to the edentulous space 3.Reduced periodontal support for remaining teeth 4.Need for cross ach stablization
  6. 6. INDICATION FOR REMOVABLE PARTIAL DENTURES continued Stewart’s Clinical removable partail prosthodontics 4th edition pg-8 5.Excessive bone loss within the residual ridge 6.Physical or emotional problem exhibited by the patient
  7. 7. INDICATION FOR REMOVABLE PARTIAL DENTURES continued 8) Immediate need to replace extracted teeth 9) Patient desire 10)Unfavourable maxillomandibular relation. Stewart’s Clinical removable partail prosthodontics 4th edition pg-8
  8. 8. PRINCIPLES OF DESIGN • 1953,Dr.A.H.Schmidt gave the basic principles of designing 1.Dentist should have thorough knowledge 2.Treatment plan must be based on complete examination and diagnosis of individual patient.
  9. 9. 3.Dentist must correlate the pertinent factors and determine a proper treatment plan 4.RPD should restore the function without injury to remaining oral strutures 5.It is a form of treatment and not a cure.
  10. 10. STRESS CONSIDERATION IN A PARTIAL DENTURE The stresses can be divided as:  Vertical  Horizontal  Torsional Displacing stresses Dislodging stresses
  11. 11. VERTICAL STRESS Displacing stresses : These are the least harmful and are borne well if within physiologic limits
  12. 12. DISLODGING STRESSES : These are the forces which tend to lift the partial denture from it’s rest position
  13. 13. 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.
  14. 14. TORSIONAL STRESS It is a twisting rotational type of force. It’s a combination of vertical and horizontal force
  15. 15. FORCES ACTING ON PARTIAL DENTURE
  16. 16. McCracken’s Removable Partial Prosthodontics 11th edition Is a rigid bar supported somewhere along its length.. The point where the bar is supported is called the fulcrum Three classes of levers (based on location of fulcrum, resistance and direction of effort (force). Class I Class II Class III LEVER
  17. 17. CLASS I LEVER Fulcrum lies in the centre, Resistance is at one end and force at the other. McCracken’s Removable Partial Prosthodontics 11th edition
  18. 18. CLASS II LEVER Fulcrum is at one end effort at the opposite end and resistance in the centre. McCracken’s Removable Partial Prosthodontics 11th edition
  19. 19. CLASS III LEVER Fulcrum is at one end, resistance at opposite end and effort is in the centre. McCracken’s Removable Partial Prosthodontics 11th edition
  20. 20. 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 . Stewart’s clinical Removable Posthodontics 4th edition
  21. 21. FULCRUM ON HORIZONTAL PLANE: • Extends through the rest of principle abutments. • Rotational movement of the denture in the sagittal plane. Stewart’s clinical Removable Posthodontics 4th edition
  22. 22. DENTURE BASE MOVES AWAY FROM SUPPORTING TISSUES: Counteracted by: Direct retainer and Indirect retainer McCracken’s Removable Partial Prosthodontics 11th edition
  23. 23. DENTURE BASE MOVES TOWARDS THE SUPPORTING TISSUES: Counteracted by: 1) Occlusal rest. 2) Tissues of supporting ridge McCracken’s Removable Partial Prosthodontics 11th edition
  24. 24. FULCRUM ON THE SAGITTAL PLANE Extends through the occlusal rest on the terminal abutment and along the crest of the ridge. Movement is in the frontal plane Stewart’s clinical Removable Posthodontics 4th edition
  25. 25. 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 McCracken’s Removable Partial Prosthodontics 11th edition
  26. 26. FULCRUM LOCATED IN MIDLINE JUST LINGUAL TO THE ANTERIOR TEETH (FULCRUM IS VERTICAL) Rotational movement of denture in horizontal plane or flat circular movements of the denture Stewart’s clinical Removable Posthodontics 4th edition
  27. 27. Counteracted by : • Stabilizing components (reciprocal arm and minor connector) • Rigid major connector • Close adaptation of denture base McCracken’s Removable Partial Prosthodontics 11th edition
  28. 28. FACTORS INFLUENCING MAGNITUDE OF STRESSES TRANSMITTED TO ABUTMENT TEETH 1. Quality of support of ridge Form of residual ridge type of mucosal covering 2. Length of span 3. Clasp factor design length material amount of tooth contact Stewart’s clinical Removable Posthodontics 4th edition
  29. 29. 4. Occlusion Type of teeth Harmony of occlusion 5. Areas of the base to which load is applied Stewart’s clinical Removable Posthodontics 4th edition
  30. 30. 1. 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. Stewart’s clinical Removable Posthodontics 4th edition
  31. 31. b. TYPE OF MUCOSA • Influences magnitude of stresses transmitted to abutment teeth. • Healthy mucosa 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 stress transmitted to abutment teeth Stewart’s clinical Removable Posthodontics 4th edition
  32. 32. 2. 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. Stewart’s clinical Removable Posthodontics 4th edition
  33. 33. 3. CLASPAS 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 Stewart’s clinical Removable Posthodontics 4th edition
  34. 34. In examination phase decide whether ridge or abutment tooth require more protection If periodontal support good less flexible clasp like vertical projection clasp If periodontal support weak use more flexible clasp like combination clasp
  35. 35. TYPE ABUTMENT TOOTH SURFACE • Surface if 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. Stewart’s clinical Removable Posthodontics 4th edition
  36. 36. 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. Stewart’s clinical Removable Posthodontics 4th edition
  37. 37. 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. Stewart’s clinical Removable Posthodontics 4th edition
  38. 38. 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. Stewart’s clinical Removable Posthodontics 4th edition
  39. 39. • 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.
  40. 40. BIOMECHANICAL CONSIDERATION OF INDIVIDUAL COMPONENT
  41. 41. REST Two basic types Primary rest Secondary rest DIFERENT TYPES OF RESTS 1) Occlusal rest 2) Extended occlusal rest 3) Incisal ,lingaul or cingulum rest 4) Rest on restoration 5) Rest on cast restorations
  42. 42. REST FUNCTIONS • Provide vertical support for the partial denture. • Maintains components in planned positions. • Maintains established occlusal relations by preventing settling of the denture base. • Prevents impingement of soft tissue. • Directs and distributes occlusal loads to abutment teeth. McCracken’s Removable Partial Prosthodontics 11th edition
  43. 43. OCCLUSAL REST McCracken’s Removable Partial Prosthodontics 11th edition
  44. 44. If angle greater than 90 degrees Forces not along long axis but will create an inclined plane effect Slippage of prosthesis away from the abutment Orthodontic like forces McCracken’s Removable Partial Prosthodontics 11th edition
  45. 45. CINGULUM REST VS INCISAL REST Cingulum rest nearer to center of rotation less tipping of tooth Incisal rest Longer minor connector required magnifies the forces being transferred to the abutment tooth
  46. 46. MESIAL REST or DISTAL REST FOR DEB RPD???
  47. 47. Kratochvil et al (JPD 1963:13;114) • Suggested using mesial occlusal rest so that the force delivered to the mesial aspect of the abutment tooth • That would tend to tip that tooth forward maintaining a tight contact with the tooth immediately anterior to it and gaining stabilization and support from the remaining anterior teeth. • They suggested that occlusal rest be moved anterior to better use the residual ridge for support. .Kratochvil et al influence of occlusal rest position and clasp design on movement of abutment teeth J Prosthet Dent 1963:13;114
  48. 48. John W. Mc Cartney (JPD 1980;43:15) Did a study on the effect of location of occlusal rest on abutment tooth movement and concluded that the mesial rest placement caused less abutment movement than distal rest placement. John W.McCartney Effect of location of rest and movement of abutment tooth J Prosthet Dent 1980:43:15
  49. 49. A major connector is the component of the partial denture that connects the parts of the prosthesis located on one side of the arch with those on the opposite side.  it also provides cross arch stability to help resist displacement stresses MAJOR CONNECTOR McCracken’s Removable Partial Prosthodontics 11th edition
  50. 50. DESIRABLE CHARACTERISTICS OF MAJOR CONNECTORS 1.Should be rigid 2.Provide vertical support and protect the soft tissue. 3.Provide means of obtaining indirect retention where indicated 4.Provide an opportunity of positioning denture bases where needed 5.Maintain patient comfort McCracken’s Removable Partial Prosthodontics 11th edition
  51. 51. MINOR CONNECTOR 1.Primary function is to join other units of the prosthesis such as clasp,rests,indirect retainers and denture bases to major connector 2.Distribution of stresses McCracken’s Removable Partial Prosthodontics 11th edition
  52. 52. DESIGN CONSIDERATIONS 1.Should have sufficient bulk to be rigid 2. Should be made thick buccolingually and thin mesiodistally 3.Should be in triangular form in embrassure 4. Should form a right angle with the major connector 5. Sharp angles should be avoided and spaces should not exist for trapping of food debris. Miller E.L. : “Text book of Removable Partial Prosthodontics”.
  53. 53. Any unit of removable dental prosthesis that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissue. DIRECT RETAINER McCracken’s Removable Partial Prosthodontics 11th edition
  54. 54. • Prothero Cone theory as basis of clasp retention • Described shape of crowns of premolar and molar teeth as 2 cones sharing a common base . Line where they meet height of contour. (represents the greatest bulge). • Suprabulge • Infrabulge McCracken’s Removable Partial Prosthodontics 11th edition
  55. 55. • Height of contour of tooth changes as the vertical position of tooth changes. • Surface is retentive if it is cervical to its height of contour. McCracken’s Removable Partial Prosthodontics 11th edition
  56. 56. • Clasp tip in infrabulge area resist the movement in occlusal direction because to release from tooth  it has to undergo deformation. • Degree of resistance to deformation determines the amount of clasp retention. • Retention varied by: depth of undercut Flexibility of clasp arm positioned in undercut Stewart’s Clinical removable partial Prosthodontics 4th edition
  57. 57. 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. Stewart’s Clinical removable partial Prosthodontics 4th edition
  58. 58. • Indicated most often in class III arches (with modification space on opposite side) QUADRILATERAL CONFIGURATION McCracken’s Removable Partial Prosthodontics 11th edition
  59. 59. 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. McCracken’s Removable Partial Prosthodontics 11th edition
  60. 60. BILATERAL CONFIGURATION For class I situations Not considered ideal, but best option available Stress must be controlled by other means. McCracken’s Removable Partial Prosthodontics 11th edition
  61. 61. REQUIREMENTS OF CLASP DESIGN : • Retention:provided by retentive terminal • Support:mainly by rest • Stability:all the component except the retentive terminal • Reciprocation:reciprocal arm • Encirclement:must be designed more than half of the circumference • Passivity:engages only when dislodging forces are applied McCracken’s Removable Partial Prosthodontics 11th edition
  62. 62. CLASP DESIGNS: • Combination clasp • Reverse circlet clasp
  63. 63. • Bar clasp • T Clasp • Modified T Clasp • Y clasp • I clasp
  64. 64. • RPI system
  65. 65. INDIRECT RETAINER
  66. 66. Function: 1. 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 McCracken’s Removable Partial Prosthodontics 11th edition
  67. 67. 2. Contributes to support and stability of the partial denture counteracts horizontal forces applied to the denture.
  68. 68. Effectiveness of indirect retainer depends upon: 1) Its distance from the fulcrum line greater the distance between fulcrum line and IR more effective
  69. 69. 2) Effectiveness of direct retainer Direct retainer must be effective if the indirect retainer is to function when the denture rotates otherwise the partial denture will be dislodged.
  70. 70. Frank and Nicholls (JPD 1977:38;494)11 -did a study on the effectiveness of indirect retainer and concluded that use of a mesial rest instead of a distal rest on the terminal abutment tooth does not decrease indirect retention. Thus the choice of indirect retainer location should be made mostly on the basis of abutment tooth support, a crown form favoring adequate rest seat preparation, and the patients esthetic desires.
  71. 71. Frechette et al (JPD 1956;6:195-212) demonstrated that removal of the indirect retainers from a RPD results in the application of more pressure to the direct abutment teeth. The indirect retainer probably is effective in distributing forces to teeth other than direct abutments, and in preventing denture base lifting.
  72. 72. PHILOSOPHIES OF DESIGN • There are three basic design philosophies: • Stress Equalization • Physiologic Basing • Broad stress distribution
  73. 73. ESSENTIALS OF PARTIAL DENTURE DESIGN • Should be systematically developed on the diagnostic cast based on the following. 1) Where is the prosthesis supported. 2) How the support is connected. 3) How the prosthesis is retained. 4) How the retention and support are connected. 5) How the edentulous base support is connected McCracken’s Removable Partial Prosthodontics 11th edition
  74. 74. WHERE IS THE PROSTHESIS SUPPORTED. Tooth supported Tooth - tissue supported:
  75. 75. TOOTH SUPPORTED 1) The most ideal support units are the RESTS. 2) The abutment selected for the support has to be evaluated for • Periodontal health. • Crown- root ratio. • Crown –root morphology • Location of the tooth in the arch • The opposing dentition
  76. 76. TOOTH- TISSUE SUPPORTED Depends on 6 factors:- 1) Quality of residual ridge 2) The extent to which the ridge will be covered by mucosa 3) The accuracy and type of impression registration 4) The design chracteristics 5) The occlusal load applied
  77. 77. STRESS EQUALIZATION • The resiliency of the tooth supported by periodontal ligament in an apical direction is not comparable to the greater resiliency and displacement of the mucosa covering the dentulous ridge. • It is the belief of this school of thought that the rigid connection between the denture base and the direct retainer on the abutment teeth is damaging
  78. 78. • Thus some form of stress director or stress equalizer is essential to protect the abutment teeth. • The most commonly used ones are composed of a hinge device interposed between the minor connector of the abutment tooth and the denture base.
  79. 79. PHYSIOLOGIC BASING  The belief is that the equalization can best and most simply be accomplished by some form of physiologic basing. • The physiologic basing is produced either by • Displacing or depressing the ridge mucosa during the impression making procedure • Relining the denture base after it has been constructed.
  80. 80.  Displacing the mucosa during the impression procedure records it in its functioning and not the anatomic form.  This denture base formed over displaced tissue, will adapt more readily to the depressed tissue when occlusal force acts and will be better able to withstand the force that is generated
  81. 81. BROAD STRESS DISTRIBUTION distributing the forces of occlusion over as many teeth and as much of the available soft tissue area as possible. This is accomplished by the use of additional rests, indirect retainers, clasps and broad coverage denture bases
  82. 82. STEP BY STEP DESIGNING Diagnostic cast area of recontouring Black-mark survey lines desired undercut is measured
  83. 83. Desired rest seat-red desired denture base-blue Major connector-brown
  84. 84. Retentive elements completed –rt side Left side occlusal
  85. 85. • CONCLUSION
  86. 86. REFERENCES 1) McCracken’s removable partial Prosthodontics 11th edition. 2) Stewart’s Removable partial Prosthodontics 4th edition. 3) David M Watt; A Roy Macgregar :Designing partial dentures. 4) Miller E.L. : “Text book of Removable Partial Prosthodontics”. St. Louis, CV Mosby Co.
  87. 87. 5) Kratochvil et al influence of occlusal rest position and clasp design on movement of abutment teeth J Prosthet Dent 1963:13;114 6) John W.McCartney effect of location of rest and movement of abutment tooth J Prosthet Dent 1980:43:15 7) David N Firtell reaction of anterior abutment of kennedy classII removable partial denture to various clasp arm designs J Prosthet Dent 1985:53;77 8) Richard P Frank direct retainers for distal extension removable partial dentures J Prosthet dent 1986:56;562
  88. 88. 9) Frank and Nicholis an investigation of effectiveness of indirect retainer J Prosthet dent 1977:38;494 10)Frechette et al the influence of partial denture design on distribution of force to abutment teeth J Prosthet Dent 1956:6;195 11)A.H.Schmidt Planning and designing removable partial denture J Prosthet Dent 1953:3;783
  89. 89. THANK YOU

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