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DIRECT RETAINERS 
By 
Dr Shebin Abraham 
Dept. of Prosthodontics
Contents 
 Introduction 
 Definitions. 
 Classification. 
 Basic part of clasp assembly. 
 Analysis of tooth contour....
Introduction
Types of retention 
 Primary retention. 
1. By clasps 
 Secondary retention. 
2. Acting through 
polished surface of the...
Definition:- 
 Direct retainer:- 
“That component of a partial removable dental 
prosthesis used to retain and prevent d...
Classification Of Direct Retainers. 
Clinical removable prosthodontics:- STEWART’S 3rd edition 
Intra coronal Extra corona...
Intracoronal 
 Proposed by Dr Herman E S Chayes in 1906. 
 Cast or attached within the contours of natural teeth(abutmen...
Extracoronal 
attachment. 
 First proposed by Henry H Boos 1900 later modified by 
Ewing F Roach in 1908. 
 Located out...
Occlusally approaching / 
Suprabulge / Ney Type I 
clasp / Circumferential: 
• Approaches the tooth 
undercut from an occl...
The basic parts of a clasp 
assembly include the following:
RES 
T 
 It is the part of the clasp that lies on the occlusal, lingual or incisal surface 
of a tooth and resist (tissue...
Body of the clasp 
 It is the part of the clasp that connects the rest and shoulder of the clasp 
to the minor connector....
Shoulder 
 It is the part of the clasp that connects the body to the clasp 
terminals. 
 The shoulder must lie above the...
Reciprocal arm 
 A rigid clasp arm placed above the height of contour on the 
side of the tooth, opposing the retentive c...
Retentive arm 
 It is the part of the clasp comprising the shoulder which is not flexible and is located 
above the heigh...
Approach arm 
 It is a component of the bar clasp. 
 It is a minor connector that projects from the 
framework, runs alo...
Analysis of tooth contour:- 
 Before moving on to principles of clasp design its vitally 
important to consider how tooth...
Prothero’s concept 
 Proposed “cone theory” of clinical 
crown in 1916. 
 Provided conceptual basis of mechanical 
reten...
 Devan [1955] referred to the 
surface occlusal to the height of 
contour as suprabulge, & the 
surface inclining cervica...
Angle of convergence
o When the surveyor blade contacts a tooth on the cast at its 
greatest convexity, a triangle is formed. 
o The apex of th...
Basic Principles of clasp 
design
According to Stewart basic principles are:- 
1. Retention. 
2. Stability. 
3. Support. 
4. Reciprocation. 
5. Encirclemen...
Retention 
“Retention is the inherent quality of the clasp 
assembly that resists forces acting to dislodge 
components a...
 The amount of retention designed into a removable partial 
denture should always be the minimum necessary to resist 
rea...
Amount of retention 
Factors that effect retention can be divided into - 
1. Tooth factors 
 Size of angle of cervical c...
Prosthesis factors:- 
 Length of clasp arm- 
 Longer the clasp arm the more flexible it will be. 
 Circumferential clas...
Diameter of the clasp: 
 The greater the diameter of a clasp arm the less flexible it 
will be.(only in uniform taper) 
...
Cross-sectional form: 
 Flexibility may exist in any form, but is limited to only one direction in the case 
of the half...
Material used for construction: 
Gold alloy  greater flexibility than chrome alloys , 
Disadvantage of cast gold alloy...
Relative uniformity of 
retention: 
1. Retention on all principal abutments should be as equal as 
possible. 
2. Retentive...
Support 
“Support is the quality of a clasp assembly that resists 
displacement of a prosthesis in an apical direction.” ...
Stabilization. 
 “Stability is the quality of a clasp assembly that resists 
displacement of a prosthesis in a horizontal...
Reciprocation 
 “Reciprocation is the quality of a clasp assembly that counteracts lateral 
displacement of an abutment w...
Points to be remembered while 
providing reciprocation 
1. To optimize reciprocation, the axial surface of an abutment 
sh...
Encirclement. 
 “Encirclement is the characteristic of a clasp assembly that prevents 
movement of an abutment away from ...
 The engagement can be in the form of continuous contact, such 
as circumferential clasp, or discontinuous contact, such ...
Passivity. 
“Passivity is the quality of a clasp assembly that 
prevents the transmission of adverse forces to the 
assoc...
Other principles 
1. Retentive clasp element should always be placed on facial surface of 
tooth.(mainly in premolars) 
2....
CRITERIA FOR CLASP SELECTION 
 Survey line 
 Requirements of retention and stability depending 
on the number, configura...
Cast circumferential 
clasp.
 First proposed by Dr N B Nebbit. Later 
modified by Dr Polk E Aker. 
 Simple and easy to construct 
 Large amount of t...
Design rules.. 
1. The clasp should arise from the main body of the clasp 
assembly above the height of contour. The reten...
5. The retentive arm should be positioned as far apically on the 
abutment as is practical.(not impinging the gingiva) 
6....
Simple circlet clasp. 
 It is one of the most commonly used 
clasps  retentive and stabilizing 
ability. 
 The basic de...
 Advantages:- 
1. Fulfils the design requirements of support, stability, 
reciprocation, encirclement, and passivity. 
2....
Reverse circlet clasp 
 Used when undercut is located at the facial distoangle adjacent to an 
edentulous space. 
 Desig...
Multiple circlet clasp: 
 A multiple circlet clasp design involves two simple circlet 
clasps joined at the terminal aspe...
Embrasure clasp 
 Also known as the Bonwill clasp. 
 fabrication of unmodified Class II 
or Class III partial denture 
s...
 Design:- 
 Double occlusal rests, two retentive clasp arms and the two 
reciprocal clasp arms either bilaterally or dia...
Ring clasp 
 Circumferential clasp encircles nearly 
all of the tooth from its point of origin. 
 It is usually used whe...
 Advantages:- 
 Provides adequate 
encirclement. 
 excellent retention with 
adequate flexibility due to 
increased len...
Hairpin clasp or reverse action or 
fish hook clasp 
 A simple circlet clasp in which the retentive 
arm loops back to en...
 Consideration:- 
 Sufficient clinical crown height. 
 Space between occlusal and apical arm. 
 Occlusal arm shouldn’t...
 Half and half clasp 
 It consists of a circumferential retentive arm arising from one direction 
and a reciprocal arm a...
Onlay clasp:- 
Indicated when the occlusal surface of the abutment 
lies noticeably apical to the occlusal plane. 
 occl...
Infrabulge clasp/bar 
clasp/roach clasp.
 Popularized by Ewing Roach in 1930 
called it the Bar Clasp. 
 An infrabulge clasp approaches the 
undercut region of a...
Design rules… 
1. The approach arm of an infrabulge clasp must not impinge on 
the soft tissues adjacent to the abutment. ...
T clasp 
 Name is from the shape of the retentive 
terminal. 
 Used in class 1 and class 2 situation. 
 distofacial und...
 In modified t clasp the non retentive arm is 
absent. 
 Y clasp is similar to t clasp with the approach 
arm ending cer...
Other types of clasp philosophies. 
 RPI, 
 RPA 
 DeVan’s Clasp 
 VRHR clasp or Grasso clasp 
 Euipose clasp
RPI concept. 
 RPI stands for Rest Proximal plate I bar. 
 Introduced by Kratochvil in 1963 it consisted of three 
diffe...
 This design had certain basic disadvantages: 
 Physiologic relief was required to prevent impingement 
of gingival tiss...
Krol in 1973 made certain modifications in the design 
under the “minimal coverage criteria” 
Rest preparations are less...
BASIC PRINCIPLES OF RPI 
CONCEPT 
 The mesiobuccal rest with the minor connector is placed 
into the mesiolingual embrasu...
 The proximal plate in conjunction with the mesial occlusal 
rest and minor connector provides the stabilizing and 
recip...
Three different approaches 
to RPI clasp 
 These approaches are based on the location of 
proximal plate ,location of the...
RPA clasps 
 The rest-proximal plate-Aker’s clasp was developed and 
described by Eliason in 1983. 
 It consists of a me...
De VAN CLASP 
 Also called as the mirror view clasp 
 Two occlusal rest on the lingual side of the teeth. 
M.M.DeVan JPD...
VRHR Clasp 
 The vertical reciprocal horizontal retentive arm concept 
was developed by Grasso in 1980 and is characteriz...
Equipoise clasp 
 Proposed by J. J. Goodman in 1990, it is an esthetic retentive 
concept for distal extension situations...
 Metal free- 
1. Natural-flex 
2. Optiflex 
3. Proflex clear wire 
4. Valplast 
5. Cu-sil
Occlusally and gingivally 
approaching clasps: 
Relative merits and demerits
Bar clasp 
The bar clasp approaches the 
undercut from below the height 
of contour  pushes towards the 
occlusal surface...
Bar clasp 
It is more flexible because of 
which it provides less bracing or 
stability against lateral stresses. 
Circumf...
Bar clasp 
Stress breaking effect 
It allows a certain degree of 
functional movement of the distal 
extension base  diss...
Bar clasp 
Contact with tooth 
Minimal tooth contact and 
less damage to tooth 
Circumferential clasp 
More tooth contact ...
Bar clasp 
Damage to oral tissues 
Minimum relief can lead to 
tissue damage to mucosa 
under the approach arm 
Circumfere...
Bar clasp 
Very less metal display so 
high aesthetics 
Circumferential clasp 
Increased metal display so 
poor Esthetics....
INTRACORONAL 
RETAINERS/ 
precision attachments
 The intracoronal retainer is usually regarded as an internal 
attachment or precision attachment. 
 Definition:- 
“A re...
INDICATIONS 
 To provide movable joint in Removable Bridgework, fixed 
removable bridges. 
 To stabilize unilateral sadd...
LIMITATIONS 
1. Large pulp size which is usually related to the age of 
patient. 
2. Length of the clinical crown, not use...
ADVANTAGES 
1. Esthetically acceptable, because not much of metal display 
like extracoronal retainers. 
2. It is preferre...
3. Stimulation to the underlying tissues greater when internal 
attachment are used because of the intermittent vertical 
...
5. It provides for excellent retention of the prosthesis on 
account of frictional resistance between opposing 
parallel v...
Disadvantages of intra coronal 
retainers 
1. They require preparation of abutment tooth and 
casting. 
2. Difficult clini...
4. Difficult to repair and replace. 
5. They are effective in longer teeth and least effective 
in shorter teeth. 
6. Diff...
MATERIAL OF CHOICE 
 Pt, Iridoplatinum, Gold and Pt, Gold and Pd. 
Type III and IV type of gold is to be used for crown ...
Classification 
Classification by Good Kind and Baker in 1976 : 
1)Intra coronal 
a. resilient 
b. non resilient
Intracoronal retainers 
Frictional resistance. 
Tapered and parallel-walled boxed and tubes. 
Adjustable metal plates ...
How To Choose An Attachment? 
 It is the length of attachment, not its width that is main criteria in 
choosing attachmen...
Precision attachment 
selection 
 Kennedy’s class I and class II partially edentulous 
arches 
 The most difficult type ...
 Another philosophy , known as the stable base precision attachment 
RPD concept or floating denture base concept recomme...
Kennedy’s class III partially edentulous arch. 
• Rigid internal attachments are recommended . 
• Provides good retention...
Kennedy’s class IV partially 
edentulous arch 
The ideal RPD design for such situation 
involves the use of a tissue bar ...
Conclusion 
Keep the prosthesis design as simple as possible… 
Make RPD more comfortable, more efficient and 
affordable...
References 
1. Clinical removable prosthodontics:- STEWART’S 3rd edition 
2. Mc cracken removable partial denture prosthod...
 Thank you
Direct retainers in removable partial dentures
Direct retainers in removable partial dentures
Direct retainers in removable partial dentures
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Direct retainers in removable partial dentures

direct retainers in removable partial dentures

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Direct retainers in removable partial dentures

  1. 1. DIRECT RETAINERS By Dr Shebin Abraham Dept. of Prosthodontics
  2. 2. Contents  Introduction  Definitions.  Classification.  Basic part of clasp assembly.  Analysis of tooth contour.  Basic Principles of clasp design.  Cast circumferential clasp.  Bar clasp.  Other types of clasp.  Intracoronal retainers.  Conclusion.
  3. 3. Introduction
  4. 4. Types of retention  Primary retention. 1. By clasps  Secondary retention. 2. Acting through polished surface of the denture. 3. Tissue coverage.
  5. 5. Definition:-  Direct retainer:- “That component of a partial removable dental prosthesis used to retain and prevent dislodgment, consisting of a clasp assembly or precision attachment” GPT-8  Direct retention :  “Retention obtained in a partial removable dental prosthesis by the use of clasps or attachments that resist removal from the abutment teeth” –GPT-8
  6. 6. Classification Of Direct Retainers. Clinical removable prosthodontics:- STEWART’S 3rd edition Intra coronal Extra coronal Precision attachment Semi precision attachment Retentive clasp assemblies Attachment s Supra bulge clasp Infra bulge clasp
  7. 7. Intracoronal  Proposed by Dr Herman E S Chayes in 1906.  Cast or attached within the contours of natural teeth(abutment).  Keyway and key…..Opposing vertical walls  provides retention.  Retention is achieved by  frictional resistance. 1. Precision attachment manufactured by high precision technique and instruments 2. Semi precision attachment less intimate contact between matrix and matrix component. Unlike precision attachment they consist of tapering walls and are casted from wax or plastic pattern.
  8. 8. Extracoronal attachment.  First proposed by Henry H Boos 1900 later modified by Ewing F Roach in 1908.  Located outside the teeth.  Retention from  mechanical resistance.  Permit vertical movement during vertical loading.  Minimize potentially damaging forces to abutment  Stress breaking or stress directing effects.
  9. 9. Occlusally approaching / Suprabulge / Ney Type I clasp / Circumferential: • Approaches the tooth undercut from an occlusal direction • It is attached to metal framework above the height of contour. Gingivally approaching / Infrabulge/ Bar/ Roach / Ney Type II Clasp: • The retentive arm originates from the metal base or denture framework traverses soft tissue and • Approaches the tooth undercut area from a gingival direction. EXTRACORONAL DIRECT RETAINERS
  10. 10. The basic parts of a clasp assembly include the following:
  11. 11. RES T  It is the part of the clasp that lies on the occlusal, lingual or incisal surface of a tooth and resist (tissue ward) movement of the clasp by ensuring that the retentive terminals of the clasp remain fixed in the desired or planned depth of undercut.
  12. 12. Body of the clasp  It is the part of the clasp that connects the rest and shoulder of the clasp to the minor connector.  It must be rigid.  Above the height of contour.
  13. 13. Shoulder  It is the part of the clasp that connects the body to the clasp terminals.  The shoulder must lie above the height of contour and provide some stabilization against horizontal displacement of the prosthesis.
  14. 14. Reciprocal arm  A rigid clasp arm placed above the height of contour on the side of the tooth, opposing the retentive clasp arm.
  15. 15. Retentive arm  It is the part of the clasp comprising the shoulder which is not flexible and is located above the height of the contour  It is the terminal end of the retentive clasp arm. It is the only component of the removable partial denture that lies on the tooth surface cervical to the height of the contour. It possesses a certain degree of flexibility and offers the property of direct retention.
  16. 16. Approach arm  It is a component of the bar clasp.  It is a minor connector that projects from the framework, runs along the mucosa and turns to cross the gingival margin of the abutment tooth; to approach the undercut from a gingival direction.
  17. 17. Analysis of tooth contour:-  Before moving on to principles of clasp design its vitally important to consider how tooth contour & RPD components must be related to allow a stable prosthetic function.  What is path of insertion??? path of removal ??and height of contour???  Point of maximum convexity or the term height of contour  Dr Edward Kennedy in 1985.  This critical area of an abutment that provide for retention & stabilization can only be identified with the use of dental cast surveyor.
  18. 18. Prothero’s concept  Proposed “cone theory” of clinical crown in 1916.  Provided conceptual basis of mechanical retention.  Contours of clinical crown resembles two cones sharing a common base.  The line formed at the junction of this base represents the greatest diameter of the tooth.  This greatest diameter is called height of contour or point of maximum convexity.
  19. 19.  Devan [1955] referred to the surface occlusal to the height of contour as suprabulge, & the surface inclining cervically as infrabulge. suprabulge infrabulge
  20. 20. Angle of convergence
  21. 21. o When the surveyor blade contacts a tooth on the cast at its greatest convexity, a triangle is formed. o The apex of this triangle is at the point of contact of surveyor blade with the tooth and base is towards the gingival tissues. o This apical angle is called angle of cervical convergence. The importance of this angle lies in its relationship to the amount of retention.
  22. 22. Basic Principles of clasp design
  23. 23. According to Stewart basic principles are:- 1. Retention. 2. Stability. 3. Support. 4. Reciprocation. 5. Encirclement. 6. Passivity.
  24. 24. Retention “Retention is the inherent quality of the clasp assembly that resists forces acting to dislodge components away from the tooth structure.”  No single component of a clasp assembly is solely responsible for prosthesis retention.  Rather, it is effective design and accurate construction that make the removable partial denture retentive.
  25. 25.  The amount of retention designed into a removable partial denture should always be the minimum necessary to resist reasonable dislodging forces.  A rigid clasp flexing over the height of contour may transfer harmful stresses to an abutment during insertion, removal, and functional movement of the prosthesis.  An only a minimum area of contact should be seen.
  26. 26. Amount of retention Factors that effect retention can be divided into - 1. Tooth factors  Size of angle of cervical convergence  How far clasp is placed in angle of cervical convergence. 2. Prosthesis factors  Clasp length  Clasp diameter  Clasp cross-sectional form[ shape]  Material used for making clasp[ alloy]
  27. 27. Prosthesis factors:-  Length of clasp arm-  Longer the clasp arm the more flexible it will be.  Circumferential clasps more retentive than bar clasp for a given clasp length.  The clasp arm should taper from the point of origin to provide its flexibility.
  28. 28. Diameter of the clasp:  The greater the diameter of a clasp arm the less flexible it will be.(only in uniform taper)  If its taper is absolutely uniform ,the avg diameter will be at a point midway between its origin & its terminal end.  But if taper is not uniform a point of flexure –therefore a point of weakness will exist.
  29. 29. Cross-sectional form:  Flexibility may exist in any form, but is limited to only one direction in the case of the half-round form  The only universally flexible form is the round form.  Clasp arm should only flex away from tooth so half round is used.  Round shaped clasp arm used only in distal extension denture bases so that it can flex in all directions during functional movement and minimize stresses.
  30. 30. Material used for construction: Gold alloy  greater flexibility than chrome alloys , Disadvantage of cast gold alloys  bulk of the prosthesis costly. Chrome alloys have a higher modulus of elasticity & therefore less flexibility. So in less undercut areas CoCr alloy can be used but in cases of deep undercut wrought metal can be used.
  31. 31. Relative uniformity of retention: 1. Retention on all principal abutments should be as equal as possible. 2. Retentive clasp arms should be located so that they lie in the same approx.. Degree of undercut on each abutment tooth. 3. Retentive clasp positioning should also be same on the contralateral side of arch.(atleast for one teeth).
  32. 32. Support “Support is the quality of a clasp assembly that resists displacement of a prosthesis in an apical direction.”  Provided by occlusal rest. 1. A properly prepared rest seat and corresponding rest serve to resist displacement of the prosthesis toward the supporting teeth and soft tissues, thereby ensuring that the clasp assembly maintains its intended relation to the abutment, and 2. Transmit functional forces parallel to the long axes of the abutments.
  33. 33. Stabilization.  “Stability is the quality of a clasp assembly that resists displacement of a prosthesis in a horizontal direction.”  It helps the denture be steady constant firm and resist displacement due to function stresses and also prevent change in position of the denture.  It is provided by :- 1. Reciprocal element. 2. The shoulder(s) of a cast circumferential retentive clasp. 3. Vertically oriented minor connectors.
  34. 34. Reciprocation  “Reciprocation is the quality of a clasp assembly that counteracts lateral displacement of an abutment when the retentive clasp terminus passes over the height of contour.”  As the retentive arm passes over the height of contour it flexes creating lateral forces  damage to the tooth.  The reciprocal element may be a 1. Retentive arm of clasp 2. Lingual plating, 3. Combination of mesial and distal minor connectors.
  35. 35. Points to be remembered while providing reciprocation 1. To optimize reciprocation, the axial surface of an abutment should be prepared parallel to the path of insertion and removal. 2. It should be placed above the height of contour. 3. To provide true reciprocation, the reciprocal clasp arm must be in contact during the entire period of retentive clasp deformation.
  36. 36. Encirclement.  “Encirclement is the characteristic of a clasp assembly that prevents movement of an abutment away from the associated clasp assembly”.  Clasp assembly  180 degrees contact.
  37. 37.  The engagement can be in the form of continuous contact, such as circumferential clasp, or discontinuous contact, such as Bar clasp.  Both provide tooth contact in at least 3 areas encircling the tooth-
  38. 38. Passivity. “Passivity is the quality of a clasp assembly that prevents the transmission of adverse forces to the associated abutment when the prosthesis is completely seated.”  When fully seated  it should be passive.  Should be activated only when dislodging forces are applied.
  39. 39. Other principles 1. Retentive clasp element should always be placed on facial surface of tooth.(mainly in premolars) 2. Only one retentive element should be used per tooth opposed by a reciprocal element. 3. Clasp retainers on the abutment adjacent to distal extension bases should be designed so they will avoid direct transmission of tipping & rotational forces to the abutment. 4. The path of escapement for each retentive clasp terminal must be other than parallel to the path of removal for the prosthesis to require clasp engagement with resistance to deformation.
  40. 40. CRITERIA FOR CLASP SELECTION  Survey line  Requirements of retention and stability depending on the number, configuration of edentulous areas.  Nature of support  Root size and form  Esthetics  Presence of excessive tissue undercut  Oral hygiene and patient awareness
  41. 41. Cast circumferential clasp.
  42. 42.  First proposed by Dr N B Nebbit. Later modified by Dr Polk E Aker.  Simple and easy to construct  Large amount of tooth surface that is covered by the clasp assembly leads to enamel decalcification.
  43. 43. Design rules.. 1. The clasp should arise from the main body of the clasp assembly above the height of contour. The retentive arm should extend cervically and circumferentially in a gently arcing manner. 2. All the components of the C clasp should be present above the height of contour except the retentive tip. 3. The retentive terminus should always be directed towards the occlusal surface never towards the gingiva. 4. It should always terminate at the mesial or distal line angle never at midfacial or midlingual surface.
  44. 44. 5. The retentive arm should be positioned as far apically on the abutment as is practical.(not impinging the gingiva) 6. Special considerations in case of distal extension case:-  A cast circumferential clasp should not be used to engage (a) the mesiofacial surface of an abutment adjacent to a posterior edentulous space or  the distofacial surface of an abutment adjacent to an extensive anterior edentulous space.
  45. 45. Simple circlet clasp.  It is one of the most commonly used clasps  retentive and stabilizing ability.  The basic design consist of 1. buccal retentive arm and 2. a lingual reciprocal arm originating from a common body. 3. Occlusal rest.  With retentive arm projecting away from the edentulous space.
  46. 46.  Advantages:- 1. Fulfils the design requirements of support, stability, reciprocation, encirclement, and passivity. 2. Its uncomplicated design features make it easy to construct and relatively simple to repair.  Disadvantages:- 1. If used in distal extension base due to fulcrum rotation of the clasp it can cause damage to teeth. 2. Can increase the circumference of teeth and lead to food accumulation and decalcification.
  47. 47. Reverse circlet clasp  Used when undercut is located at the facial distoangle adjacent to an edentulous space.  Design  It consists of a mesial occlusal rest, a horizontal reciprocal arm, and a retentive arm engaging the distobuccal undercut adjacent to the edentulous area.  Advantages:-  Decreases the harmful stresses to teeth.  Disadvantages:-  Week clasp if sufficient preparation is not done.  Poor aesthetics' if used in premolars and cuspids.
  48. 48. Multiple circlet clasp:  A multiple circlet clasp design involves two simple circlet clasps joined at the terminal aspects of their reciprocal elements.  Used in periodontally weekend teeth to splint them  Disadvantages are same as circlet clasp.
  49. 49. Embrasure clasp  Also known as the Bonwill clasp.  fabrication of unmodified Class II or Class III partial denture situation;  when there are no edentulous spaces available on the opposite side of the arch to aid in clasping.
  50. 50.  Design:-  Double occlusal rests, two retentive clasp arms and the two reciprocal clasp arms either bilaterally or diagonally opposed.  Prevent interproximal wedging by the prosthesis, which could cause separation of the abutment tooth and result in food impaction and clasp displacement.  In addition to providing support, occlusal rests also serve to shunt food away from the contact area.  Disadvantages:-  Improper clearance can give rise thin section of clasp leading to breakage.
  51. 51. Ring clasp  Circumferential clasp encircles nearly all of the tooth from its point of origin.  It is usually used when a proximal undercut cannot be approached by any other means.  In case of tilted molars  A support strut is provided on the non retentive arm.
  52. 52.  Advantages:-  Provides adequate encirclement.  excellent retention with adequate flexibility due to increased length of clasp arm  Disadvantages:-  Decalcification of teeth  Increased occlusal table.  Poor structure of clasp.
  53. 53. Hairpin clasp or reverse action or fish hook clasp  A simple circlet clasp in which the retentive arm loops back to engage an undercut apical to the point of origin.  Used when a distofacial undercut is present adjacent to the edentulous space.  Retentive arm has two horizontal components. 1. The occlusal portion  minor connector and must be rigid. 2. The apical portion  pass over the height of contour to engage the desired undercut.
  54. 54.  Consideration:-  Sufficient clinical crown height.  Space between occlusal and apical arm.  Occlusal arm shouldn’t interfere within the occlusion  This clasp is indicated when the 1. soft tissue contour precludes use of a bar-type clasp and 2. when the reverse circlet cannot be considered because of a lack of occlusal clearance.
  55. 55.  Half and half clasp  It consists of a circumferential retentive arm arising from one direction and a reciprocal arm arising from another.  used only for unilateral partial denture design.  Combination clasp  Given by O C Applegate.  This type of clasp consists of a wrought wire retentive clasp arm and a cast reciprocal clasp arm.  Wrought retentive arm is circular in cross section.  Used in deep undercut case.
  56. 56. Onlay clasp:- Indicated when the occlusal surface of the abutment lies noticeably apical to the occlusal plane.  occlusal surfaces of the abutments are covered with crowns clasp arms arises It establishes the occlusal plane. Indicated in caries free individual. Occlusal surface should be restored with gold acrylic inserts.
  57. 57. Infrabulge clasp/bar clasp/roach clasp.
  58. 58.  Popularized by Ewing Roach in 1930 called it the Bar Clasp.  An infrabulge clasp approaches the undercut region of an abutment from an apical direction.  Push type retention.  Flexibility of clasp from length and taper.  More aesthetic than c clasp.  Ex :- y clasp, t clasp, I clasp.
  59. 59. Design rules… 1. The approach arm of an infrabulge clasp must not impinge on the soft tissues adjacent to the abutment. 2. The approach arm should cross perpendicular to the free gingival margin. It shouldn’t impinge the underlying gingiva. 3. Shouldn’t be used in area of tissue undercut. 4. Uniform length and adequate taper should be given for sufficient flexibility. 5. The clasp terminus tip should be placed as apical as possible on the abutment teeth.
  60. 60. T clasp  Name is from the shape of the retentive terminal.  Used in class 1 and class 2 situation.  distofacial undercut is seen.  The retentive terminal consist of horizontal two projection the one on the distal side engages the undercut and the one on the mesial side is above the height of contour.  T clasp is contraindicated when the height of contour is at the occlusal one thirds.
  61. 61.  In modified t clasp the non retentive arm is absent.  Y clasp is similar to t clasp with the approach arm ending cervical to the retentive arm.  I clasp lack the horizontal retentive arms but only a horizontal retentive tip.  Only the retentive tip contacts the abutment surface only at the undercut region.  The amount of contact is about 2 to 3mm in height and 1.5 mm in width.
  62. 62. Other types of clasp philosophies.  RPI,  RPA  DeVan’s Clasp  VRHR clasp or Grasso clasp  Euipose clasp
  63. 63. RPI concept.  RPI stands for Rest Proximal plate I bar.  Introduced by Kratochvil in 1963 it consisted of three different parts connected to the metal framework.  Mesial occlusal rest, a distal guide plan, and an I bar retainer.  The guide plan contacts the full length of the of the proximal surface of the tooth.
  64. 64.  This design had certain basic disadvantages:  Physiologic relief was required to prevent impingement of gingival tissues during function.  Since the proximal plate covers a greater surface area of the tooth, the functional forces are directed in the horizontal direction, thus the tooth is located more than the edentulous ridge.
  65. 65. Krol in 1973 made certain modifications in the design under the “minimal coverage criteria” Rest preparations are less extensive in the RPI system. Rests extend only into the triangular fossa, even in molar preparations, and canine rest 2-3mm guide plane in which only 1mm contact was seen from the guide plate. Arthur Krol JPD 1973;23;408-415
  66. 66. BASIC PRINCIPLES OF RPI CONCEPT  The mesiobuccal rest with the minor connector is placed into the mesiolingual embrasure, but not contacting the adjacent tooth.  A distal guiding plane, extending from the marginal ridge to the junction of the middle and gingival thirds of the abutment tooth, is prepared to receive a proximal plate
  67. 67.  The proximal plate in conjunction with the mesial occlusal rest and minor connector provides the stabilizing and reciprocal aspects of the clasp assembly.  The I-bar contributes to the retentive aspect and should be located in the gingival third of the buccal or labial surface of the abutment in 0.01 inch undercut.
  68. 68. Three different approaches to RPI clasp  These approaches are based on the location of proximal plate ,location of the I bar
  69. 69. RPA clasps  The rest-proximal plate-Aker’s clasp was developed and described by Eliason in 1983.  It consists of a mesial occlusal rest, proximal plate and a circumferential clasp arm, which arises from the superior portion of the proximal plate and extends around the tooth to engage the mesial undercut.
  70. 70. De VAN CLASP  Also called as the mirror view clasp  Two occlusal rest on the lingual side of the teeth. M.M.DeVan JPD 1955;5,208-14
  71. 71. VRHR Clasp  The vertical reciprocal horizontal retentive arm concept was developed by Grasso in 1980 and is characterized by:  A distal occlusal rest supported by a minor connector.  A lingual vertical reciprocal component originating from the major connector.  A horizontal retentive arm attached to either the major connector or the retention latticework for the denture base. Joseph Grasso JPD 1980,43;618-21
  72. 72. Equipoise clasp  Proposed by J. J. Goodman in 1990, it is an esthetic retentive concept for distal extension situations.  Rests are placed away from edentulous span. Vertical inter-proximal reduction of 1 mm between abutment and adjacent tooth is done.  Optional bucco-lingual retentive groove at mid and gingival third junction on distal surface of abutment tooth is provided. Quintessence Int. 1996 May;27(5):333-40.
  73. 73.  Metal free- 1. Natural-flex 2. Optiflex 3. Proflex clear wire 4. Valplast 5. Cu-sil
  74. 74. Occlusally and gingivally approaching clasps: Relative merits and demerits
  75. 75. Bar clasp The bar clasp approaches the undercut from below the height of contour  pushes towards the occlusal surface abutment tooth • Easier to seat and more difficult to remove Circumferential clasp • Above the height of contour • Pulls towards the occlusal surface from the undercut to resist dislodgement. retention
  76. 76. Bar clasp It is more flexible because of which it provides less bracing or stability against lateral stresses. Circumferential clasp • Because of its rigidity it provides very good stability or bracing bracing
  77. 77. Bar clasp Stress breaking effect It allows a certain degree of functional movement of the distal extension base  dissipate the stresses and lessen the load on the abutment Circumferential clasp Potential to torque abutment teeth in distal extension based partial denture situations.
  78. 78. Bar clasp Contact with tooth Minimal tooth contact and less damage to tooth Circumferential clasp More tooth contact leading to food accumulation structure
  79. 79. Bar clasp Damage to oral tissues Minimum relief can lead to tissue damage to mucosa under the approach arm Circumferential clasp Damage to gingiva can take place during improper removal of clasp
  80. 80. Bar clasp Very less metal display so high aesthetics Circumferential clasp Increased metal display so poor Esthetics. Esthetics
  81. 81. INTRACORONAL RETAINERS/ precision attachments
  82. 82.  The intracoronal retainer is usually regarded as an internal attachment or precision attachment.  Definition:- “A retainer consisting of a metal receptacle (matrix) and a closely fitting part (patrix); the matrix is usually contained within the normal or expanded contours of the crown on the abutment tooth and the patrix is attached to a pontic or the removable partial denture framework.”
  83. 83. INDICATIONS  To provide movable joint in Removable Bridgework, fixed removable bridges.  To stabilize unilateral saddles.  Pier abutments.  Titled molars. F.P.D's in severely misaligned abutments.  Use in Over dentures (different forms of retainer are bar, telescopic, use of auxillary attachments).  Fixed removable implant restorations.
  84. 84. LIMITATIONS 1. Large pulp size which is usually related to the age of patient. 2. Length of the clinical crown, not used in short or abraded teeth.(6mm crown) 3. Expensive 4. Distal extension denture bases.
  85. 85. ADVANTAGES 1. Esthetically acceptable, because not much of metal display like extracoronal retainers. 2. It is preferred in many of the situation because of its vertical support through a rest seat located more favorable to the horizontal axis of the abutment tooth.
  86. 86. 3. Stimulation to the underlying tissues greater when internal attachment are used because of the intermittent vertical massage. 4. It permits proper tooth form to be maintained and allows for control of vertical, mesiodistal and buccolingual displacement of the prosthesis.
  87. 87. 5. It provides for excellent retention of the prosthesis on account of frictional resistance between opposing parallel vertical walls that serve to limit movement and resist removal of the partial denture.
  88. 88. Disadvantages of intra coronal retainers 1. They require preparation of abutment tooth and casting. 2. Difficult clinical and laboratory procedure. 3. They eventually wear, result in loss of frictional resistance to denture removal.
  89. 89. 4. Difficult to repair and replace. 5. They are effective in longer teeth and least effective in shorter teeth. 6. Difficult to place completely in the abutment teeth.
  90. 90. MATERIAL OF CHOICE  Pt, Iridoplatinum, Gold and Pt, Gold and Pd. Type III and IV type of gold is to be used for crown castings.  Base metal alloys are also used now a days as low cost  2 alternate ways to construct crown and rest seat. Rest seat may be cast against the full coverage restoration Rest seat may be soldered into place.
  91. 91. Classification Classification by Good Kind and Baker in 1976 : 1)Intra coronal a. resilient b. non resilient
  92. 92. Intracoronal retainers Frictional resistance. Tapered and parallel-walled boxed and tubes. Adjustable metal plates Springs Studs: Locks Magnetic resistance.
  93. 93. How To Choose An Attachment?  It is the length of attachment, not its width that is main criteria in choosing attachments.  For each length there are 3 different sizes (width) of precision attachments (anterior, bicuspid, molar.)  Width is measured from one side of rest to other.  Full length of a precision attachment is 8 mm for full benefit of bracing, support and retention a minimal of 5mm height is must.  This means that the clinical length of crown must be at least 7 mm so as to accommodate an attachment of 5mm and in addition a minimum of 2mm between the gingival floor of attachment and gingival margin.  Otherwise a periodontal problem may be created.
  94. 94. Precision attachment selection  Kennedy’s class I and class II partially edentulous arches  The most difficult type of treatment plan.  Some practitioners advocate non rigid and resilient attachments and some advocate resilient attachment in distal extension to minimize rotation and torquing of the abutment tooth, when the components of an attachment are rigidly connected. Int J Prosthodont. 1990 Mar-Apr;3(2):169-74
  95. 95.  Another philosophy , known as the stable base precision attachment RPD concept or floating denture base concept recommends incorporation of rigid internal attachments and a cast metal base made from mucostatic impression of the residual ridge.  The male portion of the attachment is connected to the denture base , allowing the complete seating within the abutment.
  96. 96. Kennedy’s class III partially edentulous arch. • Rigid internal attachments are recommended . • Provides good retention, support and brazing because of its rigid interlocking components. • If the posterior abutment prognosis is questionable then a resilient type of attachments are recommended with anterior abutment.
  97. 97. Kennedy’s class IV partially edentulous arch The ideal RPD design for such situation involves the use of a tissue bar placed close to the edentulous ridge and connected as a fixed unit to the abutment teeth on either side of the space using crowns.
  98. 98. Conclusion Keep the prosthesis design as simple as possible… Make RPD more comfortable, more efficient and affordable to the patient.
  99. 99. References 1. Clinical removable prosthodontics:- STEWART’S 3rd edition 2. Mc cracken removable partial denture prosthodontics – 12th edition. 3. Davenport J.C., Baskar R.M., Heath J.R., Ralph J.P. “A color atlas of RPD”, Wolfe Medical Publications Ltd., 1988. 4. Krol A.J. “Clasp design for extension base RPD”. J. Prosthet. Dent., 1973; 29 : 408-415. 5. M.M.DeVan JPD 1955;5,208-14 6. Joseph Grasso JPD 1980,43;618-21 7. Quintessence Int. 1996 May;27(5):333-40. 8. Burns DR, Ward JE. Int J Prosthodont. 1990 Mar-Apr;3(2):169-74
  100. 100.  Thank you

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