Direct and indirect retainers

forms of direct and indirect retainers in removable prosthesis

1. DIRECT AND INDIRECT RETAINERS DELLA S INDRAN II nd MDS

2. CONTENTS INTRODUCTION DEFINITION CLASSIFICATION INTRACORONAL ATTACHMENTS EXTRACORONAL ATTACHMENTS PARTS OF CLASP CRITERIA FOR CLASP SELECTION CLASP ASSEMBLY, PRINCIPLES, FUNCTIONS AND TYPES

3. OTHER CLASP DESIGN PHILOSOPHIES PREFERRED CLASP DESIGN FOR DIFFERENT KENNEDY’S CLASSES INDIRECT RETENTION FACTORS AFFECTING INDIRECT RETENTION FUNCTIONS OF INDIRECT RETENTION FORMS OF INDIRECT RETENTION CONCLUSION REVIEW OF LITERATURE REFERENCES

4. INTRODUCTION Retention is one of the important qualities that a denture should possess. RETENTION: ( Acc to GPT 9) That quality inherent in the dental prosthesis acting to resist forces of dislodgement along the path of placement. Forces of dislodgement:- Action of adherent foods Gravity in maxilla Functional forces acting across a fulcrum line. Good Retention of a denture gives physiologic and psychologic comfort to the patient.

5. DIRECT RETENTION (Acc to GPT 9) Retention obtained in a partial removable dental prosthesis by the use of clasps or attachments that resist removal from the abutment tooth. DIRECT RETAINER ( Acc to GPT 9) That component of a partial removable dental prosthesis used to retain and prevent dislodgement; consisting of clasp assembly and precision attachment.

6. Clinical removable prosthodontics:- STEWART’S 3rd edition

7. INTRACORONAL ATTACHMENTS Proposed by Dr Herman E S Chayes in 1906. Often refered to as simply attachments. Composed of two closely fitting components. -matrix: metal receptacle or keyway. Positioned within the normal clinical contours of cast restoration placed on abutment. - patrix : attached to the removable partial denture The two components interlock in a sliding joint configuration and functions to retain, support, and stabilize the RPD

8. Subdvided into 2: 1. Precision attachment: manufactured by high precision technique and instruments 2. Semi precision attachment: less intimate contact between matrix and Patrix component. Unlike precision attachment they consist of tapering walls and are casted from wax or plastic pattern.

9. INDICATIONS To provide movable joint in Removable Bridgework, fixed removable bridges. To stabilize unilateral saddles. Pier abutments. Tilted 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.

10. ADVANTAGES Esthetically acceptable, because not much of metal display like extracoronal retainers. It permits proper tooth form to be maintained and allows for control of vertical, mesiodistal and buccolingual displacement of the prosthesis. It provides for excellent retention of the prosthesis.

11. DISADVANTAGES They require preparation of abutment tooth and casting. Difficult clinical and laboratory procedure. They eventually wear, result in loss of frictional resistance to denture removal. Difficult to repair and replace. They are effective in longer teeth and least effective in shorter teeth. Difficult to place completely in the abutment teeth

12. EXTRACORONAL ATTACHMENTS First proposed by Henry H Boos in1900 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.

13. STRESS BREAKER CONCEPT A stress breaker is a specially constructed device which is interposed between the denture base and the clasp or a design of the frame work, that permits movement of the base independently of the clasp. Given to relieve the abutment tooth from heavy loads There are two variety of Stress Breakers available: • Ball and socket type of stress breaker- permits base to move in all planes. • Hinge type – vertical plane only.

14. INDICATIONS: Weak abutment tooth (lateral incisor) Well formed residual ridges Healthy bone A distal extension base with precision attachment.

15. DISADVANTAGES: Too much movement Non-uniform distribution of stress Loss of cross arch stabilisation and indirect retention Residual ridges are overburdened which may lead to resorption. Bulky- cosmetic compromise and food entrapment Costly Difficult to adjust and repair compared to conventional retainer.

16. 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 CLASP ASSEMBLIES

17. PARTS OF CLASP ASSEMBLY REST: 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 .

18. 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 .

19. 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 .

20. RECIPROCAL ARM A rigid clasp arm placed above the height of contour on the side of the tooth, opposing the retentive clasp arm. Reciprocal clasp must be rigid, it is not tapered as the retentive clasp. Reciprocal arm should be positioned on the surface of a tooth and parallel to the denture’s path of insertion and removal .

21. If it is placed on the surface that is tapered occlusally , a slight movement of denture will cause the clasp to loose contact with the tooth and reciprocation and retention is lost. It must be positioned above the height of contour. To reciprocate the forms properly, it should contact the tooth before the retentive arm does.

22. RETENTIVE ARM It is the part of the clasp that contacts the surface of abutment apical to the height of contour. Tip 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.

23. The retentive clasp is divided into 3 parts; each with its arm functional requirement. The terminal third is flexible and engages the undercut The middle third has a limit degree of flexibility and may engage a minimal amount of undercut. Proximal third or shoulder is rigid and must be positioned above the height of contour.

24. 2 basic form of retentive arms: - suprabulge clasp arm - infrabulge clasp arm

25. 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.

26. ANALYSIS OF TOOTH CONTOUR Dr Edward Kennedy in 1985. The line at which occlusally sloping surfaces meet cervically sloping surfaces is the ‘ Height of Contour’- Point of maximum convexity This critical area of an abutment that provide for retention & stabilization can only be identified with the use of dental cast surveyor.

27. 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. Devan [1955] referred : the surface occlusal to the height of contour as suprabulge , & the surface inclining cervically as infrabulge .

28. FUNCTIONAL REQUIREMENTS OF A PROPERLY DESIGNED CLASP 1. Retention 2. Stability 3. Support 4. Encirclement 5. Reciprocity 6. Passivity

29. 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. Is obtained by the incorporation of a flexible element of the clasp into the undercut.

30. Sufficient undercut to be engaged to obtain desired retention. Force from the clasp arm on flexing must be within the tolerance of the PDL and must be less to prevent deformation of the clasp arm itself 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. Only a minimum area of contact should be seen.

31. 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 a. Clasp length b. Clasp diameter c. Clasp cross-sectional form[ shape] d. Material used for making clasp[ alloy]

32. TOOTH FACTORS SIZE OF THE ANGLE OF CERVICAL CONVERGENCE: When the surveyor blade contacts a tooth on the cast at its greatest convexity, a triangle is formed, the apex of which is at the point of contact of the surveyor blade with the tooth, and the base is the area of the cast representing the gingival tissues. The apical angle is called the angle of cervical convergence.

33. To be retentive a tooth must have an angle of convergence cervical to the height of contour. Guiding planes determine the path of placement and removal of a partial denture. Therefore without the use of guide planes, clasp retention will either be detrimental or practically non-existent.

34. PROSTHESIS FACTORS:- Length of clasp arm- • Longer the clasp arm the more flexible it will be. •The clasp arm should taper from the point of origin to provide its flexibility. •Flexibility is directly proportional to the cube of its length. •By increasing the length, the horizontal stresses imparted to the abutment during placement, removal and movement of the prosthesis is reduced.

35. Diameter of the clasp: • The greater the diameter of a clasp arm the less flexible it will be (only in uniform taper) • Flexure inversely proportional to the diameter. • If it’s taper is absolutely uniform, the average diameter will be at a point midway between its origin & its terminal end.

36. CROSS-SECTIONAL FORM: •Flexibility may exist in any form, but is limited to only one direction in the case of the half-round form •Round shaped clasp since it can flex in all directions during functional movement it minimize stresses. A half round clasp typically flexes in a plane perpendicular to the flat surface of the clasp. Therefore stress distribution is limited.

37. MATERIAL USED FOR CONSTRUCTION: Alloys with lower elastic moduli exhibits greater flexibility. • 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.

38. RETENTION UNDERCUT: The retention undercut is basically of two dimensions. i . Horizontal / Medio - lateral dimension ii. Vertical / Occluso – apical dimension a: horizondal dimension B: vertical dimension

39. DEGREE OF UNDERCUT • Retentive clasp arms must be located so that they lie in the same approximate degree of undercut on each abutment tooth, despite the variation in the distance below the height of contour. • The measurement of the degree of undercut by mechanical means is achieved by the help of an undercut gauge attached to a dental surveyor.

40. 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

41. 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 i.e the proximal plate.

42. 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.”

43. The reciprocal element may be a o Cast clasp o Lingual plating, o Combination of mesial and distal minor connectors.

44. Points to be remembered while providing reciprocation To optimize reciprocation, the axial surface of an abutment should be prepared parallel to the path of insertion and removal. It should be placed above the height of contour. To provide true reciprocation, the reciprocal clasp arm must be in contact during the entire period of retentive clasp deformation.

45. 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. The engagement can be in the form of continuous contact, such as circumferential clasp, or discontinuous contact, such as Bar clasp. the clasp assembly must contact the abutment at 3 widely separated areas that encompass more than half the tooth circumference.

46. 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

47. Other principles Retentive clasp element should always be placed on facial surface of tooth (mainly in premolars) Only one retentive element should be used per tooth opposed by a reciprocal element. If a retentive clasp on one side of the arch is positioned on facial surface, atleast one clasp on contralateral side should be located on facial surface. 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.

48. 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

49. SURVEY LINE DEFINITION: • A line produced on a cast by a surveyor marking the greatest prominence of contour in relation to the planned path of placement of a restoration.

50. CLASSIFICATION OF SURVEY LINES BLATTERFEIN 1. T ypical survey line / medium 2. Atypical A or Diagonal 3. Atypical B or High 4. Atypical C or low

51. TYPICAL SURVEY LINE Extends from the occluso -gingival midpoint in the near zone to the junction between the occlusal two third and cervical one third in the far zone. Any occlusally approaching and gingivally approaching clasps based on other requirements

52. ATYPICAL A OR DIAGONAL SURVEY LINE This runs diagonally across the tooth surface from a high position in the near zone to a low position in the far zone. A reverse action or hairpin clasp Gingivally approaching clasp

53. ATYPICAL B OR HIGH SURVEY LINE This type of survey line is parallel to the occlusal surface and lies close to it. Occlusally approaching clasp (wrought wire) If accompanied by a low survey line on the opposite side of the tooth, a ring clasp/ back action/ reverse action clasps are recommended .

54. ATYPICAL C OR LOW SURVEY LINE The low survey line is parallel to occlusal surface but has just above the level of the gingival margin. The extended clasp arm is recommended. Undercut may be developed by recontouring the tooth.

55. Ney: Recommended 3 basic survey line with an appropriate clasp form. Class I: • Survey line runs diagonally across the tooth surface from a low position on the side of the rest to a high position on the other proximal side. • A cast occlusally approaching arm or its variants, back action, reverse back action and ring clasps are recommended.

56. Class II: Similar to Blatterfein atypical A or Diagonal survey line. Here gingivally approaching clasp is recommended.

57. Class III: It is the same as the Blatterfein Atypical B or High survey line. The wrought wire arm is used.

58. DEPTH AND MAGNITUDE OF UNDERCUTS. the portion of the surface of an object that is below the height of contour in relationship to the path of placement -(GPT 9)

59. Tooth Undercuts (Proximal undercuts)

60. 0.25 mm - 0.01” chrome cobalt 0.5 mm – 0.02” cast gold 0.75 mm – 0.03” stainless steel

61. AESTHETICS • Avoid circumferential clasp in the anterior part of the mouth • Keep retainer tips as close to gingival margin as is consistent with gingival health. • Use lingual or proximal undercuts where applicable • Use extended guide planes where applicable • Omit some direct retainers and rely on indirect retention to gain stability. • If it cannot avoided to place the retainer in a visible portion, then sand blast the alloy surface to reduce reflected glare and make it less obtrusive in the mouth.

62. ROOT SIZE AND FORM OF THE TOOTH: Clinical conditions of supporting structures i.e alveolar bone and periodontal ligament should be considered. Abutment teeth with short, conical roots, bone loss and periodontal ligament, mild periodontal problem may not be able to withstand lateral forces that would be within physiologic limits of a healthy sound tooth. Such tooth must be preserved by using bar clasp arm with increased length of clasp arm

63. ORAL HYGIENE AND CARIES: • Maintaining oral hygiene is pre requisite to treatment with cast partial denture. • High caries index- Contraindicate the use of clasp with an unprotected tooth surface as with a ring clasp. • Bar clasp has minimum tooth structure contact and less interference with natural cleansing action. • Patient education is essential for maintenance of oral hygiene, proper use of prostheses, its placement and removal.

64. TYPES OF CLASPS 2 basic categories: I. Circumferential / Aker’s clasps/ suprabulge / occlusally approaching II. Vertical projection / Bar / Roach / infrabulge / gingivally approaching

65. CIRCUMFERENTIAL CLASPS 1.Simple circlet clasp. 2.Reverse circlet clasp 3.Multiple circlet clasp 4.Embrasureclasp/modified crib clasp 5.Ring clasp 6.C/ fish hook/ hair pin clasp/ reverse action clasp. 7.Back action clasp 8.Half and half clasp 9.Onlay clasp 10.Clasp with extended arm 11.Devan clasp 12.Combination clasp BAR CLASPS T- clasp •Modified T- clasp •Y- clasp •I-clasp and I-bar

66. 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 tooth surface that is covered by the clasp assembly leads to enamel decalcification.

67. Design rules 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. All the components of the C clasp should be present above the height of contour except the retentive tip. The retentive terminus should always be directed towards the occlusal surface never towards the gingiva. It should always terminate at the mesial or distal line angle never at midfacial or midlingual surface.

68. The retentive arm should be positioned as far apically on the abutment as is practical (not impinging the gingiva) 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 (b)the distofacial surface of an abutment adjacent to an extensive anterior edentulous space.

69. SIMPLE CIRCLET CLASP Most versatile and widely used. Originates on the proximal surface of abutment adjacent to edentulous area, with the clasp arm projecting away from edentulous space. Simple design INDICATION: On any tooth when the retentive undercut exists in a favourable location. Tooth supported RPD Kennedy’s Class III

70. ADVANTAGES: Retention, support, stability, reciprocation, encirclement & passivity better than any other. Minimizes food entrapment. Uncomplicated design features enables easy to construct and repair if broken DISADVANTAGES: It tends to increase the circumference of the crown. Un-aesthetic Retentive undercuts on some teeth are difficult to reach with retentive terminal of the clasp. More tooth surface is involved. It is half round, so it prevents the adjustments in the increased or decreased retention

71. MULTIPLE CIRCLET CLASP Two opposing simple circlet clasps joined at the terminal end of reciprocal arms. INDICATIONS: For additional retention – when primary abutment is periodontally compromised Tooth borne partial denture Multiple clasping required, when the partial denture replaces an entire half of the dental arch. ADVANTAGES: Additional support for the weakened abutment tooth

72. REVERSE CIRCLET CLASP Generally used when the retentive undercut is on that facial/ lingual surface of the abutment tooth that is adjacent to edentulous space. Arises from mesial side. Ends on the distal undercut. INDICATIONS: When bar clasp is contra indicated due to soft tissue undercut and when hair pin clasp is contraindicated due to short crown. In kennedy’s class I and class II RPD.

73. ADVANTAGES: exerts a mesially directed force on the abutment tooth in distal extension RPD Fewer stresses are transmitted. DISADVANTAGES: Esthetics is compromised- Not a clasp of choice canine and premolars Need for creating more space for rest and shoulders- significant amount of removal of tooth structure Marginal gingiva may traumatized

74. C/FISH HOOK/HAIR PIN CLASP The C clasp is a simple circlet clasp in which the retentive arm crosses the facial surface of the tooth from its point of origin, loops back in hairpin turn to engage a proximal undercut below its point of origin. The upper part – rigid The lower part – tapered and flexible Consideration:- • Sufficient clinical crown height. • Space between occlusal and apical arm. • Occlusal arm shouldn’t interfere within the occlusion • Disto -facial undercut is present Lingual view Buccal view

75. INDICATIONS: When the retentive clasp must engage an undercut adjacent to the occlusal rest or edentulous space and a soft tissue undercut precludes the use of a bar clasp. When the reverse circlet clasp cannot be used because of lack of occlusal space. Sufficient occluso -gingival height CONTRA INDICATION: young patient or one who is prone to caries DISADVANTAGES: High coverage – food debris unacceptable esthetically(excessive display of metal) particularly on premolar teeth. Yields inadequate flexibility

76. EMBRASURE CLASP/MODIFIED CRIB CLASP/RIB CLASP/BONWILL CLASP Two simple circlet clasps joined at the body Sufficient space must be provided between the abutment teeth in their occlusal-third to make room for the body of embrasure clasp. Contact area should not be eliminated completely.

77. Abutment tooth should be protected with crowns or inlays if necessary. This depends upon the age of the patient caries index and oral hygiene. This clasp should be used with double occlusal rest. Proximal shoulder be established. To avoid interproximal wedging by the prosthesis. This clasp should have two retentive clasp arms and two reciprocal arms either bilaterally or diagonally opposed. INDICATIONS: Kennedy class II, III cases where no edentulous space on opposite side of the arch.

78. CONTRA INDICATION: Short and bulbous crown. Not preferred in teeth with more undercuts. DISADVANTAGES: Needs adequate clearance in occlusal surface. Breakage of inadequate preparation. Wedging action.

79. RING CLASP Encircles the tooth almost. Auxillary bracing arm is to be provided which usually projects from the acrylic resin. INDICATION: Tipped mandibular molars Single standing tooth

80. Unsupported mandibular molar tend to drift and tip in a mesiolingual direction & Maxillary molar tip is a mesio buccal direction. So available retentive undercut will be located on the mesiolingual line angles of a mandibular molar and the mesiobuccal line angle of maxillary molar. This ring clasp permits engagement of this undercut by encircling almost the entire tooth from its point of origin. Mandibular molar, clasp encircles the tooth beginning on the mesiobuccal surface and terminating in an infra bulge area on the mesiolingual surface.

81. Because of the length of the clasp, it must be designed with additional support, usually in the form of an auxillary bracing arm. This can provide reciprocation and some amount of stability for the denture. The entire clasp except the retentive terminal shall be placed above the height of the contour. An additional occlusal rest can be placed may provide additional support and prevent mesial migration of tooth CONTRA INDICATION: In mandibular molar, where the attachment of buccinator muscle is so close to the tooth.

82. ADVANTAGES: Excellent bracing. Decreased leverage Less stress to abutment teeth. DISADVANTAGES: Needs long crown and enough occlusal clearance. Difficult to repair

83. BACK ACTION CLASP Modification of the ring clasp. Has a rest which is unsupported. INDICATION: For unilateral and bilateral edentulous arches. Distal extension partial denture ADVANTAGES: Less metal display Less tooth coverage it braces the abutment on the mesial even if the tooth is tipped distally. Marginal gingiva left uncovered - better partial denture health

84. HALF AND HALF CLASP This clasp consists of a circumferential retention arm arising from one direction and a reciprocal arm arising from another minor connector. This principle of half and half clasp should be applied only to a unilateral denture design. The buccal arm provides for bracing only. The lingual arm utilizes an undercut adjacent to the edentulous space for retention.

85. INDICATION: Lingually inclined premolars where lingual undercut are close to the edentulous space. CONTRA INDICATION: Buccally inclined premolars

86. ONLAY CLASP Extends from an occlusal onlay into an undercut located mesio distally. Is an extended occlusal rest with buccal and lingual clasp arms. Originate from any point on the onlay that will not create any occlusal interference. INDICATION: When the occlusal surface of the abutment tooth is below the occlusal plane Only in caries resistant mouth unless it is covered by gold crown.

87. ADVANTAGES: Mesially tilted molars to be used to provide retention. 3rd molar occlusion may be improved. DISADVANTAGES: Difficult to fit clasp to tooth. Increased contact area - accurate impression and the resultant cast difficult to achieve.

88. CLASP WITH EXTENDED ARM The extended clasp arm covers two teeth. It remains above the survey line of the first tooth and crosses into the undercut of adjacent tooth. INDICATIONS: Tooth next to edentulous space has no buccal or lingual undercut. Tooth supported RPD CONTRA INDICATIONS: In distal extension RPD

89. ADVANTAGES: Has splinting and stabilising action Distributes lateral loads over two teeth. DISADAVANTAGES More tooth structure covered Easy distortion Breakage of the arm.

90. DE VAN CLASP Uses proximal undercut and has a small head that bears on tooth entirely below survey line. Clasp arises and lies closely against at the periphery of the denture base. Denture base is under extended to provide room for the approaching arm. It is reciprocated with lingual and palatal minor connecter. Two occlusal rest on the lingual side of the teeth. DeVan , M. M.: Embrasure Saddle Clasp-Its Principle and Design, J.A.D.A. 22: 1352-1362, 1935.

91. ADVANTAGES: Esthetically acceptable, because of interproximal location or it is hidden behind the buccal concavity. The distribution of stress during insertion and removal is minimal. Increased retention without tipping action on the abutment. Less chance of accidental deformation because it doesn’t project very far away from the denture base.

92. COMBINATION CLASP – wrought wire circumferential clasp Wrought wire retention arm which better dissipates functional stresses. Consists of occlusal rest, cast metal reciprocal arm and a wrought wire retentive arm. Wrought wire component circular in cross section. INDICATIONS: Kennedy’s class I & II Abutment adjacent to the distal extension where only a mesio gingival undercut exists on the abutment Weak abutment When bar retainer is contra indicated in cases of large tissue undercut. Esthetics maxillary canine / premolar

93. ADVANTAGES: Flexibility Adjustability Esthetics Minimum tooth surface coverage Less chances of failure Weak abutments

94. INFRABULGE CLASP/BAR CLASP/ROACH CLASP Popularized by Ewing Roach in 1930 called it the Bar Clasp. The bar clasp is a cast clasp that arises from the partial denture framework and approaches the retentive undercut from gingival direction Retentive clasps are identified by shape of retentive terminal, i.e. T, Y, L, I, U, and S. The shape is unimportant as long as the direct retainer is mechanically and functionally stable, covers minimal tooth structure with minimum display • Push type retention. • Flexibility of clasp from length and taper. • More aesthetic than c clasp. Roach, F. E.: Principles and Essentials of Bar Clasp Partial Dentures, J.A.D.A. 17: 124-138, 1930.

95. 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 should not impinge the underlying gingiva. 3. Should not 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. 6. The minor connector that attaches the occlusal rest to the framework should be rigid and should contribute to the overall bracing and stabilization characteristics of the prosthesis. Roach, F. E.: Principles and Essentials of Bar Clasp Partial Dentures, J.A.D.A. 17: 124-138, 1930 .

96. T CLASP Name is from the shape of the retentive terminal. Used in combination with cast circumferential reciprocal arm. The retentive terminal and its opposing encircling finger projects laterally from the approach arm to form T. The retentive terminal - engage the retentive undercut. The approach arm should taper gradually and uniformly from its origin to the retentive terminal. The approach arm contacts the tooth only at the height of contour.

97. INDICATION: In distal extension ridge - undercuts on distobuccal surface of the terminal abutment tooth i.e Used in Kennedy’s class 1 and class 2 situation Tooth supported partial denture - retentive undercut on the abutment tooth adjacent to the edentulous space. CONTRAINDICATION: Remote undercut If the approach arm crosses the soft tissue undercut. When the height contour is close to the occlusal or incisal surface of abutment tooth.

98. MODIFIED T CLASP It is a T clasp with the non retentive (mesial) terminal is omitted. INDICATION: Used on canines or premolar - esthetic. DISADVANTAGE: Encirclement of abutment sacrificed

99. Y CLASP It is basically a T-clasp, its configuration occurs when the height of contour on the facial surface of the abutment tooth is high on mesial and distal line angles but low on the center of the facial surface. The approach arm terminates in the cervical third of the abutment while the mesial and distal projections are positioned near occlusal / incisal surface The indication and contraindication of Y-clasp are same as the T-clasp.

100. I CLASP AND I BAR Used on distobuccal surface of maxillary canine for esthetic reason. DISADVANTAGE: The contact of the retentive clasp with the abutment tooth is the tip of the clasp at an area of 2-3 mm. Encirclement , horizontal stabilization may be compromised.

101. Circumferential clasp Bar clasp design 2clasp arm partially encircle the abutment tooth Extension of metal framework projects along the mucosa, crosses the gingival margin of the abutment tooth and approaches the infrabulge of the tooth in a cervico occlusal direction. advantages Easy to design and construct Excellent support, bracing and retentive qualities Fewer problems of food retention. Offers more retention Esthetic since gingival approach

102. disadvantages Enamel decalcification/ caries since more tooth surface is covered unaesthetic Reduced bracing and support qualities Greater tendency to collect and hold food debris

103. circumferential bar retention bracing Pull type retention Difficult to place ,easy to remove Push type retention Easy to place and difficult to remove Because of rigidity it provides good stability and bracing It is more flexible bcoz of which it provides less bracing or stability

104. Stress breaking effect Contact with Tooth structure Damage to Oral tissues Potential to torque on abutment teeth In distal extension based partial denture situations More tooth contact leading to food accumlation Damage to gingiva can take Place during improper removal Of clasp Minimal tooth contact and less tooth damage Minimum relief can lead to tissue damage to mucosa under approach arm Allows certain degree of functional movement , dissipates stress and lessen load on abutment

105. Other types of clasp philosophies • RPI • RPA • VRHR clasp or Grasso clasp • Equipose clasp

106. 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 plane, and an I bar retainer. LaVere M. Analysis of facial surface undercuts to determine use of RPI or RPA clasps. J Prosthet Dent. 1986 Dec;56(6):741-3

107. Krol in 1973 made certain modifications in the design under the “minimal coverage criteria” and named it RPI bar clasp design. Rest preparations are less extensive in the RPI system. Rests extend only into the triangular fossa, even in molar preparations, and canine rest. Krol, A. J.: RPI clasp retainer and its modifications. Dent Clin North Am 17:631, 1973.

108. Krol, A. J.: RPI clasp retainer and its modifications. Dent Clin North Am 17:631, 1973. The rest located on the mesial occlusal surface of the abutment tooth acts as the point of rotation and exerts a mesial force on the tooth rather than a distal displacing force Pressure exerted on the extension base causes the proximal plate to move tissue ward without torquing the tooth. The I bar also moves mesio-gingivally away from the tooth under masticatory load

109. ADVANTAGES: Elimination of the V-shaped food trap distal to the tooth. A highly polished metal contact with the marginal gingiva, rather than resin. Intimate metal-to-tooth contact to minimize food impaction. Passive in relation to tooth except for vertical displacing forces. DISADVANTAGES: Physiologic relief 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

110. CONTRAINDICATIONS TO THE R.P.I. CLASP Insufficient depth of the vestibule. (The inferior border of the I-bar must be located at least 4 mm from the gingival margin.) No labial or buccal undercut on the abutment Severe soft tissue undercut Disto -buccal undercut (less than 180° encirclement)

111. PRINCIPLES OF DESIGN : 1. The mesiobuccal rest with the minor connector is placed into the mesiolingual embrasure, but not contacting the adjacent tooth. 2. 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

112. 3. The proximal plate in conjunction with the mesial occlusal rest and minor connector provides the stabilizing and reciprocal aspects of the clasp assembly. 4. 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.

113. THERE ARE 3 APPROACHES TO THE APPLICATION OF THE RPI SYSTEM. Factors: The location of the rest, Design of proximal plate Location of the retentive arm ---- influence how this clasp system function. ONE APPROACH recommends that the guiding plane and corresponding proximal plate extends the entire length of proximal tooth surface with physiologic relief to eliminate impingement of the free gingival margin.

114. SECOND APPROACH suggests that guiding plane and corresponding plate minor connector extend from the marginal ridge to junction of middle and gingival 3rd of the proximal tooth surface. The two philosophy recommended that the retaining clasp arm be located in the gingival 3rd of the buccal or labial surface of the abutment teeth in a 0.01 inch undercut. THE THIRD APPROACH favors a proximal plate minor connector that contacts approximately 1 mm of the gingival portion of the guiding plane and the retentive clasp arm located in a 0.01 inch undercut in a gingival 3rd of the tooth at the greatest prominence or to the mesial away from the edentulous area.

115. 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.

116. VRHR Clasp The vertical reciprocal horizontal retentive arm concept was developed by Grasso in 1980 and is characterized by: 1. A distal occlusal rest supported by a minor connector. 2. A lingual vertical reciprocal component originating from the major connector. 3. A horizontal retentive arm attached to either the major connector or the retention latticework for the denture base. Grasso JE. A new removable partial denture clasp assembly. J Prosthet Dent. 1980 Jun;43(6):618-21

117. The advantages of designing a vertical reciprocal component to make minimal contact with the lingual height of contour are that 1. All lingual heights of contour are parallel to a vertical path of insertion and all vertical reciprocal components designed parallel to the path of insertion will make continuous contact with their respective tooth surface during placement and removal of the prosthesis 2. The placement of retentive arm is more aesthetic. 3. Minimizes the tooth contact of the clasp retentive arm without compromising on the efficacy of the design

118. Some disadvantages of the clasp assembly are (1) the potential of food traps on both the spaced, rigid two thirds of the horizontal retentive arm and the vertical reciprocal component, when well-defined undercuts are present on the abutment tooth and (2) the inability of the horizontal retentive arm to provide bracing.

119. 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. It is a lingual back action clasp that is fully reciprocated and extremely esthetic with no facial clasp display Goodman JJ. The Equipoise removable restoration. Trends Tech Contemp Dent Lab 1991;8:45-8, 50, 52.

120. The various alternatives available for modifying the visibility of direct retainers in the esthetic zone can be broadly classified as under: • Hidden clasps/internally braced clasps, • Masking of the clasps with resins and composites, • Metal-free clasps.

121. HIDDEN/Internally braced clasp: This design is especially suited for cases, in which anterior abutment tooth is a crowned mandibular canine and is excellent for Kennedy Class III cases. In this crown, a deep cingulum wedge-shaped rest is prepared with occlusally diverging walls and a rounded floor. An undercut is prepared in the gingivolingual third of the crown to accept the retentive arm of the RPD.

122. MGR CLASP : It is an esthetic extracoronal retainer for maxillary canines. MGR clasp design: McCartney described the MGR clasp in an effort to use the distofacial surface of the maxillary canines for retention and esthetic advantage Retention is attained with a 19-gauge wrought wire I-bar clasp arm, the end of which engages the prepared “dimple” on the distolabial surface. Reciprocation for the retentive clasp arm is provided by the distal proximal plate and the mesiolingual “rod-like” minor connector McCartney JW. The MGR clasp: an esthetic extracoronal retainer for maxillary canines. J Prosthet Dent. 1981 Nov;46(5):490-3

123. McCartney JW. The MGR clasp: an esthetic extracoronal retainer for maxillary canines. J Prosthet Dent. 1981 Nov;46(5):490-3

124. Saddle lock: Eliminates facial clasp display while achieving natural esthetics with superior stability and retention. Saddle lock eliminates facial clasps by using the available mesial/distal concave surfaces of the abutment teeth for retention instead of the buccal undercuts. The benefits of saddle lock • Superior esthetics, without visible clasps, • Improved retention with little or no adjustment, • Easy vertical insertion that protects abutments, • Applicable in most partial denture cases, • Simple preparation procedures for less chair time.

125. Spring clasp/twin flex clasp: This consists of a wire clasp soldered into a channel that is cast in the major connector. As this clasp is flexible, it does not generate as much as torque when the distal extension is depressed. The ability to adjust this clasp and its conventional path of insertion provides an excellent design option for retention to an adjacent edentulous segment. DISADVANTAGES There is extra thickness of major connector over the wire clasp, an extra laboratory step incurs extra cost, difficulty in repairing the clasp if breakage occurs.

126. Belles DM. The Twin-Flex clasp: an esthetic alternative. J Prosthet Dent. 1997 Apr;77(4):450-2

127. MASKING THE DIRECT RETAINER The use of composite resin to disguise metal clasps is in harmony with current esthetic trends. The difficulty of using acrylic/composite resin to veneer RPD metals lies in the difference between their abilities to flex and their coefficient of thermal expansion.

128. Disadvantages o Bulk that is created by adding the veneer will enlarge the total size of the clasp thus defeating the purpose of disguising the clasp, o bonding is unreliable, o Gap formation and microleakage when used in combination with composites.

129. METAL-FREE CLASPS The metal-free materials available now are ideal for flexibility and esthetics thus allowing esthetic functional care in the true sense. Opti•flex invisible clasp partials: With the Opti•Flex acetyl resin clasps, metal-free, lightweight partial dentures that provide natural esthetics and a comfortable fit can be designed. Using the Opti•Flex Coating applied to metal clasps, it is possible to give new or existing metal partial dentures a new esthetic appeal. It is available in 16 tooth-colored shades (matched to the base Vita Shades) and hence Opti•Flex can meet every patient's esthetic requirements.

130. Flexite plus cast thermoplastic: Flexite Plus 'Flexible' partial dentures eliminate the use of metal, providing patients with a metal partial denture alternative. Flexite Plus is fabricated from a flexible thermoplastic material that is available in three tissue shades. The material is monomer-free, virtually unbreakable, lightweight, and impervious to oral fluids. Flexite Plus may also be combined with a metal framework to eliminate the display of metal labial clasps.

131. FLEXITE PLUS

132. INDICATIONS 1. Partial dentures, 2. removable bridges, 3. long-term temporaries, 4. unilateral space maintainers. Available in 20 shades with three pink hues. The tooth or tissue coloured resin clasps though as slim as those made of metal provide superior strength. They are flexible and light weight. They are also up to 20 times harder than restorations fabricated from standard acrylic materials.

133. PROFLEX CLEAR WIRE CLASPS: Clear wire is an excellent new way to fabricate clear, strong, flexible clasps in minutes. This new material and technique can be used to make T-bars, I-bars, Roaches, Akers, and most other types of clasps. It can also be used to add or repair clasps in an existing partial denture.

134. SMILE-RITE PARTIALS: Smile Rite is a high strength acetyl resin-polymer used for making tooth coloured clasps on cobalt–chrome alloy partial frameworks. The combination of Smile Rite with a metal frame gives patients the proven long-term reliability of a cobalt-chrome alloy framework with the durability and esthetics of Smile-Rite tooth coloured clasps. Smile Rite is colour stable and is resistant to staining and plaque buildup. The high strength of Smile Rite makes it possible to fabricate the entire framework metal free. The framework can be made from either tissue colour or tooth colour monomer-free Smile-Rite acrylic.

135. THEMOFLEX THERMOPLASTIC CLASPS: VALPLAST Thermoflex is an improved acetal resin system that brings the many benefits of metal-free restorations without the pitfalls associated with acrylic. Thermoflex is so flexible that it can flex around the largest tooth, and then use its superior elastic memory to cling deeper into the undercut for a rigid functional hold. It is a Hypoallergenic, monomer-free material ideal for patients with allergies or patients that cannot tolerate a metal partial framework. It is hydrophobic; hence does not absorb water or saliva. Thermoflex has unsurpassed durability and it bonds well with conventional acrylics, as well as, to itself, which means it can be repaired, relined or rebased.

136. INDIRECT RETAINER Concept of indirect retention was originally advanced by Dr. W E Cummers . In absence of indirect retainer : The denture base moves away from soft tissues 2. The anterior segment of major connector impinges upon underlying soft tissues.

137. Fulcrum line: An imaginary line, connecting occlusal rests, around which a partial removable dental prosthesis tends to rotate under masticatory forces.(GPT 8)

138. INDIRECT RETAINER “The component of a partial removable dental prosthesis that assists the direct retainers in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of the fulcrum line.

139. INDIRECT RETENTION “ The effect achieved by one or more indirect retainers of a partial removable dental prosthesis that reduces the tendency for a denture base to move in an occlusal direction or rotate about the fulcrum line” The concept of indirect retention was originally described by Dr.W.D.CUMMER

140. When occlusal load is applied to a distal extension removable partial denture, the prosthesis rotates around a fulcrum line that passes through the most posterior rests, one on each side of the dental arch. This displacement is resisted by broad and accurate adaptation of the denture base to the supporting tissues.

141. During these forces, the associated fulcrum line passes through the tips of the retentive clasps and the anterior portion of the prosthesis rotates in an apical direction resulting in unwanted prosthesis impingement into the soft tissues of the floor of the mouth.

142. Indirect retainer should be placed as far as possible from the distal extension base which provides best leverage advantage against dislodgement . This impingement of the prosthesis into the floor of the mouth is negated as the fulcrum line is transferred to the anterior rest which acts as an indirect retainer

143. Auxiliary functions of indirect retainers When in positive contact with rest seat, an indirect retainer contributes to the overall support and stability of the prosthesis. For long span lingual bar, it can provide additional support and rigidity to the major connector. It tends to reduce antero -posterior-tilting leverages on the principal abutments, particularly when isolated tooth is being used as an abutment.

144. Contact of its minor connector with axial tooth surfaces aids in stabilization and also acts as auxiliary guide plane. Anterior teeth supporting indirect retainers are stabilized against lingual movement. It provides the first visual indications for the need to reline an extension base partial denture.

145. Factors influencing effectiveness of indirect retainers The principal occlusal rests on the primary abutment teeth must be reasonably held in their seats by the retentive arms of the direct retainers.

146. 2. Distance from the fulcrum line. The following three areas must be considered: a. length of the distal extension base b. location of the fulcrum line & indirect retainer. c. how far beyond the fulcrum line the indirect retainer is placed. 3. All connectors supporting the indirect retainer must be rigid . 4. The indirect retainer must be placed on a definite rest on which slippage or tooth movement will not occur. Tooth inclines and weak teeth should never be used.

147. Indirect retention can be achieved if one or more rigid indirect retainers are used. Indirect retainer should be positioned opposite to the fulcrum line. The greater the distance between the fulcrum line and the indirect retainer the more effective the direct retainer will be. Position of the indirect retainer should be perpendicular to – and as far from the primary fulcrum line as is practical. Indirect retainers should not be placed on maxillary and mandibular incisors, canines. premolars are commonly used because of their increased periodontal support.

148. FORMS OF INDIRECT REATINERS An indirect retainer is an auxillary occlusal , cingulum or incisal rest that contacts a properly designed rest when the removable partial denture is in place. An occlusal rest is preferred because of its location and vertical orientation , an occlusal rest permits forces too be directed with in the long axis of the abutment tooth. A cingulum rest is generally limited to maxillary canine due to the morphology of this tooth – appropriate rest preparation with minimal recontouring .

149. INCISAL REST An incisal rest may provide indirect retention when other rests are contraindicated. This situation is true for maxillary and mandibular incisors and mandibular canines. Because of the unfavorable lingual anatomy of these teeth, incisal rest may be the only acceptable option. DISADVANATGES :- Esthetically objectionable Exhibit long approach arm May transfer harmful tipping forces to abutment teeth.

150. IF AN INCISOR REST SEAT MUST BE PREPARED More effective indirect retention is achieved by preparing the incisor to receive either a full coverage restoration or cast metal rest bonded to lingual surface of the teeth. The result should be a well designed lingual rest seat that provides Appropriate contours Optimal force distribution Permits an effective means of indirect retention.

151. TYPES OF INDIRECT RETAINERS - Auxiliary occlusal rest or canine rest. Canine extension of the occlusal rest. Continuous bar and lingual plate . Indirect retention from the major connector. Rugae Support.

152. Auxiliary Occlusal Rest

153. Canine rest

154. Canine extension of the Occlusal rest

155. Indirect retention from the major connector

156. CONCLUSION In designing of direct & indirect retainers in RPD, the retention of the denture should not be the only prime objective of the design. In addition, restoration of function and appearance, the maintainence of comfort, preservation of health and integrity of all the oral structures, ability to distribute stress are to be considered and the simplest clasp possible is to be given that meets all the functional requirements.

157. REVIEW OF LITERATURE Change in the retentive force of Akers clasp for zirconia crown by repetitive insertion and removal test Tanaka et al J prosthodont res. 2019 Evaluated the suitability of monolithic zirconia crowns (MZC) as abutment teeth of Akers clasps on RPD by determining the change in retentive force after repetitive insertion/removal test. MZC and Ag– Pd full-metal crowns (FMC) for the mandibular 2 nd premolar were fabricated. Resin patterns of Akers clasps made with a 3D printer were casted with Ag– Pd or Co–Cr. Clasp retentive force was measured with combinations of the crown and clasp materials. After measuring the initial retentive force of the clasp, repetitive insertion/removal test was carried out. The surface of the crown before and after the test was observed with an optical microscope and a scanning electron microscope; some specimens were subjected to element analysis by an electron probe microanalyzer

158. Master model crown Buccolingual cross sec Mesiodistal cross sec Clasp design

159. Results Showed that the initial retentive force of the Co–Cr clasp was greater than the Ag– Pd clasp for both MZC and FMC. Clasp retentive force decreased with increasing number of insertion/removal cycles, and least reduction in force was observed for the Ag– Pd clasp on MZC. Wear marks were detected where FMC contacted the clasp. Discoloration of MZC due to wear of the Co–Cr clasp was observed Conclusion When repetitive insertion/removal of the clasp was performed on MZC, retentive force decreased depending on clasp materials. However, the amount of decrease in retentive force was comparable or small compared to conventional FMC. As a result, it was suggested that MZC could be used on abutment tooth for RPD

160. Esthetic Cast Direct Retainers for Distal Extension Removable Partial Dentures Hundal M, J Pak Prosth asso 2014, Intraoral examination revealed: 1. Partially edentulous condition (Missing teeth: 16,17,24,25,26,27,28&47) 2. Caries involving tooth: 21 3. Gingival health normal

161. Treatment included: 1. Thorough oral prophylaxis 2. Composite restoration in tooth: 21 3. Three unit Ceramometal FPD replacing tooth: 47 4. Maxillary cast RPD replacing the missing teeth incorporating the MGR clasp for tooth: 23

162. Conclusion To conclude the MGR clasp designs are good alternatives to the conventional extracoronal cast circumferential or bar clasp direct retainer in a distal extension partially edentulous situation thereby providing esthetically functional care which is the demand of today’s patient concern.

163. CAD/CAM Constructed Poly( etheretherketone ) (PEEK) Framework of Kennedy Class I Removable Partial Denture: A Clinical Report Harb IE et al. J Prosthodont. 2019 Feb;28(2):e595-e598 Clinical Report 56 year old female patient presented wearing a maxillary complete denture opposing a bilateral metallic RPD. Her chief complaints were a metallic taste sensation, compromised esthetics , and need for better mastication with stable prostheses. Clinical examination revealed a completely edentulous maxillary arch opposing a mandibular unmodified Kennedy class I arch form extending from the existing first premolars bilaterally.

164. TREATMENT PLAN A new maxillary conventional denture and mandibular RPD with PEEK framework using CAD/CAM milling technology were considered for the treatment. Virtual model after scanning of the definitive cast. Digital surveying.

165. Relief under lingual bar and minor connectors crossing gingival margins. Retention grids and major connector in place Rests, minor connectors, and external finish lines in place. Relation of the clasp to the survey line

166. Resin pattern of the framework made with prototyping technology Trial of the PEEK framework Finished prosthesis intraorally

167. Conclusion The use of CAD/CAM technology for constructing an RPD metal-free framework resulted in a prosthesis with adequate fit, and good patient satisfaction in terms of function and esthetics. With proper patient selection and treatment planning, milled PEEK can be considered a useful alternative framework material for RPDs restoring Kennedy Class I edentulous patients.

168. Comparison of titanium and cobalt-chromium removable partial denture clasps Purpose. This study assessed the characteristics of cast clasps made of titanium and titanium alloys to determine whether these materials are suitable alternatives for removable partial denture applications . Bridgemana JT, Marker VA, Hummel SK, Benson BW, Pace LL. Comparison of titanium and cobalt-chromium removable partial denture clasps. The Journal of prosthetic dentistry. 1997 Aug 1;78(2):187-93.

169. Material and methods . Removable partial denture clasps at two undercut depths were fabricated from commercially pure titanium, titanium alloy (Ti-6A1-4V), and cobalt-chromium. Loss of retention force was measured as the clasps underwent 3 years of simulated clinical use. Results. For the 0.75 mm undercut specimens, there was less loss of retention for clasps made from pure titanium and titanium alloy than for cobalt-chromium clasps.

170. Conclusions. The long-term retentive resiliency of the pure titanium and titanium alloy clasps suggests that these materials are suitable for removable partial dentures .

171. Mathematical Analysis of Occlusal Rest Design for Cast Removable Partial Dentures Luk NK, Wu VH, Liang BM, Chen Y, Yip KH, Smales RJ. Mathematical analysis of occlusal rest design for cast removable partial dentures. European Journal of Prosthodontics and Restorative Dentistry. 2007 Mar 1;15(1):29. To establish the minimum dimensions for a non-precious cast metal occlusal rest by using mathematical analysis

172. Methods The stress status of an occlusal rest in a posterior tooth-bounded RPD resembles that of a cantilever beam under a uniformly distributed load. A mathematical model based on a short rectangular cantilever beam was derived by using the yield strengths of a cast cobalt-chromium alloy, with an applied static occlusal force of 400 N.

173. RESULTS For the cobalt-chromium alloy, the minimum rectangular dimensions for a 2.0 mm long occlusal rest are; when the width is 2.0 mm, the depth or thickness should be at least 1.03 mm.

174. Investigation of the effect of three sprue designs on the porosity and the completeness of titanium cast removable partial denture frameworks Al- Mesmar HS, Morgano SM, Mark LE. Investigation of the effect of three sprue designs on the porosity and the completeness of titanium cast removable partial denture frameworks. The Journal of prosthetic dentistry. 1999 Jul 1;82(1):15-21. This study evaluated the ability of 3 sprue designs (tree, ball, and circular) to produce complete, void-free castings of removable partial denture frameworks made from commercially pure titanium

175. No statistically significant differences in the total number of porosities were found between the 3 sprue designs The ball- sprue design produced the most complete castings for the removable partial denture titanium frameworks.

176. Behavior of mandibular canines as abutment teeth and indirect retainers in Kennedy class II Removable Partial Denture Prosthesis Camacho MC, Gallardo YR, Stegun RC, Costa B, Sesma N. Behavior of mandibular canines as abutment teeth and indirect retainers in Kennedy class II Removable Partial Denture Prosthesis. Heliyon . 2018 Mar 1;4(3):e00575. Purpose: The purpose of this study was to evaluate the behavior of mandibular canines acting as abutment teeth and indirect retainers of a Kennedy class II according to different designs: lingual rest and lingual rest associated with a reciprocal arm.

177. RESULT The abutment teeth showed movement in the lingual and mesial directions, and this movement was less when associated with the reciprocal arm design. CONCLUSION The results suggest that a lingual rest associated with a reciprocal arm may lead to decreased tooth mobility when a canine is the abutment of a Kennedy class II RPDP.

178. The Effects of Buccolingual Width and Position of Occlusal Rest Seats on Load Transmission to the Abutments for Tooth-Supported Removable Partial Dentures Int J Prosthodont 2001;14:340–343. AIM The aim of the present study was to use three-dimensional geometric analysis to evaluate the effects of buccolingual width and the location of occlusal rest seats on load transmission to the abutments for tooth-supported removable partial dentures.

179. Materials and Methods: A tooth-supported portion of a maxillary removable partial denture with two conventional circumferential cast clasps and an indirect retainer was analyzed . Occlusal loading of 100 N was applied to the buccal mesial cuspal incline 2.0 mm from the central fossa of the first molar or to the lingual mesial cuspal tip. Four combinations of position and width (wide, buccal shift, middle, and lingual shift) were simulated.

180. Results: For buccal loading, the wide rests and buccal-shift rests produced lower tensile forces at the indirect retainer. For lingual loading, the buccal-shift rests produced the lowest compressive force to the anterior abutment. Conclusion: Based on the tooth-supported removable partial dentures that were analyzed , buccal shifting of the rest seats seems to be advantageous for load transmission to the abutments.

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182. 10. Bridgeman et al. comparision of titanium and cobalt chromium removable partial denture clasps. J Prosthet Dent 1997;78(2):187-93. 11. Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Retention ,Brit Dent J 2000;189(12):646-657 12. Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Bracing and reciprocation ,Brit Dent J 2001;190(1):10-14 13. Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Clasp design , Brit Dent J 2001;190(2):71-81 14. Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Indirect Retention ,Brit DentJ 2001;190(2):128-132 15. McCartney JW. The MGR clasp: an esthetic extracoronal retainer for maxillary canines. J Prosthet Dent. 1981 Nov;46(5):490-3 16. Harb IE et al. CAD/CAM Constructed Poly( etheretherketone ) (PEEK) Framework of Kennedy Class I Removable Partial Denture: A Clinical Report J Prosthodont. 2019 Feb;28(2):e595-e598

183. THANK YOU