Direct Retainers II

Different types of direct retainers used in RPD and its indication. Supporting literature for selection of direct retainers case-specific.

1. Recap…

2. Suprabulge clasps Infrabulge clasps Design Philosophies utilizing I-Bar Studies relevant to kinetics of direct retainer and terminal abutment. Summary References

3. Learning Objectives Sr.no Topic Domain Significance 1. Design rules of Suprabulge clasps Cognitive & Psychomotor Must know 2. The examples of Suprabulge clasp and their designs Cognitive & Psychomotor Must know 3. Design rules of Infrabulge Clasp Cognitive & Psychomotor Must know 4. The examples of Infrabulge clasp and their design Cognitive & Psychomotor Must know 5. The Design Philosophies utilizing I bar Claps Cognitive & Psychomotor Must know

4. Classification of Direct Retainers Stewart’s clinical removable partial prosthodontics 4th edition

5. Examples of Few Clasp-Type retainer Bar-type clasp Y-bar clasp I-bar clasp T-bar clasp Modified T-bar clasp Circumferential clasp Simple circlet clasp Reverse circlet clasp Embrasure clasp ring clasp back-action clasp multiple clasp Hairpin clasp Combination clasp Wrought-wire clasp McCraken’s Removable Partial Prosthodontics 13 th edition

6. Design Rules for Cast Circumferential Clasp McCraken’s Removable Partial Prosthodontics 13th edition It originates from a portion of the framework that lies above the height of contour It follows cervically in an arcing fashion Only the terminal part of the clasp arm crosses the height of contour The reciprocal arm must be located at or slightly above the height of contour The retentive terminus is directed occlusally Should terminate at the mesial or distal line angles of the abutment A Cast circumferential claps must never be given on Mesio -facial undercut of terminal abutment of a distal extension RPD Disto -facial undercut of abutment distal to long span anterior edentulous space

7. 1.Simple Circlet Clasp Clap of Choice for Tooth Supported Removable Partial Dentures. A simple circlet clasp usually originates on the proximal surface of an abutment adjacent to an edentulous area, with the clasp arms projecting away from the edentulous space. The terminus of the retentive arm engages an undercut that is remote from the edentulous space. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

8. Limitations of Simple Circlet Clasp. Difficult to Adjust, only can be adjusted in bucco-lingual direction. Tends to increase the circumference of the clinical crown. This may interfere with the elimination of food from the occlusal table and may deprive the adjacent gingival tissues of essential physiologic stimulation. Increased tooth coverage may promote decalcification and compromise dental aesthetics. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

9. 2. Reverse Circlet Clasp Used when the available undercut is located at the facial or lingual line angle adjacent to an edentulous space. Infrabulge clasp is preffered more than this clasp. Clasp of choice in Kennedy’s Class I and Class II edentulous cases. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

10. Limitations of Reverse Circlet Clasp The shoulder of a reverse circlet clasp originates from a minor connector that must traverse the marginal ridges of adjacent teeth. Significant amount of tooth must be removed if clasp is to be accommodated on a marginal ridge. Absence of rest adjacent to the edentulous area makes soft tissue susceptible to damage. Poor Aesthetic choice as it shows op on the buccal surface. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

11. 3.Multiple Circlet Clasp: It involves two simple circlet clasps joined at the terminal aspects of their reciprocal elements. Indication: when the principal abutment tooth is periodontally compromised Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition 4.Embrasure clasp design. An embrasure clasp is essentially two simple circlets joined at their bodies. Indication: Used on arch where there is no edentulous space.

12. 5.Ring Clasp Retainer of Choice on Tipped Molar Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

13. 6. Back Action Clasp Modification of Ring Clasp. The rest is not supported by a rigid minor connector. The proximal surfaces are not used as guiding plane(as they should be). The occlusal rest is flexible. Does engage the mesial undercut, just like the simple circlet clasp. McCraken’s Removable Partial Prosthodontics 13th edition Use is difficult to justify and has added disadvantage to the ring clasp.

14. 7. C-Clasp Design/Fish hook/Hairpin Clasp/Reverse Action clasp Retentive arm loops back to engage the undercut on the side of its origin. The occlusal portion till the bend follows even thickness, from this portion to terminal end it must be tapered. To accommodate this clasp there must be adequate vertical height. There must be adequate space between the occlusal and apical aspect of the retentive arm. This is one of the designs used when undercuts adjacent to the edentulous areas are to be engaged. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

15. 8. Onlay Clasp The rest is covering the entire occlusal surface and the clasps are originating from these metallic occlusal surfaces. Indicated: When the occlusal table is apical from the plane of occlusion. It is indicated in patients who have low DMFS score Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition However, if onlay clasp is indicated it is better to restore the teeth with a full coverage crown and go for more simpler designs of clasp

16. 9. Half and Half Clasp Circumferential retentive arm arising from one direction and a reciprocal arm arising from another . The second arm must arise from a second minor connector, and this arm is used with or without an auxiliary occlusal rest. There is little justification for the use of the half-and-half clasp in bilateral extension McCraken’s Removable Partial Prosthodontics 13th edition It was designed to provide double retention in cases of unilateral RPD’s

17. 10. Wrought-wire circumferential clasp (1965, O.C Applegate) Cast metal Reciprocal arm. Wrought wire retentive arm. Indicated: Deep undercuts Mesio facial abutment of distal extension type RPD’s(Class I and II) Caries prone individuals(as the round cross section makes fine contact with tooth surface) Can be used in areas of maxillary canines and premolars(Regards to esthetics ) Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

18. Infrabulge Clasps Design Rules for Infrabulge Clasps: The approach arm must not impinge on the soft tissues The approach arm should cross perpendicular to the free gingival margin The approach arm should never be designed to "bridge" an area of soft tissue undercut It must be uniformly tapered from origin to terminus The clasp terminus must be placed as apically as practical to counter lever like forces Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

19. Indications and Contraindications Indicated for all types of partially edentulous cases, but specifically for Keneddy’s Class I and II. In Esthetic Regions. Contraindicated when: Class I and Class II cases where the only available undercut is the mesio -facial undercut. If severe soft tissue undercuts are present When the height of contour is located occlusally

20. Designs Of Infrabulge Clasps T-Clasp Modified T-Clasp Y-Clasp I-Clasp/ I-Bar Indication: Useful in Distal extension cases More aesthetic than Suprabulge clasps Covers Less buccal surface.

21. Clasp Design Pecularities Name is from the shape of the retentive terminal. The retentive terminal consists of horizontal two projections the one on the distal side engages the undercut and the one on the mesial side is above the height of contour. 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.

22. RPI system Kratochvil developed an innovative clasp assembly in the early 1960s It consists of three separate units connected to each other only through the framework: Occlusal rest arising from minor connector on the side of the abutment away from edentulous space I-shaped bar clasp arm placed mid-buccally on abutment A vertical plate contacting the distal and distolingual surfaces of the abutment adjacent to the edentulous space

23. This clasp assembly consists of mesioocclusal rest with minor connector placed in the mesiolingual embrasure but not contacting abutment tooth A distal guiding plane extending from marginal ridge to junction of middle and gingival 3 rd of abutment tooth, prepared to receive proximal plate The buccolingual width of guiding plane is determined by proximal contour of the tooth Design for RPI McCraken’s Removable Partial Prosthodontics 13th edition

24. I-bar should be located in the gingival 3 rd of the buccal or labial surface of the abutment in 0.01-inch undercut Arm of the I-bar should be tapered to terminus, with no more than 2 mm of its tip contacting abutment The retentive tip, rest and proximal plate contact, provides stabilization through encirclement McCraken’s Removable Partial Prosthodontics 13th edition

25. Types of Proximal Plates in RPI The guide planes and proximal plate are in contact throughout the length of the tooth The guide planes and proximal plate are in contact only from marginal ridge to the middle third of the length of the proximal tooth. Bar clasp assembly in which the proximal plate contacts approximately 1 mm of the gingival portion of the guiding plane. During function, the proximal plate and the I-bar clasp arm are designed to move in a mesiogingival direction, disengaging the tooth. McCraken’s Removable Partial Prosthodontics 13th edition

26. Why Mesial Rest on terminal abutments in Distal saddles? Arch of rotation increases in radius and becomes linear. Mesial rests direct tipping forces towards mesial surfaces, the adjacent teeth to this provides buttressing effect. Stewarts’s Clinical Removable Partial Prosthodontics 4th Edition

27. Significance of Guiding Plane 1. Permits improved stabilization of the prosthesis 2. Reunites and stabilizes remaining teeth within the dental arch 3. Improves retentive characteristics by limiting/defining the path of insertion and removal 4. Protects the tooth-tissue junction by reducing food impaction between the tooth and the proximal plate 5. Provides reciprocation during insertion and removal of the prosthesis 6. Distributes occlusal forces throughout the arch

28. Advantages of the I-Bar Configuration. 1. Food accumulation is minimized because tooth contours are not significantly altered. 2. The clasp terminus disengages from the tooth when an occlusal load is applied to the adjacent distal extension base. 3. Because the approach arm does not contact the abutment, lateral forces are minimized. Disadvantages of the I-Bar Configuration. 1. Less horizontal stability than other types of clasp assemblies 2. Less retention

29. The RPL System The RPA System The retainer has been described as one-half T-bar or a modified T-bar clasp (L- Bar) The L-bar crosses the gingival margin of the abutment tooth in the shortest possible line, ascends to the survey line, and engages the distobuccal undercut Designed for mesially inclined abutment in cases of distal extension RPD The difference is in retentive arm. An Akers or circumferential clasp arm arises from superior portion of the proximal plate and extends around the tooth to engage the mesial undercut McCraken’s Removable Partial Prosthodontics 13th edition

30. When RPA is indicated Exaggerated buccal or lingual tilts. Severe buccal soft tissue undercuts Shallow vestibule.

31. Masao Moriko et al (1989) Compared the RPA, RPI and Akers Clasp: The Aker's clasp assembly induced the largest tooth movement. The behaviour of the RPA clasp were generally similar to those of the Aker's. They showed a larger disto -buccal inclination of the tooth. The RPI clasp seemed to be preferable for protecting the periodontal tissues from damage associated with larger tooth movement since it induced less inclination of the tooth in the distal direction. Analysis of Abutment Tooth Movement utilizing Mandibular Kinesiograph (MKG) Part 2. Effects of Clasp Design in Unilateral Free-end Denture Masao Moriko et al; Dental Materials Journal 8(1): 56-64, 1989

32. McCracken (1953) Support Requirement of Claps Design Tooth Borne From the abutments clasp should deform sufficiently during the insertion and removal Tissue Borne Elastic ,fibrous connective tissue covering over the residual alveolar bone. It is dependent upon the quality of that support for its stability under functional stresses . Clasp design flex sufficiently in the undercut to dissipate the stresses to alveolar bone A COMPARISON OF TOOTH-BORNE AND TOOTH-TISSUE- BORNE REMOVABLE PARTIAL DENTURES, JPD 1953,3,375

33. GEORGE W. HINDELS ,(1957) He stated that – the masticatory stresses exerted on the base of a distal extension partial denture are transmitted to the supporting tooth through contacting parts of the appliance Partial denture should be constructed so that the movement is vertical in relation to the supporting bone Clasps and rest should be designed to allow for this vertical movement of the denture base . Stresses other than those vertical to the abutment teeth should be reciprocated GEORGE W. HINDELS , STRESS ANALYSIS IN DISTAL EXTENSION PARTIAL DENTURES, J. Pros. Den. March, 1957 vol 7,197

34. The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures Tebrock et al ,JPD,1979,41,511 They concluded that No difference in mobility of abutment in all three cases Any mobility increases were in a buccal direction only , or towards the flexible retentive clasp arm All five patients chose the I-bar retainer as the design of choice due to its increase resistance to dislodgement

35. Motion vector analysis of an abutment for a distal-extension removable partial denture: A pilot study John W. McCartney , ,JPD, 1980,43,15 He concluded from his study that Less force to the abutment tooth was recorded when mesial rest was used as compared to a distal rest . Forces transmitted to the abutment was found to be greater when the vertical load was applied to the denture base on the same side than when applied to the opposite side of the denture base .

36. Direct Retainers Indications Rationale Supporting Literature Suprabulge Clasps Simple Circlet Clasp Class III Undercuts far from edentulous space are to be engaged. Rests derive support completely from abutments Roach FE (1908) Akers PE (1928) Multiple Circlet Clasps Class III When terminal abutment are periodontally week It splints the abutment and utilizes adjacent abutment to derive support Stewart 4 th ed McCraken 13 th ed Embrasure Clasps Class II cases where direct retention is to be derived from contra lateral arch where no edentulous space is present To achieve retention from a dentulous area. It utilizes occlusal embrasures for support Stewart 4 th ed McCraken 13 th ed Ring Clasp Mesially drifted lone distal molars which are to be used as abutment The clasp encircles the entire circumference and utilizes the mesio -lingual abutment which is usually the only abutment present Rests on both sides provides distribution of forces Stewart 4 th ed McCraken 13 th ed Other Suprabulge Clasps whose use are not justified include Half and half Clasp, Back action clasp, Onlay Clasp

37. Direct Retainers Indications Rationale Supporting Literature Direct Retainers used when tissue borne or composite support is utilized. Suprabulge Clasps Reverse Circlet Clasp Class I and II with Shallow vestibule, facial soft tissue undercut, height of contour located occlusally. The approach is Suprabulge, Less irritation to soft tissue apical to abutment. The approach is Suprabulge, Less irritation to soft tissue apical to abutment. The approach is Suprabulge, Less irritation to soft tissue apical to abutment. Stewart Reverse action Clasp Stewart Combination Clasp Periodontally week abutment, and Class I and II cases. Flexes in multiple planes, Distributes stress in multiple planes. Linear contact with tooth, thus helpful in caries prone individuals Flexes in multiple planes, Distributes stress in multiple planes. Linear contact with tooth, thus helpful in caries prone individuals Flexes in multiple planes, Distributes stress in multiple planes. Linear contact with tooth, thus helpful in caries prone individuals Roach FE (1913) Apple Gate OC (1965) Tebrock (1979) Infrabulge Retainers I bar and its modifications Class I, II and IV No soft tissue undercuts Atleast 3 mm of attached gingiva Utilizes Undercut of operators choice More esthetic, covers less area. Utilizes Undercut of operators choice More esthetic , covers less area. John W. McCartney (1980) RPI/ RPL Class I, II and IV Utilizes mesial rest Provides intermittent encirclement More esthetic Utilizes mesial rest Provides intermittent encirclement More esthetic Kratochvil(1963) Krol(1973) Tebrock (1979) Masao Moriko (1989) RPA Class I and Class II cases Presence of conditions not conducive for an I-bar design Krol (1976) Masao Moriko et al (1989)

38. References McCraken’s Removable Partial Prosthodontics 13 th edition Stewarts’s Clinical Removable Partial Prosthodontics 4 th Edition Thomas J. Donahue, Factors that augment the role of direct retainers in mandibular distal-extension dentures, JPD dec 1998 vol 60 number 6 Tebrock et al, The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures ,JPD,1979,41,511. John W. McCartney, Motion vector analysis of an abutment for a distal-extension removable partial denture: A pilot study ,JPD, 1980,43,15. GEORGE W. HINDELS , STRESS ANALYSIS IN DISTAL EXTENSION PARTIAL DENTURES, J. Pros. Den. March, 1957 vol 7,197 McCraken A COMPARISON OF TOOTH-BORNE AND TOOTH-TISSUE- BORNE REMOVABLE PARTIAL DENTURES, JPD 1953,3,375. Masao Moriko et al, Analysis of Abutment Tooth Movement utilizing Mandibular Kinesiograph (MKG) Part 2. Effects of Clasp Design in Unilateral Free-end Denture ;Dental Materials Journal 8(1): 56-64, 1989