RPD Manual 11 - Removable Prosthodontics - Dalhousie University

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Direct Retainers For Tooth and Tissue Borne <strong>RPD</strong>'s Direct and Indirect Retainers - 49 Tooth and tissue borne situations (Class I & II) require special attention in direct retainer selection, due to stresses created by rotational movements of the prostheses. When the denture bases are placed under function, rotation occurs about the rest seats of the most posterior abutments. Excessive occlusal forces on the distal-extension portion of the denture could cause a torquing action on the abutment teeth unless direct retainers are designed with stress-breaking capabilities. Stress releasing clasp assemblies include: 1. the bar clasp with mesial rest (e.g. RPI) 2. the RPA clasp 3. the combination clasp 1. Bar Clasps a. The bar clasp is a cast clasp that arises from the partial denture framework and approaches the retentive undercut from gingival direction (as opposed to a circumferential clasp that approaches the undercut from the occlusal direction). b. Retentive clasps are identified by shape of retentive terminal, i.e. T, Y, L, I, U, and S. c. The shape is unimportant as long as the direct retainer is mechanically and functionally stable, covers minimal tooth structure with minimum display (the I bar most often meets these requirements) d. T-and Y-shaped terminal ends are the most misused clasps. The full area coverage of the T and Y terminal ends is rarely necessary for adequate retention. e. L-shaped clasp is same as an I clasp with a longer horizontal component. The U-shaped clasp is same as an L-shaped clasp with a terminal like a double I-clasp. f. The S-shaped terminal end is used to avoid a mesial soft tissue undercut. g. Soft tissue relief is provided under the approach arm with 28 or 30 gauge wax, to prevent tissue impingement Contraindications: a) deep cervical undercuts - food trap or impingements result b) severe soft tissue or bony undercuts - food trap or impingements result
Direct and Indirect Retainers - 50 c) insufficient vestibular depth for approach arm (requires 4 mm - 3 mm from free gingival margin, 1 mm for thickness of the approach arm) d) pronounced frenal attachments in area - impingement The R-P-I Clasp 1. The components of this clasp assembly are: "R" - rest (always mesial) "P" - proximal plate "I" - I-bar (retentive arm) 2. The rest is located on the mesio-occlusal surface of a premolar or mesiolingual surface of a canine. The minor connector is located in the mesio-lingual embrasure but is not in contact with the adjacent tooth (prevents wedging). 3. The proximal plate (essentially a wide minor connector) is located on a guide plane on the distal surface of the tooth. The superior edge of the proximal plate is located at the bottom of the guide plane (at approximately the junction of the occlusal and middle third of the guide plane). The proximal plate extends lingually so that the distance between the minor connector and the proximal plate is less than the mesio-distal width of the tooth. The plate is approximately l mm. thick and joins the framework at a right angle. 4. The I-bar clasp is located on the buccal surface of the premolar and on the mesio-buccal surface of the canine. The I-bar originates at the gridwork and approaches the tooth from the gingival direction. The bend in the I-bar should be located at least 3 mm. from the gingival margin. This distance will prevent food entrapment and provide the length for the
Page 1 and 2:
Removable Partial Denture Manual Ro
Page 3 and 4: Table of Contents Table of Contents
Page 5 and 6: Table of Contents -iii Principles o
Page 7 and 8: Table of Contents - 2 4. poor progn
Page 9 and 10: Table of Contents - 4 F. Classifica
Page 11 and 12: Anatomy Tour - 6 Anatomy Tour for C
Page 13 and 14: Anatomy Tour - 8 ! Soft Palate ! Vi
Page 15 and 16: Anatomy Tour - 10 OTHER STRUCTURES:
Page 17 and 18: Preliminary Impressions - 12 6. Wra
Page 19 and 20: Surveying, Path of Insertion, Guidi
Page 29 and 30: Rests and Rest Seats - 24 A. Defini
Page 31 and 32: Rests and Rest Seats - 26 (d) The f
Page 33 and 34: Rests and Rest Seats - 28 Correct P
Page 35 and 36: Rests and Rest Seats - 30 2. The in
Page 37 and 38: Major Connectors - 32 Definition Ma
Page 39 and 40: Major Connectors - 34 3. Position -
Page 41 and 42: Major Connectors - 36 B. Full Palat
Page 43 and 44: Minor Connectors - 38 Definition Mi
Page 45 and 46: Minor Connectors - 40 The junction
Page 47 and 48: Minor Connectors - 42 When the dent
Page 49 and 50: Direct and Indirect Retainers - 44
Page 53: Direct and Indirect Retainers - 48
Page 65 and 66: Denture Bases - 60 Advantages: Bead
Page 67 and 68: Denture Bases - 62 of the natural d
Page 69 and 70: Principles of Partial Denture Desig
Page 77 and 78: Design Session - 72 Classification
Page 85 and 86: Clinical Protocol, Final Impression
Page 87 and 88: Clinical Protocol, Final Impression
Page 89 and 90: Framework Adjustment - 84 Removable
Page 91 and 92: Framework Adjustment - 86 3. Silico
Page 93 and 94: Framework Adjustment - 88 after adj
Page 95 and 96: Jaw Relations, Altered Cast Techniq
Page 97 and 98: Jaw Relations, Altered Cast Techniq
Page 99 and 100: Interim Removable Partial Dentures
Page 101 and 102: Coordinating Fixed and Removable Pr
Page 103 and 104: RPD Checklist - 98 7. Abutment Modi
Page 105 and 106:
RPD Checklist - 100 16. Baseplate a
Page 107 and 108:
Summary of Design Principles for Re
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RPD Manual 11 - Removable Prosthodontics - Dalhousie University

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