RPD Manual 11 - Removable Prosthodontics - Dalhousie University

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I. Retention Direct and Indirect Retainers Direct and Indirect Retainers - 43 Retention is the ability of a removable partial denture to resist dislodging forces during function. Retention depends upon several factors: a. adhesion, cohesion, interfacial surface tension and atmospheric pressure b. gravity c. frictional retention (guiding planes, bracing elements) e. indirect retention f. direction of dislodging force relative to the path of placement. g. mechanical retention Mechanical Retention Mechanical retention is obtained by placing portions of the partial denture into tooth or soft tissue undercuts. Maximizing the other retentive factors can minimize the need for mechanical retention. Most mechanical retention is derived from the use of direct retainers (clasp assemblies) utilizing tooth undercuts. There are two classes of mechanical retainers: intracoronal and extracoronal. Intracoronal retainers (precision attachments) are mechanical devices set into the casting of a full crown. These are generally reserved for removable partial denture therapy that requires exceptional effort in producing ideal esthetics. There are many contraindications and disadvantages to precision attachments. Extracoronal retainers engage an external surface of an abutment in a natural undercut or in a prepared depression. There are two main classes of clasps: 1) those that approach the undercut from above the height of contour (suprabulge retainers) and 2) those that approach the undercut from below (infrabulge retainers). II. Extra-Coronal Direct Retainers Definition - A direct retainer is a unit of a removable partial denture that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissues. It is usually composed of a retentive arm, a reciprocal (bracing) element or arm, a rest and a minor connector. Retention is derived by placing a clasp arm into an undercut area so that it is forced to deform upon vertical dislodgment. Resistance of the clasp to deformation generates retention. Resistance is proportionate to the flexibility of the clasp arm. Non-flexible portions of clasp arms must be placed occlusal to the height of contour (suprabulge area).
Direct and Indirect Retainers - 44 Requirements of Direct Retainers All clasp assemblies should meet the following requirements: 1. Support - resistance to gingival displacement (occlusal rests) 2. Reciprocity - resistance to orthodontic movement of teeth using reciprocal arms or elements placed against guiding planes. During placement and removal of the partial denture the retentive arm flexes over the height of contour and generates energy. At this point the rigid reciprocal arm should contact the guiding plane and prevent orthodontic movement from taking place. 3. Stability - resistance to lateral movement (reciprocal arms, minor connectors) 4. Retention - retentive arms located in undercuts on the abutments 5. Encirclement of greater than 180° of the tooth - prevents the prosthesis from moving away from the tooth 6. Passivity - at rest, a direct retainer should not exert force against a tooth Wherever possible direct retainers should be selected to fit the existing teeth. This is preferable to preparing teeth to fit a particular clasp design. It may be possible to select a different clasp design to meet the retentive requirements for a partial denture. Nonetheless, judicious tooth preparation should not be avoided at all costs, since it can immeasurably improve prosthesis biomechanics. Factors affecting the magnitude of retention 1. Size of the angle of convergence.
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: Minor Connectors - 42 When the dent
Page 51 and 52: Direct and Indirect Retainers - 46
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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