RPD Manual 11 - Removable Prosthodontics - Dalhousie University

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Surveying, Path of Insertion, Guiding Planes - 21 The Effects of Guiding Planes on Retention and Stability 1. Guiding Planes Maintain Retention Retention is gained by the flexible retentive tip of the clasp engaging an undercut of an abutment. Retentive undercuts exist only in relation to a fixed plane. If an undercut is found on a diagnostic cast, and the cast is tilted in another direction, the undercut can be eliminated. Likewise, in the mouth, if the partial denture does not have a single path of insertion (as dictated by guiding planes) the prosthesis could be rotated so that the retentive undercuts would be eliminated. The denture could then be easily displaced. Point contact of the reciprocal arm allows rotation of the partial denture and release of the retentive arm (left and middle). A broad flat plane does not (right). 2. Guiding Planes Minimize the Need for Retention The use of too many clasps or the use of clasps with large undercuts can impair the health of the periodontium. Frictional retention from parallel guide planes minimizes the retention required from direct retainers. 3. Guiding Planes Stabilize Teeth Guiding planes with intimate, firm and continual contact with the prosthesis are effective in stabilizing teeth. Stability can be important if there is mobility due to periodontal bone loss. This effect is most pronounced in Class III partial dentures. In Class I and II partial dentures, stability is compromised by the lack of posterior abutments. These dentures tend to rotate more and produce a torquing force, if the principal abutments are locked into the denture. Slightly shorter guiding planes are used in distal extension cases to minimize this torquing action. Loading of a Class I denture base causes rotation around the rest seat. A short guiding plane allows rotation into the gingival relief area. A long guiding plane has no area to move and thus immediately torques the tooth.
Surveying, Path of Insertion, Guiding Planes - 22 Alteration of Other Axial Contours While guiding plane surfaces are the most common axial tooth preparations made for removable partial dentures, other axial preparations may also be required. These include: A. Lowering Height of Contours 1. Lowering height of contours to eliminate tooth interferences in areas where rigid frameworks elements will be placed (such as rigid portions of retentive arms). 2. Lowering height of contours to improve esthetics (e.g. to allow retentive arms to be placed more gingivally to reduce clasp display). When preparing axial contours for these situations, the heights of contour are most quickly lowered by placing the bur parallel to the path of insertion. B. Raising Height of Contours The only time that a height of contour would be raised would be when there is no retentive undercut present or when the undercut is so far gingival that the retentive tip would either impinge on the free gingival margin or cause a hygiene problem due to its proximity to the free gingival margin. In general, the inferior portion of the retentive undercut should be at least 1mm above the free gingival margin. Raising the height of contour is only feasible when the axial surface is parallel or slightly divergent to the path of insertion. If the surface is grossly divergent from the path of insertion, then raising the height of contour may be impossible. The tooth on the right is grossly divergent from the path of insertion, so that excessive preparation is required just to gain the appropriate undercut. Dentin, or in extreme cases, the pulp could be exposed. Minimal preparation will be required on the tooth on the left since its long axis is close to the path of insertion. Raising the height of contour for retentive undercuts can be accomplished by: 1. Preparing a retentive undercut. Prepare an ovoid undercut with the inferior border at least 1 mm from the free gingival margin, using a round or chamfer diamond bur. Correct Should be more Too close to ovoid, like clasp free gingival tip margin
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 25: 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 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
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Design Session - 72 Classification
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Clinical Protocol, Final Impression
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Clinical Protocol, Final Impression
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Framework Adjustment - 84 Removable
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Framework Adjustment - 86 3. Silico
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Framework Adjustment - 88 after adj
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Jaw Relations, Altered Cast Techniq
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Jaw Relations, Altered Cast Techniq
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Interim Removable Partial Dentures
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Coordinating Fixed and Removable Pr
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RPD Checklist - 98 7. Abutment Modi
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RPD Checklist - 100 16. Baseplate a
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Summary of Design Principles for Re
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RPD Manual 11 - Removable Prosthodontics - Dalhousie University

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