BASIC PRINCIPLES AND FUNDAMENTALS OF CAST PARTIAL DENTURE DESIGNING

Principles of cast partial denture design
Philosophy of design
Basic guidelines for designing
Kennedy's Class I-IV designs
Indications of specific components in designing cast partial denture
Distal extension CPD
Clinical cases
Exam oriented questions

1. CAST PARTIAL DENTURE DESIGNING BASIC PRINCIPLES DR. AAMIR GODIL DEPARTMENT OF PROSTHODONTICS M.A.R.D.C

2. STEPS IN PLANNING A CPD

3. KENNEDY’S CLASSIFICATION (1923)

4. KENNEDY’S CLASSIFICATION (1923)

5. Applegate's Rules for Applying the Kennedy Classification Rule 1: Classification should follow rather than precede extraction. Rule 2: If the 3rd molar is missing and not to be replaced, it is not considered in the classification. Rule 3: If the 3rd molar is present and to be used as an abutment, it is considered in the classification. Rule 4: If the second molar is missing and not be replaced, it is not considered in the classification. Rule 5: The most posterior edentulous area determines the classification. Rule 6: Edentulous areas other than those determining classification are called modification spaces. Rule 7: The extent of the modification is not considered, only the number. Rule 8: There is no modification space in Class IV.

6. SURVEYING

7. GENERAL PRINCIPLES OF CAST PARTIAL DESIGNING

8. General Principles - Minimize framework elements (minimize minor connectors, plating, etc.) – more hygienic - Obtain good base adaptation - better stress distribution; use altered cast for mandibular distal extensions - Use what is present (e.g. existing rest seats) - Plan for the future (e.g. designing for continued use of RPD framework if a critical abutment is lost; placing rest seats, guide planes and undercuts on crowns to allow fabrication of an RPD later) - Never plan an RPD using a single cast alone. You can’t assess abutment mobility, compressibility of mucosa, the level of the floor of the mouth, prominent freni , or occlusion. Use mounted models and assess these features intraorally as you plan and check your design.

9. General Principles Occlusion – AVOID: o centric contacts on rests (also ensure no increase in OVD) o heavy buccal contacts on denture teeth– causes more movement of removable partial denture When other dental treatment is planned, and an RPD will be made at the end of treatment – ALWAYS PLAN THE RPD FIRST. You will see which abutment modifications will be needed, and will ensure the planned RPD is feasible, prior to beginning treatment

10. DIRECT RETAINERS reciprocal arm retentive arm EMBRASSURE CLASP Direct Retainers Kennedy Cl III & IV (Tooth Borne) Clasp of choice: cast circumferential if can’t use cast circumferential next to edentulous space, use double embrasure clasp if abutment is severely tilted use (depending on location of undercut): Cast circumferential clasp with lingual retention Ring clasp with support strut Rotational path removable partial denture CIRCUMFERENTIAL CLASP

11. Direct Retainers Kennedy Cl I & II (Tooth & Tissue Borne) For posterior abutments, or any tooth needing stress release: Clasp of choice: RPI (mesial rest, distal proximal plate and I-bar) I BAR T BAR RPI CLASP REVERSE CIRCLET CLASP

12. Direct Retainers Kennedy Cl I & II (Tooth & Tissue Borne) If can’t use an I-bar in vestibule, because of •frenum • shallow vestibule • deep soft tissue undercut then use an RPA retainer (mesial rest, distal proximal plate and wrought wire clasp [Akers]) If can’t use a mesial rest because of: • rotation • heavy centric contact on mesial • large amalgam restoration on mesial then use Combination Clasp (distal rest, buccal wrought wire retention, lingual bracing) for abutments adjacent modification spaces (use tooth borne retainers) RPA CLASP COMBINATION CLASP wrought wire retentive arm

13. RESTS OCCLUSAL REST CINGULUM REST INCISAL REST Incisal rests/rest seats don’t use : poor esthetics more tilting/ torquing forces (long lever arm from center of rotation) Cingulum rests/rest seats use composite build up, if no prominent cingulum (less dentinal sensitivity) size - min 1 mm (if deeper, chance of dentin exposure) ensure sufficient clearance from opposing occlusion for maxillary cingulum rests Occlusal rests/rest seats size - 1/3 of B-L width of the tooth depth : 1.5 mm of clearance from opposing occlusion (critical at junction of rest & minor connector) line angle of the marginal ridge should be rounded deepest part should be located centrally (positive)

14. INDIRECT RETAINER Indirect Retainers 90° from fulcrum line & as far away from primary abutment as possible none required on tooth borne (Cl III & IV) cases canine is usually the most anterior tooth used for indirect retention usually don’t use a lateral (root length) or central incisor (speech) also helpful for seating and support, but not always possible or necessary

15. Rest Seats/ Rests Ensure sufficient depth, especially at junction of the rest & minor connector (1.5mm minimum) Tooth Borne (Kennedy Class I & II) place rests adjacent to edentulous space (both ends) Tissue/Tooth Borne (Kennedy Class I & II) mesial rest preferred (less torquing of abutment) distal rest preferred when: abutment is rotated (limited access for minor connector to mesial) plunger cusp/heavy centric contact on mesial large restoration on mesial no long guiding planes with distal rests - potential torquing if tooth is severely weakened periodontally – sometimes move rest to the next tooth anterior

16. MAJOR CONNECTORS (MAXILLARY) PALATAL STRAP BROAD PALATAL COMPLETE PALATAL COVERAGE ANTERO-POSTERIOR BAR HORSE-SHOE Maxillary Major Connectors No tissue relief Tooth borne (Class III & IV): Palatal Strap Tooth & Tissue borne (Class I & II): A-P Strap whenever possible better sensation, preferred (minor salivary glands & taste buds) Full Palatal Strap periodontal involvement of abutments less than 6 teeth left displaceable mucosa (increased coverage Anterior Strap (Horseshoe) only if inoperable torus is present NEVER for Class I or II

17. MAJOR CONNECTORS (MANDIBULAR) LINGUAL BAR LINGUOPLATE Mandibular Major Connectors Lingual Bar whenever possible (less tissue coverage - hygiene) Lingual Plate if: high floor of mouth tori frenum terminate at FGM Tissue relief – mandibular major connector (29-30 gauge relief) to avoid tissue impingement

18. MINOR CONNECTOR Minor Connector connecting direct retainer to major connector Minor Connector connecting denture base to major connector Minor Connector connecting auxillary rest to major connector

19. BIOMECHANICAL CONSIDERATIONS Forces acting on cast partial dentures in function

20. BIOMECHANICAL CONSIDERATIONS

21. FORCE

22. LEVER

23. FULCRUM LINES Horizontal fulcrum line passing between two principal abutment teeth controls rotational motion of denture towards or away from supporting ridge

24. FULCRUM LINES

25. FULCRUM LINES

26. FULCRUM LINES

27. PRINCIPLES OF DESIGN The dentist must have a thorough knowledge of both the mechanical and biologic factors involved in removable partial denture design. The treatment plan must be based on a complete examination and diagnosis of the individual patient. The dentist must correlate the pertinent factors and determine a proper plan of treatment. A removable partial denture should restore form and function without injury to the remaining oral structure. A removable partial denture is a form of treatment and not a cure. (A.H. SCHMIDT 1956)

28. PHILOSOPHY OF DESIGN

29. STRESS EQUILIZATION Resiliency of the tooth secured by the periodontal ligament in an apical direction is not comparable to the greater resiliency and displaceability of the mucosa covering the edentulous ridge. Most common type is a hinge device interposed between the minor connectors of the abutment tooth and the denture base. It permits vertical movement of the denture base when forces are applied to the artificial teeth . It can be adjusted to control the amount of vertical movement.

30. STRESS EQUILIZATION

31. PHYSIOLOGIC BASING That there is a significant disparity between the apical displaceability of teeth and compressibility of the soft tissues. It believes that stress equalization can be best achieved by either displacing or depressing the ridge mucosa during the impression making procedure or by relining the denture base after it has been constructed

32. PHYSIOLOGIC BASING This theory believes that denture bases formed over compressed tissue will show an increased ability to withstand vertical forces. They also recognize the prosthetic teeth and occlusal rests will be positioned above the existing the occlusal plane when the prosthesis is not in function. To permit vertical movement of the partial denture from its rest position to its functioning position , the number of direct retainers must be limited.

33. PHYSIOLOGIC BASING

34. BROAD STRESS DISTRIBUTION Advocates of this school of thought believe that trauma to the remaining teeth and residual ridge can be prevented by distributing the forces of occlusion over as many teeth and as much of the available soft tissue area as possible. It is achieved by means of additional rests and clasps assemblies and broad coverage denture bases.

35. BROAD STRESS DISTRIBUTION

36. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH 1. Length of edentulous span 2. Quality of support of ridge 3.Clasp. Qualities Design Length Material 4. Surface characterization of the abutment 5. Occlusal harmony

37. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH THE LENGTH OF THE EDENTULOUS SPAN Longer the edentulous span: Fulcrum: near occlusal rest at terminal abutment Load: applied to artificial teeth Length of lever arm: Denture base determines the amount of force the abutments can withstand Thickness of mucosa over the ridge & area of ridge covered by denture base. Efforts made to preserve the posterior abutment tooth.

38. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH THE QUALITY OF THE SUPPORTING STRUCTURES Large well formed ridges withstand greater loads than small ,thin or knife edged ridges. Broad ridges absorb more of the occlusal load and permit the use of well contoured denture flanges. Type and health of mucosa also influence the loads transferred to abutment. Soft, flabby tissue contributes little to the vertical support of the denture & nothing to lateral stability: transmission of stress to adjacent abutment tooth.

39. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH CLASP CONFIGURATION

40. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH SURFACE CHARACTERIZATION OF THE ABUTMENT Surface of gold crown or restoration offers more frictional resistance to clasp arm movement than does the enamel surface of the tooth. Greater stress is exerted on a tooth restored with gold than on a tooth with intact enamel.

41. FACTORS INFLUENCING THE STRESS TRANSMITTED TO ABUTMENT TEETH OCCLUSAL HARMONY Deflective contacts: leverage Ideally, the occlusal load should be applied in the center of the denture –bearing area, both antero-posteriorly and bucco -lingually Partial denture constructed opposing a complete denture will be subjected to a much less occlusal stress than one opposed by natural dentition. Force exerted by natural teeth –300 pounds per square inch. Complete denture – 30 pounds per square inch. Occlusal load applied to the distal end of denture base will result into more stress transmitted to the abutment

42. COLOR CODING FOR CPD DESIGN

43. CAST PARTIAL DESIGNS FOR DIFFERENT CLINICAL SITUATIONS DESIGN CONFIGURATION TOOTH SUPPORTED VS TOOTH-TISSUE SUPPORTED CPD KENNEDY’S CLASS I AND II KENNEDY’S CLASS III AND IV

44. DESIGN CONFIGURATION Triangular Bilateral Quadrilateral Quadrilateral

45. SEQUENCE OF COMPONENT DESIGNING

46. TOOTH SUPPORTED VS TISSUE SUPPORTED DENTURES TOOTH SUPPORTED TOOTH-TISSUE SUPPORTED SUPPORT DERIVED From abutment teeth Primarily from tissues Secondarily from abutment teeth IMPRSSION TECHNIQUES Static (anatomic) impression Functional impression for tissues Anatomic impression for teeth INDIRECT RETENTION Not needed Needed, depending on fulcrum line and axis of rotation BASE MATERIALS Generally metal No need for reline Generally acrylic For ease of reline STRESS BREAKING Not needed Recommended for long span CLASS III mod 1 CLASS I

47. DISTAL EXTENSION CASES KENNEDY’S CLASS I AND II

48. SUPPORT FOR DISTAL EXTENSION McCraken 1. Contour and quality of the residual ridge 2. Extent of residual ridge coverage by the denture base 3. Type and accuracy of the impression registration 4. Accuracy of the fit of the denture base 5. Design of the removable partial denture framework 6. Total occlusal load applied

49. KENNEDY’S CLASS I AND II DESIGN CONSIDERATIONS: DIRECT RETAINER RPA CLASP COMBINATION CLASP wrought wire retentive arm RPI CLASP REVERSE CIRCLET CLASP For posterior abutments, or any tooth needing stress release: Clasp of choice: RPI (mesial rest, distal proximal plate and I-bar) If can’t use an I-bar in vestibule, because of • frenum • shallow vestibule • deep soft tissue undercut then use an RPA retainer (mesial rest, distal proximal plate and wrought wire clasp [Akers]) If can’t use a mesial rest because of: • rotation • heavy centric contact on mesial • large amalgam restoration on mesial then use Combination Clasp (distal rest, buccal retention, lingual bracing)

50. KENNEDY’S CLASS I AND II DESIGN CONSIDERATIONS: INDIRECT RETAINER Tissue/Tooth Borne (Kennedy Class I & II) mesial rest preferred (less torquing of abutment) distal rest preferred when: abutment is rotated (limited access for minor connector to mesial) plunger cusp/heavy centric contact on mesial large restoration on mesial no long guiding planes with distal rests - potential torquing if tooth is severely weakened periodontally – sometimes move rest to the next tooth anterior OCCLUSAL REST CINGULUM REST INCISAL REST

51. KENNEDY’S CLASS I AND II DESIGN CONSIDERATIONS: MAJOR CONNECTOR SUPPORT Maxillary: plate type design preferred over strap type Mandibular: Major connector does not provide support (no contact with edentulous mucosa) LOCATION OF EDENTULOUS AREA Must connect all edentulous areas ANTICIPATED LOSS OF NATURAL TOOTH Plating lingual surfaces of natural teeth: ease of replacing in future FUNCTIONAL DEPTH OF LINGUAL VESTIBULE Lingual bar (7-8 mm depth required) vs lingual plate INCLINATION OF REMAINING TEETH Consider labial bar TISSUE RESTRICTIONS Consider tori/ undercuts PATIENT PREFERENCE Based on previous partial denture

52. MANDIBULAR KENNEDY’S CLASS I Direct Retainer RPI: 34 44 Indirect Retainer and Auxillary Rest Should be provided as cingulum rests with a common minor connector from the mesial rest of 34 and 44 OR by giving lingual plate Minor Connector Lattice for 35 36 37 + 45 46 47 Connecting retainers and rest to major connector Major Connector Lingual bar

53. MAXILLARY KENNEDY’S CLASS I Direct Retainer Combination clasp: 14 24 Indirect Retainer and Auxillary Rest Cingulum rest: 13 23 Minor Connector Lattice for 15 16 17 + 25 26 27 Connecting retainers and rest to major connector Major Connector Antero-posterior palatal bar (palatal torus)

54. MANDIBULAR KENNEDY’S CLASS II Direct Retainer RPI: 34 Embrassure clasp: 46 47 Indirect Retainer and Auxillary Rest Mesial rest: 44 Minor Connector Lattice for 35 36 37 Connecting retainers and rest to major connector Major Connector Lingual bar/ plate

55. MANDIBULAR KENNEDY’S CLASS II MOD 1 Direct Retainer RPA: 34 Simple circlet: 44 47 Indirect Retainer and Auxillary Rest Mesial rest: 44 Minor Connector Lattice for 35 36 37 Mesh for 45 46 Connecting retainers and rest to major connector Major Connector Lingual bar

56. TOOTH SUPPORTED CPD KENNEDY’S CLASS III AND IV Strap type major connectors for maxillary Support derived from dento -alveolar segment Clasps with minimum tooth coverage to reduce plaque accumulation Nail bead type minor connector for smaller spans

57. KENNEDY’S CLASS III AND IV DESIGN CONSIDERATIONS: DIRECT RETAINERS & MAJOR CONNECTORS PALATAL STRAP ANTERO-POSTERIOR BAR HORSE-SHOE

58. MANDIBULAR KENNEDY’S CLASS III Direct Retainer Ring clasp: 47 Simple circlet clasp: 44 36 Auxillary Rest Mesial rest: 34 (not needed) Minor Connector Mesh for 45 46 Connecting retainers and rest to major connector Major Connector Lingual bar

59. MAXILLARY KENNEDY’S CLASS IV

60. SUMMARY

61. EXAM ORIENTED QUESTIONS I) LAQ: 1. Discuss the cast partial framework design for maxillary/ mandibular Kennedy’s Class I/II II) SAQ: 1. Philosophy and principles of CPD designing 2. Stress equalization or stress breakers in cast partial dentures 3. Support for distal extension denture bases 4. Direct retainers for distal extension denture bases 5. Kennedy’s class III/IV design 6. Factors influencing stress transmission to abutment teeth in cast partial dentures 7. Difference between tooth supported and tooth-tissue supported cast partial dentures

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