tooth preparation and it's modifications
- 1. PROSTHODONTICS Dr Kamal Shigli Professor & Head, Dept. of Prosthodontics, DY Patil Dental School, Lohegaon, Pune
- 2. PROSTHODONTICS Prosthodontics is the dental specialty pertaining to the diagnosis, treatment planning, rehabilitation, & maintenance of the oral function, comfort, appearance, & health of patients with clinical conditions associated with missing or deficient teeth &/or maxillofacial tissues by using biocompatible substitutes. (G.P.T-9) 1
- 4. FIXED PROSTHODONTICS • The branch of prosthodontics concerned with the replacement and/or restoration of teeth by artificial substitutes that cannot be removed from the mouth by the patient. (G.P.T-9) 3
- 5. FIXED PARTIAL DENTURE • Any dental prosthesis that is luted, screwed, or mechanically attached or otherwise securely retained to natural teeth, tooth roots, &/or dental implants/abutments that furnish the primary support for the dental prosthesis & restoring teeth in a partially edentulous arch; it cannot be removed by the patient. (G.P.T-9) 4
- 6. EXAMINATION, DIAGNOSIS & TREATMENT PLANNING • Making the correct diagnosis is essential to formulating an appropriate treatment plan. • This requires the following information be obtained: a) a complete history including a comprehensive assessment of the patient's general & dental health, b) individual needs, c) patient preferences. • Mounted study casts for treatment planning 5
- 7. PARTS OFAN FPD • RETAINER • PONTIC • CONNECTOR 6
- 9. ABUTMENT Abutment: 1. that part of a structure that directly receives thrust or pressure; an anchorage; 2. a tooth, a portion of a tooth, or that portion of a dental implant that serves to support and/or retain a prosthesis. (G.P.T-9) 8
- 10. NEED FOR SELECTION OFABUTMENT • Every restoration must be able to withstand constant occlusal forces to which it is subjected. • Abutment teeth are therefore called upon to withstand the forces normally directed to the missing teeth, in addition to those usually applied to the abutments. 9
- 11. SELECTION OFABUTMENT This will be discussed under different heads as – • Abutment evaluation • Special cases - Pier abutments - Tilted molar abutment - Canine replacement fixed partial denture - Cantilever fixed partial denture 10
- 12. ABUTMENT EVALUATION • The supporting tissues surrounding the abutment teeth must be healthy. • Should not exhibit mobility. 11
- 13. FACTORS INFLUENCINGABUTMENT SELECTION 1. Crown-root ratio 2. Root configuration 3. Periodontal ligament area 12
- 14. 1. Crown-root ratio • The physical relationship between the portion of the tooth not within the alveolar bone, as determined by a radiograph, compared with the portion of the tooth within alveolar bone. (G.P.T-9) Optimum C: R ratio is 2:3 Minimum C:R ratio is 1:1 2 3 1 1 13
- 15. 2. Root configuration Roots with broader faciolingual dimension are preferred Divergent roots preferred over the convergent roots 14
- 16. 3. Periodontal ligament area • Ante’s Law: the combined pericemental area of all abutment teeth supporting a fixed partial denture should be equal to or greater in pericemental area compared with the tooth or teeth to be replaced. (G.P.T-9) 15
- 17. PierAbutment /An IntermediateAbutment • A PIER abutment is a natural tooth/implant abutment that is located between terminal abutments that serve to support a fixed or removable dental prosthesis. (GPT-9) 16
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- 19. • The mesiolingually tilted molar is a commonly encountered problem Tilted MolarAbutment 18
- 20. When a mandibular molar tilts mesially , there is a discrepancy between the long axis of the molar & that of the premolar The fixed partial denture will not seat as the distal tooth intrudes on the path of insertion 19
- 21. Orthodontic appliance for uprighting a tilted molar Tilted Molar Abutment 20
- 22. Tilted MolarAbutment Fixed partial denture using a Proximal half crown as a retainer 21
- 24. Cantilever Fixed Dental Prosthesis • A fixed complete or partial denture in which the pontic is cantilevered & retained & supported by one or more abutments. (GPT-9) • The pontic acts as a lever that tends to be depressed under forces with a strong occlusal vector. 23
- 25. •Selection of the abutment is the key point of success for fixed partial denture design. 24
- 27. Tooth Preparation • The process of removal of diseased &/or healthy enamel & dentin & cementum to shape a tooth to receive a restoration. (G.P.T-9) 26
- 28. Objectives of Tooth Preparation • Reduction of the tooth in miniature to provide retainer support. • Preservation of healthy tooth structure to secure resistance form. • Provision for acceptable finish lines. • Performing axial tooth reduction to encourage favorable tissue response. 27
- 29. 5 principles • Preservation of tooth structure • Retention & Resistance • Structural durability • Marginal integrity • Preservation of the periodontium 28
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- 31. Preservation of Tooth Structure In addition to replacing lost tooth structure, a restoration must preserve remaining tooth structure. Use of partial coverage restorations rather than complete coverage restorations. Whenever possible, the margin of the preparation should be supragingival. 30
- 32. Retention & Resistance • Retention : It is the ability of a preparation to prevent removal of restoration along its path of insertion. • Resistance: It is the ability of the preparation to prevent dislodgement of the restoration by forces directed in oblique, apical or horizontal direction. • Retention & Resistance are interrelated. 31
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- 34. • To produce 6º Angle of convergence, the opposing axial wall should have an inclination of 3°. TAPER 33
- 35. SURFACEAREA 34
- 37. LENGTH 36
- 39. STRUCTURALDURABILITY Occlusal Reduction • For gold alloys- 1.5mm on functional cusps & 1mm on nonfunctional cusp. • Metal ceramic crowns- 1.5 to 2mm on functional cusps & 1 to 1.5mm on nonfunctional cusp. • All ceramic- 2mm clearance. 38
- 40. • Occlusal surface reduction should follow the anatomic planes. 39
- 42. Axial reduction • Crown should duplicate contours and profile of the original tooth. • Avoid overcontouring. 41
- 43. MARGINALINTEGRITY • Whenever possible, the margin of the preparation should be supragingival. • Subgingival margins often lead to the periodontal disease 42
- 44. Feather edge • Advantage: Conservation of tooth structure • Disadvantage: Does not provide sufficient bulk • Indications: Not recommended 43
- 45. Chisel edge • Advantage: Conservation of tooth structure. • Disadvantage: Location of margin is difficult thus produces overcontouring • Indication: Occasionally on the tilted tooth, Not acceptable 44
- 46. Chamfer • Advantages: Distinct margin, adequate bulk, easier to control • Disadvantages: unsupported lip of enamel • Indications: Cast metal restorations, lingual margin of metal ceramic crowns 45
- 47. Shoulder • Advantages: Bulk of material. • Disadvantages: Less conservative. • Indications: Facial margins of metal ceramic crowns, all ceramic crowns 46
- 48. Sloped shoulder • Advantages: Bulk of material, reduce unsupported enamel. • Disadvantages: Less conservative. • Indications: Facial margins of metal ceramic crowns. 47
- 49. PRESERVATION OF THE PERIODONTIUM • Placement of finish lines plays an important role in the success of the restoration. • Whenever possible, the finish line should be placed in an area where margins of the restoration can be finished by the dentist & cleaned by the patient. 48
- 51. DEFINITION • Gingival Retraction/displacement is deflection of the marginal gingiva away from a tooth. (GPT-9) • Gingival retraction is a process of exposing margins when making impression of prepared teeth. 50
- 52. METHODS Mechanical method Chemicomechanical methods Rotary Gingival curettage Electrosurgery 51
- 53. Impressions For Fixed Partial Denture 52
- 54. •Impression Techniques • 1.Stock Tray Technique Double Mix Single Mix • 2.Custom Tray Technique Single Mix 53
- 56. • DEFINITION A fixed or removal prosthesis designed to enhance esthetics, stabilization & function for a limited period of time after which it is to be replaced by definitive prosthesis . 55
- 57. REQUIREMENTS 56
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- 60. Types Of Provisional Restorations 59
- 61. Types of Provisional Restorations 60
- 62. RETAINER • The part of a fixed partial denture or fixed complete denture that unites the abutment(s) to the remainder of the restoration. (G.P.T-9) 61
- 63. CLASSIFICATION 1. Amount of tooth coverage a) Complete coverage or full veneer retainers b) Partial coverage or partial veneer retainers c) Conservative retainers 2. Mechanism of retention a) Extracoronal b) Intracoronal c) Radicular 3. Material used a) All ceramic b) Metal ceramic c) All metal d) Acrylic 62
- 64. Complete coverage retainers 1. Amount of tooth coverage 63
- 65. 7/8th Crown Proximal 1/2 crown Partial coverage retainers 64
- 66. 2. Mechanism of retention Extracoronal retainers Intracoronal retainers Radicular retainers 65
- 67. Metal with ceramic facing retainer on left and full metal retainer on right. All ceramic retainers Metal-ceramic retainers Metal retainers 3. Material used 66
- 68. PONTICS 67
- 69. DEFINITION • PONTIC - Latin ‘pons’ meaning bridge. • An artificial tooth on a fixed dental prosthesis that replaces a missing natural tooth, restores its function, & usually fills the space previously occupied by the clinical crown. (G.P.T-9) 68
- 70. CLASSIFICATION • Pontics are classified : A. Mucosal contact B. No mucosal contact 1. Ridge lap 1.Sanitary (hygienic) 2. Modified ridge lap 2. Modified sanitary (hygienic) 3. Ovate 4. Conical 69
- 71. 2. Depending on the materials i. All metal- Gold, cobalt-chromium, nickel- chromium ii. Non metallic – Porcelain iii. Combination – PFM 70
- 72. 3. Depending on manufacturer design ▫ Flat back ▫ Trupontics ▫ Pontips ▫ Long pin facing ▫ Reverse pin facing 71
- 73. CONNECTOR • In fixed prosthodontics, the portion of a fixed partial denture that unites the retainer(s) & pontic(s). (G.P.T-9) 72
- 74. CLASSIFICATION 1. Rigid connectors i. Cast connectors ii. Soldered connectors iii. Loop connectors 2. Non-rigid connectors i. Tenon-mortise connectors ii. Split pontic connector iii. Cross pin & wing connector. 73
- 79. Conclusion The success of treatment with fixed prosthesis depends on: • Examination, Diagnosis & Treatment Planning, • Abutment Evaluation • Tooth Preparation • Gingival Displacement • Impression • Provisional Restoration 78
- 80. ACKNOWLEDGEMENTS ! • Dr Chandrasekharan Nair • Dr Gangadhar Angadi • Dr Suresh Sajjan • Dr Deepti Fulari • Dr Ashish Bhagat • Dr Lovely M • Dr M. Shivasakthy • Dr Mansi Oswal Dagha 79
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Editor's Notes
- #27: Tooth preparation is an irreversible procedure.
- #30: The principles of tooth preparation may be divided into three broad categories: 1. Biologic considerations, which affect the health of the oral tissues 2. Mechanical considerations, which affect the integrity and durability of the restoration 3. Esthetic considerations, which affect the appearance of the patient The optimum restoration should satisfy biologic, mechanical, and esthetic requirements.
- #34: The recommended convergence between opposing walls is 6 degrees, which has been shown to optimize retention for zinc phosphate cement.
- #39: Enough of tooth structure should be removed to provide adequate bulk of material & strength to restoration.
- #40: 3. Preparation of the occlusal surface so reduction follows the anatomic planes to give uniform thickness in the restoration
- #44: Although they are conservative of tooth structure, featheredge or shoulderless crown preparations should be avoided because they fail to provide adequate bulk at the margins. Overcontoured restorations often result from featheredge margins because the technician can handle the wax pattern without distortion only by increasing its bulk beyond the original contours.
- #45: A variation of the featheredge, the chisel edge margin, is formed when there is a larger angle between the axial surfaces and the unprepared tooth structure. Unfortunately, this margin is frequently associated with an excessively tapered preparation or one in which the axial reduction is not correctly aligned with the long axis of the tooth.
- #46: A chamfer margin is particularly suitable for cast metal crowns and the metal-only portion of metal-ceramic crowns. It is distinct and easily identified, provides room for adequate bulk of material, and can be placed with precision, although care is needed to avoid leaving a ledge of unsupported enamel. Probably the most suitable instrument for making a chamfer margin is the tapered diamond with a rounded tip; the margin formed is the exact image of the instrument. The chamfer should never be prepared wider than half the tip of the diamond; otherwise, an unsupported lip of enamel could result.
- #47: Because a shoulder margin allows room for porcelain, it is recommended for the facial part of metal-ceramic crowns, especially when the porcelain margin technique is used. It should form a 90-degree angle with the unprepared tooth surface. An acute angle is likely to chip . Some authorities have recommended a heavy chamfer rather than a shoulder margin, and some find a chamfer easier to prepare with precision.
- #48: A 120-degree sloped shoulder margin is used as an alternative to the 90-degree shoulder for the facial margin of a metal-ceramic crown. The sloped shoulder reduces the possibility of leaving unsupported enamel and yet leaves sufficient bulk to allow thinning of the metal framework to a knife-edge for acceptable esthetics.