Types of tooth preparations
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This document discusses different types of crown preparations including full metal crowns, metal-ceramic crowns, and all-ceramic crowns. For full metal crowns, extensive tooth reduction is required due to their high retentiveness. Metal-ceramic crowns provide better aesthetics than full metal crowns but still require significant tooth reduction. All-ceramic crowns are the most conservative preparation and provide excellent aesthetics but have less strength than other options. Proper preparation is critical for all-ceramic crowns to withstand occlusal forces. The document outlines the armamentarium, steps, and criteria for preparing teeth for each of these crown types.
Types of tooth preparations
- 1. Dr Ishani Sharma MDS 1st Year Paedodontics
- 2. Contents Preparations for full veneer crowns - Full metal crown preparation - Anterior metal ceramic crowns and posterior metal ceramic crowns - All ceramic crowns
- 3. Definition Preparation: The selected form given to a natural tooth when it is reduced by instrumentation to receive a prosthesis, guided by clinical circumstances and physical properties of the material.
- 4. Types Complete Crown / Full Veneer Crown: A restoration that covers the entire coronal tooth surfaces (mesial, distal, facial, lingual and occlusal) Partial veneer crown: A restoration that restores all but one coronal surface of a tooth or dental implant abutment, usually not covering the facial surface(GPT-8)
- 6. Full metal crowns Used where the break down of tooth structure is severe to the extent that has been described in operative dentistry as “the final attempt to preserve the tooth” Most retentive of veneer preparations
- 7. Indications Extensive destruction from caries Endodontically treated tooth Existing restoration that needs the use of a more conservative restoration Necessity for maximum retention Minor correction of malinclinations Recontouring of axial surfaces. Provide contour to receive removable appliances Correction of occlusal plane
- 8. Contraindications Less than maximum retention necessary Aesthetics
- 9. Advantages Strong High retentive qualities Easy to obtain adequate resistance form Option to modify form and occlusion
- 10. Disadvantages Removal of large amount of tooth structure Adverse effects on tissue Vitality testing not easily feasible Display of metal
- 11. Preparation
- 12. Armamentarium Tapered carbide bur- for occlusal guiding grooves. Narrow round-tipped tapered diamond (regular grit) (0.8mm)- for occlusal reduction , axial alignment grooves, axial reduction, chamfer prep Wide round tipped tapered diamond (fine grit) (1.2 mm)- for finishing
- 13. Step by step procedure Guiding grooves for occlusal reduction:- Tapered carbide is recommended. Place depth groove holes app 1mm deep in central, mesial, and distal fossa and connect them. Guiding grooves in buccal and lingual developmental grooves Place a functional cusp bevel Depth – 0.8 mm for central groove & nonfunctional cusp, 1.3 mm for functional cusp
- 14. Occlusal reduction :- by 2 steps Half occlusal surface is reduced first and other half can be maintained as reference Minimum clearence of 1.5 mm on functional cusp and 1mm on nonfunctional cusp.
- 15. Axial reduction :- place 3 alignment groove on each buccal and lingual wall with narrow round end tapered diamond. The bur should be parallel to proposed path of withdrawal of restoration. diamond bur with 6 degree taper is used and identical axial taper will result in preparation.
- 16. The remaining islands of tooth structure between alignment grooves are removed while the chamfer margin is placed. Place cervical chamfer of app 0.5 mm width. Finishing – with fine grit carbide bur. Round off all line angles.
- 18. Chamfer and seating grooves
- 19. Features of full metal crown preparation
- 21. Metal-ceramic crowns (PFM) Use grew with the development of first commercially successful porcelain/gold alloy by Weinstein etal in 1950s. Ceramic layer bonded to a thin cast metal coping that fits over the tooth preparation Greater strength than all ceramic crowns
- 22. Indications Aesthetics If porcelain-jacket crown is contraindicated Contraindication Large pulp chamber Intact buccal wall When more conservative retainer is technically feasible
- 24. Disadvantage Removal of substantial tooth structure Subject to fracture because porcelain is brittle Shade selection can be difficult Inferior aesthetic compared to all ceramic Expensive
- 25. Preparation
- 26. Armamentarium Round tipped rotary diamonds (regular grit for buccal reduction, fine grit for finishing) Foot ball or wheel shaped diamonds ( for lingual reduction) Flat end tapered ( for shoulder prepration) Finishing stones Hatchet and chisel
- 27. Steps of prepration Guiding grooves:- place 3 depth grooves- centre, mesiofacial and distofacial line angles. Place in 2 planes- the cervical portion is parallel to long axis of tooth, for incisal (occlusal) follows normal facial contour. 1.3 mm deep
- 28. Incisal (occlusal)reduction:- Bur – tapered round tipped diamond bur. Criteria – 1.2 to 1.5mm reduction for the metal and porcelain.
- 29. Labial reduction guide grooves ( two plane):- Bur – tapered- round tipped diamond bur Criteria- 1.2- 1.5mm reduction for metal and porcelain. Labial reduction ( two plane):- Bur – tapered flat- tipped diamond
- 30. Axial reduction:- Bur – tapered round tipped diamond Lingual reduction:- Bur – football shaped diamond Criteria- 1mm clearance .
- 31. Finishing of shoulder (or beveled shoulder):- Bur – tapered flat tipped bur , hand instrument Criteria – extend 1mm lingual to proximal contact area. Finishing :- Bur – tapered round tipped diamond or carbide bur Criteria – round off all line angles
- 34. Radial shoulder
- 35. Features of metal ceramic preparation
- 36. Metal ceramic preparation for posteriors
- 41. Indications: 1. High aesthetic requirement 2. Incisal egde reasonably intact 3. Endodontically treated teeth 4. Considerable proximal caries 5. Favourable distribution of occlusal load.
- 42. Contraindications: 1. When superior strength is needed 2. Insufficient coronal tooth structure 3. Thin teeth faciolingually 4. Unfavourable distribution of occlusal load.
- 43. Advantages: 1. Excellent aesthetic 2. Good tissue response 3. More conservative of facial wall
- 44. Disadvantages: 1. Less strength. 2. Proper preparation extremely critical. 3. Brittle nature of material. 4. Expensive
- 45. Preparation
- 46. Depth grooves for the incisal reduction:- Bur – tapered diamond Criteria – 1.3 mm deep to allow the for additional reduction during finishing, perpendicular to the long axis of opposing tooth.
- 47. Incisal reduction :- Bur – tapered diamond Criteria – clearance 1.5 mm Depth grooves for the facial reduction:- Bur – tapered diamond Criteria – 0.8mm needed for the additional reduction during finishing.
- 48. Facial reduction:- Bur- tapered diamond Criteria – reduction of 1mm is needed Depth grooves and lingual reduction:- Bur –tapered and football-shaped diamonds Criteria – initial depth 0.8mm , recreate the concave configuration (avoid stress)
- 49. Depth grooves for cingulum reduction:- Burs – tapered diamond Criteria – parallel to cervical aspect of facial preparation. - 1mm reduction - shoulder follows free gingival margin
- 50. Lingual shoulder preparation:- Bur – square-tipped diamond Criteria – shoulder 1mm wide , 90 degree cavosurface angle. Finishing :- Bur – fine grit diamond or carbide Criteria- all surfaces smooth and continous - no unsupported enamel - 90 degree cavosurface angle
- 51. Preparation:
- 52. Features of all-ceramic crowns
- 54. Thank you.