This presentation discusses the principles of metal crown preparations (full veneer crowns). These restorations cover all coronal surfaces (facial, lingual, mesial, distal and occlusal). The advantages and disadvantages of this type of restoration are discussed along with the indications and contraindications for use. The ideal finish line form suggested is discussed and demonstrated in detail. The clinical steps used in preparation of teeth for complete coverage metal crowns are nicely demonstrated. Valuable suggestions are made regarding preparation design for tilted teeth used as abutments for fixed partial dentures in order to enhance resistance form and retention form.

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  • 1. Charles J. Goodacre, DDS, MSD Professor of Restorative Dentistry Loma Linda University School of Dentistry This program of instruction is protected by copyright ©. No portion of this program of instruction may be reproduced, recorded or transferred by any means electronic, digital, photographic, mechanical etc., or by any information storage or retrieval system, without prior permission. Tooth preparation guidelines for complete coverage metal crowns
  • 2. Topics to be Covered •  Definition – a restoration that covers all coronal surfaces (facial, lingual, mesial, distal, and occlusal) •  Advantages & disadvantages •  Indications & contraindications •  Type of finish line •  Principles •  Type of finish line and steps
  • 3. Advantages •  Complete coverage affords greatest retention and resistance form •  Allows for the greatest change in esthetic tooth form and occlusion •  Makes it successful in a wide range of situations such as tooth form or alignment is not ideal and therefore a less than perfect tooth preparation will be a likely result
  • 4. Disadvantages •  Complete metal crowns are not esthetic to many people and therefore they are often limited to non-visible areas of the mouth •  They require more extensive tooth preparation than partial coverage crowns •  If the finish line is subgingival around the entire tooth, it is more likely there will be a less than optimal gingival response
  • 5. FINISH LINE FORM
  • 6. •  Chamfer finish lines are recommended for all – metal crowns because they are easy to form, adequately distinct on the tooth and die, and provides sufficient space that the metal is adequately rigid. A depth of 0.3 – 0.5 mm is recommended
  • 7. •  Chamfer finish lines exhibit a continuous cervical slope. They are formed by using a diamond instrument with a rounded tip and a diameter of 0.6 – 0.8 mm •  The tooth is reduced until ½ of the instrument diameter is located within the tooth. The rotary instrument is then moved around the tooth perimeter while maintaining the desired depth
  • 8. •  Some teeth that are tipped can be prepared with knife-edge finish lines to avoid excessive reduction of the surface toward which the tooth is tipped.
  • 9. AXIAL REDUCTION
  • 10. •  The axial surfaces (facial, lingual, mesial, distal) are reduced using a tapered round – end diamond instrument so they converge occlusally within the range of 10 to 20 degrees of total convergence
  • 11. Preparation of a mandibular left first molar for a complete gold crown
  • 12. Reduction of the mesial surface
  • 13. Placing facial depth grooves to promote uniform reduction.
  • 14. Placing lingual depth grooves to promote uniform reduction of that surface.
  • 15. Reducing the facial surface using the grooves to guide reduction depth The tooth is reduced to a depth equal to ½ the instrument diameter, forming a chamfer of the proper depth. The instrument is aligned with the desired path of placement.
  • 16. The instrument is held parallel with the slope of the surface prior to reduction. Reducing the occlusal aspect of the facial surface using grooves to guide reduction depth
  • 17. •  The completed axial reduction. The axial walls converge occlusally within the desired 10 to 20 degrees of total occlusal convergence.
  • 18. •  The completed axial walls should converge occlusally within the desired 10 to 20 degrees of total occlusal convergence.
  • 19. •  Many molars, particularly mandibular molars that will be used as fixed partial denture abutments, require axial modifications (grooves or boxes) to increase resistance form because of their limited occlusocervical dimension after tooth preparation
  • 20. Tipped abutments frequently need axial grooves to enhance resistance. The facial grooves were used because there will be an anterior cantilevered pontic.
  • 21. Due to severe malalignment of the abutments, a nonrigid connector will be used between the pontic and the premolar abutment. Both facial and proximal grooves were used to enhance resistance.
  • 22. Casts where multiple axial surface modifications were placed to enhance the resistance form of the prepared molar abutments.
  • 23. REDUCTION FOR OCCLUSAL CLEARANCE
  • 24. Occlusal depth grooves are prepared to a uniform depth of 1.0-1.5 mm using a coarse grit diamond. They should follow the pathways and depths of the developmental grooves.
  • 25. A depth groove prepared along the entire mesiodistal length of the central developmental groove is very helpful in achieving adequate reduction in an area that is commonly under reduced.
  • 26. The entire occlusal surface is uniformly reduced using the depth grooves as guides.
  • 27. Checking the occlusal clearance by having the patient bite through wax.
  • 28. Measuring the wax thickness and familiarity with the amount of light that passes through a given thickness of wax are used to assess reduction adequacy.
  • 29. ROUNDING LINE ANGLES
  • 30. Line angles are rounded to facilitate pouring impressions without trapping air bubbles and investing wax patterns without air inclusions.
  • 31. Furthermore, should nodules occur in the casting, they are easier to remove when the line angles have been rounded.
  • 32. •  The prepared surfaces and finish line are smoothed using a fine grit diamond that is the same size as the coarse grit diamond used for the initial reduction •  A coarse grit diamond that has been used multiple times for initial tooth reduction and sterilized multiple times can also be used as it will no longer create the roughness it once produced
  • 33. ANOTHER EXAMPLE OF THE STEPS USED TO PREPARE A MOLAR FOR A COMPLETE GOLD CROWN
  • 34. Preparation of a mandibular right first molar for a complete gold crown.
  • 35. AN EXAMPLE OF A COMPLETE GOLD CROWN PREPARATION FOR A MANDIBULAR FIXED PARTIAL DENTURE
  • 36. •  The initial form of the premolar partial coverage tooth preparation is established first since it is the more critical of the two tooth preparation. •  The molar complete crown preparation will be aligned with the premolar partial coverage tooth preparation
  • 37. Since the premolar and molar are not aligned with each other, the diamond instrument has been aligned with the prepared premolar.
  • 38. •  The completed tooth preparation for a fixed partial denture. This prepared molar possesses greater occlusocervical dimension than most mandibular molars and therefore did not require auxiliary resistance form features.
  • 39. Working cast of the completed tooth preparations for a mandibular three unit fixed partial denture (fixed dental prostheses).
  • 40. Working cast of the completed tooth preparations for a mandibular three unit fixed partial denture (fixed dental prostheses).
  • 41. Cemented finished fixed partial denture
  • 42. Complete Metal Crown – Tooth Preparation Review •  A chamfer finish line that is 0.3 – 0.5 mm in depth •  Axial reduction with 10 to 20 degrees of total occlusal convergence •  Reduction for occlusal clearance of 1.0 – 1.5 mm •  Auxiliary axial resistance form features as needed •  Rounding of all line angles
  • 43. Thank You For Your Kind Attention Charles J. Goodacre, DDS, MSD Professor of Restorative Dentistry Loma Linda University School of Dentistry
  • 44. v Visit ffofr.org for hundreds of additional lectures on Complete Dentures, Implant Dentistry, Removable Partial Dentures, Esthetic Dentistry and Maxillofacial Prosthetics. v The lectures are free. v Our objective is to create the best and most comprehensive online programs of instruction in Prosthodontics