This document provides guidelines for tooth preparation for complete metal crowns. It discusses advantages like maximum retention and resistance form, as well as disadvantages like requiring more tooth reduction. Ideal preparation includes a 0.3-0.5mm chamfer finish line and 10-20 degrees of axial wall convergence. Occlusal reduction should be 1.0-1.5mm. Additional grooves may enhance resistance for teeth with limited dimensions. Line angles should be rounded to prevent casting defects. Examples demonstrate preparation steps and required modifications for fixed partial dentures.

1. Charles J. Goodacre, DDS, MSD
Professor of Restorative Dentistry
Loma Linda University School of Dentistry
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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

7. FINISH LINE FORM

8. • 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

9. • 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

11. • 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.

13. AXIAL REDUCTION

14. • 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

15. Preparation of a mandibular left first
molar for a complete gold crown

16. Reduction of the mesial surface

18. Placing facial depth grooves
to promote uniform reduction.

20. Placing lingual depth grooves to promote
uniform reduction of that surface.

22. 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.

23. 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

24. • The completed axial reduction.
The axial walls converge occlusally
within the desired 10 to 20 degrees
of total occlusal convergence.

25. • The completed axial walls should converge occlusally within
the desired 10 to 20 degrees of total occlusal convergence.

26. • 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

28. Tipped abutments frequently need axial grooves to
enhance resistance. The facial grooves were used
because there will be an anterior cantilevered pontic.

29. 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.

30. Casts where multiple axial surface modifications
were placed to enhance the resistance form of
the prepared molar abutments.

32. REDUCTION FOR
OCCLUSAL CLEARANCE

33. 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.

35. 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.

37. The entire occlusal surface is uniformly
reduced using the depth grooves as guides.

38. Checking the occlusal clearance by
having the patient bite through wax.

40. 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.

41. ROUNDING LINE ANGLES

42. Line angles are rounded to facilitate pouring
impressions without trapping air bubbles and
investing wax patterns without air inclusions.

43. Furthermore,
should nodules
occur in the
casting, they are
easier to remove
when the line
angles have
been rounded.

44. • 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

47. ANOTHER EXAMPLE OF THE
STEPS USED TO PREPARE A
MOLAR FOR A COMPLETE
GOLD CROWN

48. Preparation of a mandibular right first
molar for a complete gold crown.

50. AN EXAMPLE OF A
COMPLETE GOLD CROWN
PREPARATION FOR A
MANDIBULAR FIXED
PARTIAL DENTURE

52. • 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

53. Since the premolar and molar are not aligned
with each other, the diamond instrument has
been aligned with the prepared premolar.

54. • 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.

56. Working cast of the
completed tooth
preparations for a
mandibular three
unit fixed partial
denture (fixed dental
prostheses).

57. Working cast of the
completed tooth
preparations for a
mandibular three
unit fixed partial
denture (fixed dental
prostheses).

58. Cemented finished fixed partial denture

59. 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

60. Thank You For Your
Kind Attention
Charles J. Goodacre, DDS, MSD
Professor of Restorative Dentistry
Loma Linda University School of Dentistry

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