Metal Crown Flashcards
What’s is metal crown
Nd what it’s made up of
It is an artificial metallic restoration used to cover the all surfaces of the
clinical crown
It is made only from metal:
Gold
Base-metal alloy
• (nickel, chromium or titanium)
Adv of metal crown
Advantages
1. greater strength
2. Allow teeth modification
(misaligned teeth)
3. Restore function and give
maximum retention.
Disadv of metal crown
Disadvantages
1. Less conservative than partial coverage and inlay.
2. Metal display.
Can endanger pulp vitality or cause gingival inflammation.
Does not allow electric vitality test
Metal crown indication
- Extensive coronal destruction
- Extensive large restoration
- Tooth fracture
- Endodontically treated teeth
- To change axial contour of the abutment for removable partial denture
- Correction of occlusal plane
- In patient with high caries index
8.Short abutments - Long edentulous span
10.High occlusal forces - Improperly aligned abutment teeth
Large failing restorations which undermine & weaken cusps.
Crowns are needed to restore & strengthen teeth
Full coverage
Metal Crowns
Contraindications
- High aesthetic requirement (anterior teeth)
- When more conservative restoration can give the treatment objectives e.g. partial coverage
- Intact buccal or lingual wall
- If less than maximum retention and resistance are needed (short span FPD)
- When caries extend gingivally, as that the finish line cannot be made
- In case of uncontrolled caries
Principles of Fixed Prosthodontic Preparations
Preservation of tooth structure
Retention & resistance
Structural durability of the restoration
Marginal Integrity
Preservation of the periodontium
Finish Line Placement & Geometry
(Marginal Integrity)
Placement:
• Always on healthy tooth structure-enamel preferred
• In an area of accessibility for finishing & cleaning
• Supra-gingival recommended when possible
• Sub-gingival if necessary for length of the preparation, caries,
old restorations or esthetics
• Geometry:
• Slip joint for Metal
• Chamfer, beveled shoulder & knife edge
• Shoulder best for esthetics
Margin is
Junction of prepared tooth structure & crown-often referred
to as the margin
Chamfer finish line
Used for most metal margins.
• 0.3 to 0.7 mm
Shoulder finish
line
• Facial of some PFMs
• Proximal boxes of gold inlays & onlays
• Facial of mandibular 3/4 gold crowns
• Functional cusp of MOD onlays.
• 1 to 1.2 mmo
Shoulder (Angled or Radial
Shoulder)
• Used for
• All porcelain crowns
• Facial of PFM crowns where maximum esthetics desired
• Ceramic inlays and onlays
• 90 degree angle at cavosurface & rounded internal angle
• Margin of restoration is porcelain
Knife edge or Feather edge
Done by needle burs
• Minimum reduction at
area of finish line
• Not suitable for all
ceramic
Full Metal Crown Preparation Armamentarium
Armamentarium
Hand piece
2. Round-end fissure tapered
diamond
3. Flat end fissure tapered
4. Needle diamond
5. Torpedo diamond
6. Flame or wheel bur
Steps of Preparation
1) Occlusal reduction ( Functional cusp bevel).
2) Axial Reduction ( Facial and lingual)
3) Interproximal Reduction.
4) Auxiliary retention if needed.
5) Checking the reduction.
6) - Bevels and Finishing.
Occlusal
Reduction/Clearance
round-end tapered diamond
to make depth orientation grooves on:
The triangular ridges.
The primary development
grooves.
1.5 mm of functional cusp a
1mm on the nonfunctional cusp.
Depth of occlusal reduction 1.0
mm deep as measured against
uncut tooth structure.
Occlusal clearance measured
Occlusal clearance measured with
Instrument (1.0mm dia)-It passes
freely over occlusal surface from
mesial to distal
It can be checked asking the patient
to close on red utility wax held over
the preparation.
Inject Bite registration
materials onto occlusal &
close-After it sets, remove,
section & measure clearance
Functional cusp bevel
Functional cusp bevel
It should be:
• Parallel the inward facing inclines of the
cusps of the opposing tooth
• Depth of 1.5 mm
• Usually forming a 45-degree angle with
the axial wall.
Axial reduction
The facial axial reduction is done with the torpedo diamond,
producing a definite chamfer finish line at the same time of
axial reduction
The sides of the diamond will
produce the desired axial
reduction while the tip forms
the chamfer finish line.
Initial reduction is done in the
middle 1/3 of the wall
• Reduce wall & create chamfer
finish line
Gingival margin
Supra gingival margin, equigingival to
less than 1.0mm from the gingival margin
• Chamfer finish line, 0.5 to less than
1.0mm
Chamfer preferred bcos
Chamfer is widely preferred for the
gingival finish line:
o It is distinct and easy to capture in an impression
o It will make a slip joint between the
crown margin and the preparation
o It provides space for an adequate
thickness of metal in the margin
Lip on finish line due to
The chamfer should never be prepared
wider than half the tip of the bur ,
otherwise an unsupported lip of enamel
could result
Interproximal Reduction bur
needle diamond bur to do initial interproximal reduction
without nicking the adjacent teeth , using short thin, tapered
diamond bur to complete
Emphasis on reduction at
line angles to create a
smooth, continuous finish
line
C. Interproximal Reduction
Avoid
• Adjacent tooth damage
• Overtapering
• Excessive axial reduction
• Lip in the finish margin.
