All Metal and Zirconia Preparations Flashcards
What are the parts of a crown prep?
- Axial wall
- Interproximal wall
- Finish line
- Occlusal anatomy
A full coverage restoration can survive in the biologic environment of the oral cavity only if the margins are…
closely adapted to the surface finish line of the preparation.
The design of the ___________ ________ _______ dictates the shape and bulk of restorative material in the marginal area of the restoration.
preparation finish line
What are the types of finish line designs?
–Knife Edge
–Chamfer (Light and Heavy)
–Shoulder
–Beveled Shoulder
What is the knife edge margin design for?
- full metal crowns only
- especially full Gold crowns
Why is a knife edge margin good for gold crowns?
Due to Gold’s malleability, the margin can be burnished, adapted and polished to a precise fit with this margin design.
What type of bur is used to make the knife edge margin?
flame or needle shaped diamond bur
What type of margin is the most conservation preparation design?
knife edge
What are the disadvantages of knife edge margin?
-Difficult to see finish line in an impression or scan
-Metal can be thin and is susceptible to distortion under heavy occlusal load
-Often leads to an over-bulking of crown material to compensate for thinness along margin
-Easy to miss creating distinct end of finish line and instead axial wall never terminates
To compensate for thin marginal area, labs will _________ crown at margin
overbulk
What are the indications for the use of Knife Edge Margins?
Generally NOT indicated.
-In certain instances like a tipped molar, a knife edge margin is possible to be conservative in an abnormal area.
-Must have an excellent lab technician
What crowns do you use a light chamfer?
Metal Crowns
Zirconia Crowns
What crowns do you use a heavy chamfer?
Ceramic Crowns
Zirconia Crowns
Metal-Ceramic Crowns
How do you make a chamfer margin?
Typically using a round ended diamond bur
Axial depth more than ½ the bur, can create…
lipped edges of the margin which leave unsupported enamel likely to chip or break leaving an open and exposed margin
What are the advantages of a chamfer margin design?
- Chamfer is well suited to Full Metal Crowns and Zirconia Crowns
- Ease of seating crown and placing of crown
- Ease of detecting margin on impression or scan
- If Full Metal, chamfer is easy to wax and cast
- Provides adequate thickness of restoration material at margin area
A light chamfer is ________ mm deep into axial wall
0.3–0.5
What degree of margin does a light chamfer create?
Produces 30 to 45 degree margin with rounded internal angle
What two concepts does a light chamfer combine?
combines knife edge burnish-ability with bulk of material for all metal crowns
A heavy chamfer is ________ mm deep into axial wall
1.0 – 1.2mm (with internal rounded angle)
Heavy Chamfer provides room for _____ ceramic margin
thicker
What type of bur do you use to do a heavy chamfer?
large round ended diamond bur
A shoulder margin design is close to a _____ degree angle
90
What is a shoulder margin design used for?
- Metal Ceramic crowns
- All Ceramic crowns
- sometimes Zirconia Crowns
What is the angle of a modified shoulder margin?
rounded angle
Why is the angle at the axial wall and finish line for a shoulder 90 degrees?
decreases stresses on restoration material
Some Shoulder finish lines can include a bevel at a ________ degree angle
30 – 45
What are shoulder with bevel margins used on?
- Inlays and Onlays
- Metal ceramic crowns
What does the bevel on a shoulder with bevel margin allow for?
adaptability of metal to ensure marginal fit
Significant roughness of preparation finish line can prevent…
close adaptation of crown margin
What can a rough margin cause?
plaque accumulation = recurrent decay
A ____________ margin improved the biomechanical performance of posterior single zirconia crown restorations, which might be attributed to greater thickness and rounded internal angles.
deep chamfer
Which preps allow for better seating: ones with finish lines that allow for good sealing or ones that have poor sealing?
finish lines like shoulder preparations which exhibit poor sealing prior to complete cementation allow good seating whereas margins which seal earlier do not allow escape of cement and do not seat completely
What is a shoulder margin design?
It is the type of tooth preparation in which the finish line forms a 90-degree angle with the unprepared tooth surface
What are the advantages of a shoulder margin?
- Less distortion of crown margins
- provides adequate bulk
- good crown contours
- good esthetics
What are the disadvantages of a shoulder margin?
- Marginal adaptation can be affected
- more tooth structure needs to be removed
What are the indications for a shoulder margin?
All-ceramic crowns
PFM crowns
What is a shoulder with bevel margin design?
Similar to shoulder but has a bevel placed at the border
- mostly used to hide a margin due to aesthetic reasons
What are the advantages for a shoulder with bevel margin?
- proper marginal adaptation
- the bulk of the material in border
What are the disadvantages for a shoulder with bevel margin?
- More tooth structure is removed
- less conservative approach
- preparation should be extended apically
What are the indications for a shoulder with bevel margin?
- Gingival finish line on the proximal box of inlays or onlays
- Occlusal shoulder of onlays
- Finish line for extremely short walls
- The facial margin of Posterior metal-ceramic crowns with a supragingival margin
What is the chamfer margin design?
A finish line design for tooth preparation in which the gingival aspect meets the external axial surface at an obtuse angle
What are the indications for a chamfer margin?
- Cast metal restorations
- Lingual margin of metal-ceramic restorations
What are the advantages for a chamfer margin?
- Conservative tooth prep
- good marginal adaptation
- provides bulk to the restoration
What are the disadvantages for a chamfer margin?
- technique sensitive
- any defect in fabrication can lead to unsupported tip of the Crown
What is the heavy chamfer margin design?
Similar to Chamfer finish line but comes with a 90 degrees cavosurface angle with a large radius rounded internal angle. In case of metal restorations, a bevel can be added to the finish line.
What are the indications for a heavy chamfer?
- ceramic crowns
- metal crowns with a bevel
What are the advantages for a heavy chamfer margin?
Best finish line for a Ceramic crown
What are the disadvantages for a heavy chamfer margin?
- Technique sensitive
- the little discrepancy can lead to the formation of a lip or unsupported fragile enamel
What is the design of a knife edge/feather edge margin?
As the name suggests it has a knife-edge or thin edge
What are the indications for a knife/feather edge margin?
- Young patients
- Metal restorations
- MOD Onlay
- Inaccessible areas
- When the finish line extends to the cementum
- The lingual surface of mandibular
posterior teeth - Pin ledge 3/4th quarter crown
What are the advantages of the knife/feather edge margin?
- Conservative
- Helps in preserving tooth structure
- Ideal for marginal adaptation
- Useful in gold and metal crowns/restorations as it lets you burnish it to a fine finish
What are the disadvantages of the knife/feather edge margin?
- Distinct or proper finish is not visible,
- Waxing, polishing and casting become critical
- Overcontouring of restorations to obtain the bulk needed
What happens to the pulp during a crown prep?
pulp becomes irritated and inflamed
A rise in pulp temperature by ___ degrees significantly increases the chance of pulpal necrosis.
10
What do we do to protect the pulp during a crown prep?
-Use lots of water
-Use sharp burs
-Use light pressure
-Use high speed
-Use Diamond burs
-Avoid desiccation of the teeth
The main cause of postoperative inflammation or necrosis of the pulp is probably the injury of the ________
dentin
What instruments/tools do you use to prepare?
- High Speed Handpiece
- Air/Water spray
- Diamond Burs
What instruments/tools do you use to finish?
- Slow Speed Handpiece
- Fine Diamond burs (possibly some carbide burs)
- Can also use hand instruments
What instruments/tools do you use for caries removal?
- Slow Speed with 2, 4 or 6 round bur
- Spoon Excavators
Diamond burs remove enamel and dentin by _________ it away
grinding
Carbide burs remove tooth by ________ it away
shearing
Which burs are more efficient: diamond or carbide?
Diamond burs are most efficient. 2 – 3 times faster than carbide burs
What are carbide burs used for during crown preps?
Often used to place extra retention features in a crown preparation such as seating groove
What hand instruments can be used to help smooth finish lines of a crown prep?
- Chisel
- Hatchet
- Hoe
- Margin Trimmer
What are the advantages of a full metal crown?
-Gold and many Metal crowns are soft metals
-Gentle to opposing teeth
-Metal is strong so material can be quite thin
-Allows for very conservative preparations
-Metals have some antibacterial properties making recurrent decay less likely
-Most Gold and Full Metal Crowns are much gentler on the gingiva
-Metal Crowns are very durable
-If contact is missing, you can add material to the contact
What are the disadvantages of full metal crowns?
Esthetics!
What is the margin design for a full metal crown?
Can use knife edge margin, but usually a light Chamfer is recommended. 0.3 – 0.5mm
What is the finish line/margin width for a full metal crown?
0.3-0.5 mm
What should the axial wall TOC be for a full metal crown?
6 to 10 degrees ideally, but can have TOC up to 20 degrees
Axial walls can be reduced as little as ____mm on a full metal crown
0.5
- can reduce more if needed
What is the occlusal reduction for a full metal crown?
1.0 to 1.5mm
Nothing is sharp in dentistry except for…
our tools
Line angles and corners need to be _______ to prevent pressure points and possible fracturing of a restorative material.
rounded
___________ preparations make the crown fabrication process easier
Rounded
Why do you finish/smooth the crown preparation?
This ensures the preparation walls are scored, but with a smoother more consistent shape for seating and for longevity of the restoration
What are the measurements for a full metal crown (finish line, axial, TOC, occlusal)?
- Chamfer finish line 0.3 – 0.5mm
- Axial reduction as little as 0.5mm
- Total Occlusal Taper of 6 – 10 degrees
- Occlusal Clearance 1.0 – 1.5mm
What are the characteristics of zirconia crowns?
- relatively new material
- “metal-free”
- can have properties similar to metal
- can be very hard and tough
- less translucent than natural teeth
What was the original Bruxir zirconia crown like?
very very tough, and very very ugly
What has beeen compromised in order to make zirconia crowns more esthetic?
the strength of the Zirconia crowns has been reduced
Depending on the _____ of Zirconia crown, your prep can be as minimal as a Full Metal Crown preparation or as extensive as an All Ceramic Crown Preparation.
TYPE
How do the measurements change from the BruxZir zirconia crown full-strength to the esthetic version?
The esthetic version has more reduction required!
Esthetic
- 1.25 mm reduction
- Chamfer or modified shoulder margin
Full-strength
- 1.0 mm reduction
- Chamfer or modified shoulder (feather-edge is ok)
All metal Crowns are long lasting, allow for conservative preparations
because of…
their strength and they wear opposing teeth less
All metal Crowns are not used as much any more because of _______
esthetics
Zirconia crowns can be as tough as an _________ crown
all metal
The more esthetic your Zirconia is, the _______ reduction will be needed.
more
What is important to know about zirconia crowns?
Zicronia is rapidly changing still so knowing which kind of Zirconia your lab is using is really important so that your preparation is appropriate for the type of zirconia being used.
