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A Little Byte

Porcelain Jacket Crowns: Preventable Failures

Even though ceramic crown systems have greatly improved – clinical failures still occur. Favorable results are largely dependenton

(1) Proper evaluation of the presenting clinical situation
(2) Implementation of valid principles of design
(3) Optimum cementation techniques

While there may not be a simple explanation to what can be a complex problem, some stress related failures can easily be prevented. This dental byte outlines some of the most likely causes of stress related PJC failures.


Diagnostic Phase:

Undesirable occlusal loading pattems:
Patient has a deep anterior overbite – reconsider using a PJC
Patient is a bruxer or a grinder – reconsider using a PJC


Crown Prep Phase:

Inadequate tooth preparation:
There is no shouIder margin on lingual surface – shoulder required for strength
There are sharp line angles on prep -sharp angles are source of stress
A lab technician recently told me, “Given the same prep, I could fabricate a better porcelain bonded to metal crown that porcelain crown.” Something to think about…


Laboratory Phase:

Improper porcelain application:
For example: Lab may use feldspatic porcelain for core instead of using aluminous porcelain for core


Delivery Phase:

Cementation technique:
Zinc phosphate used as a cement – Consider using a resin cement “bonded crown”

Occlusion Veriflcation:
Occlusion checked prior to cementation – Uncemented crown more subject to break.
Crown high in lateral excursions and/or protrusion.