Jacket porcelain crowns (PJC):

Lect.9 Crown and Bridge Dr. Ameer H. AL-Ameedee


The word ceramic is derived from the Greek word Keramos which means"burnt stuff" meaning a material produced by burning or firing. It consists mainly of kaolin which blends with other minerals such as silica and feldspar to produce the translucency and extra strength required for dental restoration. A material containing these additional important ingredients was given the name porcelain.

Jacket porcelain crowns (PJC):
Full coverage restorations, , it is an artificial non metallic restoration used to cover the all surfaces of the clinical crown. It is made only from porcelain, as, these are restorations used to restore the all surfaces of the clinical crown, classified according to the material used in their construction:
1. Metal crowns (or restorations).
2. Non-metal crowns (or restorations) Full veneer.
3. Combination of both of the two above crowns (constructed as a thin metal shell covered by layers of porcelain).

Technical Considerations:
The porcelain jacket crowns are made using the platinum foil matrix technique.
Platinum Foil Matrix:
The porcelain jacket crowns are constructed with high fusing feldspathic porcelains. A platinum foil is first adapted to the die. The platinum foil functions as matrix. It supports the porcelain during condensation and firing. After completion of the restoration the platinum foil matrix is discarded.

Condensation and Firing:
The platinum foil matrix is carefully removed from the die and the core porcelain is carefully condensed on to it. It is then placed in the furnace and fired. After cooling, the rest of the body is built up using dentin, enamel and other porcelains

Removing the Foil: After completion of the restoration the platinum foil is gently teased out and discarded. This can be quite difficult.


PJC: Indications of use:
1. For anterior teeth (especially incisors).
2. For severely discolored anterior teeth.
3. Over an existing post and core substructure.

PJC: Contraindications of use:
1. In Posterior teeth (when maximum resistance and retention is needed).
2. In case of tooth with short clinical crown (no enough tooth structure to support the porcelain).
3. In case of edge to edge or overbite occlusion (Overbite: is the vertical overlap of the upper incisor teeth over the lower ones).
4. as a retainer for FPD.

The PJC advantages:
1. Have the best cosmetic effect of all dental restorations.
2. Are very strong.
3. are the best to use on the incisors.

The PJC disadvantage:
Have high risk of fracture (because they are brittle).

Ceramic crowns may be cemented with zinc phosphate, glass ionomer. or a dual- polymerizing resin cement such as Enforce with Fluoride.
Ceramic crowns that have been etched internally and bonded with composite resin cement are 50% stronger than similar crowns cemented with zinc phosphate cement.




Depth orientation grooves




Labial, incisal reduction




Interdental reduction



cervical collar Palatal Cingulum reduction





Gingival margin End cutting bur


? Shade selection
A shade guide contains samples of all available shades and is used to match the natural tooth color.
• Moisture helps achieve a more accurate match.
• Use natural sunlight.
• Record the shade on the patient s chart and on the laboratory prescription.

? The tooth is prepared so the cast restoration can slide into place and be able to withstand the forces of occlusion.
• Rotary instruments are used to reduce the height and contour of the tooth.
• Hand cutting and rotary instruments prepare the gingival margins.


? Cord temporarily displaces the gingival tissue and widens the gingival sulcus so impression material can flow around all parts of the preparation.
• Nonimpregnated
• Impregnated




? Elastomeric impression materials are used to create these extremely accurate impressions.
• Mixing and application of light-bodied material around the prepared tooth.
• Mixing and loading of tray with heavy-bodied material to be seated onto the quadrant or arch.


Bite Registration:
? Provides the laboratory technician with a reproduction of a patient’s bite and opposing arch registration for designing the anatomic structures of the fixed prosthetic.
• Open bite
• Closed bite


Provisional Coverage:
? Used to keep the patient comfortable during the period from tooth preparation to final cementation of the fixed prosthetic.
• Reduces sensitivity and discomfort.
• Maintains the function and esthetics.
• Protects the margins.
• Prevents shifting.


Delivery:
? When the casting has been fitted and is acceptable, the dentist cements it to the tooth.
• Permanent cementation
• Temporary cementation