FABRICATION OF A CROWN TO FIT AN EXISTING PARTIAL DENTURE

TAKING A CROWN & BRIDGE IMPRESSION & SENDING THE PARTIAL SEPARATELY WILL ALMOST ALWAYS GUARANTEE FAILURE

*If the partial is not picked up in the crown impression it will not fit on a plaster model*

Helpful Technical Suggestions

You can never give the laboratory too much information. In the case of a crown to fit an existing partial denture, you may consider:

  1. Prior to starting the case, examine the intimacy of the fit of the partial in the patient’s mouth & advise Friendship as to your observations.
  2. Does the partial’s major connector fit the mouth properly?
  3. Do the clasps and struts make intimate contact with all teeth?

Prior to tooth preparation, take a pre-op impression of the dentition with & without the partial inserted.

The best impression options to achieve the most intimate fit of the partial denture when fabricating a crown:

  1. Coping Technique
  2. Partial-In-Impression Technique
  3. Matrix Technique

COPING TECHNIQUE

Pros:

  • Results in the most accurate and intimate fit of the partial to the crown.
  • Standard or routine initial impression which assures the best fit of the coping margins.

Cons:

  • This procedure can only be used when fabricating a PFM (Porcelain Fused to Metal) or PFZ (Porcelain Fused to Zirconia) crown as a coping is necessary for luting to the partial prior to the final pick-up impression.
  • The patient will need to “give up” their partial denture for no less than two days.
  • There will be three patient appointments.

Procedure for the Coping Technique

  1. Initially, the dentist will prepare and impress the tooth as he/she would with any usual crown preparation. The impression, opposing model (or impression) and a bite registration will be sent to Friendship for coping (metal or Zirconia) fabrication.
  2. The coping will be sent back to the dentist for try-in. During this appointment, the dentist will lute the coping to the partial using a Duralay type material or composite. (This will ensure no movement of the coping during the final pick-up impression. Note: Be certain that the coping does not impede the seating of the partial. If the partial touches the coping or does not allow enough room for the porcelain application, that area of the coping may remain in metal in the finished restoration. To achieve the most esthetic porcelain result, there should be a minimum of 1.5mm of space between the coping and the major connector, strut and clasps of the partial denture in addition to allowing for occlusal clearance to the opposing dentition.
  3. A quadrant or full arch impression is then taken, picking up the partial with the attached coping. This impression and all original models are sent to Friendship for final fabrication of the crown. Because the coping is already fabricated, the model fabrication and porcelain application can usually be achieved allowing for one full day in the laboratory. (To assure the quickest turn-around time, call ahead to schedule the porcelain application).

PARTIAL-IN-IMPRESSION TECHNIQUE

Pros:

  • The crown can be fabricated from any material including full cast metal or Full-Zirconia
  • Results, although often excellent, can be less than accurate due to the difficulty of complete seating of partial during impression.
  • Only two patient appointments necessary.

Cons:

  • As mentioned above, the partial must be properly and completely seated during impression. Any movement will distort the final fit.
  • The patient must “give up” their partial during the entire fabrication time.

Procedure for the Partial-In-Impression Technique

  1. The tooth is prepared as usual. Check to verify that there is enough room (min 1.5mm) between the partial and the prepared tooth.
  2. As normal, impression material is injected around the margin and over the entire tooth. The partial is then “squished” into this material (be certain that the partial is fully seated and that enough impression material has been placed to capture the clasps, rests and strut of the partial) followed by the insertion of the impression tray loaded with impression material.
  3. As usual, take an opposing impression and bite registration. Send to Friendship.

MATRIX TECHNIQUE

Pros:

  • Patient will not have to “give up” their partial at any time during this procedure.
  • Initial final impression is taken as a standard or routine impression.
  • The crown can be fabricated from any material including full cast metal or Full-Zirconia.
  • Only two patient appointments are necessary.

Cons:

  • The matrix impression must be accurate and will work best with a very heavy body impression material.
  • The fit of the final restoration is often less than perfect, but offers a reasonable result.

Procedure for the Matrix Technique

To better ensure the proper fit of the final restoration, it is highly recommended that you take and send Friendship more than one matrix impression.

  1. The initial prepared tooth is impressed utilizing your usual technique, including opposing impression and bite registration.

Forming the matrix

  1. The matrix is formed by using a very heavy body impression material. The material is injected over the prepared tooth being certain to get a good adaptation.
  2. The partial is then “squished” into this material (be certain that the partial is fully seated and that enough impression material has been placed to capture the clasps, rests and strut of the partial).
  3. Prior to the complete set-up of the impression material, with your finger, wipe away any excess material that may have buried the clasp and strut.
  4. Remove the partial from the mouth and carefully work the matrix impression off of the partial.
  5. Send all impressions, models and a bite registration to the laboratory.

Note: Due to the small size of the matrix impression, we recommend placing it in a tooth box or baggie when sending to the lab and indicating on the lab script that a matrix impression is enclosed.

Another article for this technique can be found by CLICKING HERE

Another Available Option

Send the partial to Friendship utilizing the *Partial-In-Impression* Technique. The laboratory will fabricate the *Matrix* and return the partial prior to the fabrication of the crown.

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This article was written by Roy Levine, CDT, Ceramics Department Manager with technical collaboration from Tony Vlassis, CDT, General Manager. The claims & findings of the commentary are based on their combined 74+ years of technical experience. If you have any questions or comments, please do not hesitate to contact them at:
 
Phone: (410) 780-7700
Email: roy@friendshipdentallab.com or tony@friendshipdentallab.com