The Twin Clasp Technique - How to make a crown under an existing partial without the appliance

Having to send an existing partial denture to the laboratory while a crown is being fabricated for a tooth that happens to be clasped has always been a major inconvenience and disappointment to patients. In the fall of 1995 we introduced the Twin Clasp Technique which eliminates this frustrating problem. Since the introduction of the Twin Clasp we have fabricated hundreds of successful crowns that fit under existing partials using this method. Since this technique continues to be very popular we thought it would be appropriate to republish the procedure for our new customers and those who have not yet used the technique.

1. Prior to tooth preparation be sure to observe the seating of the partial. Success of this technique is dependent upon a positive and accurate seat of the partial after the tooth is prepared.
2. Prepare the tooth and place retraction cord.
3. Inject heavy-bodied polyether or one-step polyvinyl around only the prepared tooth, making sure the entire margin is captured.
4. Fully seat the partial into its proper position in the mouth allowing the clasp around the prepared tooth to imbed itself into the impression material. Do not allow the clasp to be totally covered, if material covers the clasp, wipe it off. The object is to register the tooth surface of the clasp, rest and minor connector. Covering the entire clasp will render this technique ineffective.
5. Allow the material to set under the clasp without occlusal contact.
6. Remove the partial and clasp impression from the mouth. The small impression will most likely be removed with the partial. Separate the impression from the partial without altering it in anyway.
7. Perform your normal C&B impression procedure without the partial in place.
8. Provide us with a study model of the partial in place. (optional)
9. Send us the clasp impression (in an old ROE box so it will not be lost), regular C&B impression, bite, opposing model, study model and work authorization for the construction of the crown.

At the laboratory we use the twin clasp impression to wax and cast a clasp assembly that mimics the existing partial.  The new crown is fabricated to fit within the duplicate clasp.

Over the last four years this technique has proven to be quite successful.  We encourage you to try the Twin Clasp Technique the next time a patient complains about giving up their partial denture while a crown is being constructed.