Endodonticly treated teeth are different from than normal "vital" teeth .  Root canal treated teeth are usually badly damaged due to decay and old fillings.  They also are more brittle than vital teeth. once the root canal has been performed, these teeth need special treatment, or they tend to break a few years down the line.  This is especially true of back teeth that have broad biting surfaces.  They are likely to shear off because of biting forces.  These teeth need to have crowns placed in order to protect the investment in the root canal treatment.  

But sometimes the crowns are not placed for whatever reasons. These teeth fracture under the load of biting forces.  For this reason, we need to prepare the remaining part of the tooth in such a way that the crown to be placed on top does not dislodge later. The tooth needs to be supported from inside.

The inside of the canals are enlarged and shaped to receive a specially made metal "post" that exactly fits the hole. These posts are usually pre-manufactured and come in many different shapes.  The post is then cemented in the hole so that it is firmly embedded in the root of the tooth, and projects up above the level of the gums in order to help retain a filling that will be placed over it. The filling is now retained on the tooth by whatever undercuts are available on the inside of the remaining tooth stump as well as the post which is firmly anchored in the root. This filling is meant to be prepared as a core for a crown, but it may remain temporarily as a finished restoration

Finally, the tooth and filling are prepared to receive a crown.  This is done by grinding down the filling and what remains of the tooth above gumline . The prepared part of the tooth above the gumline is called a core.

Once the tooth has been prepared, an impression is made of the preparation, as well as the surrounding teeth.  This impression is sent to the lab where a technician fabricates a porcelain crown to fit the shape of the prep.  This is cemented onto the prepared tooth in the mouth.  

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