Three pins placed in tooth before adding filling material.

Many times, teeth can be so broken down due to extreme decay or fracture that there is not enough tooth structure available to hold a filling in place. In most of these cases, a crown (cap) would be indicated. However, certain situations may call for a change in plans. Things like inability to afford a crown, an unstable gum situation, waiting to see if a recent root canal will work, or any situation where the long term progression (outlook) is questionable are all possible reasons to go with just a filling. When there is not enough tooth structure to hold a filling, then pin retention is indicated. Pins are tiny threaded screws that are placed about ½ millimeter into dentin. A pilot hole ever so slightly smaller than the pin is drilled into the tooth, then the pin is screwed into place. An amalgam (metal) or composite (tooth-colored) filling is then placed over the top. The pin is only used for retaining the filling on the tooth. It does not reinforce like a rebar does with concrete. Pins have been known to cause microcracks in the dentin, however, I have not seen a fracture of the underlying tooth structure that was severe enough to lose the tooth that was caused by the pin alone.