Dental Education Lecture: Cavity Under Crown

It is generally thought that our teeth are easy to get cavity because they are exposed to the mouth full of germs.  Once we put a crown on one of the teeth, the latter is isolated from the mouth and will never get cavity again.  In fact, it is not true.

Mrs. Hao came to our office three years ago and requested putting a tooth back in the area labeled as #19 in Fig.1.  The tooth #18 has a crown.  The end of the crown (denoted by an arrowhead: <) is slightly underneath the gum line (white line). It is difficult to find out anything bad happening underneath.

A year later, the patient is complaining of pain between the tooth #18 and implant #19 (Fig.2 I).  A small cavity passes unnoticed (long curved arrow).  Two more years later, the dull pain persists.  This time the cavity is quite obvious (Fig.3,4 between >), whereas the implant tooth is alright.

Finally the tooth #18 is extracted (Fig.5,6).  The cavity is so big (Fig.5 single >) that one of the roots is snapped during extraction (double arrowheads).  Fig. 6 shows the side view of the extracted tooth.  Single arrowhead points to the large cavity on cheek side, whereas double arrowheads point to the cavity on the tongue side.

We should double our effort in oral hygiene after extensive dental treatment (such as root canal (white < in Fig.4) and crown), because crown does not provide protection against cavity.  After root canal, our tooth loses sharp pain sensitivity.  New cavity does not cause severe pain.  It delays our diagnosis and treatment.

Xin Wei, DDS, PhD, MS 1st edition 12/22/2009, last revision 06/10/2012