Lesson Learned from Crack Tooth

Crack tooth is intriguing to dentists, because it causes severe pain.  The patient cannot eat and demands immediate treatment.

Jenny is 49 years old.  She has not visited our office for a long time, because she does not think that there is any problem with her teeth.  But she has lost two molars on the right side since she was young (Fig.1 *).  Two remaining lower molars shift to the missing tooth region (arrows).  It is not easy to chew on this side.  But this must be not a big deal to her.  She can chew on the left side anyway.  Her left back teeth are complete (Fig.2).

The day before yesterday she had to come to our office on emergency, because the upper left first molar (#14) has excruciating toothache.  This tooth has a silver filling (F), which is not too big and which still has some distance to the nerve (*).  We could not figure out why this tooth causes severe nerve infection.  When the filling was removed, several fine crack lines were visible on the bite surface (Fig.3 arrowheads; red ones point to finer crack lines).  The pattern of crack lines are shown in Fig.4C.  The crack lines extend to the nerve underneath.  The latter was found to be dead and infected.  When the infected nerve was cleared out, the pain was gone.  Finally a crown is required to prevent the tooth from being split completely (1 2 3 4 5).

How can a tooth become cracked?  In fact our tooth consists of 4 or 5 parts when it is initially forming (Fig.4A).  As it grows, these four parts fuse to form an apparent one-piece tooth (Fig.4B).  The fusion may be incomplete with formation of crack lines (Fig.4C).  But crack lines do not necessarily cause problems. 

The following are the reason that crack lines lead to troubles.  As we age and eat and use teeth more, they become brittle.  When we suddenly bite something hard (such as nuts, crab leg), unfavorable force (Fig.4D black arrowheads) makes crack lines larger (red arrowheads; great canyon).  Germs have chance to enter the nerve in the middle of the tooth.  Infection settles in, followed by pain.  The pure enlargement of crack lines can cause mechanic force upon the nerve.  The result is also excruciating pain.  How can we eat with crack tooth? 

Our tooth with crack lines becomes weaker when it has a big filling and when we only chew with this tooth exclusively.  The poor guy finally gives up, because we abuse it.  Do we have to fix small cavities and restore missing teeth as soon as possible?

Xin Wei, DDS, PhD, MS 1st edition 01/08/2013, last revision 01/09/2013