Fig.1  Fig.2 Fig.3  Fig.4 

Dental Education Lecture: Premolar Root Canal

We have two premolars in each quadrant of our mouth.  We call them premolars because they are in front of our molar teeth.  There is one or two canals in each premolar.

Mrs. Wang has severe abscess in one of her bottom premolars. It has a large silver filling (Fig.1 S).  There is a cavity underneath the silver filling (white arrowheads).  There is a large shadow in the root tip (black arrowheads).  So we need root canal.

Fig.2 shows X-ray taken when root canal (R) is almost finished.  The size of the root tip shadow is as large and dark as that in Fig.1.  Three months after root canal, Mrs. Wang has no discomfort at all.  X-ray shows that the root tip shadow is shrinking (Fig. 3 black arrowheads, as compared to Fig.1 and 2).  A nice white filling is placed (F) after root canal to prevent re-infection.  Asterisk (* in Fig.3) indicates an important nerve traveling inside the lower jaw and providing sensation to our lower lip.  While root tip shadow continues to decrease 1 year after root canal (Fig.4), the shadow of the nerve remains the same (*).  

There are two important points associated with closeness between the root tip and the nerve.  First, severe root tip infection in the lower premolar is sometimes accompanied by numbnes of the lower lip.  The nerve is compressed by local swelling.  Second, the dentist should be very careful when he is cleaning up the root canal with stiff metal files.  Sticking out too much these files may damage the nerve underneath the root tip.  The distance between the root tip and the nerve is a matter of 2-3 mm.  Anyway, every root canal is not easy.

Xin Wei, DDS, PhD, MS 1st edition 05/21/2010, last revision 05/21/2010