Dental Education Lecture: Introduction to Root Canal Therapy

When we have severe toothache, we cannot help thinking of root canal (therapy).  What is it?  To answer this question, we need to know a little bit tooth structure and what causes toothache.

As we learn from lecture Tooth Structure, every tooth has three hard tissues (enamel, dentin, and cementum) and one soft tissue (pulp, so-called nerve) (Fig.1).  Fig.1 and 2 show front and back teeth, respectively.  A front tooth usually has one root, whereas a back tooth has two or more roots.  The pulp is actually a piece of meat (soft tissue) inside our tooth (green area in Fig. 1 and 2).  It is divided arbitrarily into two portions: coronal (inside the crown, above arrows in Fig.1 and 2) and radical (inside the root, below arrows).  

When cavity (black in Fig.3) involves the pulp in early stage, infection may be limited to the coronal pulp shown as red in Fig.3.  It is reasonable to remove the coronal portion of the pulp to relieve pain and leave the uninfected radical pulp intact as shown in Fig.4.  Arrow in Fig.4 points to the junction of coronal and radical pulp; gray area represents filling after partial nerve removal.  This procedure is called pulpotomy.  In western countries, pulpotomy is limited to treat baby teeth with nerve infection, whereas this procedure is also used for adult teeth in eastern countries, such as China and Russia.

Success rate of pulpotomy in adults is not high, because when tooth nerve is infected, the doctor does not know whether the infection is confined to the most coronal portion of the pulp (Fig.3) or not.  The infection may involve all of the coronal pulp and initial portion of the radical pulp as shown in the left root in Fig.5 or all of radical pulp in the right root.  Even worse, the infection may extend outside the root tip, as shown by a red circle.  When nerve infection is not so limited, pulpotomy is not indicated.  It is safe to remove all of potentially infected pulpal tissue from the tooth.  The procedure is termed root canal therapy.  When the radical pulp is removed, the root becomes empty.  The space is called root canal.  To prevent re-infection, the doctor needs to fill the space (root canal) with a special rubber-like material (1, brown, in Fig.6).  After this step, we need to fill the space previously occupied by the coronal pulp and cavity (2, gray area, Fig.6).  The procedure is called crown build-up.  Next procedure is fabrication of a crown for protection (3, Fig.6).  After successful root canal therapy, the infection outside root tip (red circle in Fig.5) will heal by itself over time (blank circle in Fig.6).  Next lecture will discuss root canal therapy in detail.

Xin Wei, DDS, PhD, MS 1st edition 01/28/2009, last revision 02/17/2009