The base of a mature tooth is shown in the image at left. This section is taken right through the middle, showing the dentin of the wall (D), and (since this is the region below the gum line) the cementum (C) that overlies it. The pulp cavity (PC) communicates with the space around the tooth via the root canal (RC).
The root canal is an important location. It's the channel by way of which blood vessels and nerves enter the living matter of the pulp cavity. The tooth isn't directly attached to the jawbone (B); rather, it's held in place by the tough CT of the periodontal membrane (PM) that's attached to the cementum and to the surrounding bone. The root canal opens into this space.
If a tooth is damaged to the point where the pulp cavity is exposed to infection, this root canal is the channel by which the infection can spread to the bone of the jaw and even to become a systemic problem; hence it has to be plugged by the dentist when the tooth is being repaired. The process of "having a root canal" is so exhilirating because what the dentist is doing is drilling out this channel and then stuffing filling material in it. The nerve fibers in there (afferent processes of sensory neurons) quite naturally take exception to this maltreatment and tell the pain centers of the brain all about it.
At right you see a forming tooth in situ. This image is from an 18 day mouse fetus (three
days before birth). You can see that it has two roots, and that
the pulp cavity and the root canals are in
communication. It is via these root canals that nerves and
blood vessels enter and leave the pulp cavity; the tooth proper is
noncellular material and is technically "dead"—merely the product of
cellular activity.
This late in development the tooth is very well formed, and this image shows the way that differential deposition of material can "sculpt" the tooth into the proper shape. (How this fantastically complex process is controlled to produce the right shape every time is a complete mystery, and anyone looking for a Nobel Prize would do well to consider it as a research project.) Incidentally, the enamel had to be removed before cutting; that is, the specimen has been decalcified and the enamel is gone. All you see here is the dentin. The enamel, in life, filled the white area between the dentin and the overlying gingiva (E).
Mouse fetus; H&E stain, paraffin section, 20x
