Tooth Anatomy “ part 2” Tooth roots

The tooth roots:

the part of the tooth that is embedded in bone. The root makes up about two-thirds of the tooth and holds the tooth in place.
The roots are embedded in the tooth socket in the jaw bone. 

the anchor to a human tooth, the root extends into the bone of the jaw and houses the nerves and blood vessels that carry nutrients to the tooth. A tough, yellowish bone-like tissue, cementum, covers the root and helps hold the tooth in its socket. The cementum contains the periodontal membrane and is in contact with the gum tissue that separates the tooth from the underlying bone. Fibers of the periodontal membrane are embedded in the cementum. The root end openings allow passage of the neural and circulatory elements out of the tooth. Each human tooth has from one to four root canals that carry veins, arteries, lymph vessels, and nerves to the living pulp of the tooth.

For those suffering severe tooth pain and decay and facing the dreaded root canal surgery, there is no doubt that human teeth, including the roots, contain nerves. When the pulp in the root canal becomes infected due to a deep cavity or fracture, bacteria seep in and the root can die. With the damaged or dead pulp in the root, there is increased blood flow and cellular activity for attempted repairs, creating a pressure within the tooth that cannot be relieved. Severe pain in the tooth is sensed when biting down, chewing with the diseased tooth, or applying heat or cold, such as by drinking hot coffee or eating a frozen dessert. Root canal work involves severing the neural and circulatory elements, cleaning out the infected canal, and sealing it off from further infections. Without the endodontic surgery, the infection will spread, the jawbone will begin to degenerate, and the tooth will fall out. Infections in root canals of teeth are common and sometimes they become toxic, requiring tooth extraction. New research is exploring replacing decayed tooth pulp above the root as an alternative to root canal surgery.

Molecular biologists and geneticists are exploring how the tooth root is laid down and are trying to harness the natural processes to aid in reconstructive surgery and to treat genetic disorders such as cleft palate. The ultimate goal for dentists will be the ability to regenerate lost or diseased teeth instead of replacement with dentures and dental implants. As part of the Human Genome Project, the genes controlling cementum and root development have been elucidated and now researchers are exploring what mechanisms turn on and off these genes.

Comparative morphological studies of the tooth root structures in primates including humans provide clues to dietary adaptations of ancestral and extant primates. Using biomechanics, tooth roots must resist the loads applied to the tooth crown, and their various forms appear to be adapted to the varying loads experienced by different teeth within the mouth of a primate. Variation among primate species suggests different dietary histories over evolutionary time. Inferences from this work have been used to discern ancestral feeding patterns based on fossil hominid skulls. Forensic scientists are exploring the use of root coloration as a method of aging a victim with a high correlation found between increasing chronological age and increased root coloration.

Root canals:

A "root canal" is actually only a part of the dental pulp.  It has all the same characteristics and functions as the rest of the dental pulp, except that it is located inside the root portion of the tooth and is thus rather thin and spindly.  When we tell a patient that they need a "root canal", we are not talking about the anatomical structure itself.  We are talking about a procedure.  We really mean that the nerve is sick and must be removed in its entirety from the tooth, the empty space where it used to live cleaned and sterilized and finally sealed with a form of rubber called gutta percha or one of the newer materials designed for this purpose.  The technical name for this procedure is "endodontic treatment".  The root canal(s) in any given tooth start out just like the rest of the nerve, as a solid piece of soft tissue.  Blood vessels and nerves enter through a hole at the tip of each root.  The tip of the root is called the "apex", and the hole that allows the nerve tissue, with its accompanying blood vessels to enter the tooth is called the apical foramen.   Of course, blood must traverse through the root canals in order to infuse the nerve.  As we age, the root canals too replace themselves with more and more dentin until they become less tube like and more like a network of blood vessels and nerves running down approximately the center of the root.  The image to the right shows some of the complex anatomy that the dentist is presented with when he must perform a root canal procedure to relieve pain and infection.  In fact, the nerve anatomy can become even more complex as we age.  As the canal becomes thinner and thinner, we say that it has become sclerosed.  One can see that it could be quite difficult to remove ALL the dead tissue in the root canals if its internal anatomy has become more and more sclerosed and difficult to negotiate as the tooth ages or becomes sick.  While it is important for the endodontist to remove as much dead nerve tissue as possible from the pulp chamber and root canals, the final line of defense against endodontic failure is to make sure that any remaining dead nerve tissue inside the tooth is properly sealed off at the apical foramen and any other openings in the root by properly fitted and placed sealing materials.

The Cementum:

Cementum is to the root of a tooth as enamel is to the crown.  Cementum is a  relatively soft bony tissue that covers the root surface in a thin layer.  Its main function is to act as an attachment layer for the periodontal ligament which is a soft tissue sheath that acts as a cushion between the bony socket and the tooth itself.  It is relatively soft and does not wear well against environmental assaults, so it abrades  away rapidly whenever it is exposed to the oral environment because of recession.   The image to the right shows the relationship of the enamel that covers the crown of a tooth, to the cementum that covers the root.  Unless there is wear of the cementum due to recession, or attrition of the enamel due tobruxing or mechanical abrasion, the dentin is never exposed.  The cementum meets the enamel in a line that surrounds the tooth.  This line is called the cemento-enamel junction.