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Root Canals and Their Morphology

To know about the root canal we will first have to know about the general anatomy of a tooth. Externally, a tooth has only two parts, the crown and the root. The crown portion of the tooth is what is visible in the oral cavity and is white in color and smooth on the surface. However, the root part of the tooth is not visible in the oral cavity and therefore, an extracted tooth specimen is needed to observe the color and surface texture of the root.

Structure of a tooth

Internally, the tooth has a layered configuration where the outermost covering is that of the enamel. It’s the hardest substance that can be found in the human body and is made of a calcium compound called hydroxyapatite. Inner to the enamel, lays the dentin; the most typical feature of which is the presence of dentinal tubules that have a major role to play in tooth sensitivity. While the enamel is thin, approximately 2.5mm at the cusps of the teeth, the dentin is comparatively thicker with a width of maximum 3mm in the molars i.e. the back teeth which play a primary role in chewing food.

The deepest layer of the tooth houses the pulp which contains the blood and nerve supply of the tooth. The pain associated with any dental procedure is because of the sensations carried by the nerve supply in the pulp region to the brain. Also, when the caries or bacterial infection is deep enough to reach the pulp, it may cause excruciating pain and selling around the infected tooth.

The root canal system

Orifice of the root canal- it begins from around the cervical constriction of a tooth and is somewhat funnel-shaped. It may also be said to be located at the corners of the floor of the pulp chamber.
  • Apical foramen- the tip of the root canal where the canal meets the cementum part of the tooth root is apical foramen and the canal is the most constricted at this point. It generally marks the length of the root canal.
  • Accessory canals- though rare, but sometimes the primary root canal may have branches which are called accessory canals. These are quite difficult to clean during a root canal treatment and may cause the failure of the treatment in some cases.
  • Furcation canals- these extend from the floor of the pulp chamber to the periodontal space and are a major cause for failure of a root canal treatment if undetected. These are, rarely but typically found in the molars.
  • Canal isthmus- in a multirooted tooth, several canals may be present according to the number of roots and these canals may communicate with each other via isthmus. An isthmus is the thin strip of pulp that extends between two canals and thus joins them. An isthmus is the toughest to clean during the root canal treatment.
  • Classification of root canals

    There are various authors who have classified the root canals according to their anatomy. The most popular classifications that are followed include those by Vertucci et al and Gulabivala et al.; the basis for their classification being the number of canals found in the tooth as well as how those canals fuse together and then separate again to give rise to the complex canal configuration.

    Canal anatomy of different teeth

    The major difference between the pulp space of upper and lower teeth is the size of the pulp space which is quite smaller in the mandibular teeth as compared to their maxillary counterparts. The canal anatomy, however, varies widely in individual tooth.

    The incisors– the upper and lower central and lateral incisors have one root and one root canal but there is always a possibility of a second root canal in the lower central and lateral incisors.

    The canines– these are the longest in terms of root canal length and generally have one root and one root canal in both, the upper and lower canines.

    The premolars

    First premolars– the upper first premolar has two roots and thus two root canals in majority of the cases. Sometimes, however, the roots may show abnormal anatomy and may have accessory canals. The lower first premolars have one root and one root canal.
    Second premolars- both, the upper and lower second premolars have one root and one root canal but there is a possibility of a third canal.

    Upper molars– by a general rule, the upper molars have 3 roots and root canals namely, mesiobuccal, distobucaal and distal. However, these have been reported to have a fourth root canal in many instances.

    Lower molars– generally these have two roots and three root canals but the finding of a fourth root canal is very high in lower molars.

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