Pulp and Root Morphologies  |
| Root morphology |
Successful root canal therapy requires a thorough knowledge of root and root canal morphology.
- Practitioners must be aware that the main root canals in a tooth may only provide access to the complexities of the root canal system, which must be fully cleaned of all microorganisms.
- Research has shown that the dental anatomy learned as a dental student may now be out of date.
- Knowledge of canal anatomy is essential in designing and executing access cavities that give straight line access to the main root canals.
The pulp chamber in the coronal part of a tooth consists of a single cavity with projections (pulp horns) into the cusps of the tooth . With age, there is a reduction in the size of the chamber due to the formation of secondary dentine, which can be either physiological or pathological in origin. Reparative or tertiary dentine may be formed as a response to pulpal irritation and is irregular and less uniform in structure.
The entrances (orifices) to the root canals are to be found on the floor of the pulp chamber, usually below the centre of the cusp tips. In cross-section, the canals are ovoid, having their greatest diameter at the orifice or just below it. In longitudinal section, the canals are broader bucco-lingually than in the mesiodistal plane. The canals taper towards the apex, following the external outline of the root. The narrowest part of the canal is to be found at the 'apical constriction', which then opens out as the apical foramen and exits to one side between 0.5 and 1.0 mm from the anatomical apex. Deposition of secondary cementum may place the apical foramen as much as 2.0 mm from the anatomical apex. It must be realized, however, that the concept of a 'single' root canal with a 'single' apical foramen is mistaken. The root canal may end in a delta of small canals, and during root canal treatment cleaning techniques should be employed to address this clinical situation.
Lateral and accessory canals
Lateral canals form channels of communication between the main body of the root canal and the periodontal ligament space. They arise anywhere along its length, at right angles to the main canal. The term 'accessory' is usually reserved for the small canals found in the apical few millimetres and forming the apical delta. Both lateral and accessory canals develop due to a break in 'Hertwig's epithelial root sheath' or, during development, the sheath grows around existing blood vessels. Their significance lies in their relatively high prevalence, Kasahara et al finding 60% of central incisors with accessory canals, and 45% with apical foramina distant from the actual tooth apex. Kramer found that the diameter of some lateral canals was often wider than the apical constriction. Lateral canals are impossible to instrument and can only be cleaned by effective irrigation with a suitable antimicrobial solution. Consequently, sealing such canals is only moderately successful.
