![]() Root canal morphology of the human maxillary second premolar. Radiographic evaluation of root canal anatomy of in vivo endodontically treated maxillary premolars. The vascular architecture of the human dental pulp. ![]() Root canal systems of the maxillary central incisor. Kasahara E, Yasuda E, Yamamoto A, Anzai M. The anatomy of the root canals of the teeth of the permanent dentition and the anatomy of the root canals of the deciduous dentition and the first permanent molars. The access cavity represents the shape of the pulp chamber, enlarged slightly, and flared up on to the mesiobuccal aspect of the occlusal surface to accommodate the angle of instrument approach when working at the back of the mouth. The palatal root has a tendency to curve towards the buccal and the apparent length on a radiograph will be shorter than its actual length. The curvature of the roots can be difficult to visualize from radiographs, and the second mesiobuccal canal is nearly always superimposed on the primary mesiobuccal canal. Anastomosis between these two canals may take the form of narrow canals or wide fins, both almost impossible to instrument. The canals of the mesiobuccal root are often very fine and difficult to negotiate consequently, more errors in instrumentation occur in this tooth than in almost any other. Stropko, reporting an extensive in vivo study, 6 found second canals in 73% of cases before the use of an operating microscope, but 93% following its use. In vitro studies have usually reported a higher incidence than in vivo studies. The percentage of mesiobuccal roots having two canals reported in the literature has increased steadily as research techniques have developed. The palatal root is the longest, with an average length of 22 mm the mesiobuccal and distobuccal roots are slightly shorter, at 21 mm average length. Consequently, sealing such canals is only moderately successful. 3 Lateral canals are impossible to instrument and can only be cleaned by effective irrigation with a suitable antimicrobial solution. Kramer found that the diameter of some lateral canals was often wider than the apical constriction. 2 finding 60% of central incisors with accessory canals, and 45% with apical foramina distant from the actual tooth apex. ![]() Their significance lies in their relatively high prevalence, Kasahara et al. 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. The term 'accessory' is usually reserved for the small canals found in the apical few millimetres and forming the apical delta ( Fig. ![]() They arise anywhere along its length, at right angles to the main canal. 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.Īs previously discussed, lateral canals form channels of communication between the main body of the root canal and the periodontal ligament space. It must be realized, however, that the concept of a 'single' root canal with a 'single' apical foramen is mistaken. Deposition of secondary cementum may place the apical foramen as much as 2.0 mm from the anatomical apex. 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. ![]() The canals taper towards the apex, following the external outline of the root. In longitudinal section, the canals are broader bucco-lingually than in the mesiodistal plane. In cross-section, the canals are ovoid, having their greatest diameter at the orifice or just below it. 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. Reparative or tertiary dentine may be formed as a response to pulpal irritation and is irregular and less uniform in structure. 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. 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 ( Fig. ![]()
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