Maxillary first molars usually present 3 roots. The presence of an additional canal in the mesial root (MB2) has been the subject of several studies that includes the use of histological techniques, microcomputed tomography or by clinical observation through the use of magnifications during the root canal treatment. It is accepted that the use of the operative microscope has resulted in an increase of the detection rate of the MB2 system. Failure to treat and fill this additional canal can lead to failure of the root canal treatment.
The root canal space is an arborizational, anastomotic, labyrinthine complexity, morphologically comparable to the pathways of a maze. While primary canals exist, the tributaries, accessory branches and lumina of the dentinal tubuli harbor extensive tissue and microflora. The existence of these vast, capacious passages has been demonstrated throughout the past century beginning with the work of Hess and continues to this day with the use of micro computed tomography.
Presence of multiple foramina, additional canals, fins, deltas, intercanal connections, loops, C-shaped canals and accessory canals are an integral part of the pulpal anatomy. Morphology of the apical portion of the root varies tremendously, including numerous accessory canals formed as a result of entrapment of periodontal vessels in Hertwig’s epithelial root sheath during calcification, areas of resorption and its repair, attached, embedded and free pulp stones, varying amounts of irregular dentin, intercanal connection that may become exposed and single foramen may become multiple.Adding to these is the root curvature especially in the apical portion, which makes the endodontic treatment all the more complex.
The maxillary first premolar is located in the upper jaw. At least 55% of maxillary first premolar present a single root, 41% present 2 roots and 3% presents 3 roots (Pecora et al. 1991). This roots presents deep longitudinal depressions , enlargement of the root canal system for post placement should be performed with caution to avoid accidents.
The maxillary lateral incisor is narrower mesio-distally than the central incisor. This tooth can be variable. Often the tooth is narrow, conical, or peg-shaped. Dental anomalies include the presence of talon cusp, palatogingival groove, dens invaginatus, conical crown or peg-shaped
Dens Invaginatus is an uncommon anomaly of teeth probably resulting from an infolding of the dental papilla during tooth development. The most widely used classification of dens invaginatus has been proposed by Oehlers (1957), who’s described the malformation in three forms:
Type I: an enamel-lined minor form occurring within the confines of the crown not extending beyond the amelocemental junction.
Type II: an enamel-lined form, which invades the root but remains confined as a blind sac. It may or may not communicate with the dental pulp.
Type III: a form which penetrates through the root perforating at the apical area showing a ‘second foramen’ in the apical or in the periodontal area. There is no immediate communication with the pulp. The invagination may be completely lined by enamel, but frequently cementum will be found lining the invagination.
According Ridell et al. (2001) the Type I is the most prevalent (79%), in sequence Type II (15%) and Type III (5%).
The maxillary central incisor presents commonly one root canal. However, the occurrence of additional canals has been reported. Traumatic injury of the maxillary central incisor is not uncommon in children and adolescents. In 50-70% of trauma cases the maxillary central incisor is affected by fractures that can involve the dental pulp. Common pathological complications after trauma include pulp necrosis, pulp obliteration, dental ankylosis, internal resorption and external cervical resorption.
The mandibular canine usually present one root canal and in overall offer a low level of difficulty for proper access to the apical third. The presence of additional root canals has been previously reported by Pecora et al (1993). In addition, a two rooted mandibular canine is presented in the attached pictures.
Mandibular incisors have a flat single root with the longest diameter in the bucolingual direction. The prevalence of two root canals appears to be variable but basically are located at the middle third of the root usually divided by an isthmus. Mauger et al.1998 showed that an isthmus separing the root canals is present in 55% of mandibular incisors at 3mm level. This anatomical finding can compromise the correct cleaning of the root canal system making the filling of the middle third difficult. Apically, almost all mandibular incisors present one root canal.
Knowledge of the dimensional variations of complex root canal systems such as those in mesial roots of mandibular molars is indispensable to support clinical decisions during endodontic procedures. Anatomical knowledge includes distinguishing the presence of isthmuses during surgical or non-surgical treatment and an appropriate determination of the apical anatomical diameter.
Adequate apical diameter determination is only reliable if the cross-sections are taken perpendicular to the long axis of the root canal. However, the determination of the apical diameter in curved root canals, such as mesial root canals of mandibular molars can be difficult using this last method. At least 3 limitations are identified to perform adequate cross-sections: 1. the root canal foramen is not always present at the anatomic root apex, consequently the root canal curvature in the last apical millimeter does not always resemble the trajectory of the external anatomy. 2. Mandibular molars present multiplanar curvatures in 100% of cases in both mesiodistal and bucolingual directions. 3. The main apical foramen of the buccal and lingual canals can be present at different levels making it difficult to find an exact section at the same level for both canals. In addition, the presence of isthmuses are not uncommon and this data has not been related during the canal diameter determination. To date, there is no report addressing the apical diameter of mandibular molars using micro-CT. The aim of this study was to determine the mesio-distal, buco-lingual diameter, apical volume and the presence of isthmuses at the apical level of mesial root canals of mandibular molars.
The mandibular premolar can present several anatomical variations. Usually, the presence of 2 or 3 canals or a c-shape morphology needs to be identified in order to improve the access and cleaning of the apical third.
The C-shaped canal is an anatomical variation that was first reported by Cooke & Cox (1979) and mostly seen in mandibular second molars (Manning 1990). Many reports describe this variation among different populations with it prevalence reported to be between 2.7% to 31.5% (Yang et al. 1988, Weine et al. 1998, Haddad et al. 1999, Gulabivala et al. 2001, Gulabivala et al. 2002). These studies indicate that the occurrence of C-shaped canals is more frequent in the Asians population than in other races.
The C-shaped canal configuration has special features, such as: fused root with a longitudinal groove in the middle of the root, on its lingual or buccal aspect, a pulp chamber floor usually deeply positioned with an uncommon anatomical appearance (Min et al. 2006), and the main anatomic feature of the C-shaped canals in mandibular molars is the presence of one or more isthmuses connecting individual mesial and distal canals (Melton et al. 1991).
From: Ordinola-Zapata et al. International Endodontic Journal 2009
