NSRCT mandibular anterior teeth Flashcards
What percentage of mandibular incisors have a second canal? What anatomic characteristics of mandibular incisors require special consideration?
While mandibular incisors are typically single rooted teeth, the prevalence of two canals is relatively high. A small percentage of these teeth have two distinct roots.The complex root canal anatomy of mandibular incisors versus their maxillary counterparts is repeatedly confirmed in the literature (Table 8.1). As such, all mandibular central and lateral incisors should be approached as having two canals until proven otherwise.
The operator is encouraged to take angled radio- graphs preoperatively and during treatment for the purpose of identifying additional anatomy
(Figure 8.9). Alternatively, the cone beam‐computed tomography (CBCT) scan can clearly show the propensity for mandibular incisors to harbor two canals or even two roots (Figure 8.10) (Paes da Silva Ramos Fernandes et al. 2014). The prevalence of mandibular canines having two roots is the highest among mandibular incisors with the percentage reported as high as 12% (Rahimi et al. 2013).
What are the anatomic considerations when designing the access preparation for a mandibular incisor?
As with all endodontic cases, the access prepara- tion is the most important step in treatment of mandibular incisors.The entrance to the second canal on these mandibular incisors is lingual to the more easily located labial canal; hence proper access preparation is crucial to locate both canals. Ideal straight‐line access to the apical foramen on the central and lateral incisors is topographically located at or labial to the incisal edge. A labial access prepa- ration would also conserve more coronal dentin (Logani et al. 2009). For aesthetic reasons, however, the standard clinical access is through the center of the lingual surface of the tooth. Proper access preparation for mandibular incisors is depicted in Figure 8.11. Of note is the triangular outline on the central and lateral incisors to include the pulp horns. This important step will prevent future coronal discoloration due to pulp tissue left behind.The access shape may revert to oval in patients over the age of 40 as a result of the deposition of secondary dentin in the pulp chamber facilitating the conserva- tion of coronal dentin (Nielsen & Shamohammadi 2005). It is important to extend the preparation both incisally and lingually toward the cingulum in all incisor teeth. It is the incisal extension that affords a straight‐line instrument access to the apical foramen and the lingual extension along the cingulum that provides the operator visualization of the lingual canal orifice (Figure 8.12). Given the relatively high percentages of two canals in these teeth, radio- graphic imaging with varied horizontal angulation is recommended to determine the presence or absence of a second canal (Mahajan et al. 2016). Of course, if CBCT imaging was available, it would be the most definitive means of determining the root canal anatomy. Once the access preparation is properly oriented and extended, the case becomes more predictably treatable. There are three circumstances in which to con- sider the use of a labial surface access preparation in the smaller incisors: overdenture abutment, trau- matic horizontal fracture of the crown, and planned full coverage restoration after endodontic treatment. This labial approach offers a true straight‐line access to the apical region of the canal(s) while maximizing the amount of remaining coronal dentin.
What instruments are useful when looking for a second canal on mandibular incisors?
When looking for a second canal on a mandibular incisor, the first step is to prepare the access open- ing as described above.The Endo-Z® bur (Dentsply Sirona, Ballaigues, Switzerland) can be used to extend into the cingulum area for proper lingual access to the site where the second canal would be located. An important adjunct is the use of the operating microscope or loupes with high magnification and illumination to search for the lingual canal on these incisor teeth.The value of higher magnification in these delicate procedures cannot be overstated.The use of the microscope has been found to be instrumental in uncovering 93% of second canals in single‐rooted teeth (Rahimi et al. 2013). If troughing is required, an ultrasonic tip is useful to remove tooth structure without impairing operator vision. A sharp endo explorer is very useful in initiating the penetration at the orifice. A size #10 hand file can then be advanced to map out the canal.
How does one determine if a radiographic radiolucency is endodontic in origin or non‐odontogenic?
When faced with a diagnosis of apical periodontitis involving a seemingly intact mandibular incisor, one must consider either trauma, incisal wear (attrition) into the calcified former pulp space, or external cervical invasive resorption (ECIR) as being the cause of the pulp necrosis. Without one of these extraneous insults to the pulp tissue, it is imperative to utilize pulp testing to verify the odontogenic relationship to the lesion. Both cold testing and electric pulp testing (EPT) should be used to confirm the diagnosis of apical periodon- titis secondary to pulp necrosis. If a tooth with apical periodontitis responds positively to pulp vitality testing, it is likely that the apical lesion is non‐odontogenic in origin.The differential diag- nosis of apical periodontitis associated with vital mandibular incisors includes: fibrous dysplasia, cemento‐osseous dysplasia, central giant cell granuloma (CGCG), and less frequently, meta- static neoplasms such as multiple myeloma, squamous cell carcinoma, breast cancer, etc. (Özgūr et al. 2014).The salient point is to always use a pulp test for any case when an apical periodontitis exists.This is especially true when there is no obvious etiology for the radiographic pathology associated with the tooth. A biopsy of any suspect lesions without odontogenic etiology is highly recommended.
What is the best restoration for the endodontically treated mandibular incisor?
The restoration of mandibular central and lateral incisors bears its own set of unique issues. A retrospective study determined that coronal coverage crowns did not significantly improve the success of endodontically treated anterior teeth (Sorensen & Martinoff 1984). Many dentists prefer not to use full coverage on these teeth as there is little coronal dentin to work with after endodontic treatment, and full crown preparation with an aesthetic result in shape and contour is difficult to achieve given the limited space for the restoration. Post and core restora- tions have been implicated in a higher percent- age of root fracture in these small teeth. In fact, mandibular incisors with intact natural crowns exhibit greater resistance to transverse loads compared to teeth with posts and cores (Gluskin et al. 1995). If a post is determined to be neces- sary due to lack of remaining coronal tooth structure, the narrow mesio‐distal width of the central and lateral incisors should limit the ultimate width of the canal or post preparation. Keeping in mind the conservative restoration of a mandibular incisor, the access preparation should preserve mesial and distal coronal dentin, yet the incisal–lingual extension of the prepara- tion must be sufficient for second canal location and straight‐line access to the apical root canal. For many reasons the access preparation is the key to long term successful treatment on these diminutive teeth.
