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REVIEW ARTICLE
Year : 2013  |  Volume : 1  |  Issue : 1  |  Page : 3-10

The root and root canal morphology of the human mandibular premolars: A literature review


Department of Conservative Dentistry and Endodontics, Subharti Dental College, 718, Rishinagar, Meerut, Uttar Pradesh, India

Date of Web Publication29-Apr-2013

Correspondence Address:
Padmanabh Jha
Department of Conservative Dentistry and Endodontics, Subharti Dental College, Subhartipuram, N.H. 58, Delhi Haridwar Byepass, Meerut, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2321-4619.111226

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  Abstract 

The objective was to review thoroughly the literature of the root and root canal morphology of the human mandibular premolars. Published studies were divided into anatomic studies reporting the number of roots, number of canals, and apical anatomy. Differences caused by gender and ethnicity have also been reported. Individual case reports of anomalies were included to demonstrate the extreme range of variation. Almost all of the teeth in the anatomic studies were single rooted (99.6%). The incidence of two roots (0.3%) and three roots (0.1%) was extremely rare. Anatomic studies of the internal canal morphology found that a single canal was present in 91.0% of the teeth. A single apical foramen was found in 91.8% of the teeth. However, the root and root canal morphology of the mandibular premolars can be extremely complex and requires careful assessment.

Keywords: Abnormal morphology, mandibular premolars, number of canals, number of roots, root canal morphology


How to cite this article:
Jha P, Nikhil V, Arora V, Jha M. The root and root canal morphology of the human mandibular premolars: A literature review. J Res Dent 2013;1:3-10

How to cite this URL:
Jha P, Nikhil V, Arora V, Jha M. The root and root canal morphology of the human mandibular premolars: A literature review. J Res Dent [serial online] 2013 [cited 2019 Nov 21];1:3-10. Available from: http://www.jresdent.org/text.asp?2013/1/1/3/111226


  Introduction Top


Knowledge of basic root and root canal morphology as well as possible variation in anatomy of the root canal system is important in achieving successful root canal treatment. This is followed by negotiation, cleaning and shaping, and obturation of the entire canal system in three dimensions. [1],[2],[3]

Ingle [1] has reported that the most significant cause for endodontic failures was incomplete canal instrumentation, followed by incorrect canal obturation. Slowey [4] has indicated that probably because of the variations in canal anatomy, the mandibular premolars are the most difficult teeth to treat endodontically. Variation in root canal morphology was suggested as the most likely reason for the high frequency of endodontic flare-ups and failures.

The mandibular premolars are typically described in textbooks as single-rooted tooth with a single root canal system. [5],[6],[7],[8],[9],[10],[11] The ovoid-shaped root in cross-section normally has developmental grooves or depressions on the mesial and distal surfaces. Woelfel and Scheid [11] have described the depression on the distal surface as being the deeper of the two. There are also numerous case reports and anatomic studies that have reported variations.

The incidence of the number of roots [12],[13],[14],[15],[16],[17],[18],[19] and of the number of canals [12],[13],[14],[15],[16],[18],[20],[21],[22],[23],[24],[25],[26],[27] reported in anatomic studies varies greatly in the literature [Table 1] and [Table 2]. The root morphology and canal morphology of the mandibular premolars can be extremely complex and highly variable. [3],[6],[8],[28],[29] The factors that can contribute to differences observed in the various anatomic studies have been reported previously, [29] and these factors include ethnicity, [16],[28],[30],[31],[32],[33],[34],[35],[36],[37],[38],[39],[40],[41],[42],[43],[44],[45],[46],[47],[48],[49],[50],[51],[52],[53],[54] age, [23],[55],[56],[57],[58],[59],[60] gender, [43],[50],[61] unintentional bias in the selection of clinical examples of patients or teeth (specialty endodontic practice vs. general dental practice), [29] as well as study design (in vitro vs. in vivo). [62],[63],[64]

Normal root and root canal anatomy of the mandibular premolars are well documented in numerous textbooks, but there is a great deal of variation in the reporting of the incidence of anomalies. [2],[3],[5],[6],[7],[8],[9],[10],[11],[65],[66] As a result, there is no consensus on the range of variation or possible anomalies. The purpose of this article was to review the literature and conduct an analysis of the variations found in studies that reported on root and root canal morphology of the human mandibular premolars.
Table 1: Number of roots in the mandibular premolars

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Table 2: Number of canals and apices in the mandibular premolars

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  Materials and Methods Top


A review of the literature was performed on the human mandibular premolars with respect to the number and type of roots and the root canal morphology. Keywords used in the search included "mandibular premolars," "mandibular bicuspid," "number of roots," "number of canals," "root canal morphology," "extra roots," "anomalies," and "abnormal morphology." Peer-reviewed studies of the mandibular premolars were identified first through PubMed, and then other related articles were added by hand searching of bibliographies and Internet articles pre-1966 that might be missed in a PubMed search and articles in which keywords do not match the subject of the search. Case studies were included to illustrate anomalies and genetic variation not reported in the larger anatomic studies. The data were analyzed, and weighted averages were determined for each of the following: (1) Number of roots, (2) number of canals and apical foramina, and (3) summary of case reports of other anomalies.


  Discussion Top


A great deal of variation can be found in the literature with respect to the root and root canal morphology of teeth, and the human mandibular premolars are no exception. The primary cause of endodontic failure is overlooked root canals. The presence of extra roots or canals in mandibular premolars is undoubtedly an endodontic challenge. Together with diagnosis and treatment planning, a knowledge of common root canal morphology and its frequent variations is a basic requirement for endodontic success. [75] Studies have emphasized on the fact that a root with tapering canal and a single foramen is an exception rather than a rule. [67] The clinician must be familiar with the various pathways that root canals take to the apex. The pulp canal system is complex and canals may branch, divide, and rejoin; according to Ingle, the percentage of two canals and one foramen in mandibular first premolar is 6.5%. [75]

The anatomies of mandibular premolars have been examined extensively (Pineda and Kuttler, 1972; ElDeeb, 1982; Shapira and Delivanis, 1982; Vertucci, 1984; Bram and Fleisher, 1991; Wong, 1991; Kartal and Yanikoglu, 1992; Caliskan et al., 1995). Vertucci (1984) determined the incidence of a second canal in mandibular first premolars to be 26% and 3% for second premolars. The prevalence of lateral canals was 44% for the first premolar and 48% for the second premolar. The incidence of an apical delta in these teeth was 9%, whereas the ratio of apical foramina was 85% for the first premolar and 84% for the second premolar. [15]

Caliskan et al. (1995) encountered a single canal in 64% of first premolars and 94% of second premolars. They also reported 53% and 39% of these teeth had lateral canals, respectively. Sert et al. reported that 62% of mandibular first premolars had a single canal, whereas the prevalence of a single canal in the second premolars was 71%. In the first premolars, lateral canals existed in 16.5% of the cases, whereas in the second premolars, the prevalence was 14%. [15]

Studies by Trope et al. [16] and Sabala et al. [24] reported their in vivo results on root number and internal canal morphology by the number of patients rather than by the total number of teeth. Two or more canals were found in the mandibular second premolar tooth in 5.2% and 4.4% of the patients, respectively. Reporting data by number of patients instead of number of teeth leads to higher incidences of anomalies (more than one root or canal), unless the anomaly is 100% bilateral. Because the occurrence of two or more roots also can occur unilaterally or bilaterally, the results in these studies are higher than the in vitro anatomic studies reporting by the number of teeth.

The study by Trope et al. compared the number of roots and number of canals in mandibular premolars between African American and white patients. The African American group had an incidence of two or more roots in the mandibular second premolar tooth at 4.8% of the time compared with a 1.5% incidence in the white patient group. Although the incidence of multiple roots was greater in the African American patients compared with white patients in both the mandibular first and second premolar teeth, the differences were statistically significant only for the mandibular first premolar. Ethnic differences in internal canal morphology were also found in this study but were not statistically significant. The African American group had an incidence of two or more canals at 7.8% of the time, whereas the white group had an incidence of 2.8%. [16]

In their study on a Turkish population, Kartal and Yanikoglu (1992) found the incidence of multiple canals in mandibular premolars to be 28% and that completely separate and independent two or three canal variations existed in a single root with a prevalence of 10%. More than 24% of the teeth with two canals had one root canal at the apex. [15]

Two studies compared gender differences for number of roots or canals in a known population. A study by Serman and Hasselgren reported on the incidence of two canals and two roots for the mandibular first and second premolars. They found gender differences with respect to the number of canals and roots in an analysis of radiographic surveys of 547 patients. The distribution of men (252 patients) and women (295 patients) was approximately equal. In their study, more women had multiple roots and/or canals than men (50 women vs. 29 men) in the mandibular first premolar, whereas more men exhibited multiple roots and/or canals (29 men vs. 15 women) in the mandibular second premolar. [101] The study by Sert and Bayirli assessed the canal morphology in 100 Turkish male and 100 Turkish female patients. Men (43%) exhibited two or more canals much more frequently than the female patients (15%) in the study. [43]

The roots have a more complex structure in patients with Turner syndrome. The most frequent deformities were: Two-rooted mandibular first and second premolars with fully developed mesial and distal roots or separate root apices. Varrela (1990, 1992) in his study in 87 patients with 45, X karyotype reported 83 first premolars with separate roots (48% of cases) and only two such premolars in the control group (1% in first premolars). He also found 39% of premolars with two roots in the 45, X/46, XX group (mosaics). In this study, most anomalies were found in the 45, X group with 34% cases with two roots in mandibular first premolars and 39% cases in mandibular second premolars. [102]

The interesting finding of the study was the noticeable prevalence of C-shaped canals (2.4%) in the mandibular first premolars and the 2% prevalence of C-shaped canals in the mandibular second premolars. The prevalence of C-shaped canals in the mandibular first premolars had only been reported in three previous studies (Baisden et al., 1992; [14%] Sikri and Sikri, 1994; [10%] Lu et al., 2006; [18%]). The differences between the results obtained in various studies regarding the anatomy of mandibular first premolars and the prevalence of C-shaped canals may arise from racial differences and methods of studying. The location of the C-shaped morphology in the mandibular first premolar is quite different. In a study by Tzu-Yi Lu et al., the location of C-shaped canal was found at apical 3 mm and/or 6 mm level cross-sections. Coronally, it could be single oval or two canals. Therefore, C-shaped canals would be difficult to detect from coronal approach. [72]

Case reports that describe two or more roots or two or more canal systems in mandibular premolar teeth are found in the literature. The examples in [Table 3] include mandibular premolar teeth. The complex nature of the root and root canal morphology of the mandibular premolars has been underestimated. The following clues from diagnostic information and techniques might help clinicians to detect additional root(s) and canal(s). A second radiograph from 15° to 20° from either mesial or distal from the horizontal long axis of the root is necessary to accurately diagnose the number of roots and canals in premolar teeth. Yoshioka et al. [26] have indicated that sudden narrowing of the canal system on a parallel radiograph suggests canal system multiplicity. Martinez-Lozano et al. have suggested a 40° mesial angulation of the X-ray beam to identify additional canals. A general guideline is that if the mid-root image diameter appears equal or greater than the crown image diameter, then the tooth most likely has a variation in root canal configuration (Miyoshi et al., 1977). The presence of additional canal should be suspected whenever an instrument demonstrates an eccentric direction on deeper penetration into the canal, termed directional control, as reported by Green (1973), or if the working length file appears off center in the radiograph. [81] The use of magnification has been demonstrated to improve the clinician's ability to visualize and access canals. [59]
Table 3: Case reports of mandibular premolar anomalies

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The use of three-dimensional imaging methods in future large anatomic studies would be of value in assessing the occurrence and the frequency of anomalous canal morphology. The role of genetics is just being appreciated in identifying anomalies caused by syndromes and even ethnicity or gender variation in morphology.

A review of the literature has revealed that the human mandibular premolar tooth can have an extremely complex root and root canal morphology; however, the incidence of both multiple roots and multiple canals in the mandibular second premolar is lower than that found in the mandibular first premolar.


  Conclusion Top


The incidence of more than one root, more than one canal, and more than one foramen is less frequent in the mandibular second premolar than in the mandibular first premolar, but numerous case reports cite many variations, and anomalies might occur. Although reported in only a few studies, variations in incidence of single canal versus two or more canals might occur as a result of ethnicity or gender. More research in the area of gender and ethnic differences is required to arrive on definite conclusions. When performing root canal therapy, additional canals might be missed, leading to a greater failure rate, unless there is constant vigilance in locating two or more canal systems in the mandibular premolars.

 
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