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REVIEW ARTICLE
Year : 2013  |  Volume : 3  |  Issue : 1  |  Page : 10-16

Endodontic considerations on the variations of the anatomy of the mandibular premolars


1 Private Practice, School of Dentistry, University of Athens, Athens, Greece
2 Department of Endodontics, School of Dentistry, University of Athens, Athens, Greece

Date of Web Publication7-Aug-2013

Correspondence Address:
Eleftherios-Terry R Farmakis
27 D. Gedeon Str, Peania, Athens 19002
Greece
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1658-5984.116274

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  Abstract 

Objectives: This article investigates the internal and external morphological variability of mandibular premolars along with clinical and radiographical signs that leads to early identification of these cases. Materials and Methods: The authors identified articles by searching the PubMed, Medline and Scopus databases. Inclusion criteria were case reports of mandibular premolars with aberrant internal and external anatomy, articles that describe the origin of anatomy of mandibular premolars, the traits that may influence their external and internal variability through species revolution and articles of new technologies like cone beam computed tomography that help the diagnosis of difficult cases. Results: In the majority of the cases, mandibular premolars are reported to have one root canal running a single root. On the other hand, anatomic irregularities in this group of teeth, such as the existence of more than one root or more than one root canals or even a more complicated root canal system cannot be considered infrequent as it appears in 10-25% of the cases. Conclusion: Successful endodontic treatment of mandibular premolars is a challenge for the clinician as they often present morphological and anatomical abnormalities.

Keywords: Endodontic treatment, mandibular premolars, multiple root canals, pulp space anatomy


How to cite this article:
Gakis P, Farmakis ETR. Endodontic considerations on the variations of the anatomy of the mandibular premolars. Saudi Endod J 2013;3:10-6

How to cite this URL:
Gakis P, Farmakis ETR. Endodontic considerations on the variations of the anatomy of the mandibular premolars. Saudi Endod J [serial online] 2013 [cited 2019 Sep 19];3:10-6. Available from: http://www.saudiendodj.com/text.asp?2013/3/1/10/116274


  Introduction Top


The most significant cause of failure of root canal therapy is ineffective mechanical and chemical debridement of the entire root canal system. [1] Moreover, a lack of knowledge of pulp space anatomy irregularities can adversely affect the success of therapy. [2] These deficiencies lead to insufficient treatment. [1],[2]

Mandibular premolars present pulp space with aberrant anatomy at a high rate. [3],[4] According to Nallapati, [3] these teeth pose many difficulties in achieving successful endodontic treatment due to variations in anatomy.

Approximately, 98% of mandibular first premolars are single rooted, [4] whereas 99.6% of mandibular second premolars have a single root. [5] A single root canal is present in 75.8% and 91%, of the cases respectively. [4],[5] In addition, Vertucci reported that mandibular first premolar have one canal at the apex in 74.0% of the teeth and mandibular second premolar have one canal at the apex in 97.5%. [6] As a result, the possibility of the existence of aberrant anatomy in this group of teeth cannot be ignored.


  Materials and Methods Top


In order to investigate the incidence of aberrant anatomy in this group of teeth, the authors identified articles by searching the PubMed, Medline and Scopus databases. Keywords included endodontic treatment, mandibular premolars, multiple root canals, pulp space anatomy, anthropology and species evolution. Inclusion criteria were case reports of mandibular premolars with aberrant internal and external anatomy (two or more root canals, two or more roots and any of their combination), articles that describe the origin of anatomy of mandibular premolars, the traits that may influence their external and internal variability through species revolution and articles of new technologies such as cone beam computed tomography (CBCT) that help the diagnosis of difficult cases. In addition, acclaimed endodontic textbooks that are currently been taught in most dental schools globally, were used to draw more resources on the knowledge that students are taught on this subject.

Interestingly enough, the complex pulp space system of the mandibular premolars was addressed as early as 1925 [7] and this complexity is the reason why especially the mandibular first premolars are referred as an endodontist's enigma. [8],[9]

External anatomy

The external dental morphology reflects the overall morphology of the pulp chamber - every cusp hosts a pulp horn and the external dimensions of the crown are usually associated with the size and position of the pulp chamber. Further, the variations in the mandibular premolars' external morphology should make the clinician suspicious about possible variations in internal dental anatomy, because in cases of mandibular premolars with more than one root, the mesial-distal or the buccal-lingual dimension is increased. [10],[11]

Specifically, mandibular premolars are teeth that vary in external morphology at high frequency along with third molars and lateral maxillary incisors, [12] causing difficulties in creating a proper opening access that needs to be modified from the classical oval shape.

The crown of the mandibular first premolar has two cusps namely one buccal and one lingual. The mesial-distal dimension is smaller from all mandibular posterior teeth. In contrast, the mandibular second premolar can have two or three cusps.

Externally, mandibular premolars have one root in most cases; the rate of two or more roots in the first premolar is 1.8% and 0.4% in the second premolar. [4],[5]

In general, the root of the first mandibular premolars present smaller mesial-distal and bigger buccal-lingual dimensions and the apex usually presents a distal deviation. [13]

In 99.6% of cases, second premolars have one root that assumes a triangular formation in a transverse cross-section, with rounded angles. Their apex also has a distal deviation. [13]

Cases with two roots when located in the mesial-distal axon, the conventional periapical (PA) radiograph masks the true anatomy. If there are three or four roots, they can be buccal and lingual. In the fortuitous event of a 90° rotation, the clinician is able to visualize most of the complex anatomy [Figure 1].
Figure 1: Orthopantomogram of both mandibular premolars, each with two roots

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Internal anatomy

In general, the root canal of the mandibular first premolar is conical and undifferentiated. At the coronal portion, the root canal has an oval cross-section, an oval or round section at the middle segment and a round section at the apex. The pulp chamber is connected to the root canal without a distinct limit, which is typical of the bifurcation of the root canal at the apex. [4],[14]

With regard to anatomical aberrations, 24.2% of mandibular first premolars have two or more root canals. The rate of multiple foramina at the apex is 20%. [15],[16] There are reports on the treatment of mandibular first premolars with three roots and three root canals; [17] one root and three root canals; [18] two root canals in one root; [18] two roots and three canals; [19] and one root that has separated into three root canals with distinct apex foramina. [3] In addition, another irregularity reported is the C-shaped root canal space anatomy, which is observed in 10-18% of the cases. [20]

The root morphology of the mandibular second premolar is similar to that of the first premolar, but its dimensions are slightly wider. Bifurcation is present in these teeth, but at a lower rate compared with the first premolars, approximately 8%. [4],[12]

Mandibular second premolars have variations in morphology and the number of root canals. Specifically, the rate of such teeth with one root is 99.6% and 90% with one foramina. [12]

Despite the greater variability in first premolars, the most significant cases refer to the second premolar group. There are case reports of second premolars with one root and three root canals; [3] three roots and three root canals; [21],[22],[23] two roots and four root canals; [24],[25] four root canals in one root; [26],[27] four roots and four canals. [11],[28]

In [Table 1], the cases reported for both groups of teeth are presented, along with the anatomical root configurations and root canal locations.

A case report with four roots and four canals [28] is documented in [Figure 2]a and b. Furthermore, a single case of five root canals within one root has been reported. [29]
Table 1: The cases reported for both first and second mandibular premolars, along with the anatomical root configurations and root canal locations


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Figure 2: (a) Pre-operative radiograph of tooth #35, showing irregular root morphology. (b) Post-operative radiograph showing complete obturation of the four root canals

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The rate of lateral root canals in first mandibular premolars is 44.3% versus 48.3% in second premolars. It is likely that lateral canals exist at the apical portion of the root. [6]

Mandibular premolars with two roots and/or two root canals have not been reported, probably due to the fact that they appear frequently in the clinical practice.

Ethnic and genetic differences

The morphological and anatomic abnormalities of the first lower premolars are associated with ethnic differences and genetic disorders, [30] a finding that has not been observed with second premolars. For example, first mandibular premolars are three times more likely to present with over numbered root canals in African-Americans compared with Caucasians. [30] In addition, a more number of root canals in these teeth has been observed in Chinese, Turkish and Kuwaiti persons. [4] The genetic syndrome Turner (45X) is linked to over numbered roots compared with females with normal genotypes. [31]

The pulp chamber in second premolars is often longer in 45X females and 45X/46XX females compared with healthy women. [32]


  Discussion Top


A complicated root canal system poses a challenge in every phase of endodontic therapy; thus, if not accomplished correctly, the success rate is expected to be lower − a tenet that applies to premolars. [33]

The complex internal anatomy of first premolars and the high rate of congenital absence and variations in the external anatomy of second premolars [34] can be attributed in part to genetic traits and evolutionary patterns.

Modern people belong to the developed species Homo sapiens. Early humans, such as early Homo, were dentally similar to African apes. [35] Specifically, mandibular premolars had crown outlines that approximated molars, with more cusps, wider mesial-distal and buccal-lingual dimensions and multiple roots that were wider. [36] Further, these teeth had a broad occlusal polygon surface and an asymmetrical outline. [37],[38]

According to the tritubercular theory of dental evolution, proposed by Cope and then Osborn in the late 19 th century, multi-cusped teeth, such as molars and premolars in mammals, developed through cusp budding of simple conical teeth. [39],[40]

As humans evolved, the dimensions of mandibular premolars decreased due to selective pressures. [36] It is unclear when the unique, prolonged human pattern of growth and development originated. [35]

Over eons, the four multi-rooted premolar teeth of hominids fused their roots and declined in volume and number, [36] resulting in today's two single-rooted premolars, of which the second is more frequently single-rooted with a single canal, impacted or absent. [41],[42]

Despite their complex original form, endodontic treatment of these teeth remains a challenge. Diagnostic information directly influences clinical decisions and accurate data effect better treatment-planning decisions and potentially more predictable outcomes. [43]

To overcome these challenges, an initial PA radiograph should be performed. Although PAs are 2D images of 3D anatomical structures, they contain most of the necessary initial information. [18]

If the root anatomy (external and/or internal) is elusive (e.g., the tooth appears to have one well-defined canal in the cervical third of the root that disappears or narrows suddenly as it travels apically), additional PAs at various horizontal angulations (Clark's technique) can facilitate the diagnosis. If a radiolucent line is present mesial or distal to the main canal, an additional canal should be suspected [44] [Figure 3].
Figure 3: Pre-operative radiograph demonstrating aberrant internal anatomy of the mandibular premolars

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During clinical examination, if gingival recession is present and a furcal external morphology is present in these teeth, may hint the presence of two buccal roots. [3]

The working length-establishing PA or the fitting cone PA can also reveal a second canal, if the file (or the gutta-percha cone) is positioned off-center from the axis of the root.

These irregularities have clinical significance as untreated canal space can lead a root canal treatment to failure. According to Hoen and Pink, missed root canals are noted in 42% of teeth that have been retreated. [45] If the irrigation protocol is meticulously applied, sealer and/or warm Gutta-percha can reveal the presence of lateral root canals [Figure 4].
Figure 4: Periapical (PA) radiograph revealing the presence of a lateral root canal filled by sealer that is associated with a lateral PA lesion on tooth #44

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If there are doubts with regard to the internal structure of the tooth that is receiving endodontic treatment, a CBCT is advised [17] [Figure 5]. CBCT imaging is gaining rapid acceptance in dentistry and endodontics, based on its ability to generate undistorted 3D images of the maxillofacial skeleton, the teeth and their surrounding structures. [46]
Figure 5: Cone beam computed tomography imaging revealing both right mandibular premolars with three root canals

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Furthermore, in failing cases without any obvious cause, CBCT can aid in locating missed canals better than PAs. [47]

However, CBCT imaging should not be performed for every mandibular premolar that is treated endodontically, due to high costs and difficulty in accessing this system and to protect patient from unnecessary exposure to radiation. Alternatively, conventional PA is an accessible, cost-effective, high-resolution imaging modality. [48] Furthermore, CBCT imaging creates distortions with regard to materials, such as metal posts and endodontic filling materials, due to differential absorption - known as cupping artifacts - which create star-shaped streak artifacts, mimicking crack lines on CBCT images and complicating the interpretation of the acquired images. [49]

Magnification also aids the clinician throughout endodontic treatment. Examination of the pulp chamber with magnification, by microscope [3],[6],[24],[25],[26],[28],[29] or magnifying loops [19],[21] or fiber-optic endoscope [23] is invaluable in treating complex cases. With magnification, the pulp chamber can be examined more properly and by following its landmarks, all of the root canal system's orifices can be located. The cost of an optical microscope might be high for the general dentist. Nevertheless, magnifying loops are affordable and effect results that are comparable with microscopy. [50]

Finally, if a patient complains of insistent pain of a mandibular premolar and sensitivity to cold and hot and has received endodontic therapy, the clinician should determine whether the root canals have been detected and instrumented. [6]


  Conclusion Top


Endodontic therapy of mandibular premolars, because of their frequent morphological and anatomical abnormalities, is a challenge for the clinician. On each given case, robust knowledge of the literature (both statistical data and case reports equally), a thorough study and analysis of the external and internal morphology and careful interpretation of the radiographic imaging, is needed, in order to achieve a high degree of success in their treatment.


  Acknowledgment Top


The authors would like to thank Associate Professor E.G. Kontakiotis (School of Dentistry, University of Athens, Greece) for his valuable comments on the review.

 
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    Figures

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