An In-Vitro Cone-Beam Computed Tomographic Evaluation of Root Canal Anatomy of Permanent Mandibular Incisor Teeth in an Indian Population

Introduction

The main goal of an endodontic treatment is the correct diagnosis, optimal mechanical instrumentation and chemical disinfection, followed by three-dimensional fluid tight seal of the entire root canal system [1]. Failure of treatment is not uncommon despite rigid adherence to all basic treatment protocols. One of the major reasons for this is inability of the operator to identify the root canal anatomy and locate the extra canals if any [2]. The mandibular permanent incisors are succedenous teeth located adjacent to the midline in the lower arch. Known to be the smallest adult human teeth; they are also flat and narrow in the labio-lingual dimension. They are almost always single rooted but the internal root canal anatomy is prone to exhibit complex variations. As these teeth are usually radiographed only in one plane, they appear single canaled and more accessible than they really are. Adding to the difficulty while treating these teeth, the narrow crown offers restricted area of access to the root canals. There are various studies reported in literature on root canal anatomies of these teeth in different populations with rare exploration in Indian population [1, 3]. A number of destructive and non-destructive methodologies have been described in the literature including decalcification, radiography, vertical and cross- sectional cutting, histological evaluation, stereomicroscopy analysis, surgical microscopy, plastic casts, scanning electronic microscopy, cone beam computed tomography (CBCT) and micro-computed tomography (mCT) [4, 5, 6]. Traditional radiography although commonly used, portrays a 2-dimentional image of a 3-dimentional structure, which results in compression of vital anatomical information about the root canal anatomy [6]. Besides this most of the time the conventional antero-posterior radiographs does not reveal the mesio-distal anatomy of the tooth. For this reason CBCT has been evaluated as an accurate diagnostic tool to define the number of root canals in vitro [7, 8]. As the root canal anatomy of permanent mandibular incisor teeth of an Indian population has not been explored extensively, this study was devised to evaluate the number of root canals, and the possible variations seen in the root canal morphologies in the permanent mandibular incisors of an Indian population.

Discussion

It is assumed that mandibular incisors are associated with a single root and a single canal. However literature shows that complicated configurations are present, and that canal configurations vary with respect to ethnicity and race [9, 10]. A number of techniques are used to study the internal anatomy of the teeth, most conventional being radiographic and clearing & staining and radiography [11]. Although clinically conventional periapical radiographs present as a valuable diagnostic tool, they cannot be relied on completely because of inherent limitations like; distortion and superimposition of bony and dental structures [11]. Although the canal staining and clearing technique is considered the gold standard method of studying root canal anatomy, it has a number of demerits like the tooth morphology can get distorted in the clearing process as the tooth structures are weakened during demineralization process [12, 13]. The weakened tooth thereafter could be distorted during the dying process of the specimen and, small structures like accessory canals or isthmuses could be distorted or missed. Another problem with this technique is limited dye penetration. Root canal blockage resulting from narrowing and calcification below the grain size of dye solution hinders the infiltration of the dye solution [12, 13]. The use of cone beam computed tomography (CBCT) has proved to serve as a boon in endodontics. CBCT scans are able to differentiate between many types of structures and airspaces including bone, teeth, airway, paranasal sinuses, and sometimes soft tissue while avoiding diagnostic limitations inherent in 2-D images like superimposition of structures, non uniform magnification, distortion and no depth information. Patel et al., have reported CBCT to be as precise as the conventional techniques of clearing and staining in the determination of root canal anatomy [14, 15]. The high accuracy, comparatively less exposure time and radiation dose added to the ability to have a 3 dimensional reconstruction and visualization have made CBCT the investigation of choice in modern dentistry [16, 3]. In the current study, the root canal anatomy of mandibular incisor teeth was evaluated using three- dimensional cone beam computed tomography in vitro. Every specimen was analyzed in multiple sections and all three dimensions to accurately assess the internal anatomy of the root canal systems. Of the samples evaluated, 57% of mandibular central insisors and 54% of mandibular lateral incisors presented with a single canal. Of the 100 mandibular central incisors, 12% showed type II, 24% showed type III and 4% showed type IV canal system according to Vertucci’s classification. However, 46% of permanent mandibular lateral incisors showed the presence of multiple canals of which 15% showed Type II, 27% showed Type III and 2% showed Type IV canal system (according to Vertucci’s classification). The results of the current investigation show that almost half (43% central and 46% lateral) of the specimen collected from an Indian population showed a second canal with the bifurcation most commonly being in the middle third of the root. The failure to identify this complex anatomy due to lack of anatomic knowledge or lack of skill to negotiate these canal systems account for majority of endodontic failures of mandibular incisors [17, 18]. These results were in accordance to the results of the study conducted by Sikri and Sikri that showed the presence of single canal (Vertucci’s Type I) in 58.33% permanent mandibular central incisors and 59.78% of mandibular lateral incisors. Vertucci’s Type II canal anatomy was seen in 12.5% mandibular central incisors, Type III in 4.16% and Type IV in 4.16%. While 4.3% mandibular lateral incisors showed Vertucci’s Type II, 3.26% showed Type III and 6.52% showed Type IV canal configurations [1]. Boruah and Bhuvan showed that in the mandibular incisors of North Eastern Indian population, possess a slightly higher percentage (63.75%) of Type I canal system. One third of the teeth (36%) exhibited two canal system and of the teeth with two canals, Type III configuration was most common followed by Type II and Type V [3]. Jaju, Sushma P.; Jaju, Prashant P.; Garcha, Vikram conducted A retrospective study of 130 Indian patients who underwent a CBCT scan for implants and assessed variation in the root canal anatomy in the mandibular incisors [19]. They found that Vertucci type I and type III configurations were more prevalent in both mandibular central and lateral incisors [19]. 81.37% of teeth had a single canal and 28.43% of teeth had two canals, Type 1 Vertucci configuration was found to be the most prevalent one, and type 4 the least prevalent in the study conducted by Kamtane & Ghodke on the mandibular incisors of Indian sub population of Pune [20]. The study conducted by Benjamin and Dawson in 1974 also showed similar statistics of root canal systems in permanent mandibular central incisors [21]. However, for the Chinese population Type I root canal morphology is more common according to the studies by You-nong & Bao-li and Qing-ping & Xing [22, 10]. The frequency of multiple canals was 5.0% for central incisors and 14.7% for lateral incisors in the study conducted by Yang ZhengyanluKeke Wang Fei li Yueheng Zhou Zhi in the permanent mandibular anterior teeth in Chinese population [23]. All of these studies reported a much higher prevalence of a single canal in the specimen. These differences in findings can be attributed to the different methods of conducting the studies and more to the anatomic differences in the teeth of people of different geographic regions and ethnicities. A comparison of the current study to the previous reported studies on the root canal morphology of mandibular anterior teeth in various populations is presented in Table 2.

Number

No Investigato

Teeth studied

rs Year Region

of samples Benjamin &

Mandibular

1 Dawson

1974 Unknown 364

central incisor (21) Mandibular

2 Kartal&Yani

koglu (9) 1992 Turkish 100

central incisor Mandibular

96 central incisors Radiogra

3 Sikri&Sikri

(2) 1994 Indian

Mandibular

92 lateral incisors Mandibular

You- nong&Bao-li

1995 Chinese 108

central incisors

4 (22) Canal classification according to Vertucci’s

types (%) Nature of

Study

I II III IV V VI VIIVIII OTHE

MULTI-

RS

ROOT

Radiogra

phy (In-

58.640.1 0 1.3 0 0 0 0 0 41.4

vitro) Staining & clearing 55 16 20 4 3 0 0 0 2 45

107 Mandibular 71.00.09 18.6 0 5.61 0 0 0 8.41 28.97

lateral incisors Mandibular

5 Caliskan et

al (26) 1995 Turkish 100

lateral incisors Mandibular

6 Miyashita et

al (4) 1997 Japanese 85

central incisors Mandibular

200 central incisors Staining & clearing

7 Sert et al

(27) 2004 Turkish

Mandibular

201 lateral incisors Mandibular

100 central incisors Staining & clearing

8 Vertucci (7) 2005 American

Mandibular

100 lateral incisors Al- Qudah&Aw awdeh (28)

Mandibular

Staining & clearing 87.6 9.3 0 1.4 1.7 0 0 0 0 12.4

Staining & clearing 73.810.9 6.7 5.1 3.6 0 0 0 0 26.2

Radiogra

Table 2: Percentage of root canal anatomies of permanent mandibular incisor teeth of various populations using different methods of evaluation by numerous authors compared to the current study. Clinical methods like dental operating microscope, loops, and dyes can be used to identify the 2nd canal. Optimizing the access preparation by extending the traditional lingual access toward the cingulum overcomes the challenge of locating the second canal in mandibular incisors. Exposing a labial or incisal approach has also become more acceptable with the advent of highly aesthetic restorative materials in dentistry [21, 25, 26].

Conclusion

A comprehensive understanding about the normal root canal anatomy and all possible variations is necessary for the success of any endodontic procedure. Almost, 50% of permanent mandibular incisors (Central and Lateral) in the studied Indian population showed the presence of more than one canal. The clinicians should give due consideration to such population based studies, make more efforts, use 3D radiography whenever possible and indicated, modify the traditional access cavity extending it towards the cingulumetc to reduce the changes of missing the extra canal and prevent subsequent failure of the root canal treatment. Although some studies have been conducted on the root canal anatomy of mandibular incisors, further research is always helpful to better understand root-canal anatomy, thus increasing the success rate of endodontic treatment.