Investigating root canal morphology in maxillary first and second permanent molars by CBCT method in Iranian people

Dissertation for obtaining a professional doctorate degree in dentistry

Abstract

Introduction: One of the common causes of non-surgical root canal treatment failure is the inability to effectively treat all root canals due to the complex anatomy of the root canal system. Due to the fact that so far no comprehensive and extensive study has been conducted on the anatomy of the root canal system in maxillary first and second molar teeth using CBCT in the Iranian race, so the purpose of this study was to investigate the variations and anatomical features of these teeth in a population of Iranian race.

Materials and methods: In the present study, 250 extracted human maxillary first and second molar teeth were used. After disinfecting the teeth, first the number and condition of the roots were recorded for each case.  The morphology of the dental canals was determined using Cone Beam Computed Tomography (CBCT), in such a way that after preparing stereotypes, the images in all three axial, sagittal, and coronal sections were morphologically evaluated with the help of Romexis software. To determine the total number of canals in each tooth, the number of canals in each root and the morphology of the canals (using Vertucci's classification and Gulabivala's supplementary classification) in one root. All evaluations were done by 2 calibrated endodontists. The data was entered into SPSS software version 11.5 and the frequency percentage of each type of root morphology was described using frequency distribution tables and average, median and standard deviation indices.

Results: The prevalence of three-rooted first and second molar teeth was 98.4% and 97.6%, respectively, and the prevalence of four-rooted first and second molar teeth was 1.6% in both cases. In 0.8% of the second molar teeth, the teeth had two roots. Root adhesion was observed in 2.4% of first molars and 8.8% of second molars. The prevalence of the fourth canal in the mesiobuccal roots of the first and second molars was 52.8% and 16.84%, respectively. The most common canal morphology in the mesiobuccal root of the first molar was type I, type VI, and type II, respectively, and in the second molar, type I, type III, and type IV. It was also observed in 2.3% of the first molar and 0.8% in the second molar of the fourth canal in the distobuccal root.

Conclusion: According to the results of this study, the prevalence of the fourth channel in the Iranian race is relatively high. Considering the non-invasiveness and high accuracy of CBCT to identify additional canals and the importance of discovering these canals in the success of a root canal treatment, the use of CBCT during root canal treatment is recommended in cases with anatomical complications.

Keywords: Root canal morphology, maxillary first molar, maxillary second molar, CBCT

(1-1) Preface

The goal of root canal treatment is complete debridement of the root canal and complete removal of microorganisms and their byproducts from the root canal system and effective flooding of the canal system. This goal will not be achieved without complete knowledge of root canal morphology (1).

One ??of the common causes of non-surgical root canal treatment failure is the inability to effectively treat all root canals. Many studies have been presented on the morphology of the root canal in different populations, which is certainly of great importance to endodontists and general dentists who want to perform root canal treatments (2). rtl;">(2-1) General

1-2-1 tooth development

The first signs of macroscopic development of maxillary milk molar teeth begin at 12/5 weeks. The time of the first signs of calcification of the maxillary first deciduous molar is at 15.5 weeks and the maxillary second deciduous molar at 19 weeks. At birth, three quarters of the occlusogingival height of the maxillary first deciduous molar and one quarter of the occlusogingival height of the maxillary second deciduous molar are calcified (3).

First and second permanent molar teeth They begin to develop in the 20th embryonic period. This is done in a series of steps. Crown development occurs around 2.5 to 3 years old, while the tooth root is completed around 9 to 10 years old.. These events occur during a sequence including the initiation of cell division, cell growth, differentiation and deposition of plaque and enamel (4).

The tooth first consists of a layer of epithelial cells called the dental lamina. The stages of tooth formation from the dental lamina are divided into three stages according to the shape of the tooth. First, a mass similar to a flower bud appears[1]. The characteristic of this stage is the proliferation of epithelial cells into the ectomesenchyme. Then, this mass is invaginated and it is called cap-shaped [2]. This cell mass is also called the enamel organ. Finally, with the growth of the tooth bud and the deepening of this intussusception, the bell-shaped stage occurs [3]. During the development of the tooth crown, the tissue that is trapped inside this intussusception or the same enamel organ produces dental pulp and in the initial stages it is called dental papilla (5). 

The cells of the outer layer of the enamel organ become ameloblasts as a result of differentiation, which produce enamel. On the other hand, the internal cells of the enamel organ participate in the formation of dentin by differentiating into odontoblasts (5).

Also, the ectomesenchyme surrounding the enamel organ turns into a dental sac and participates in the formation of the periodontal ligament (5).

The deposition of non-mineralized dentin matrix occurs from the tips of the cusps. The first mineral layer of dentin that is formed is called dentin mantle, which is about 20 microns thick (5).

After the deposition of the first dentin, ameloblasts begin to form enamel, and with the completion of deposition and formation of enamel, the root also begins to form. In the place where the internal and external cells of the enamel organ connect to each other, it is called the cervical loop. As this cervical loop begins to grow, a structure called Hertwig's epithelial sheath is formed. This sheath determines the size, shape and length of the tooth roots. In the case of a single-rooted tooth, these pods grow from different sides until only a small hole remains. This proliferation is called an epithelial diaphragm. In two teeth, diaphragm roots grow in two areas and meet on both sides, resulting in two holes. In teeth with three roots, this multiplication occurs in three directions and three holes are created (4). 

When the first layer of dentin is formed in the root, dental sac cells begin to form cementum by migrating near the root and differentiating into cementoblasts (5).

Root formation begins shortly before the tooth erupts into the mouth, and when the tooth has reached its final position, about two-thirds of the root has been formed. The completion of the root is completed about two to three years after the completion of growth (5). 

2-2-1 How to form lateral canals

When the integrity of Hertwig's sheath is lost or a part of the root odontoblasts are not able to make dentin, a defect occurs in the dentin wall of the root, which eventually causes the formation of a secondary canal between the dental sac and It is pulped. These sub-channels may be formed in any region of the root, but they are more prevalent in the last third of the root (6). But the most accepted theory about the formation of secondary channels is the trapping of a blood vessel in Hertwig's epithelial sheath. If the surrounding parts of this vessel do not undergo dentin formation, eventually a sub-channel will be formed (7). 

3-2-1 Identification of lateral canals

Although these lateral canals may exist in most teeth, due to their thinness and small diameter, it is often difficult to identify and diagnose them through perical radiographs. These channels are revealed when the channels are filled with filling materials and the sealer penetrates into these channels (8).

In various studies, it has been observed that the ability of conventional radiographs to identify sub-channels is significantly lower than other methods. To discover these channels, CBCT, micro CT, ultrasonic, or the use of a microscope are auxiliary methods with high accuracy (9).