text new page (beta)
English (pdf)
Article in xml format
Automatic translation
Cited by SciELO 
Cited by Google 
Similars in
SciELO 
Similars in Google 
Permalink
INTRODUCTION
Knowledge of tooth morphology is fundamental in root canal treatment. Clinicians should consider the configuration of the root canal and its variations before performing endodontic treatment (Tomaszewska et al., 2018; Baruwa et al., 2020). The failure to locate a complete canal system can adversely affect the prognosis of endodontic treatment because root canal therapy can fail if a few portions of pulp tissue are not successfully filled (Kharouf & Mancino, 2019). In addition, variability in anatomical structure should consistently be recognized because a lack of awareness of tooth morphology may increase the possibility of missing root canals throughout treatment, resulting in treatment failure (Baruwa et al., 2020).
Maxillary molars have the highest number of roots in various forms and structures, which explains why their internal canal system is complex (Betancourt et al., 2015). Previous studies have reported that the root canals of the maxillary second molars were more variable than the maxillary first molars (Ghoncheh et al., 2017; Wolf et al., 2017). Many studies on the anatomy of the maxillary second molar have shown the complexity of the root canal morphology. These studies were conducted based on population and demographics in vivo and ex vivo and found significant variations in root length, number of roots, root canal type, and root deviation (Wolf et al., 2017; Wu et al., 2017; Naseri et al., 2018; Xia et al., 2020; Rosaline et al., 2021).
The typical anatomical structure of the maxillary second molar comprises three roots (Ghasemi et al., 2017; Xia et al., 2020). In terms of canal configuration, the mesiobuccal root shows the most variation compared to the distobuccal and palatal roots (Ghoncheh et al., 2017; Tomaszewska et al., 2018). The mesiobuccal root mostly has one or additional canals, such as the second mesiobuccal (MB2) canal (Naseri et al., 2018; D'Souza et al., 2021).
The existence of the MB2 canal is one of the factors responsible for the morphological complexity of maxillary second molars (Rosaline et al., 2021). Numerous studies in various populations using various methods have shown considerable variation in identifying the MB2 canal in the maxillary second molars (Betancourt et al., 2015; Ghoncheh et al., 2017; Naseri et al., 2018; Kharouf & Mancino, 2019; D'Souza et al., 2021; Magalhães et al., 2022). Therefore, one of the primary reasons an endodontic treatment on maxillary second molars is incomplete might be the failure to detect the MB2 canal (Betancourt et al., 2015; Kharouf & Mancino, 2019).
This article aimed to present an overview of prevalence, classification, anatomical features, including the second mesiobuccal root canal characteristic, the geometric location of the orifice, and the internal architecture of the root canal. In addition, the method to locate is also described. We searched for published literature concerning the second mesiobuccal canal of the permanent maxillary second molar using the PubMed database and hand searching. The keywords searched were ‘maxillary molar’, ‘root morphology’ and ‘root canal anatomy’. Titles and abstracts pertinent to the study were reviewed. This review included English papers and root canal anatomy texts published from 2011 to 2022 and relevant study of Vertucci and Weine classification published earlier.
Prevalence
Among the 47 examined studies, the prevalence of the MB2 canal represented data from 20 countries. The overall results are summarized in Table I. The MB2 canal in the maxillary second molar has been revealed frequently in Asian countries. In Iranian population studies, maxillary second molars had 14 % to 67.5 % of MB2 canals (Rouhani et al., 2014; Ghoncheh et al., 2017; Khademi et al., 2017; Zand et al., 2017; Khosravifard et al., 2018; Naseri et al., 2018; Donyavi et al., 2019). Investigations in Turkey reported MB2 canals frequency of 17.75 % to 47.3 % (Magat & Hakbilen, 2019; Keskin et al., 2021; Yanık & Nalbantog˘lu, 2022). Studies in the Indian and the Saudi Arabian population found that maxillary second molars had a wide range of MB2 canals between 8.47 % to 86 % (Singh & Pawar, 2015; Shetty et al., 2017; Kosaraju et al., 2018; Manigandan et al., 2020; D'Souza et al., 2021; Rosaline et al., 2021) and 17.7 % to 93 % (Al-Fouzan et al., 2013; Alfouzan et al., 2019; Alnowailaty & Alghamdi, 2022), respectively. Among Southeast Asian countries, the Thai population (Ratanajirasut et al., 2018) showed a much higher prevalence of MB2 canals than the Chinese in the Malaysian population (Pan et al., 2019). In East Asian countries, Korea (Lee et al., 2020), Taiwan (Lin et al., 2017; Su et al., 2019; Tzeng et al., 2020) and China (Tian et al., 2016; Wang et al., 2017; Wu et al., 2017; Martins et al., 2018; Xia et al., 2020) reported a 7.7 % to 41.3 % prevalence of MB2 canals, the lowest and the highest were identified in the Taiwanese population.
Table I Prevalence of MB2 canal in the maxillary second molar.
CT: Root Canal Treatment. DOM: Dental Operating Microscope. R: right maxillary second molar tooth. L: left maxillary second molar tooth. Classification of MB2 based on Vertucci, except with † symbol is based on Weine.
In the South American population groups, the Chilean population had a prevalence of MB2 canals in maxillary second molars of 42.48 % to 48 % (Abarca et al., 2015; Betancourt et al., 2015, 2016). However, it had a different range of 22.72 % to 83.4 % in the Brazilian population (Reis et al., 2013; Silva et al., 2014; Candeiro et al., 2019; Mohara et al., 2019). Moreover, studies on the American and Canadian populations showed 55.1 % to 73 % of MB2 canals (Domark et al., 2013; Park et al., 2014; Coelho et al., 2016; Parker et al., 2017). In the European population, the MB2 canals ranged from 23.2 % to 64.9 % (Nikoloudaki et al., 2015; Olczak & Pawlicka, 2017; Pérez-Heredia et al., 2017; Martins et al., 2018; Kharouf & Mancino, 2019). In Africa, the percentage of the MB2 canal was more than 50 % (Ghobashy et al., 2017; Fernandes et al., 2019).
The present study found varying percentages of MB2 canal in the mesiobuccal root of the maxillary second molar, from 7.7 % to 93 %, with a pooled mean of 32.74 %. This finding is lower than the previous result of the systematic review, which reported that the prevalence of MB2 canal in the maxillary second molar was 39 % (Martins et al., 2020). The MB2 canal prevalence in the mesiobuccal root of the maxillary second molar varies widely, which agrees with the previous studies, ranging from 14.0 %-83.4 % in a prevalence study consisting of data from 28 countries (Martins et al., 2019) and 21.8 %-83.4 % in prevalence study in Brazilian sub-populations (Silva et al., 2021).
Ethnic predilections and research methods can cause these wide variations. It includes different types of studies, sample selection, and equipment used. Variations may still be found using the same tool, for example, cone beam computed tomography (CBCT), due to the differences in tool specifications and techniques. In sample justification, eight studies stated the sample size calculation to provide an adequate estimate of prevalence (Reis et al., 2013; Park et al., 2014; Naseri et al., 2018; Fernandes et al., 2019; Julia Yen Yee et al., 2019; Manigandan et al., 2020; D'Souza et al., 2021; Alnowailaty & Alghamdi, 2022), and 4 of those studies performed power analysis for sample size (Reis et al., 2013; Manigandan et al., 2020; D'Souza et al., 2021; Alnowailaty & Alghamdi, 2022). Although some studies have large samples, the remaining studies only informed the sample size without verifying whether the representative addressed the target population.
Some previous studies have shown a relationship between gender and the prevalence of the MB2 canal in maxillary second molars. Studies in Chile, Poland, Chinese, India, Thailand, South Africa, Malaysia, and Taiwan have reported that MB2 canal was higher in males than in females (Abarca et al., 2015; Betancourt et al., 2015, 2016; Olczak & Pawlicka, 2017; Wu et al., 2017; Kosaraju et al., 2018; Ratanajirasut et al., 2018; Su et al., 2019; Fernandes et al., 2019; Pan et al., 2019; Manigandan et al., 2020; Tzeng et al., 2020; Xia et al., 2020; D'Souza et al., 2021). In contrast, studies in Egypt and Saudi Arabia showed that the MB2 canal was higher in females than in males (Ghobashy et al., 2017; Alnowailaty & Alghamdi, 2022). Studies in Iran, Brazil, and Turkey have found contradictory results. Some studies have found that MB2 canal was higher in males than females, whereas others found the opposite (Khosravifard et al., 2018; Naseri et al., 2018; Mohara et al., 2019; Yanık & Nalbantog˘lu, 2022).
Classification
Several classifications are suggested to provide a better comprehension of root canal anatomy. The most frequently used classifications of the second mesiobuccal canals are the Weine classification and the Vertucci classification. The Weine classification was first proposed in 1969, consisting of a root canal configuration of types I, II, III, and IV (Fig. 1). Type I: One canal from the pulp chamber to the apex. Type II: A bigger buccal canal and a smaller lingual canal that unifies from 1 to 4 mm from the apex. Type III: Two different canals and two different apical foramina, with the buccal canal being bigger and generallylonger from the roof chamber to its apical foramen. Type IV: A single coronal canal splits to leave the root in two canals with two distinct foramina (Weine et al., 1969). According to the Weine classification, the Iranian populations have the highest prevalence of type III canal configurations in the mesiobuccal roots of maxillary second molars (Khosravifard et al., 2018). However, a study in France has reported that the percentage of types II and III are similar (Kharouf & Mancino, 2019). On the other hand, the Indian population had an equal proportion of types II and III, each 50 % (Shetty et al., 2017).
The Vertucci classification was proposed in 1974, consisting of eight types of root canal configurations (Fig. 2). Type I: One canal extends from the pulp chamber to the apex. Type II: Two distinct canals exit the pulp chamber and merge only short of the apex to create a single canal. Type III: A single canal exit the pulp chamber, separating into two within the body of the root, then uniting again to leave as a single canal. Type IV: Two different canals extend from the pulp chamber to the apex. Type V: A single canal exits the pulp chamber and separates short in the apex into two independent canals with distinct apical foramen. Type VI: Two different canals exit the pulp chamber, joining in the body of the root and dividing into two separate canals in the short of the apex. Type VII: A canal exits the pulp chamber, separating and reconnecting within the root body, and then dividing into two different canals in the short of the apex. Type VIII: Three distinct canals extend from the pulp chamber to the apex (Vertucci et al., 1974; Vertucci, 1984, 2005).
Fig. 2 Vertucci’s root canal configurations of the MB2. MB: mesiobuccal, DB: distobuccal, P: palatal.
The Vertucci system classifies the MB2 canal configuration, except for type I, which only has one canal. Vertucci types II and IV canal configurations were the most prevalent in recent studies in Iran, Taiwan, China, Thailand, Malaysia, Egypt, India, Brazil, Spain, and Turkey (Singh & Pawar, 2015; Ghobashy et al., 2017; Ghoncheh et al., 2017; Khademi et al., 2017; Lin et al., 2017; Pérez-Heredia et al., 2017; Zand et al., 2017; Ratanajirasut et al., 2018; Candeiro et al., 2019; Donyavi et al., 2019; Pan et al., 2019; Manigandan et al., 2020; Xia et al., 2020; Yanık & Nalbantog˘lu, 2022). This result is consistent with a study and meta-analysis which reported that the most common configuration was types II and IV (Tomaszewska et al., 2018). However, studies in Iran discovered types III and VI as the highest prevalent (Rouhani et al., 2014; Zand et al., 2017; Naseri et al., 2018). On the other hand, there was a large variety of root canal configurations in some studies, the Portugal population and the Iranian population had types II to VII (Rouhani et al., 2014; Martins et al., 2018), the Chinese population had types II to VIII (Tian et al., 2016), and the Brazilian population had types II to VI and VIII (Candeiro et al., 2019; Mohara et al., 2019).
According to Vertucci and Weine classifications, the root canal system configuration represents various MB2 canal structures. The MB2 canal that separates from the pulp chamber to the foramen apical is found in type IV and VIII Vertucci classification and type III Weine classification. From previous studies (Table 1), the configuration of the MB2 canal in the second maxillary molar was the most in type 2- 1 (two different canals leave the pulp chamber and join the apex to form a single canal) and type 2 (two different canals from the pulp chamber to apex). Since all other types of MB2 canal configuration were reported to be present, the presence of types 1-2-1, 1-2, and 1-2-1-2 should be noted. Only detecting one orifice in the pulp chamber does not mean there is only one canal in the mesiobuccal root.
Anatomical features
The morphological aspects of the mesiobuccal root of the maxillary second molar are as follows: the root length is 12.9 mm (9.0-18.2 mm), longer than the distobuccal root and shorter than the palatal root. In root grooves, there are mesial and distal depressions. Most mesiobuccal roots have a distal-buccal deviation. Apical root curvature is commonly distal (54 %), straight (22 %), and others (24 %). The mesiobuccal root's apical foramen is mostly straight in the coronal plane and deviates distally in the sagittal plane (Naseri et al., 2018; Versiani et al., 2019).
The mesiobuccal root canal has the following characteristics: the shape of the root canal cross-section is oval or flat-oval in coronal and middle and round in apical (Versiani et al., 2019). On the radiograph, the mesiobuccal canal is not located in the center of the mesiobuccal root, indicating more than one canal in the root (Liu et al., 2019). Moreover, the canal taper of MB2 is 0.05 mm/mm in the buccolingual direction. The canal diameter of MB2 is 0.19 mm (0.14-0.23 mm) in the buccolingual direction and 0.16 mm (0.15-0.16 mm) in the mesiodistal direction (Versiani et al., 2019).
The MB2 canal in maxillary second molars is frequently found next to the mesiobuccal canal. It could occur in a single orifice, two separate but adjacent orifices, or two somewhat distant orifices (Shah et al., 2014). The orifice of the MB2 canal is located approximately mesiopalatally to the orifice of the first mesiobuccal (MB1) canal (Shah et al., 2014; Betancourt et al., 2015). Figure 3 presents the orifice location. The geometric location study in Chile showed that the MB2 canal was located 2.2 ± 0.54 mm palatally and 0.98 ± 0.35 mm mesially to the MB1 canal (Betancourt et al., 2015). In a study with a more extensive sample, the MB2 canal was located at 2.41 ± 0.64 mm palatally and 0.98 ± 0.33 mm mesially (Betancourt et al., 2016). However, a study in Saudi Arabia found a lower distance; the location was 1.24 ± 0.76 mm palatally and 0.43 ± 0.18 mm mesially (Alnowailaty & Alghamdi, 2022). Two studies in Turkey reported a wide range of distances; the location was 1.39 ± 0.88 mm and ± 0.67 mm palatally (Magat & Hakbilen, 2019; Keskin et al., 2021). A study in Korea found it to be 1.98 ± 0.42 mm palatally (Lee et al., 2020). A case report in China found that the MB2 canal was nearer to the palatal side than the buccal side; it was 3.25 mm palatally (Liu et al., 2019).
Fig. 3 Illustration of orifice location and rhomboidal access preparation. MB1: first mesiobuccal, MB2: second mesiobuccal, DB: distobuccal, P: palatal.
In maxillary second molars, the internal architecture of the mesiobuccal root, including dentin thickness, was observed to differ greatly associated with the existence of the MB2 canal (Rosado et al., 2022). According to recent research, the dentinal wall enclosing the MB2 root canal in maxillary second molars was thinner than the neighboring MB1 root canal (Azimi et al., 2020; Rosado et al., 2022; Yanık & Nalbantog˘lu, 2022). The dentinal wall in the distal concave region of the maxillary second molar mesiobuccal root near furcation was thinner than in the mesial convex region distant from furcation (Yanık & Nalbantog˘lu, 2022), and the palatal wall was thinner than the buccal wall (Daga et al., 2011).
Some studies have examined the root canal configuration by separating the roots into three-thirds: coronal, middle, and apical. The presence of the MB2 canal was checked in each third. They discovered that MB2 canals were less common in the middle and apical thirds than in the coronal third. As the root nears the apical third, the prevalence of MB2 canals decreases (Reis et al., 2013; Abarca et al., 2015; Wolf et al., 2017). Abarca et al. (2015) found that MB2 canals were present in all root thirds over 13 % of maxillary second molars. Wolf et al. (2017) also studied the number of main foramina, accessory canals, and connecting canals. Only 43.1 % of the samples had a main foramen in the MB2 canal. In all apical thirds, connecting and accessory canals were observable (Wolf et al., 2017).
Locating the second mesiobuccal canal
When locating the MB2 canal, to maximize the visibility of the MB2 canal orifice, the shape of the access cavity is suggested to be rhomboidal (Fig. 3) (Daga et al., 2011; Betancourt et al., 2015; Manigandan et al., 2020; Alnowailaty & Alghamdi, 2022). To achieve a sufficient access opening, a wide canal with a flat, flared, and finalized axial wall is recommended (Corneli et al., 2020). Direct vision, dental operating microscope (DOM), selective dentin removal, and CBCT was used to locate and negotiate the MB2 canal (Manigandan et al., 2020). The use of magnification, ranging from loupes and magnifying glasses to an operating microscope, has improved the detection rate of MB2 canals. In endodontics, the DOM has significantly improved magnification and illumination for the clinician. Troughing should be performed to remove the dentinal shelf that conceals the underlying orifice or to remove calcification using specially built ultrasonic tips or burs. Using multiple straights and angled radiographs both before and during surgery gives a visual representation of the existence of extra canals. CBCT, one of the contemporary diagnostic techniques, improves access to the internal root canal morphology (Daga et al., 2011; Manigandan et al., 2020). CBCT has shown to be a reliable and accurate method for locating MB2 canals (De Carlo Bello et al., 2018).
One study compared direct vision, DOM, selective dentin removal under DOM, and CBCT in the clinical detection of MB2 canal and showed that MB2 canal could be clinically detected in 86 % of maxillary second molars using DOM combined with selective dentin removal. Clinical detection of MB2 canals was increased successively using direct vision, DOM, selective dentin removal, and CBCT (Manigandan et al., 2020). Another study found 74.1 % of MB2 canals during routine pulp chamber access, with the majority of these discovered during the initial treatment. A total of 14.2 % required troughing with burs or ultrasonic tips to locate the canal orifice. A further 11.7 % were found using the aid of CBCT imaging. In this study, DOM was used in the treatment of each case. With the use of CBCT images in preoperative treatment, more MB2 canals were found in the maxillary second molar (Studebaker et al., 2018).
CONCLUSION
From the literature we reviewed, the prevalence of the MB2 canal in the second maxillary molar is relatively high, and the configuration is variable. Based on our investigation, the prevalence varies from 7.7 % to 93 %, averaging 32.74 %. According to gender, it mainly showed that the percentage of males was higher than that of females. Type II and IV Vertucci are the two most prevalent configurations of the second mesiobuccal canal in the maxillary second molar. Overall, the presence of the MB2 canal significantly altered the anatomical features of the mesiobuccal root canal. Moreover, to locate the MB2 canal, preparation of the tooth with a rhomboidal access outline, direct vision method, DOM, selective dentin removal, and CBCT are advisable. Therefore, understanding its internal anatomy is highly recommended for the clinician to optimally locate and negotiate the canal.
