A tiny canal overlooked during root canal treatment of an upper molar can become the source of prolonged problems for a patient. This is the central message of a scientific article written by drg. Sri Larnani, MDSc., a faculty member of the Department of Biomedical Dentistry at the Faculty of Dentistry, Universitas Gadjah Mada (UGM), together with a research team from Seoul National University, South Korea. Published in the April 2024 issue of the International Journal of Morphology, the article provides an in-depth review of the morphology of the second mesiobuccal (MB2) canal in maxillary second molars—a canal that is frequently overlooked by dentists and is one of the major causes of root canal treatment failure worldwide.
A Small Canal, A Big Problem
The maxillary second molar, or the second upper molar, is one of the most structurally complex teeth in the human mouth. It generally has three roots, and the mesiobuccal root often contains more than one canal.
The second canal is known as the MB2 canal. Its presence is not always easy to identify, even for experienced dentists. If this canal is not located and adequately treated, residual pulp tissue within it can trigger infection, prolonged pain, and even complete failure of the treatment.
This review compiled data from 47 studies covering 20 countries, mapping how frequently MB2 canals are found, their shapes and configurations, their location within the tooth, and the most effective methods for detecting them.
Surprising Figures from 20 Countries
One of the most striking findings of the review was the wide variation in MB2 prevalence across populations worldwide. Overall, MB2 canals were detected in 7.7% to 93% of the samples studied, with a pooled prevalence of 32.74%.
This means that nearly one in three patients undergoing root canal treatment on a maxillary second molar may have an MB2 canal that requires treatment. This figure cannot simply be ignored.
The wide variation is influenced by numerous factors, including ethnic differences, research methods, and the type of imaging or detection equipment used. In Saudi Arabia, for example, one study using micro-CT reported a prevalence as high as 93%, whereas a study in Taiwan using cone-beam computed tomography (CBCT) recorded a prevalence as low as 7.7%.
Regarding sex, most studies reported that MB2 canals were more frequently found in male patients than in female patients, although several studies from Egypt and Saudi Arabia reported the opposite pattern.
Understanding the Shape and Location of MB2
Not all MB2 canals have the same configuration. Researchers have used two major classification systems to describe root canal configurations: the Weine classification, introduced in 1969, and the more detailed Vertucci classification, introduced in 1974 and comprising eight configurations.
Across the data analyzed, Vertucci type II and type IV configurations were the most commonly identified. Type II consists of two separate canals that emerge from the pulp chamber and merge before reaching the root apex, whereas type IV consists of two completely separate canals extending from the pulp chamber to the root apex.
Anatomically, MB2 canals have a very small diameter, averaging only 0.19 mm in the buccolingual direction, with thinner dentinal walls than the first mesiobuccal canal (MB1). The MB2 orifice is located approximately 2.2 mm palatally and 0.98 mm mesially from the MB1 orifice, although these distances vary among populations.
“Finding only one orifice in the pulp chamber does not mean that there is only one canal in the mesiobuccal root. The presence of 1-2-1, 1-2, and 1-2-1-2 configurations should always be considered,” the research team wrote in the article.
How to Find MB2: From Magnification to CBCT Technology
The most clinically practical section of the article discusses how dentists can locate MB2 canals during treatment. Several approaches have proven effective.
First, the access cavity is recommended to have a rhomboid rather than a conventional square shape, allowing the MB2 orifice hidden on the palatal side to be visualized more clearly. Second, the use of a dental operating microscope (DOM) has been shown to significantly improve detection. One study demonstrated that combining DOM with selective dentin removal successfully detected MB2 canals in 86% of maxillary second molars.
CBCT technology also plays an important role. This three-dimensional imaging technique allows dentists to visualize root canal anatomy comprehensively before treatment, thereby minimizing the likelihood of missing an MB2 canal.
The study emphasizes that an in-depth understanding of dental anatomy is not merely academic knowledge but a direct foundation for successful clinical treatment. A canal as small as 0.19 mm can determine whether a patient recovers successfully or has to return to the dental chair for a problem that could potentially have been avoided.
Authors: Achmad Zam Zam Aghasy, DDS, M.Kes.; Hazra Alifia Muharam
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