Page 9 - The Beauty and Sorrow in Endodontics-Chapter 4 - Part 1

The Pulpal Floor Serves as a Map to Aid in Locating the Various Canal

Orifices

It is generally accepted that most molars have four root canals. In a maxillary

molar, they are themesiobuccal 1 (MB1), mesiobuccal 2 (MB2), distobuccal (DB), and

palatal (P) canals. In a mandibular molar, they are the mesiobuccal (MB),
mesiolingual (ML), distobuccal (DB), and distolingual (DL) canals.

Although a large proportion of mandibular molars only have two roots (mesial and
distal), in most cases, there are two separate canals in each root. Of course, there are

times when the tooth exhibits only three canals, often times this is because the DB and
DL canals have merged into a single wider distal canal. Another variation in a

mandibular molar is the existence of a separate distolingual root. In addition, the

mandibular mesial root often has two root canals (MB, ML), however, sometimes
either a single mesial (M) canal or three separate (MB, middle mesial, ML) canals can

also occur. Asians have a higher prevalence of C-shaped canals in the mandibular
second molar. This is the result of the fusion of the mesial and distal roots during

development. Most cases, the fusion happens on the buccal (B) side, and the operator

will either find a separate ML canal along with a C-shaped canal (B and D canals
connected) or a single C-shaped canal (MB, B, D canals all connected). In rare cases,

the fusion can also happen on the lingual (L) side, in which case, the operator will find
a C-shaped canal connecting the MB, L, and D canals.

In maxillary molars, on the other hand, most variations are found in the MB root,

including the presence of either C-shaped canalsor MB2, or in odd cases MB3, or one
single orifice splitting into two canals mid-root, etc. Sometimes, two individual canals

can also be found in each of the DB and P roots.
How can we then, as clinicians, determine how many canals are in a tooth then?

According tothe article “Anatomy of the Pulp-Chamber Floor” published by Krasner
and Rankow in the Journal of Endodontics (2004), the pulpal floor is located right at

the centre of the tooth at the level of the cementoenamel junction (CEJ) (Fig AA-1).

This pulpal floor serves as the road map to locate the various canal orifices, which is
why it is important to avoid damaging it during access cavity prep. Of course, dentists

also need to have a basic understanding of the anatomy of the tooth in question (Fig
AA-2). For example, how many roots does it have? What are the root positions (Fig

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