Measured diagram
How many canals does a lower first molar have, and where do they start?
Looking down through the opening of the same measured molar, with the whole roof of the chamber removed so that no ledge hides an entrance. Three canals is the commonest arrangement, two in the front root and one behind; about a third of these teeth have a fourth.
What the drawing is measured from
- The canal count comes from a systematic review of 41 studies covering 18,781 lower first molars: three canals in 61.3 per cent and four in 35.7 per cent; the front root held two canals in 94.4 per cent, and the back root a single canal in 62.7 per cent. de Pablo et al. 2010, Journal of Endodontics. DOI
- The entrances sit where the textbook places them in this tooth: the cheek-side front entrance close to the front cheek-side cusp tip, the tongue-side front entrance in a more central position rather than under its cusp, and a single back canal's large entrance just behind the centre of the crown. Woelfel's Dental Anatomy.
- Finding them follows the laws for locating pulp chambers and canal entrances that Krasner and Rankow proposed after examining 500 pulp chambers of extracted teeth. Krasner and Rankow 2004, Journal of Endodontics. DOI
- The opening removes the whole roof of the chamber, leaving no ledge over the pulp horns, so that every entrance lies in view. Poor access design and missed canals are among the recognised causes of inflammation at the root tip that persists after treatment. Nair 2006, International Endodontic Journal, review. DOI
Use this diagram
Free to use, including commercially, with credit.
This diagram is published under CC BY 4.0. You may reproduce it in articles, teaching material, presentations and patient information, print or online, without asking. The one condition is that you credit Dr. Khalid Aletaibi and link back to this page.
It is published this way on purpose. The measurement in this drawing is not something the people selling the treatment tend to publish, so it is more useful spread than kept.
Credit line
The floor of the pulp chamber. Dr. Khalid Aletaibi, CC BY 4.0. https://khalidaletaibi.com/en/diagrams/root-canal-chamber-floor
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The floor of the pulp chamber. <a href="https://khalidaletaibi.com/en/diagrams/root-canal-chamber-floor">Dr. Khalid Aletaibi</a>,
<a href="https://creativecommons.org/licenses/by/4.0/">CC BY 4.0</a>
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