Root canal anatomy tooth by tooth
- Anatomy and histology
Each tooth has a usual number of roots and canals, but extra canals are common. A missed, infected canal is a leading cause of root canal failure.
What it is
The pulp space has a chamber in the crown and one or more canals in each root, ending at the apical foramen. Canals branch, join, curve and narrow with age. The apical constriction, the narrowest point just short of the root tip, is where cleaning and filling should end. Knowing the usual and the frequent variant anatomy of each tooth guides the access cavity and the search for canals.
Clinical anatomy
- Upper incisors and canines: usually one root and one canal; the canine has the longest root in the mouth.
- Lower incisors: one root, but often two canals (labial and lingual) that may join near the apex.
- Upper first premolar: usually two roots or two canals (buccal and palatal); upper second premolar: often one.
- Upper first molar: three roots; the mesiobuccal root often has a second canal (MB2), frequently missed.
- Lower first molar: two roots, usually two mesial canals and one or two distal; sometimes an extra distolingual root.
- Lower second molars can have C-shaped canals, more often in people of East Asian ancestry.
Function
- Lateral and accessory canals connect the pulp with the periodontal ligament, so pulp infection can show up on the side of the root.
- Secondary dentine narrows the chamber and canals with age, making older teeth harder to treat.
Clinical correlation
- A missed canal leaves bacteria behind and is a common reason for persistent apical periodontitis.
- Magnification, good light and sometimes CBCT help find extra canals such as MB2.
- Overfilling past the constriction pushes material into bone; underfilling leaves infected canal behind.
Next step / Initial management
- Before treatment, read the periapical radiograph for root number, curvature and canal width.
- Expect the common variants (two canals in lower incisors, MB2 in upper molars) and look for them.
- Calcified, very curved or unusual canals: refer to an endodontist.
Test yourself
Think of the answer, then tap the question to see it.
Which canal is most often missed in the upper first molar?
The second mesiobuccal canal (MB2).
How many canals does a lower incisor often have?
Two, labial and lingual, frequently joining near the apex.
Where should root canal cleaning and filling end?
At the apical constriction, the narrowest part of the canal just short of the root tip.
Connections
Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.
Sources: Endodontics, Pulp Space Anatomy and Access Cavity of Anterior Teeth (StatPearls Publishing (NCBI Bookshelf), 2025); Anatomy, Head and Neck, Dental Pulp (StatPearls Publishing (NCBI Bookshelf), 2025); Anatomy, Permanent Dentition (StatPearls Publishing (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.