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Endodontics · patient case question

What should be suspected in Patient D, and why does it matter?

Patient case: Four developmental anomalies

Patient: Four patients

Chief Complaint: A: “One back tooth bleeds when I floss.” B: referred for orthodontic assessment. C: mother reports the child's teeth on one side “look different”. D: referred for root canal treatment.

Background: A, 45-year-old male: excellent plaque control, no periodontal disease elsewhere. B, 13-year-old female: no medical history. C, 8-year-old male: unremarkable medical and family history. D, 36-year-old female of East Asian ancestry.

Findings: A: an ISOLATED 8 mm furcation pocket on a molar in an otherwise healthy mouth, with a well-defined radiopaque nodule at the furcation. B: the maxillary canine and first premolar have exchanged positions in the arch. C: several ADJACENT teeth in one quadrant with markedly thin enamel and dentine, disproportionately large pulp chambers and poor contrast, with an abrupt cut-off at the midline. D: mandibular first molar in which the root outline appears unusually wide and the periodontal ligament outlines do not resolve into two roots.

  1. Radix entomolaris — an additional distolingual root on the mandibular first molar, easily missed at access
  2. A third root on a maxillary central incisor
  3. An extra root on the maxillary third molar, of no clinical consequence
  4. Nothing — any extra root would be plainly visible on a standard periapical
Show answer and explanation

Correct answer: A. Radix entomolaris — an additional distolingual root on the mandibular first molar, easily missed at access

  • A. CORRECT. RADIX ENTOMOLARIS is an additional DISTOLINGUAL root on the mandibular first molar. Its prevalence varies markedly with ancestry — under 5% in white European populations but reaching 30% or more in people of East Asian and Native American descent, which is why the stem specifies it. It matters because the extra canal is easily MISSED during endodontic access, and because the root lies LINGUALLY it is superimposed on the others on a standard periapical, producing exactly the finding described: an unusually wide root outline whose periodontal ligament outlines do not resolve. Suspect it, then take a second film at an altered horizontal angle using the SLOB rule, or a CBCT. The mirror-image variant with an extra BUCCAL root is radix paramolaris.
  • B. Maxillary central incisors are essentially always single-rooted. This is not a recognised variation.
  • C. The maxillary third molar has highly variable and often fused root anatomy, but it is not the clinically significant variation being tested here.
  • D. This is precisely the trap. An extra root superimposed lingually is what a single periapical FAILS to demonstrate — the reason the variation is missed so often is that the standard film does not show it.

Note: Other root-number variations worth carrying: mandibular CANINES have two roots in roughly 5% of cases; maxillary FIRST PREMOLARS have two roots in 60–70%; and the MB2 canal of the maxillary first molar is present in the majority of teeth and is the single most commonly missed canal in endodontics.

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