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Anatomy & Histology · patient case question

How many roots and pulp horns does tooth #4 typically have?

Patient case: Blood pressure rise after local anaesthetic

Patient: Male, 41 years old

Chief Complaint: “The outside of my back tooth broke.”

Background: No systemic disease, no medications, no allergies. Reports being anxious about injections.

Vital Signs: On seating BP 105/65 mmHg · HR 72 bpm. Five minutes after infiltration with 2% lidocaine with 1:100,000 epinephrine: BP 138/86 mmHg · HR 96 bpm. Patient is alert, comfortable, no chest pain, no shortness of breath, no palpitations reported.

Findings: Fractured buccal cusp of tooth #4 with the fracture line above the gingival margin. No pulp exposure. Tooth vital.

  1. One root and one pulp horn
  2. Two roots and one pulp horn
  3. One root and two pulp horns
  4. Two roots and two pulp horns
Show answer and explanation

Correct answer: C. One root and two pulp horns

  • A. One pulp horn would imply a single cusp. Premolars are bicuspid by definition, and each cusp is underlain by a pulp horn.
  • B. Two roots with one pulp horn is not a configuration seen in any premolar.
  • C. CORRECT. Tooth #4 is the maxillary right SECOND premolar. It typically has a SINGLE root with a single canal — in contrast to the maxillary FIRST premolar, which usually has two roots and two canals — and TWO pulp horns, buccal and palatal, corresponding to its two cusps. The buccal horn is the more prominent, which is exactly what matters when a buccal cusp fractures.
  • D. Two roots and two pulp horns describes the maxillary FIRST premolar (#5 and #12), the premolar most commonly bifurcated. Second premolars are usually single-rooted.

Note: Carry the pulp-horn count into every deep preparation: it tells you where the pulp is closest to the surface. Maxillary first premolar — two roots, two canals, two horns. Maxillary second premolar — one root, usually one canal, two horns. Mandibular first premolar — one root, one canal, a large buccal horn and a very small lingual one. Mandibular second premolar — one root, one canal, two or three horns depending on the cusp form.

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