Anatomy & Histology · patient case with 3 questions
Deep caries on an upper premolar
Patient: Female, 36 years old
Chief Complaint: “Cold drinks hurt on my upper right, but it stops as soon as I swallow.”
Background: Healthy, no medications.
Findings: Tooth #4 has deep occlusal caries approaching the pulp with no radiographic periapical change; it responds sharply but briefly to cold and is not tender to percussion. Tooth #7 in the same patient is non-vital with a well-circumscribed periapical radiolucency; the excised soft tissue was submitted for histopathology.
Question 1
What is the typical root and pulp horn anatomy of tooth #4?
Show answer and explanation
Correct answer: C. One root with two pulp horns
- A. Two roots is the maxillary FIRST premolar (#5 on this side), which is bifurcated buccopalatally in most cases — the classic distinction between the two maxillary premolars.
- B. Three pulp horns implies a three-cusped tooth — a mandibular second premolar of the three-cusp type, or a molar.
- C. CORRECT. Tooth #4 is the maxillary right SECOND premolar. It has a single root the large majority of the time (roughly 85 to 90 percent), usually with a single canal, and its two-cusped crown gives it TWO PULP HORNS, buccal and palatal. The buccal horn is the taller of the two.
- D. A single pulp horn belongs to a single-cusped tooth such as a canine.
Question 2
Which material is used specifically to stimulate formation of a reparative dentine bridge?
Show answer and explanation
Correct answer: B. Calcium hydroxide
- A. Glass ionomer bonds to dentine and releases fluoride, making it an excellent base or liner, but it does not induce tertiary dentine formation.
- B. CORRECT. CALCIUM HYDROXIDE has a pH near 12.5. That high alkalinity produces a superficial zone of coagulation necrosis, and the irritation of the underlying odontoblasts and pulp stem cells drives differentiation and deposition of REPARATIVE (tertiary) DENTINE — the dentine bridge. It is also strongly antibacterial for the same reason. Its weaknesses are solubility over time and low strength, so it is placed as a thin liner and covered.
- C. Zinc phosphate is a luting cement with a low initial pH that can irritate the pulp — the opposite of what is wanted here.
- D. Zinc oxide eugenol is palliative and obtundent — eugenol sedates the pulp — but it does not induce a dentine bridge and eugenol inhibits resin polymerisation.
Note: Modern practice increasingly favours calcium silicate bioceramics (MTA, Biodentine) for direct pulp capping, with better long-term seal and comparable bridge formation. Calcium hydroxide remains the keyed answer for the classic dentine-bridge question.
Question 3
The tissue from the periapical lesion at tooth #7 shows a cyst lined by stratified squamous epithelium with a dense inflammatory infiltrate in the wall. What is the diagnosis?
Show answer and explanation
Correct answer: B. Radicular (periapical) cyst
- A. The lateral periodontal cyst has a thin lining with focal nodular thickenings of glycogen-rich clear cells, occurs lateral to a VITAL tooth, and lacks inflammation.
- B. CORRECT. A non-keratinised STRATIFIED SQUAMOUS lining of variable thickness, with arcading rete ridges and a fibrous wall heavily infiltrated by chronic inflammatory cells, on a NON-VITAL tooth, is the RADICULAR CYST — the most common odontogenic cyst. It arises when the cell rests of Malassez proliferate in response to pulpal necrosis. Cholesterol clefts and Rushton bodies may also appear.
- C. The dentigerous cyst has a thin, non-inflamed lining of two to four cells attached at the cementoenamel junction of an UNERUPTED tooth. The tooth here is erupted and non-vital.
- D. The odontogenic keratocyst has a thin, uniform PARAKERATINISED lining of six to eight cells with a palisaded, hyperchromatic basal layer and a corrugated surface — and characteristically a non-inflamed wall.