Endodontics · patient case question
What is the actual function of a post in an endodontically treated tooth?
Patient case: A Premolar Missing Its Lingual Cusp
Patient: 51-year-old male
Chief Complaint: “Half the tooth broke off while I was eating.”
Background: Heavy clencher. Multiple worn restorations. Root canal treatment on this tooth was completed last week.
Medications: None
Vital Signs: BP 126/80 mmHg · HR 72 bpm · RR 16 · T 98.4°F
Findings: Maxillary right first premolar with a fractured and missing LINGUAL cusp. Remaining buccal wall is sound but thin. Access cavity present and root filled. Wear facets are present on the lingual inclines of the maxillary buccal cusps on the right side.
Show answer and explanation
Correct answer: A. To retain a core when insufficient coronal tooth structure remains
- A. CORRECT. A post is PURELY RETENTIVE. Its single job is to hold a core build-up in place when there is not enough coronal dentine to retain it on its own. If enough coronal structure remains — a common rule is four sound walls, or enough to give a 1.5–2 mm ferrule — no post is needed.
- B. This is the most persistent misconception in restorative dentistry. Posts do NOT strengthen roots. Preparing the post space REMOVES radicular dentine and measurably WEAKENS the root, which is why post-related vertical root fracture is a leading cause of loss in root-treated teeth.
- C. Load distribution comes from the FERRULE — the 1.5–2 mm circumferential band of sound tooth structure engaged by the crown — not from the post.
- D. The apical seal is provided by the root filling. Post space preparation actually threatens it — always leave at least 4–5 mm of gutta-percha apically.
Note: Ranked determinants of success in a root-treated tooth: (1) ferrule, (2) remaining coronal dentine, (3) coronal seal, (4) cuspal coverage posteriorly. The post ranks nowhere near the top.