Restorative & Materials · patient case with 2 questions
Deciding whether two teeth can be saved
Patient: Female, 59 years old
Chief Complaint: “My dentist said one of these teeth has to come out but I want to keep them.”
Background: Both teeth were root-treated and posted more than ten years ago. No systemic disease.
Findings: A posterior tooth: previous root canal treatment, a persistent periapical radiolucency, a crown-to-root ratio of approximately 2:1, minimal remaining coronal tooth structure, and no opposing tooth in that position. Tooth #9: the post appears displaced on the radiograph and the tooth is mobile; tooth #8 also carries a post but is sound and immobile.
Question 1
For the posterior tooth, which of the following is NOT a reason to extract it?
Show answer and explanation
Correct answer: A. Absence of an opposing tooth
- A. CORRECT as the exception. Having NO ANTAGONIST is not by itself a reason to remove a tooth. An unopposed tooth may over-erupt, and that is managed with monitoring, an opposing restoration, enameloplasty or orthodontic intrusion. Extracting a sound tooth because nothing bites against it is not justified — the tooth may also become an abutment later.
- B. A crown-to-root ratio of 2:1 is severely unfavourable. The ideal is 1:2 and the minimum acceptable is roughly 1:1. At 2:1 the lever arm above the bone overwhelms the support below it.
- C. Without enough sound tooth structure to give a ferrule of 1.5 to 2 mm, a crown will fail no matter how well the post is placed. This is a legitimate extraction criterion.
- D. A periapical radiolucency that persists after root canal treatment signals failure. If retreatment or apical surgery is not feasible, extraction follows.
Question 2
The radiograph shows the post in tooth #9 is displaced and the tooth is mobile. What is the most appropriate treatment for tooth #9?
Show answer and explanation
Correct answer: C. Extraction
- A. Rebuilding both teeth ignores the fact that #9 is failing structurally, and it would subject a sound tooth (#8) to unnecessary intervention.
- B. Retreatment and crown lengthening address canal and margin problems. They cannot restore a root that has fractured or a post that has displaced through it.
- C. CORRECT. A DISPLACED post with tooth MOBILITY means the post has separated from the remaining root structure — in practice this indicates a vertical root fracture or catastrophic loss of the root. Neither is restorable, and EXTRACTION is the appropriate treatment, followed by a plan for replacement. Tooth #8, which is sound and immobile, is left alone and may serve as an abutment.
- D. Recementing treats a loose crown on a sound tooth. Here the failure is at the root, not the cement interface.