Prosthodontics & Occlusion · patient case question
The impression and the resulting cast both show margin defects. What is the appropriate action?
Patient case: Restoring a broken-down tooth
demo: 45-year-old female
chief: Wants to restore a heavily broken lower molar and to improve the appearance of her upper front teeth.
history: Nothing relevant medically. She has had a crown placed on tooth 12 elsewhere.
meds: None.
findings: Tooth 30 has minimal remaining coronal structure with 0.5 mm of sound dentin above the crown margin circumferentially. An impression and a working cast from the first attempt show voids at the margin and a torn finish line. The crown on tooth 12 is markedly brighter than the adjacent very yellow natural teeth.
Show answer and explanation
Correct answer: A. Remake the impression
- A. Correct. The margin is the one part of the preparation that cannot be guessed. If it is not recorded cleanly the crown will not seat accurately, and an inaccurate margin means plaque retention, recurrent caries and periodontal inflammation for the life of the restoration. Retake the impression and address the cause, which is usually moisture control or inadequate tissue displacement.
- B. Waxing a cast invents anatomy that was never recorded. The result is a crown fitted to a fiction.
- C. Asking a technician to guess at a margin transfers a clinical error to someone with no access to the patient.
- D. Chairside adjustment cannot compensate for a margin that was never captured.
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