Prosthodontics & Occlusion · patient case question
What is the recommended margin design for the incisal aspect of a porcelain veneer preparation?
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. A shoulder or heavy chamfer
- A. Correct. Porcelain is brittle and needs bulk to resist fracture. A shoulder or heavy chamfer of roughly 1 mm at the incisal provides that bulk and creates a definite, readable finish line for both the technician and the seating of the restoration.
- B. A knife edge leaves porcelain feathered to nothing at the point of greatest load, and it fractures.
- C. A feather edge has the same problem and additionally makes the margin impossible to locate accurately on the die.
- D. A bevel thins the porcelain at the margin and is used with metal restorations, not with ceramics.
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