Restorative & Materials · patient case question
The configuration factor (C-factor) of a cavity preparation refers to:
Patient case: Erosion in a High-Acid Diet
demo: 27-year-old female
chief: “My back teeth feel notched and everything is sensitive.”
history: Consumes 5–7 whole lemons daily. Reports nocturnal bruxism. No reflux, no purging behavior.
meds: None
findings: Cupped, smooth, glossy defects on the occlusal surfaces of the posterior teeth with amalgam restorations standing proud of the surrounding enamel. Generalized dentin hypersensitivity.
Show answer and explanation
Correct answer: B. The ratio of bonded to unbonded surfaces — a higher ratio produces greater polymerization shrinkage stress
- A. Filler loading affects shrinkage magnitude but is a material property, not the C-factor.
- B. Correct. C-factor is bonded surfaces divided by unbonded (free) surfaces. Fewer free surfaces means less opportunity for the composite to flow during curing, so shrinkage stress concentrates at the bond — which is why a Class I preparation has the highest C-factor and a Class IV the lowest.
- C. The enamel-to-dentin ratio affects bond quality but is a different concept.
- D. Depth-to-width ratio describes preparation geometry generally, not the configuration factor.
Note: The source wording for this item was garbled. The definition above is the accepted one; incremental layering and flowable liners are the standard means of reducing C-factor stress.
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