Restorative & Materials · patient case question
The configuration factor (C-factor) refers to what?
Patient case: Polymerisation stress, irrigation and occlusal guidance
Scenario: Three items.
Show answer and explanation
Correct answer: A. The ratio of bonded to unbonded surfaces in a cavity preparation
- A. Correct. C-factor is bonded surfaces divided by unbonded (free) surfaces. Unbonded surfaces let the composite flow during polymerisation and relieve shrinkage stress; the fewer of them, the higher the stress at the adhesive interface.
- B. Depth-to-width relationships influence cavity design and stress distribution but are not what C-factor describes.
- C. The enamel-to-dentine ratio affects bond strength and marginal seal but is a different concept.
- D. Filler loading determines strength, wear resistance and shrinkage magnitude, again separate from the C-factor.
Note: A Class I preparation has five bonded walls to one free surface — C-factor 5, the worst case. This is the argument for incremental placement and for a flowable stress-breaking layer.
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