The ideal film thickness for cementing a permanent restoration.

• A. 25 mm or less
• B. 2 cm or less
• C. 50 mm or less
• D. 1 mm or less

Answer: (A)

The idea behind this question is that the cement layer under a permanent restoring material must be extremely thin to let the restoration seat properly and create a good seal. In dental practice, the ideal film thickness is about 25 micrometers (0.025 mm), just enough to fill microscopic irregularities without creating a bulky layer. So among the given statements, the one describing a very small thickness aligns with that goal. Remember that in real life this thickness is measured in micrometers, not millimeters, but the underlying concept is that a very thin cement film is needed to ensure proper seating, margins, and esthetics. The other options imply thicker layers that would hinder seating and compromise the fit.