In usage tests, pulpal inflammatory response to composites is low to moderate after 72 hours, with ______ mm dentin.

• A. 0.25
• B. 0.5
• C. 1.0
• D. 2.0

Answer: (B)

The main concept is that the dentin remaining between a restoration and the pulp acts as a barrier that controls how much irritants from the composite reach the pulp. In usage-type tests, about half a millimeter of dentin provides enough diffusion resistance to keep the pulpal inflammatory reaction at a low to moderate level after 72 hours. Dentin thinner than that would let more irritants and heat reach the pulp, increasing inflammation, while thicker dentin would further dampen the response toward minimal inflammation. So, 0.5 mm dentin is the thickness that best matches the observed low-to-moderate response at 72 hours.