**Core Concept**
In composite resin restoration, the oxygen inhibition layer refers to the zone of inhibited polymerization caused by oxygen diffusion from the air, which prevents the curing of the resin at the surface. This layer limits the depth of cure and affects the strength and longevity of the restoration.

**Why the Correct Answer is Right**
Oxygen inhibits the polymerization of composite resins during curing, forming a diffusion barrier. The thickness of this inhibition layer is typically in the range of **50–500 micrometers**, depending on the type of light-curing system and the composite formulation. This range is established through clinical and experimental studies using oxygen diffusion models and depth-of-cure testing. The inhibition layer is most significant in direct composites where surface exposure to air is high.

**Why Each Wrong Option is Incorrect**
Option A: 1–50 micrometer – This range is too shallow and does not reflect the actual depth of oxygen diffusion in clinical settings.
Option B: 15–150 micrometer – This range underestimates the inhibition layer; it is too narrow and not supported by depth-of-cure data.
Option D: 1000–2000 micrometer – This is excessively large and contradicts known diffusion kinetics; oxygen cannot penetrate that deep in a short curing time.

**Clinical Pearl / High-Yield Fact**
Always use a **high-intensity LED light** and ensure **adequate curing time** to minimize the oxygen inhibition layer. In deep cavities, consider using **dual-cured composites** or **curing with a dual-phase light** to improve depth of cure.

✓ Correct Answer: C. 50-500 micrometer