**Core Concept**
Classical conditioning is a learning process in which a neutral stimulus becomes associated with an unconditioned stimulus to elicit an unconditioned response. This concept was first introduced by Ivan Pavlov in his experiments on salivary response in dogs.

**Why the Correct Answer is Right**
In this scenario, the child's unpleasant experience of extraction (unconditioned stimulus) is associated with the dentist (neutral stimulus). This leads to an unconditioned response of fear and anxiety. Over time, the dentist becomes a conditioned stimulus that elicits the conditioned response of fear, even before any actual painful procedure. This phenomenon is a classic example of classical conditioning, as described by Pavlov in 1927.

**Why Each Wrong Option is Incorrect**
**Option A:** Operant conditioning by Skinner (1938) is incorrect because it involves learning through consequences, such as rewards or punishments, rather than through associations between stimuli.

**Option B:** Classical conditioning by Pavlov (1972) is incorrect because Pavlov's work on classical conditioning was established much earlier, in 1927, and his theory did not evolve significantly by 1972.

**Option D:** Operant conditioning by Skinner (1952) is incorrect because, although Skinner's work on operant conditioning began in the 1930s, his seminal book "Science and Human Behavior" was published in 1953, not 1952.

**Clinical Pearl / High-Yield Fact**
Pavlov's work on classical conditioning has far-reaching implications for understanding human behavior, including dental phobias. Recognizing the associative nature of fear responses can help dentists and healthcare professionals develop more effective strategies for managing patient anxiety.

**✓ Correct Answer: C. Classical conditioning by Pavlov (1927)**