Answer: higher-order conditioning
Almost 60% of the people have anxiety or afraid of going to the dentist. About 5-10% are said to have dental phobia.
What Denny is experiencing is a Higher-order conditioning.
Higher-order conditioning is a form of learning in which a stimulus (fear of a dentist ) is made meaningful. Because of this fear, Denny becomes anxious even with the smell of the dentist’s office. This stimulus in turn creates muscle tension and anxiety even before the dentist can attend to him.