Final answer:
An increase in average income usually leads to a rise in demand for normal goods and services, such as preventative dental visits, because they're seen as desirable with increased financial power. This is represented by a rightward shift in the demand curve for these goods or services.
Step-by-step explanation:
When average income increases, there is a tendency for demand for most goods and services to increase as well. This economic phenomenon is particularly evident with goods such as luxury cars, European vacations, and fine jewelry, but also applies to services like preventative dental visits. These goods and services are known as normal goods, meaning that as income rises, the demand for these goods also rises. This pattern, however, is not universal as some goods, known as inferior goods, experience a reduction in demand as income increases.
For example, as incomes rise, demand for generic-brand groceries typically decreases while demand for name-brand groceries goes up. Similar trends are observed with choices between used cars versus new cars and renting an apartment versus buying a home. In the case of preventative dental visits, the increase in income would generally result in a rightward shift of the demand curve, indicating an increased quantity demanded at every price point, reflecting that more people are likely to invest in their dental health.