In humans, there are a total of 32 teeth. These include 8 incisors, 4 canines, 8 premolars, and 12 molars. However, as we grow older, it is common for people to lose some of their teeth due to various reasons such as decay, injury, or disease. When teeth are lost, they can be replaced with artificial teeth through dental procedures.

The correct answer to the question is option 4, which states that 16 teeth are replaced in humans. This suggests that the person asking the question is referring to the number of teeth that can potentially be replaced with artificial ones. It is possible to replace any number of teeth depending on the individual`s needs and dental health.