Dreaming about teeth falling out usually means a person is going through a period of transition, experiencing a loss, or feeling insecure. Dreams about teeth often coincide with major life events or traumas.
Ancient cultures around the world assigned divine and symbolic meaning to dreams. The psychologist Sigmund Freud was the first clinician to assign meaning to dreams. After Freud published "The Interpretation of Dreams" in 1899, assigning meaning to dreams became standard practice.
According to the New York Times, some sleep researchers disagree stating that the brain clears out neural activity that interferes with proper memory and function during REM sleep. Thus, dreams are discarded neural impulses that are no longer needed.