They're easier to use for people with dexterity issues.
The American Dental Association (ADA) says people who have physical conditions (such as arthritis, limited mobility in their hands or arms or manual dexterity problems) that make it difficult to use a manual toothbrush should consider using an electric toothbrush. Why? Electric toothbrushes have larger handles, which are easier to grip. Plus, their powered brushes do the cleaning for you, especially in the tricky areas that require fine motor skills to get at, such as the backs of molars and behind your upper and lower front teeth [source: ADA].