Paul J. Vankevich, assistant professor of general dentistry at the Tufts School of Dental Medicine, responds:

It depends! The choice of toothbrush is best determined by individual considerations, including dental health status, special needs and cost.

The purpose of tooth brushing is to remove the soft plaque from the teeth and gums and to promote soft tissue circulation. Dental plaque is the cause of the two most important oral and dental diseases, dental caries-tooth decay-and inflammatory periodontal disease, such as gingivitis and periodontitis. Dental plaque cannot be totally eliminated. The goal of brushing and flossing is to reduce the daily accumulation. 

A 2003 Cochrane Oral Health Group study concluded that powered toothbrushes with rotational-oscillation action result in a modest reduction in plaque and gingivitis (7 and 17 percent, respectively) compared with manual toothbrushes. But when properly used, manual and powered brushes can be equally effective.
Ideally, people should manually brush their teeth for 2 to 3 minutes, twice each day. The typical American, however, brushes for only 45 to 70 seconds, twice daily.

Manual toothbrushes are available in different shapes and sizes, marketed for specific patient needs and desires. Manual or powered (motorized electric or sonic) brushes have a variety of bristle and handle designs to accommodate individual needs.
The choice of a toothbrush should be one that is effective, easy to use and non-destructive-that means using a soft bristle, because overzealous tooth brushing is potentially damaging.

A number of other factors come into play in deciding which method of brushing is most effective for you. They include health status,; manual dexterity and the ability to learn proper brushing techniques,; type of plaque; and cost. Manual toothbrushes cost $1 to $3, and should be replaced every three months; a powered toothbrush costs $60 to $120. Given these variables, ask your dentist what kind of toothbrush is right for you.

Brushing alone, though, does little to help with plaque control between the teeth, so daily flossing is necessary and recommended.
Whatever the choice of toothbrush, the user will do well to follow the adage: you only need to brush those teeth that you wish to keep, and you only need to brush them on the days of the week that end with the letter "y."