DENTISTS LIKE Dr. Lana Rozenberg are overly familiar with two eternal fibs: that their clients floss regularly, and that they brush their teeth for at least two minutes twice a day. “Most people don’t brush their teeth for two minutes,” said the Manhattan-based industry veteran. “Thirty seconds is more like it,” or under a second for each of their 32 teeth.

But what if, in those 30 seconds, a device could reach the front, back and sides of every tooth at once? That’s the proposition of new “whole mouth” toothbrushes, which rely on vibration and a preponderance of bristles packed inside a structure resembling a mouthguard to deliver an up-to-snuff scrubbing in as little as 20 seconds—10 each for top and bottom sets of teeth.

The flexible Y-Brush uses dense, nylon bristles at a variety of dentist-recommended angles to reach all sides of every tooth. $147 for a starter pack, y-brush.com

Photo: F. Martin Ramin/The Wall Street Journal

“It helps make things way faster, way easier and feels a little more guaranteed because you actually feel it on each one of your teeth,” said Kristopher Paul, a medical-transportation driver in St. Petersburg, Fla., who has bit down on a 360 Sonic Brush Pro ($70) each morning for the past year. Mr. Paul, 36, also likes the tool’s 15-minute whitening mode, which combines a blue LED light and whitening gel to fade bothersome coffee stains.

The 360 Sonic Brush for Kids uses 48,000 vibrations per minute to blast plaque with what the company claims to be one of the fastest motors on the market. $80, 360sonicbrush.net

Photo: F. Martin Ramin/The Wall Street Journal

Parents weary of waging a twice-daily war with their tots over toothbrushing also appreciate the devices. Madison, Wis., homemaker Cindy Kieler is mom to a 9-year-old with a sensory processing disorder that makes her extra-sensitive to the feeling of a brush moving around her mouth. Sick of chasing her daughter around the house with a toothbrush, Ms. Kieler tried out a Y-Brush sized for children’s mouths. Despite its forbidding bulk, it was a hit. “She can now do it herself without me, and knows it’ll be over in a few seconds,” she said. “So far, she hasn’t complained about it at all.” While pricier than a normal toothbrush, the $147 Y-Brush promises to last three months on a charge; a $36 replacement brush head should be switched in every six months.

The Myst’s silicone mouthpiece and bristles are antibacterial and more comfortable than other models we tried, but some dentists say these less-dense bristles lead to a less-effective cleaning. $60, mystoralcare.com

Photo: F. Martin Ramin/The Wall Street Journal

In our own tests, inserting such a mouthful of a toothbrush was initially uncomfortable (though one colleague who owns the Myst version raves about it), and the amount of toothpaste required seemed extreme. (Y-Brush sells a handy rubber applicator for $6 that you pop onto the top of your tube to paint an ultrathin line.) Pro: teeth that felt clean after 20 seconds. Con: the inability to scour one’s tongue.

Though Dr. Rozenberg doesn’t think you should toss your ordinary toothbrush yet—she’d like to see more studies on whole-mouth models’ efficacy and customization options to fit individual palates—she urges them on her most brushing-averse clients as a “much better than nothing” alternative. “My teenage twins are excellent candidates,” she joked. “At almost 16, they still don’t like to brush.”

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