U.S. consumers spend nearly $4 billion annually on products to keep their pearly whites as bright as Julia Roberts's. According to Mintel, a market research firm, power toothbrushes accounted for $350 million in 2006. Procter & Gamble's Oral-B brand -- the category leader with more than 40% market share -- bet it could grow the market.

During testing at the company's robot center in Kronberg, Germany, Oral-B's flagship power toothbrush, Triumph, achieved "up to 100% plaque removal," says Alex Hilscher, section head of global R&D for oral care. But there was a problem: People don't brush for as long, or as evenly, as a robot. (Dentists recommend brushing for two minutes.) People also often push too hard, which can lead to gum recession. Could a high-tech toothbrush encourage better habits?

Oral-B designers drew inspiration from "smart" products in other markets, such as GPS devices and Adidas running shoes that adjust their cushioning based on the terrain. They began dreaming of an electronic display, wirelessly linked to the toothbrush, that could direct users how to brush.

At first, the designers conceived a display that would instruct users to move from tooth to tooth. "We learned from consumer testing that this much information is overwhelming," Hilscher says. The next iteration simply divided the mouth into four quadrants, visually cueing users every 30 seconds to switch sectors.

The designers tried using infrared technology on its prototypes (rear). "As a light beam, it needs a visible connection," Hilscher says. "You needed lenses on the handle and display. But if people didn't clean them well, you had a problem." The next version, using 2.4-GHz radio frequency (like microwaves and cordless phones), was more effective. Data is processed in the toothbrush and transmitted to the display. If users walk out of range, the display automatically updates how long they’ve been brushing upon their return.

Dentists recommend a new toothbrush every three months. But most people don't keep track. Designers added an integrated electronic sensor with a counter that ticks down every 15 seconds of use. "It's like a service indicator in the car," Hilscher says. When it hits zero, it sends a signal to the display: time for a new brush.

The handle contains a springloaded force sensor to prevent overbrushing by measuring if people are applying the right amount of pressure. When users apply a load greater than two-thirds of a pound, it triggers a red hazard light on the display.

Brush for two minutes, and you get a reward: a smiley face. Brush for an extra 30 seconds and you get more -- a randomly selected supersmiley. The kid-friendly feature has also tested well with adults.

Triumph With Smart Guide debuted in stores in September. All the technology doesn't come cheap -- the unit retails for $149.99. P&G made a major presentation at the annual ADA convention, as part of the launch, since dentist recommendations are its best marketing. Oral-B says early sales are better than expected.