If you're tempted to pick up one of those tooth-whitening products at the drugstore or dentist's office, rest assured: a new review of existing research suggests there's a good chance they're effective.
"All the products seem to work," said Dr. Hana Hasson, clinical associate professor at the University of Michigan and lead author of the review. "They were dependable in terms of effects and safety."
But Hasson and colleagues don't consider the studies in favor of the products to be rock-solid, and they couldn't find evidence supporting anything other than short-term use.
Tooth-whitening products started to become popular in the 1990s, and their appeal has grown mightily over the past decade. Now, store shelves are filled with tooth-whitening products, all claiming to brighten smiles.
The products bleach the teeth with chemicals — instead of cleaning them with abrasives — and are designed to be used only for a couple weeks at a time.
In the new review, Hasson and colleagues tried to assess the state of research into tooth-whitening products that are designed to be used in the home. Tooth-whitening toothpastes weren't included in this review.
The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews like this one draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The review authors looked at 416 studies and chose 25 that they thought were of the highest quality. Then they analyzed the findings of those studies.
All 25 studies reviewed were funded or conducted by manufacturers of tooth-whitening products, and all measured their effectiveness after two weeks. Only 13 examined effectiveness after three weeks, and just six after one month or longer.
The studies looked at whitening strips, trays filled with gel that are placed over the teeth, and paint-on films. All were available over the counter or by prescription.
While the review authors weren't impressed with the quality of the studies — most were deemed to have a "high" risk of bias — they did find plenty of evidence that the products actually whiten teeth.
"They all work, no matter what type or how they're applied," Hasson said. However, products with lower concentrations of active ingredients — such as hydrogen peroxide or carbamide peroxide — took longer to work.
In the studies that analyzed side effects, some patients reported mild-to-moderate tooth sensitivity and irritation to the gums. Whitening strips and products with high concentrations of hydrogen peroxide were most likely to cause tooth sensitivity.
The review authors said there's a need for independent studies that compare tooth-whitening products to one another. The authors also called for studies into the effects of using the products for more than six months.
"Most of these products say use them for two weeks and that's it. But we know that people are using them a lot more than that," said Clifford Whall, a scientist at the American Dental Association who's familiar with the findings of the review. "I've heard reports of some people using them every Friday night to get ready for the weekend."
Whall said the Cochrane review is "very reasonable," but he cautioned that many products probably weren't included because only a small number of studies were deemed worthy of review. "We don't know anything about those other products," he said. "We don't know if they are safe or effective."
The ADA has given its seal of acceptance seal to only two tooth-whitening products other than toothpaste — Colgate Platinum Daytime Professional Whitening System and Opalescence Whitening Gel. Both are available directly from dentists.
Whall, director of the ADA Acceptance Program, said all the products went through a rigorous review, including an analysis of unpublished studies if available. The manufacturers paid a submission fee to the ADA and must pay an annual fee to continue using the seal.
So what is the general message for dental patients who want to use tooth-whitening products? "You could have mild to moderate tooth sensitivity and (gum) tissue irritation, and as far as we know, there are no long-term studies on the effects and harms of these products," Hasson said.
On the other hand, "They all work, and it's their choice."