The results, published in The Cochrane Library, state that "tongue scrapers or cleaners are slightly more effective than toothbrushes as a means of controlling halitosis (bad breath) in adults."
However, the evidence was "weak and unreliable" and relief from bad breath "appeared to be very short lived," write the review's authors. They included Trent Outhouse, DDS, MS, ABGD, a lieutenant commander in the U.S. Navy's Dental Corps serving in Bahrain.
Battling Bad Breath
Currently, there is "controversy" and "no standard and accepted protocols" for treating bad breath, the researchers write. Besides mechanical methods -- brushing or scraping the tongue -- strategies include using chemicals that attempt to destroy odor-forming bacteria and/or mask bad breath.
Outhouse and colleagues searched for high-quality scientific studies in which people with bad breath were randomly assigned to use tongue scrapers, toothbrushes, or mouthwashes to fight bad breath.
The researchers only found two short-term trials, neither of which included mouthwashes. Both trials excluded smokers and people with illnesses that might affect their breath's smell.
The studies both used machines to measure participants' levels of volatile sulfur compounds (VSCs), which are linked to bad breath. That way, results weren't based on personal opinions about breath quality.
Studying Bad Breath
One of the studies was done in Germany. It included 30 adults with high levels of volatile sulfur compounds.
Participants were assigned to use one of three devices to brush their tongues: a regular toothbrush, tongue scraper, or brush-scraper combination. Once a week for four weeks, participants had their VSC levels checked before and after a tongue-cleaning session.
VSC levels dropped 42% with the brush-scraper, 40% with the scraper, and 33% with the brush. But those reductions didn't last more than 30 minutes, according to the review.
The other study included 10 adults at Brazil's University of Sao Paolo. Participants cleaned their tongues with a tongue scraper one week and a soft-bristle toothbrush another week, taking a two-day break between treatments.
Before-and-after VSC tests showed that average VSC levels dropped 75% with the tongue scraper, compared with 45% with the toothbrush.
Six participants in the Brazilian study complained of nausea and one of tongue trauma while using the toothbrush. All were "receptive to the tongue scraper," the researchers write.