June 25, 2012 — An acidic low-fluoride toothpaste may fight caries better than standard toothpaste formulations while also reducing the risk for fluorosis, researchers reported today at the International Association of Dental Research (IADR) 90th General Session and Exhibition in Iguacu Falls, Brazil.
A randomized clinical trial showed that children using a dentifrice containing 550 parts per million (ppm) of sodium fluoride with a pH of 4.5 had fewer caries in their teeth and less fluoride in their toenails than patients using an 1100 ppm fluoride with a pH of 7.0, said the researchers.
"For this reason, according to our results, the low-fluoride acidic dentifrice seems to be the best option for young children," one of the study's coauthors, Marília Buzalaf, DDS, PhD, professor of biochemistry and cariology at the University of São Paulo in Bauru, Brazil, told Medscape Medical News.
The debate about fluoride concentrations in toothpaste is intensifying as more fluoride has been introduced in community water supplies and mild fluorosis is diagnosed in more children. Toothpaste is a major source of fluoride in young children because they tend to swallow it.
Recommendations from professional organizations around the world vary widely for preschool children's toothpastes, with some calling for "low" concentrations (below 600 ppm) and others for "standard" concentrations (1000 - 1500 ppm).
Toothpastes with less than 600 ppm of sodium fluoride are available in many countries, including Europe, Australia, and Brazil. In other countries, fluoride toothpastes must contain a higher concentration.
Under US Food and Drug Administration regulations, sodium fluoride toothpastes in the United States must contain at least 1000 ppm.
A meta-analysis presented at the American Association for Dental Research (AADR) 2012 Annual Meeting in March showed that low-fluoride toothpastes do not reduce the risk for fluorosis but, rather, increase the risk for caries in very young children. However, those studies did not focus on acidic toothpastes.
Dr. Buzalaf and colleagues reasoned that acid could enhance the ability of fluoride to combat caries. "We believe that the main mechanism of action of acidic dentifrices is by increasing plaque fluoride concentrations," she said.
Another way in which acid might help is by acting as an etch, Clifton Carey, PhD, professor of cariology at the University of Colorado, Denver, told Medscape Medical News.
"A toothpaste of 4.5 pH is going to have a slight acid etch, which would make it so fluoride would react with the surface," he said. "Fluoride uptake is much higher than without doing that."
To test the acidic toothpaste, the researchers randomly divided children aged 2 to 4 years in a fluoridated area (0.6 - 0.8 ppm), with or without active caries lesions, into 3 groups.
Group 1, with 104 children, brushed with a toothpaste containing 1100 ppm of fluoride and a pH of 7.0. Group 2, with 107 children, brushed with a toothpaste containing 550 ppm of fluoride and a pH of 7.0. Group 3, with 104 children, used a toothpaste with 550 ppm of fluoride and a pH of 4.5.
After 12 months, the researchers measured whether the children's lesions had progressed or regressed, using the variation in lesion area. They also evaluated white spot lesions by quantitative light-induced fluorescence (QLF) in a subsample of 75 children with active caries, and they measured fluoride concentrations in the children's toenail fluoride.
The researchers could not see significant differences in caries progression by visual inspection, and QLF analysis detected no significant difference between group 1 and group 3. However, both group 1 and group 3 were significantly better than group 2 in both lesion area and changes in fluorescence.
The investigators found significantly lower toenail fluoride concentrations when children used the low-fluoride dentifrices.
"According to our results, the low-fluoride acidic dentifrice seems to be the best option for young children," Dr. Buzalaf said.
However, a high-acid toothpaste could also soften enamel, increasing the risk for erosion and abrasion, said Dr. Carey. "It's a good study," he said. "It shows the caries efficacy, irrespective of what else it did to the tooth. The question is how much erosion and abrasion took place."
Erosion and abrasion are hard to measure in a clinical trial, he acknowledged, but he suggested the investigators could have placed a sealant on some surfaces and not on others to measure how much enamel was lost.
When asked about this point, Dr. Buzalaf responded that her team has studied the acidic toothpaste's effects on abrasion, although not in a clinical trial.
She cited a study published in the November 2009 issue of the European Archives of Paediatric Dentistry in which the researchers used a machine to brush enamel blocks made from cow's teeth using dentifrices of various fluoride levels and neutral vs 4.5 pH.
They measured the surface loss by comparing the profile of the brushed surfaces to surfaces protected with adhesive tape and found no significant difference between the acid and neutral toothpastes or between the low- and standard-fluoride toothpastes.
Dr. Buzalaf and Dr. Carey have disclosed no relevant financial relationships.
International Association of Dental Research (IADR) 90th General Session and Exhibition: Abstract 160257. Presented June 23, 2012.
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