By Laird Harrison
WebMD Health News
December 28, 2016
The finding shows that practitioners have options in finding the best way to deliver the caries-fighting mineral to patients at high risk for the condition.
Although the efficacy of fluoride is well established, much remains unknown about the relative merits of various application methods.
To shed light on this question, an expert panel of the World Health Organization conducted a review of the literature with recommendations, and a team of researchers in Denmark assigned schoolchildren to either rinse with fluoride mouthwash or receive professionally applied varnish.
Both the review and the trial were published in 2016 in Community Dental Health.
Taking a comprehensive look at the ways fluoride can be delivered, the expert panel, headed by D. M. O'Mullane PhD, FFD, from the Oral Health Services Research Centre, University College Cork, Ireland, found some pros and cons to both fluoride varnish and rinses.
Dr O'Mullane and colleagues quoted a Cochrane review of 22 trials of varnish in moderate quality that found a 43% reduction in caries in permanent teeth and 37% in primary teeth of children and adolescents compared with placebo or no treatment.
Although the optimum number of applications of varnish has yet to be established, most studies reported one to four per year.
A single dose typically contains 5.65 mg of fluoride ion; this is well below the "probably toxic" dose of 5 mg/kg body weight, even if all of it is swallowed, the researchers report.
Varnish lends itself to "young or pre co-operative children," the expert panel reports. In places where water is fluoridated, its use is only recommended for people at high risk for caries. Where fluoridated water is not available, the varnish is recommended for all children and young adults, they report.
Fluoride mouth rinse can be applied either weekly in a 900 ppm concentration or once or twice daily in a 100-500 ppm concentration, the expert panel reports. Both applications are associated with a 26% reduction in caries in children, they found. There is also some evidence that rinses can prevent root caries, making them a possibility for adults.
The authors note that fluoride mouthwash is not recommended for children below the age of 6 or 7 years because children this young lack the ability to spit it out properly. For older children, however, there is "little or no danger of acute toxic reactions" for the daily-use mouthwash, they say, and even the high-concentration weekly-use mouthwash has a wide margin of safety for a 6-year-old.
The authors also point out that some concerns about alcohol have led to the advent of alcohol-free formulations of mouthwash.
Turning to other topical fluoride delivery systems, the expert panel points out that fluoride gel can be quickly applied to an entire dental arch, and in some cases, patients can apply it themselves. However, gel poses a risk for excessive ingestion of fluoride, especially in young children.
There is inadequate research to establish the efficacy of fluoride foams, silver diamine fluoride, and slow-release devices, the expert panel concludes.
To test fluoride mouthwash against varnish, M. K. Keller, PhD, DDC, from the University of Copenhagen, Denmark, and colleagues randomly assigned children aged 6 to 12 years to one or the other protocol by class unit.
The children lived in the Vollsmose district of Odense, Denmark, which the researchers describe as a "deprived multicultural suburban area."
Specially trained dental assistants applied the 5% sodium fluoride varnish to all accessible teeth surfaces of 489 children every 6 months for 2 years.
Another 472 children rinsed with fluoride mouthwash for 2 minutes once per week under supervision.
All children were encouraged to brush with fluoride toothpaste twice daily and received free comprehensive dental care at public health clinics.
After 2 years, the fluoride rinse group showed an increase of 0.41 decayed, missing, or filled surfaces in permanent teeth, going from a mean of 0.54 at baseline to 0.95 at follow-up. The varnish group showed an increase of 0.35, going from 0.56 to 0.91 decayed, missing, or filled surfaces. The difference was not statistically significant.
The rinse group went from a mean of 1.25 to 2.16 initial caries in permanent teeth, for an increase of 0.91, whereas the varnish group went from 0.92 to 1.76, for an increase of 0.84, which was also not a significant difference in change.
During the 2 years, the time used for each subject was 90 minutes in the mouthwash group and 24 minutes in the varnish group.
Previous head-to-head trials have shown that varnish has about a 10% higher preventive fraction, the researchers report. The children regularly used fluoride toothpaste under supervision, which could have obscured the difference between the varnish and the rinse, they say.
The researchers note other limitations, including cluster randomization, a single-blinded design, a large number of examiners, and inconsistent use of bitewings.
However, they also point out that the low overall incidence of caries during the trial in both groups was encouraging, given the high-risk population.
The authors have disclosed no relevant financial relationships.