Dental caries is a prevalent condition affecting children in particular. Recent reductions in disease levels have been observed, but the issue still poses a large burden of disease and financial cost to the nation. Preventive treatment is required to reduce pain, suffering, loss of functional dentition and treatment cost and for these reasons should be a priority for dental services.

For many years fluoride preparations have been known to prevent dental decay, and several high strength topical preparations are available for this purpose. The most commonly used in the United Kingdom is fluoride varnish, a 22,600ppmF- preparation applied at least twice yearly to help prevent decay.1 A recent Cochrane review indicated that following treatment with fluoride varnish the prevented fraction for primary teeth was 37% (95% CI; 24% to 51%) and 43% (95% CI; 30% to 57%) for permanent teeth.2 Despite its efficacy, fluoride varnish is expensive, technique sensitive and requires multiple applications per year; therefore alternative preparations that provide further benefits may be of interest.

Several silver based fluoride preparations are in development and are showing promising results, of these Silver Diamine Fluoride (SDF) is the most widely tested and seems to provide good caries protection with a once yearly application at low cost. It is not without its downfalls however. When caries lesions arrest under SDF they create a dark stain which is unsightly.3 An alternative silver based preparation, Nano-Silver Fluoride (NSF), has been developed to combat this problem and is tested in the paper reviewed here.

The authors of this paper aimed to show that NSF was effective at arresting caries in children following a once yearly application. They did this by designing a randomised control trial which tested the efficacy of this preparation against a control (water). The approach to answering the primary research question was methodical and thorough with many key points from a RCT covered, this included accounting for cases lost to follow-up and sample size calculation.

Attempts were made to blind all participants to the treatment and randomise children to treatment arms. The explanation of the process of randomisation in the paper is vague and confusing. It was unclear if the randomisation was based on the teeth or patient level and how the sealed envelopes they describe were used to aid this process. Blinding was achieved for some participants in the study; patients, their parents and the final examiner were all effectively blinded for the trial. The dentist administering the treatment however would not be blind to treatment as the treatments were different. A greater volume of NSF was used compared to water (two drops against one drop), and the NSF is described as having a ‘reddish’ colour, therefore it would be apparent to an operator that it was different from the control, water. There is no mention of any difference in taste or smell between the NSF and water but this could be another factor in blinding. Losses were well documented but not explained in any detail. Knowledge of whether losses were exfoliated or extracted would have been relevant.

These differences in the control and intervention create some bias in the findings as we do not know how this might have affected the operator or their actions. Further confounding was introduced when all children were given oral hygiene instruction and tooth brushing packs, which included fluoride toothpaste, at the same time as the teeth were treated. Toothbrushing may contribute to the arrest of carious lesions and therefore the effect of the treatment may be overstated in this paper.

The authors provide results for arrested lesions at seven days, five months and one year. The most important of these are the one year results as it is intended to be a once yearly application. At this time point 66.7% of lesions were arrested compared to 34.7% in the control group; a preventive fraction of 50% and number needed to treat of 3.12.

The authors also provide logistic regression models to account for differences between the groups, however no significant additional information is discovered from this.

This is a good preliminary study of a new dental preparation but the use of a control (water) that is known to have no anti-cariogenic effect does raise ethical issues. For although all children participating in the trial were supplied with fluoridated toothpaste, it would have been interesting to have compared the NSF against another topical fluoride preparation.

In conclusion, despite some ethical and methodological concerns, this study appears to show that NSF may provide some benefit when considering prevention of caries, especially in deprived communities or non-clinical settings, due to its cost, preparation and application methods. There are some lingering concerns as the authors do not suggest adequate safety information regarding this preparation or the potential toxicity levels for children, but it provides a basis for future research.