Fluoride-containing materials and the prevention of demineralization during orthodontic treatment - which research method should we now use?

The effectiveness of fluoride in reducing the incidence of dental caries has been known for many years,1 but with time cariologists have changed their understanding of how fluoride works. There is now general agreement that the main mechanism of action is not the result of a systemic effect, ie, by changing the enamel structure to form less-soluble crystals as was originally thought, but as the result of a local effect, ie, by changing the balance of the process toward remineralization.2 This occurs at fluoride levels as low as 0.01 ppm.3 The critical pH for hydroxyapatite (the pH at which it starts to dissolve and hence is lost) is 5.5; however, between pH 4.5 and 5.5 saliva and plaque fluids are still supersaturated with regard to fluor apatite. This means that fluor apatite will tend to precipitate, preventing the loss of mineral ions. Another important compound formed during topical fluoride treatment is calcium fluoride (CaF2), which also acts as an important reservoir of fluoride and has an important cariostatic effect.4

These findings have been discovered predominantly through work conducted in laboratories. How should we apply these findings to determine the effectiveness of the fluoride-containing materials that are developed to prevent demineralization in orthodontic patients today? Should we be undertaking laboratory-based research or clinically based research?

A search by hand of all articles published in 4 orthodontic journals (American Journal of Orthodontics Dentofacial Orthopedics, The Angle Orthodontist, European Journal of Orthodontics, and the Journal of Orthodontics) during the last 2 years (January 2008 to November 2009) found 4 laboratory studies examining the effect of fluoride-containing materials on demineralization around orthodontic brackets and only one clinical study. Do we have this balance right, or is it time to reevaluate how we conduct research in this area?

The relative advantages and disadvantages of investigating the effects of fluoride on the demineralization process in the laboratory compared with investigations carried out in a patient or volunteer have been debated by cariologists for many years.5 I will briefly outline these.