[Calcium fluoride or not? That is the question!]

The relative cariostatic effect of fluoride as fluorapatite, calcium fluoride-like material, loosely bound fluoride or KOH-soluble fluoride is debated. The present study was carried out to investigate this further in an intraoral caries model. Pair of premolars extracted for orthodontic reasons were used. Enamel from one tooth of each pair was used as controls (untreated). Two slabs were cut from the enamel of the other contralateral premolar. These slabs were treated with 2% NaF for 24 h. One slab was then treated with 1 mol/L KOH for 24 h to remove all loosely bound fluoride. The slabs treated with 2% NaF and then 1 mol/L KOH would contain the KOH-insoluble fluoride. Those treated with only 2% NaF would, in addition, contain KOH-soluble fluoride. Each slab, control, KOH-insoluble F and KOH-soluble and insoluble F, was mounted on different upper removable appliances. The slabs were covered with orthodontic banding material, allowing space for plaque accumulation. Five individuals wore the appliances in 3 separate 4-week periods. The slabs were analyzed by quantitative microradiography. The average mineral loss (delta Z) was 1680 +/- 1000 vol% z microns in the control teeth, 620 +/- 76 vol% . microns in the KOH-soluble and insoluble F teeth and 2167 +/- 1278 vol% . microns in the KOH-insoluble F teeth. The average lesion depths were 90 +/- 41 microns in the control teeth, 35.3 +/- 5.5 microns in the KOH-soluble F teeth and 88 +/- 35 microns in the KOH-insoluble F teeth. It was concluded that only KOH-soluble fluoride reduced mineral loss and lesion depths significantly compared with the untreated teeth.