[Bio-metabolic changes produced by 2 commercial fluoride-containing compounds on human keratinocytes]

Although fluoride has been used for decades either systemically or topically to prevent dental caries, the cellular and molecular mechanisms underlying its action are poorly understood.

An in vitro study of the human keratinocyte cell line NCTC 2544 was conducted in the presence of two different fluoride-containing commercial compounds (Zymafluor and Elmex) to investigate their toxicity threshold and the sequence of events involved in fluoride ion toxicity in this cell population. The toxicity threshold was determined by incubating cells with rising concentrations of Zymafluor and Elmex for 20 h. The study of the sequence of events involved in ion toxicity was performed through a time-effect study by exposing cells to 4 mM fluoride ions and testing them at 2, 6, and 20 h. Cell viability and ultrastructural parameters were assessed: degree of confluence, semiquantitative assessment of dead cells and debris in the supernatant, and morphology.

Ultrastructural morphological analysis showed different cell behaviours with the two compounds; moreover, their toxic effect appeared to be both concentration- and time-dependent.

These data underline the susceptibility of the intracellular communication system to fluoride and show that exceeding the therapeutic dose of fluoride involves substantial risk of toxicity.