Fluoride and enamel permeability in vivo

Objectives:

The study evaluated in vivo the effects of fluoride application on enamel permeability.

Methods:

Twelve permanent sound upper central incisors from six subjects aged 25–40 yr were selected. Each tooth was brushed with a prophylactic brush and air dried for 10 s. The method used has been previously described (Bertacci et al., Eur J Oral Sci 2007).

First impressions of buccal enamel of two central incisors for each subjects were made using polyvinylsiloxane (Affinis ligth body). Oral-B Fluorinse® (Procter & Gamble) was applied for 2 min., then the right tooth was brushed and the left tooth was only washed and air dried before second impressions. Third impression was made after 1 h.

After 5 min setting, each impression was removed and casted in polyether (Permadyne Garant; 3M ESPE,). Samples were gold-sputtered and inspected by scanning electron microscope.

Results:

First replica showed presence of droplets on surface that represent water outflow from enamel. The second replica of left tooth (not brushed group) revealed a deposition of globular aggregates (well recognized as CaF2 like), but right tooth (brushed group) didn't show any droplets or globular aggregates. The same results were observed in the left teeth brushed after 1h. On the contrary, the right teeth impressed after 1h (brushed after fluoride treatment) showed again droplets. Fluoride reduced enamel permeability and produced deposition of globular aggregates. Mechanical removal of aggregates resulted in a temporary absence of permeability and later , just after 1 h., changed back to the previous permeability. Presence of calcium fluoride like deposits still maintained low permeability after 1 h.

Conclusions:

The preventing action of fluoride on caries could be ascribed to the decreasing permeability of enamel. CaF2 like-globules are indirectly involved in protecting during time.