The effect of fluoride on the resorption of dentine by osteoclasts in vitro.

Osteoclasts were isolated mechanically from bones of prehatch chicks and cultured on dentine for 24 or 39 h in medium without or with added sodium fluoride at concentrations of 0.15, 1, 15, or 30 mg/liter. Fixed and toluidine blue-stained specimens were examined by light microscopy and osteoclasts were counted, all cells were removed and resorption pits were counted. The dentine was then prepared for scanning electron microscopy (SEM) and pits located on a raster search using backscattered electron imaging. Stereophotogrammetric measurements were made of the depths, plan and true surface areas and volumes of pits, and the volume:area ratio and a three-dimensional form factor calculated for each. The presence or absence of a ring of demineralization around each pit was recorded. Pits with the same plan area were significantly (p less than 0.001) less deep in cultures containing 15 or 30 mg/liter NaF and the incidence of rings around pits was higher (controls 2.7%, 15 mg/liter 31.3%, 30 mg/liter NaF 39.7%). In one experiment, pits were larger in the specimen cultured with added 1 mg/liter NaF, but in a much larger series of 631 (251 in the control and 380 in the 1 mg/liter NaF cultures) pits measured, depths, volumes and volume:plan-area ratios were significantly lower (p less than 0.001), and rings round pits 2.5 times more common, in the fluoride-treated group. A complex interplay of stimulation of some cells in the culture with indirect stimulation of osteoclasts and direct inhibition of osteoclastic resorptive function may be operating at this concentration of fluoride. In vivo, therapeutic doses of sodium fluoride would be expected to act not only to increase the formation of osteoid but also to suppress osteoclastic activity.