Fluoride in enamel lining pits and fissures of the occlusal groove-fossa system in human molar teeth

The fluoride (F) distribution in enamel lining the occlusal fissures of hum an molars and premolars is difficult to investigate by normal microsampling techniques, yet this information is of importance as fissures are particul arly susceptible to caries. We have used the proton probe to map the distri bution of F and Ca in sections of 17 molar teeth collected from Danish and New Zealand populations. The caries status of the sectioned fissure was det ermined by microradiography or visually after drying. The probe scans were graphed as density images, surface plots and topographical plots. Sound ena mel bordering grooves and fissures showed a high-F surface layer, in 1 samp le approximately 60 mu m wide near the fissure bottom but gradually widenin g to double this width near the fissure opening, and up to 200 mu m wide in grooves, while underlying enamel had a low and almost constant F level. In this respect fissure and groove enamel resembled smooth surface enamel. Th e F concentration fluctuated along the surface layer, reaching maximum valu es ranging from 1,800 to 4,200 ppm in 5 non-carious fissures. Incipient car ies in fissure enamel usually but not always resulted in an increase in F i n the outer layer, the F maximum values in 5 such samples ranging from 1,90 0 to 7,200 ppm. F maximum values in outer enamel were higher in 7 samples s howing advanced caries, 2,700-10,000 ppm. The lesion subsurface body usuall y showed normal F values, as did carious dentine in the advanced lesions. T he variable characteristics of the outer layer in sound fissure enamel are likely to be the result of a developmental process rather than environmenta l influences. The fact that we normally failed to find increased F concentr ations in subsurface carious fissure enamel or in underlying carious dentin e suggests that F does not diffuse into the deep part of fissure lesions, a nd probably has minimal effect on slowing the progress of such lesions, a s uggestion in accord with clinical findings on the F effect on fissure carie s.