Micromorphology of zinc fluoride-induced reaction products on ground human enamel

Zinc in combination with hexetidine has been shown to be an effective chemical antiplaque agent clinically and in the laboratory. The effects of zinc fluoride on ground human enamel were studied by SEM and the sizes and numbers of the resulting globular structures measured from photomicrographs. Prepared enamel specimens were immersed in zinc fluoride solutions containing 250 and 750 ppm F- at pH 6 and 4 for 4 min. The specimens were examined as such or after washing in water for 5 min, 60 min or 24 h and the globuli categorized as larger or smaller than 0.5 um. The sizes and numbers of the globuli on the enamel were pH and concentration dependent. At pH 6, the two solutions tested produced few small globuli on enamel which were removed after 5 min (250 ppm F-) and after 60 min (750 ppm F-) in water. At pH 4, markedly more globuli were present, particularly with the 750 ppm F- solution. Large and small globuli were present after the 250 ppm F- treatment with most being removed between 5 and 60 min in water. After the 750 ppm F- treatment only small globuli were found on enamel and were removed between 60 min and 24 h of water washing. Zinc fluoride-induced globuli were generally smaller than those induced by sodium fluoride at the same pH values and fluoride concentrations.