Formation and structure of dentine in the rat incisor after chronic exposure to sodium fluoride

Weanling rats were chronically exposed to sodium fluoride by feeding them for eight weeks with a standard powdered diet incorporating sodium fluoride at 0.025%, 0.05% and 0.1% by weight. After eight weeks blood was removed by cardiac puncture and the levels of plasma calcium and phosphate determined. The incisor teeth were removed and their structure examined in the scanning electron microscope (SEM) using backscattered electron imaging to determine the relative concentration and distribution of the mineral phase in the dentine. There was no significant alteration to the normal serum calcium and phosphate levels. Small scattered interglobular spaces were seen in the incisor dentine of rats consuming the 0.025% sodium fluoride diet. The principle feature with the 0.05% diet were marked striations in the circumpulpal dentine but with the 0.1% diet there was severe disruption of dentine structure with continuous bands of interglobular spaces. These spaces were larger labially than lingually reflecting differences in the size and shape of calcospherites. The distribution of interglobular dentine would suggest that its formation takes time to establish.