Crystallographic nature of fluoride in enameloids of fish

Abstract

X-ray diffraction studies on calcified tissues (teeth and/or scales) of fish and of shark showed that the presence of fluoride affects the crystallite size and lattice parameters of the apatite phase. An inverse correlation between F contents (ranging from 0.2 to 3.8 wt% F) and alpha-axis dimensions (9.441 to 9.375 +/- 0.003 A) exists for both synthetic and enameloid apatites and is consistent with the F-for-OH substitution in the apatite, idealized as Ca10(PO4)6(OH)2 and Ca10(PO4)6F2, for fluoride-free and maximum fluoride-substituted apatite, respectively. In synthetic systems, the incorporation of F is found to be dependent on the F concentration of the media from which the apatite formed. This dependency is also observed between F content of the dentine apatites and the F concentration of the water from which the fish can (i.e., less than 0.08 ppmF in fresh water, about 1.3 ppm in seawater). However, no such dependency was observed between the F incorporation in fish enameloid apatite and the F concentration in the water of origin. In some cases, the F incorporated in the enameloid apatite is much in excess of what can be expected from the F concentration of water. These observations suggest that in some fish, a fluoride-concentrating mechanism is operative during the formation of the enameloid but not during the formation of the dentine, and this mechanism appears to be specie-related.

Chemical Stability of Carbonate- and Fluoride-Containing Apatites

“…All the materials used in this study gave the crystallographic and spectroscopic properties o f CO3 for PO4 (coupled with Na-for-Ca) substituted apatites, namely, a contraction in the a-and expansion in the c-axes (compared to carbonate-free Ca-OH-apatites), and the characteristic C O r ' IR absorption bands [Bonel et al, 1975;LeGeros, 1965LeGeros, , 1981bLeGeros et al, , 1970LeGeros et al, , 1971LeGeros and Suga. 1980;Nelson.…”

“…, 1981aLeGeros et al, 1973;Frazier. 1967;LeGeros and Suga. 1980;Moreno et al, 1977], Such differ ences in chemical stability have also been observed in biological apatites such as bone [LeGeros et al, 1982a] and enamel [Frazier.…”

“…The unit-cell dimensions, a-and c-axes were calculated from the appropriate hkl reflections (dif fraction peaks) using Si as standard, and the 'crystal linity' was assessed as line-broadening at half height of diffraction peak, /) 1/2, of the 002 and 300 reflec tions [X/ug and Alexander, 1974], (b) Infrared absorption spectroscopic analyses were made on a Perkin-F.lmer 337 Double Grating Spectrometer, using normal slit, scanning speed of 30 min for ranges4,000-1,500, and 1,500-400 cm 1 on samples pressed on KBr disks at 12,000 psi, using sample concentrations of 0.8 mg/300 mg KBr (IR grade). IR absorption band assignments were ac cording to Herzberg [1945] and other IR studies on apatites [LeGeros et al" 1970: LeGeros andSuga. 1980;Fowler el al., 1966;A rends and Davidson.…”

“…The effects o f fluoride, F~, incorpora tion on the crystallite properties of syn thetic and biological apatites are opposite to the effects of carbonate. The incorpora tion o f F~ causes an increase in crystallite size (therefore a decrease in surface area) and decrease in strain; contraction in the a-axes but no effect on the c-axes, com pared to the properties of F-free apatites [Beevers and McIntyre, 1947;Frazier, 1967;LeGeros, 1981 a,b;LeGeros and Suga, 1980;LeGeros et al, 1973LeGeros et al, , 1982aYoung and Elliott, 1966).…”

High-resolution X-ray diffraction with no sample preparation

“…16. dimension suggests a fluorine content of 3.6 wt% based on the analysis of LeGeros & Suga (1980). The fluorine content of pure Ca 5 (PO 4 ) 3 F is 3.77 wt%.…”