Determination of mineral concentration in dental enamel from X-ray attenuation measurements

The mineral content of dental enamel is commonly measured by X-ray attenuat ion experiments. Most studies have used contact microradiography in which i ntensities are measured with photographic film which is convenient and give s high spatial resolution. However photon counting intensity measurements a re to be preferred in many experiments (longitudinal and scanning microradi ography, and microtomography), as illustrated here, because they have a lar ger dynamic range and greater sensitivity to small intensity changes. Addit ionally, the detector and specimen are well separated which allows the pseu docontinuous study of de- and remineralization. The mineral content is ofte n quoted as 95 wt% or 87 vol% hydroxyapatite for permanent human enamel. Th is determination from attenuation experiments requires accurate values of e lemental mass attenuation coefficients and a number of assumptions. The eff ects of possible choices of these are considered and it is shown that the m ost important is the density of enamel mineral used in conversion of wt% to vol%, If the density is taken as 2.99 g cm(-3) as recently suggested (J.C. Elliott, Dental Enamel, Ciba Foundation Symposium 285, Wiley, Chichester, pp, 54-72, 1997), instead of 3.15 g cm(-3) as for hydroxyapatite, the calcu lated vol% is similar to 93 instead of similar to 87.