Formation of Brushite, Monetite and Whitlockite during Equilibration of Human Enamel with Acid Solutions at37C

Abstract

The residues of 5 samples of powdered human enamel, each subjected to 5 sequential equilibrations at 37°C with either 17 or 4 mmol/l phosphoric acid, were examined microscopically. With 17 mmol/l acid, both brushite and monetite were found after 1 equilibration but, after further equilibrations, brushite was no longer present and the abundance of monetite crystals increased. Formation of monetite probably contributed to the lower metastability of this system compared to similar low-pH systems at 25 °C, where monetite does not form. Neither brushite nor monetite were present after equilibration with 4 mmol/l acid. Whitlockite was identified by transmission electron microscopy and electron diffraction in all residues. In the 4 mmol/l systems, the ionic activity product (IMwh) for magnesium whitlockite, Ca₉Mg(HPO₄)(PO₄)₆, became constant after 1–3 equilibrations, at a mean value of 3.6 ( ± 0.51 SE)·10^––105, which may reflect saturation with respect to this solid. For the 17 mmol/l systems, higher values of IMWH, and supersaturation with respect to monetite, were interpreted as evidence for persistent metastability due to slow crystal growth of whitlockite and monetite. It is concluded that neither brushite nor monetite are likely to form within carious lesions, but the results are consistent with the known association of whitlockite with caries.

In situ Fluoride Response of Caries Lesions with Different Mineral Distributions at Baseline

“…Although there is still considerable debate in the literature, brushite (or dicalcium phosphate dihydrate -CaHPO 4 ! 2H 2 O) [Moreno and Zahradnik, 1974], mo netite (CaHPO 4 ) [Featherstone et al, 1978] and Mg-substituted whitlockite [WHM -Ca 9 Mg(HPO 4 )(PO 4 ) 6 ] [Shellis et al, 1997] have all been reported. This is not surprising, as brushite and monetite are more stable than HA under acidic conditions [Brown, 1973]; whereas the mineral phase associated with Mg in (sound) enamel was proposed to be WHM [Driessens and Verbeeck, 1982].…”

Apparent solubility distributions of hydroxyapatite and enamel apatite

“…To determine the saturation status of each solution, pI for a given solid was compared with the negative logarithm of the relevant solubility product (pK). The following pK values were used: octacalcium phosphate (OCP), Ca 4 H(PO 4 ) 4 ·2H 2 O, 48.7 [28]; brushite (BR), CaHPO 4 ·2H 2 O, 6.64 [29]; magnesium whitlockite (MWH), Ca 9 Mg(HPO 4 )(PO 4 ) 6 , 104.4 [30,31]; fluorapatite (FA), Ca 5 (PO 4 ) 3 F, 60.5 [7]; dolomite, CaMgCO 3 , 17.47 [32].…”

Formation of Caries-Like Lesions in vitro on the Root Surfaces of Human Teeth in Solutions Simulating Plaque Fluid

“…In experiments 3 and 4, the magnesium-containing solutions with pI HA ^ 58.6 had pI values for magnesium whitlockite of 99.44-103.21 and so would be supersaturated with respect to this solid according to the data of Verbeeck and de Bruyne [1989] and Shellis et al [1997].…”