Identification and indexing of lattice planes through high-resolution transmission electron microscopy provided precise measurements of intertubular crystals of arrested caries in dentine compared to sound dentine. In arrested caries, mean crystal width was 310 Å (SD 44) with a range from 200 to 400 Å. Mean thickness was 86 A (SD 19.3) with a range from 57 to 130 Å. In sound dentine, mean width was not very different at 296 Å (SD 39) with a similar range from 200 to 400Å. Mean thickness was lower: 31.6 Å (SD 5.4) with a range from 24 to 41 Å. A growing process due to thickening of the crystallites was pointed out. The coexistence of whitlockite and apatite within the large crystals of intratubular dentine in arrested caries was shown through high-resolution electron microscopy and micro-electron diffraction. Two stages of arrested caries could be found at the crystal level: firstly, a precipitate of the material dissolved at the very beginning of the carious process, and secondly, remineralization of decalcified dentine by growth of residual crystals (intertubular dentine) and by a maturating process of whitlockite towards apatite (intratubular cry