Table 2. Mass density variation in dentine.

sample	mass density [g/cm3]	distance [mm]
E	1.77 ± 0.02–2.06 ± 0.03	2.0
G	1.79 ± 0.02–2.12 ± 0.03	1.8
N	1.93 ± 0.02–2.10 ± 0.03	1.0
R	1.95 ± 0.02–2.08 ± 0.03	1.0
S	1.83 ± 0.03–2.08 ± 0.04	1.3
U	1.80 ± 0.02–1.99 ± 0.03	1.0

Values are calculated for small VOIs at different heights of the samples. The error takes into account (i) the standard deviation of the gray levels in the VOI and (ii) the reading error in the inter-grating distance estimated to be 0.5 cm. The last column gives the distance over which the density change appears.