<b><i>Background/Aims:</i></b> Mechanical removal of carious dentine based on perceived hardness is subjective and tends to be excessively destructive; chemo-mechanical techniques have been proposed as being more objective and conservative. The aims of the present study are to use X-ray microtomography (XMT/micro-CT) to determine the three-dimensional mineral concentration distribution in sound, carious and excavated dentine using hand excavation (HE) and a chemo-mechanical, Carisolv (CS), removal technique for primary molars, and to compare the volume of sound dentine removed in order to validate the efficacies of these two techniques. <b><i>Methods:</i></b> Twenty-one primary molars with open carious cavities were hemisected. The carious tissue in one half was then removed by HE and the other by CS. XMT scans were taken before and after caries removal. After alignment, subtracted XMT images from the two scans revealing the tissues removed were generated, from which mineral distributions were determined, and volumes of sound dentine removed by each technique were calculated. <b><i>Results: </i></b>It was found that the sound dentine removed by HE and CS techniques accounted for 4.0 and 2.1% of total tissues removed, respectively. The mean cut-off linear attenuation coefficients at 40 keV to which HE and CS excavated to were 1.27 and 1.09 cm^–1, respectively. The corresponding Knoop hardness number for the cut-off for CS was 25 kg·mm^–2. <b><i>Conclusion:</i></b> It is concluded that using XMT, CS is validated to be more conservative than HE and preserves a layer of partially demineralised dentine with a mineral concentration >0.97 g·cm^–3.