Because demineralization elutes hydroxyapatite from the dentin, carious dentin chiefly comprises organic material. Reportedly, the constituent ratio of organic to mineral material continuously alters as the caries progresses, with corresponding changes in hardness.48–51 In this study, carious human dentins were diagnosed by their optical appearances and palpation by dentists. The three categories of carious lesions “remove,” “not remove,” and “unclear” were categorized by the Vickers hardness. The threshold of Vickers hardness separating the “remove” and “not remove” categories was around 30 to 40, suggesting that the Vickers hardness provides an index parameter for selective removal of carious dentin. In fact, some studies have reported a relationship between caries progression and hardness, and the effectiveness of hardness in caries diagnosis.52,53 In the ablation experiment undertaken at , areas categorized as “remove” and “unclear” were removed more rapidly than the areas categorized as “not remove”; that is, the technique preferentially ablated soft carious dentin. These findings are likely explained by the relationship between the counteracting force of photomechanical ablation and the hardness of carious dentin. High absorption energy density increases the counteracting force. High of the target increases the absorption energy density. As the organic material maximally absorbs at , consequently, the counteracting force is higher at than at . The increased counteracting force is likely responsible for the nonselective excavation at . On the other hand, the counteracting force at was below the mechanical strength of hard carious dentin but exceeded that of soft carious dentin. Consequently, soft carious dentin was ablated while the hard dentin remained intact.