Figure 1. Schematic of sample preparation. First, we prepared two sections (2 mm apart) in the central part of the teeth (in the buccal-lingual direction following the coronal-apical axis), dividing each tooth into 3 sections (mesial, central, and distal). The coronal-central part was then further sectioned to provide buccal and lingual samples. We used a scalpel under a microscope to separate the enamel and dentin tissues.