“…11 As reported, the well-known toughening mechanisms including ligament bridging, crack branching, and diversion are likely to appear in softer dentin or in anatomically varying regions. 12 As the highly mineralized tissue in human body, mature enamel consists of calcium hydroxyapatite (HAP; 96 wt %), organic materials (3 wt %), and water (1 wt %). Amelogenesis encompasses the secretory, transition, and maturation stages of ameloblasts (Figure 1C).…”