Figure 3. SEM micrograph of cryofractured phosphoric-acid-etched dentin following the application of an oxalate desensitizer. Bi-pyramidal calcium oxalate crystals (open arrowhead) were identified in the dentinal tubules, at 8–10 µm beneath the dentin surface, where calcium ions were available from the adjacent mineralized dentin (D). In contrast, the demineralized collagen matrix (asterisk) was almost completely devoid of these angular crystals. Since no acidic, fluoride-containing dentin adhesive was further applied to the desensitizer-treated dentin, the etched dentin surface was devoid of the spherical calcium-fluoride-like structures. Only demineralized collagen fibrils (pointer) were identified from the surface of the acid-etched dentin.