**6. Ultrasonic demineralization for dentin scaffold**

Dense structure without pores inhibits the cell invasion and the body fluid permeation into the inside of the biomaterials. This situation is so-called material's wall. Material's wall means the exclusion of cells and body fluid. Dentin has compact structure with dentinal tubes. We have been challenging to create biological dentin scaffolds, using ultrasonic demineralization technology [14, 16, 37]. The whole structure design of dentin by the artificial pores and the ultrasonic treatment might produce functional 3D scaffolds, which control the bioabsorption rate and the adsorption ability for proteins and cells [2, 38] (**Figure 1**). The innovative technology can create the adequate 3D geometry and the surface structure of commercially available materials [14, 15](**Figure 3**). Geometrical factors will improve the performance of biomaterials for bone regeneration [39–42].

#### **Figure 3.**

*SEM views of HAp dense plate before and after dissolution for 20 min in 2.0% HNO3 by ultrasonic treatment at 600 W and 28 kHz. (a, c) Normal HAp dense plate (Cell-yard®); (b, d) ultrasonic demineralized plate; (a) dense flat plate; (b) knife cut-like grooves; (c) dense round crystals; (d) crater-like holes.* 
