**5. Advantages of demineralization**

There are several advantages about demineralization process of dentin and bone. In our preparation, 2% HNO3-demineralized dentin (DDM) is sterile material. The strong acid solution (pH < 1) can kill bacteria and decelluralize organ. Therefore, the strong acid treatment has antiseptic properties and decreases antigenicity. Bacteria-free DDM was detected after the culture for 7 days in blood agar medium of dentin granules demineralized in 2% HNO3 for 20 min [35]. HAp crystals inhibit the release of BMPs along with growth factors [36]. After the removal of HAp crystals by ultrasonic demineralization, the surface area of dentin and bone increases remarkably [16]. In our study, human DDM and human DBM induced bone and cartilage independently at 4 weeks in the subcutaneous tissues of nude mice [34]. In addition, adult rat cortical bone plate treated with ultrasonic demineralization induced bone at 2 weeks, while fresh cortical bone plate never induces bone until 6 weeks [20]. These results indicated that highly calcified tissues such as cortical bone and calcified dentin did not have a better capability in bone induction than DDM and DBM. The delayed inductive properties of highly calcified dentin and bone may be related to the inhibition of BMP release by HAp crystals [36]. We never think, therefore, fresh bone is a gold standard. DDM and DBM have a better performance in bone induction than fresh dense bone.
