Abstract
Demineralized dentin matrix (DDM) granules with excellent biocompatibility were designed using extracted human teeth by the cooling-pulverizing and supersonic demineralizing technique. Extracted teeth were pulverized together with saline ice at 12,000 rpm of a ZrO2 blade for 30 s in a ZrO2 vessel. The pulverized granules having 0.5-2.0 mm in granular size were dissolved by the supersonic treatment at 120 W and 38 kHz or 600 W and 28-100 kHz in 2.0 % HNO3 solutions to obtain partially or completely DDM granules. Dissolution efficiencies of the pulverized granules increased with increasing the supersonic time. At 600 W, dissolution efficiencies for DDM treated at 28 kHz were higher than those at other frequencies. The Ca/P molar ratios of the granules were 1.60-1.66, suggesting that partial DDM granules were composites of Ca2+-deficient hydroxyapatite (HAp) and collagen. At 120 W, as supersonic time increased, asperity on the surfaces of granules became outstanding due to elution of mineral components. At 45 min, DDM granules were completely demineralized and the weight decreased to about one-fifth. Hard asperity on surfaces and micro-crack were observed. Partially or completely DDM granules were implanted into the subcutaneous tissues of the back region of rats. At 4 weeks, completely DDM granules had a little smaller and more irregular shape than partially DDM ones. Infection and exclusion of DDM granules were not recognized, but inflammatory cell invasion was seen through bio-absorption of DDM due to the enzyme-digestion. To improve surface activity of DDM, DDM granules were soaked at 309.5 K and pH 7.40 in a simulated body fluid. At 48 h, HAp nano-crystals were almost homogeneously coated on the surfaces of completely DDM granules, while at 144 h, porous bone-like apatites were found. The HAp nano-crystals coating for DDM granules would form bioactive surface with specific pore structure and chemical nature.
