ACTION OF METALLOPROTEINASES ON PORCINE DENTIN MINERALIZATION

Samples containing predentin and mineralized dentin involving the mine ralized front (newly formed dentin) were prepared by scraping developi ng porcine teeth after odontoblastic cell debris had been removed from the predentin surfaces. An extract was obtained separately from the m atrices of predentin and of the newly formed dentin with a 4 M guanidi ne solution before and after demineralization with acetic acid solutio n. Enzymography detected 56 and 61 kDa gelatinases and 25 kDa proteogl ycanase as neutral metalloproteinases in both extracts and proved them to be in an active form. Approximately half of the 56 and 61 kDa gela tinases binds to collagen fibers in predentin matrix. Three high molec ular weight proteoglycans (70-85 kDa, 130-180 kDa, and 290 kDa) were f ound in the predentin matrix, but not in the newly formed dentin. The proteoglycanases in predentin degraded 290 kDa proteoglycan, if incuba ted together with calcium (Ca) ions. The results of this investigation indicate that active proteoglycanases which existed in the predentin perform no substantial work in proteoglycan degradation because the Ca ions are masked in the predentin matrix by coexisting proteoglycans. When mineralization occurs, however, they can degrade the proteoglycan at the mineralization front because excess Ca ions may be supplied vi a odontoblastic processes.