Cementum(redirected from Crusta petrosa)
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the bony tissue that covers the root and neck of a tooth in mammals and humans. The cementum keeps the tooth firmly in its socket. Like other structures containing collagenous fibers, cementum is elaborated by special cells. The cells, known as cementoblasts, are buried deep in the cementum and are converted into cementocytes. Cementum contains 29.6 percent organic matter, 57 percent calcium phosphate, 8 percent calcium carbonate, 1.2 percent calcium fluoride, and 1 percent magnesium fluoride.