True pulp stones are made up of dentine that is lined by odontoblast. One important antimicrobial agent produced by odontoblast is beta-defensins (BDs). The odontoblast process is located in dentinal tubules. These cells can differentiate into osteocytes, adipocytes, odontoblast, and chondrocytes "in vitro". Reactionary dentin is formed by odontoblasts when the injury does not damage the odontoblast layer. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix. The odontoblast cell bodies decrease in number and size before any inflammatory changes occur. Enamel spindles however, are in fact odontoblast processes that extend into the enamel.