Analytical electron microscopy and ultracytochemistry of a mechanism of dentine resorption mediated by odontoclasts in physiological root resorption of human deciduous teeth.

Abstract

Abstract:The author examined the ultrastructure and acid phosphatase activity of odontoclasts in physiological root resorption of human deciduous teeth. Extracted teeth undergoing resorption were fixed with a mixture of formaldehyde and glutaraldehyde and processed for scanning (SEM)-and analytical transmission-electron microscopy (STEM). In SEM observation of resorbing dentine surfaces treated with NaOCl, the peritubular matrices were strongly dissolved resulting in the enlargement of dentinal tubules. The multinucleated giant cells, odontoclasts, were characterized by an abundant mitochondoria, Golgi complexes, many lysosomes, endocytotic vacuoles, and well-developed ruffled borders against the resorption lacunae. The odontoclasts located in resorption lacunae contained numerous small fragments of dentine crystals in endocytotic vacuoles and extracellular canals of ruffled borders. A STEM analysis confirmed remarkably lower energy spectrum peaks of Ca and P in crystal fragments in these endocytotic vacuoles than those in unresorbed dentine matrix.The resorbing dentine surfaces consisted of alternative two electron-dense and two electron-lucent layers:these dense and lucent layers showed lower Ca and P peaks than those from unresorbed dentine. Lysosomal acid phosphatase activity was further demonstrated in the Golgi complex, dark lysosomes, and some endocytotic vacuoles of odontoclasts. These results suggest that odontoclasts are responsible for decalcification of dentine crystals at resorbing dentine surfaces and subsequent resorption and digestion of mobilized crystals.