Ultrastructural study of the root dentine surface resuming resorption on human deciduous teeth

Resorption of deciduous teeth is not continuous, but alternates with period s of repair or rest. Dentine surfaces in periods of rest or repair resume r esorption by odontoclasts during physiological root resorption of the decid uous teeth. However, no observations of such dentine surfaces have been sho wn. The characteristic feature of the dentine surfaces resuming resorption remains unknown. Tartrate-resistant acid phosphatase activity (TRAP) was de tected on human deciduous teeth. The root resorbing surfaces on these teeth were photographed with a whole-mount light microscope, and the photographe d areas were serially sectioned into 0.5 mu m semithin sections. Preodontoc lasts and odontoclasts were three-dimensionally reconstructed. On root reso rbing surfaces, areas with small scattered TRAP-positive cells were observe d among areas with many TRAP-positive resorbing odontoclasts and TRAP-negat ive areas. The sections showed that areas with small scattered TRAP-positiv e cells have features similar to those of TRAP-negative areas, but there we re three kinds of characteristic TRAP-positive cells: preodontoclasts, odon toclasts forming small lacunae, and preodontoclasts and odontoclasts with c ytoplasmic processes extending to the dentine surface, which is covered wit h cells. These results suggest that the areas with small scattered TRAP-pos itive cells could be at the stage of resuming resorption, and show that the presence of preodontoclasts and odontoclasts with cytoplasmic processes ex tending to the covered dentine surface is a characteristic feature of the d entine surface at this stage.