Differences in the pattern of lanthanum diffusion into predentine and dentine in mouse incisors and molars

Lanthanum nitrate was either perfused intravascularly or segments of mouse tooth were immersed in a fixative solution containing the tracer. The tracer deposits were examined in young (8-day-old) and older (8-week-old) mouse incisors and molars, demineralized or undemineralized. Lanthanum passed the distal junctional complex of odontoblasts and appeared in the predentine of incisors as large electron-dense stellate aggregates, 40–70 nm in diameter, and in molars as round, 20–40 nm dots. In dentine, tracer deposits were detected at three locations. Near the predentine–dentine junction, the tracer densely stained a band 0.5–2.5 μm in width, also termed metadentine; in the inner circumpulpal dentine, the staining was weaker or lacking in an area extending 5–7 μm from the predentine–dentine junction; in outer circumpulpal dentine, lateral diffusion had occurred in porosities of intertubular dentine. Lanthanum impregnated the walls of dentine tubules and a peritubular–like dentine. In contrast, the mantle dentine was never stained. These differences in the pattern of diffusion prove that lanthanum staining is age-dependent and varies between mouse incisors and molars, independently of tissue processing. Architectural properties and driving flux are involved in the transport and localization of lanthanum in predentine and dentine.