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 microm in width, also termed metadentine; in the inner circumpulpal dentine, the staining was weaker or lacking in an area extending 5-7 microm 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.