Atom Probe Tomographic Exploration Of Carious Rodent Enamel

Objectives: Dental caries, one of the world’s most prevalent infectious diseases, progresses via the acidic dissolution of tooth enamel. Recent explorations into the nanoscale composition and structure of enamel through atom probe tomography (APT) have demonstrated the existence of amorphous intergranular phases (AIGPs) between the hydroxylapatite nanowires that compose enamel. Furthermore, in vitro acid etching experiments have demonstrated that variations in the minority elements segregated to these boundary regions can have a strong effect on the acid susceptibility of the overall tissue. Building on these findings, the objective of the current investigation is to explore how the composition of these AIGPs influences and is affected by lesion development in vivo.
Methods: A rodent caries model is employed to generate a large pool of early-stage subsurface lesions, X-ray microtomography serves to non-destructively map the lesion structure in 3D, and using these maps, lesions are cross-sectioned to extract targeted volumes that are then analyzed via APT.
Results: APT reconstructions of volumes taken from sound, intact surface zone, and mildly demineralized lesion body enamel reveal 3-5nm wide regions of magnesium enrichment indicative of the AIGPs observed in the enamel of many other species, but with much less order than previously observed. Preliminary comparisons between the Mg-rich regions in tips from each enamel location also suggests an increase in the disorder of the AIGPs with the severity of demineralization, but more reconstructions are necessary to establish this trend with statistical significance. Preliminary reconstructions are presented in the context of the broader microtomography data to establish the potential of the experimental approach and demonstrate for the first time APT datasets successfully collected from carious enamel.
Conclusions: Applying this approach to a large number of extracted enamel volumes will enable detailed comparisons of the changes to composition within AIGPs during caries, and elucidate how the acid susceptibility of these boundary regions plays a role during caries initiation in vivo.