Mass transport in dentine: An X-ray microtomographic study

Objectives: The hydrodynamic theory of dentine hypersensitivity proposes that external stimuli cause changes in fluid flow within rigid tubules triggering mechanoreceptors. The present aim was to observe diffusion through dentine, within and perpendicular to the dentinal tubules. Methods: 2.0 mm thick dentine disks were cut from disease-free human third molars parallel to the occlusal surface. Each disk was masked with polyethylene tape to leave half of the upper surface exposed. Specimens were mounted in a plastic syringe filled with deionised water and imaged by X-ray microtomography (XMT). The water was then replaced with 0.50 M caesium acetate solution; further XMT scans were taken at 1 day and 6 days. The XMT images were used to measure the change in X-ray attenuation coefficients resulting from caesium acetate diffusion through the dentine. Results: Caesium acetate diffusion into the dentine beneath the exposed surface was clearly apparent; little or no penetration was observed into the dentine tissue located beneath the sealed surface. Distribution of the diffusant was not uniform across each XMT axial section, with the lowest concentration observed at the periphery of the dentine abutting the enamel. Conclusion: XMT images of the 3D distribution of caesium acetate following diffusion through dentine suggested that transport is along the dentinal tubules, but there was no evidence of significant lateral transport. The direction of diffusion appeared to be dependent on dentinal tubule orientation. Acknowledgement: This work has been supported by GlaxoSmithKline and Intistute of Dentistry QMUL.