Scanning Ion Conductance Microscopy Investigation of Dentine Morphology and Permeability

Objective: The exposure of dentine, due to enamel erosion or receding gums, leads to the condition of dentinal hypersensitivity. There is a pressure difference that leads to fluid flow across dentine from the pulp into the oral cavity. This fluid flow increases in response to external stimuli, leading to a pressure change within the tubule, ultimately triggering a mechanoreceptor response. Key to the development of new ‘targeted' treatments for hypersensitivity is a fundamental understanding for this transduction mechanism, the nature of fluid flow and local ion permeability on the scale of individual microtubules. This talk details the use of a novel, high-resolution technique for imaging dentine topography and local permeability.

Method: A scanning ion conductance microscope (SICM) has been developed within the Electrochemistry and Interfaces group at the University of Warwick. SICM has a resolution limited by the diameter of an imaging nanopipette tip, and potentially affords sub-micron to nanoscale spatial resolution. Measurements were made on coronal dentine obtained from bovine mandibular incisors, polished successively down to 2400 grit. All specimens were etched (2 min 10%w/w citric acid) prior to use.

Results: In this study, SICM has successfully been used to image the permeability of dentine and to assess the effect of the brushing process and the presence of an occlusion active on the permeability. The technique employs only an inert electrolyte solution, such as potassium chloride, and thus potassium fluxes across dentine have also been elucidated. A key result is that the permeability of individual microtubules varies significantly within a sample.

Conclusion: SICM has been shown to be a powerful, high-resolution imaging technique for the measurement of local permeability in dentine slices, in-vitro, and for evaluating the potential of novel occlusional actives. There are prospects for using the technique more widely in physicochemical studies of dentally-relevant interfaces.