Objectives: This study sought to evaluate the utility of nanoindentation and atomic force microscopy (AFM) to characterise the nanomechanical properties and surface topographic structure of dentine following exposure to sodium lauryl sulphate (SLS).
Methods: Dentine disks were cut from buccal sides of bovine incisors and polished using standard procedures. A Hysiton Nanoindentor in combination with a Nanoscope AFM, operating under ‘wet' conditions in accordance with published operating procedures, was employed to explore the indentation modulus, hardness, and topography of dental hard tissue as a function of surface pre-treatment and subsequent acid challenge. Surface pre-treatments consisted of (i) brushing with either deionised water or SLS solution for 30minutes or (ii) soaking for 10hrs in water or SLS. Following pre-treatment the surfaces were exposed to citric acid solution (1%, pH3.8) for 2minutes. At each stage of the methodology the nanomechnical properties and topography of the substrate were examined.
Results: Following exposure to SLS the elastic modulus of dentine is observed to reduce from (i) 16GPa (baseline) to 14GPa on brushing and (ii) 16GPa to 7GPa on soaking. Post exposure to citric acid the elastic modulus of ‘brushed-SLS dentine' is observed to reduce further to 4GPa compared to 6GPa for the water control. AFM imaging revealed a concomitant loss of peritubular and ‘matrix' material.
Conclusion: This exploratory nanoindentation study appears to demonstrate that SLS induces ‘softening' of the near-surface nanomechanical properties of dentine following exposure to SLS. In addition, an SLS pre-treatment appears to enhance acid mediated surface softening. The results are explained in terms of denaturing and decalcification of collagen fibrils.