Towards quantitative analysis of enamel erosion by focused ion beam tomography

Objectives

The purpose of this work is a proof of concept to introduce a new quantitative 3D-analysis of dental erosion obtained by focused ion beam (FIB) tomography associated with silver nitrate penetration into porosities in etched enamel.

Methods

One sample selected was sound enamel after removal of the aprismatic surface. The other was studied after applying an additional attack with orthophosphoric acid. Both surfaces were infiltrated with silver nitrate via immersion. After dehydration, samples were observed in a dual column FIB/SEM station. Serial FIB sectioning was conducted with a current of 3 nA at 30 keV and an increment step of 20 nm for the healthy enamel and of 40 nm for the etched one. 3D analysis was performed with Fiji software and BoneJ plugin and several parameters were obtained to characterize the tissue: non-mineralized phase content (NMP), connected porosity fraction (CPF) and degree of anisotropy (DA) of the NMP.

Results

Healthy enamel showed an NMP content of 0.5 vol.%, with a bimodal distribution of non-mineralized regions, inside the prisms and between the prisms. No silver penetration was noticed in the healthy enamel, demonstrating the absence of open porosity. In contrast, silver nitrate penetration after acidic exposure was observed, up to a depth of 12 μm, which allowed the calculation of an interconnected porosity volume fraction (CPF) of 3.1 vol.%, mostly between the prisms. Values for DA of 0.56 for sound enamel and 0.81 for acid-etched surface were determined, highlighting a higher degree of anisotropy in the latter.

Significance

Quantitative analysis of FIB tomography using NMP, CPF and DA should contribute to a better understanding and follow up of dental erosion, correlation between erosion and attrition or abrasion process, and the ability to develop enamel remineralization procedures.