Objective: The aim of the present study is to investigate the ultrastructural changes within the different zones of carious dentine and compare those changes with sound dentine.
Methods: Transmission electron microscopy and electron diffraction techniques were used to investigate the effect of caries on the inorganic phase of dentine. Areas of interest were identified with optical and scanning electron microscopes.
Results: The results demonstrated that the intertubular mineral crystallites decrease in size as caries lesion progresses. In the transparent zone of carious lesion, both intratubular and intertubular dentine consisted of nano-size apatetic crystallites with smaller size in the former. The intratubular mineral phase in transparent zone was found to be chemically similar to the intertubular dentin.
Conclusions: The study suggests that a 'dissolution and precipitation' mechanism is important in understanding the process of formation of intratubular dentine within the transparent zone induced by caries attack. The observed partial demineralisation of intertubular dentine in transparent zone is discussed in terms of dissolution of tubule microbranches and exposure of intertubular dentin to acids.