Progress of Artificial Carious Lesions in Enamel

Abstract

Progress of lesions with time is important from a practical point of view, but especially because it provides information on the mechanism of the caries process. Firstly, a theoretical description of lesion progress with time is derived. It is based on the assumption that (1) steady-state diffusion during the caries process takes place through very tiny holes in the enamel surface, (2) inhibitors make the enamel surface insoluble and diffuse during the process inwards (the inhibitors, e.g. diphosphonates or fluorides may be coming from an external solution or may orginate from the enamel itself), and (3) the inhibitor blocks enamel dissolution effectively if the inhibitor concentration X_L exceeds the fraction of surface phosphate sites X_L*. The theory shows that lesion depth (r₁) is about proportional to the third root of demineralization time (t), and can be written as r₁³ = αt + q, α and q being constants. Second, a comparison is made with experimental lesion depth data from various authors in artifical lesion systems. The results show that lesion progress in human and bovine enamel at pH 4, 4.5 and 5 is very well described by the above formula. This result indicates strongly that inhibitor action and inhibitor penetration are important during the caries process. From the experimentally determined slope a the apparent diffusion coefficient Dapp of the process is determined as ≈ 10^––5 cm²s^––1. This value is comparable to D of Ca⁺⁺ and phosphate ions in aqueous solutions and indicates that ion transport during the process takes place in water-filled channels.