A New Model for Nanoscale Enamel Dissolution

Abstract

The dissolution kinetics of human tooth enamel surfaces was investigated using nanomolar-sensitive constant composition (CC) and in situ atomic force microscopy (AFM) under simulated caries formation conditions (relative undersaturation with respect to hydroxyapatite = 0.902, pH = 4.5). Scanning electron microscopic (SEM) examination of the resulting etched enamel surfaces showed that deminerzalization, initiated at core/wall interfaces of rods, developed anisotropically along the c-axes. After an initial rapid removal of surface polishing artifacts, the dissolution rate decreased as the reaction proceeded in accordance with our recently proposed crystal dissolution model, resulting in hollow enamel cores and nanosized remaining crystallites, resistant to further dissolution. Generally, dissolution of minerals is regarded as a spontaneous reaction in which all the solid phase can be dissolved in undersaturated solutions. However, the dissolution of some biominerals may be suppressed when the crystallites approach nanometer size. This study shows that CC demineralization of enamel in acidic medium follows this new model that can be used to mimic carious lesion formation. In dissolution studies, nanosized enamel crystallites exhibit a remarkable degree of self-preservation in the fluctuating physiological milieu.

Dynamics of crystallization and dissolution of calcium orthophosphates at the near-molecular level

“…When r is closer to r * , there is no fast movement of its stepwave and the dissolution rate approaches zero. The application of this model demonstrates that for CaP crystallite sizes approaching the critical values, the bulk rates decrease markedly with time, despite the sustained driving force [38,42].…”

“…The effects become more important as the particle size approaches the critical length because more of the surface is likely to be composed of steps shorter than the critical length. This new dissolution model incorporating particle size considerations [38,39] can explain bulk demineralization of sparingly soluble salts such as HAP [40][41][42][43][44], which is generally initiated and accompanied by the formation and development of pits on the crystal surfaces; the dissolution rates are also determined by the pit densities and spreading velocities. The rate of step movement from a pit of radius r can be obtained from:…”

Structural Changes on Human Dental Enamel Treated with Er:YAG, CO2 Lasers and Remineralizing Solution: EDS Analysis

“…Tooth enamel, the hardest mineralized human tissue, (Harris & García-Godoy, 1999;Wang, et al, 2005), is composed almost exclusively (more than 95 wt%) of hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAP) (Pan, et al, 2008), with incorporated trace elements (Reitznwrová, et al, 2000). However, enamel is also porous, with the inorganic component representing only 87% of the total volume.…”

“…Apatite-like crystallites are highly organized hierarchical structures, and scanning electron microscopy (SEM) of enamel surfaces shows well-organized, rod-like apatite crystals, bundled in ordered prisms and elongated in their c-axis directions, which lie predominantly parallel to the rod axes. Despite these complex hierarchical structures, the basic building blocks for mineralized tissues are of nanoscale dimensions (Wang, et al, 2005;Pan, et al, 2008). The hydroxyapatite crystals are oriented by a protein network that makes up the enamel matrix (Harris & García-Godoy, 1999).…”

“…The hydroxyapatite crystals are oriented by a protein network that makes up the enamel matrix (Harris & García-Godoy, 1999). Amelogenin proteins constitute the primary structural entity of the extracellular protein framework of the developing enamel matrix (Wang, et al, 2005). Although enamel is not considered a living tissue because it has no cells or blood vessels, the overall protein network facilitates the diffusion of fluids, ions and small-sized molecules throughout the enamel (Harris & García-Godoy, 1999 elements found in enamel are Ca, P, sodium (Na), magnesium (Mg) and chlorine(Cl), and their mean concentrations are 37% Ca, 18% P, 0.4% Mg, 0.7% Na and 0.28% Cl (Reitznwrová, et al, 2000).…”