An Update on Demineralization/Remineralization

Mark E. Jensen, MS, DDS, PhD; Robert V. Faller, BS

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To understand the concept we can examine this lesion that has been prepared for microscopic examination. We can easily note the outer layer, the surface layer, and the inner demineralized area termed a subsurface lesion.

Polarized-light micrograph (in water) of an early enamel subsurface lesion. Blue area is normal enamel and surface zone over lesion. Brown area is the early lesion. (Image provided by: Dr. James Wefel)

The calcium and phosphate are dissolved from the crystals in a complex environment. The concept of a "critical pH" is the situation under which this net loss occurs. Previously this was thought to be a fixed value, but it is now accepted that it is rather a value that is inversely proportional to the calcium and phosphate concentrations in solution in the localized environment.4 Larsen and Pierce5 developed a computer program for examining the solubility of enamel. Small pH changes around a pH of 4 were demonstrated to significantly impact the demineralization potential of enamel.

What has actually happened? Acids diffuse through the interprismatic rod substance and travel along the rod margin to an area of lowered fluoride content. (Note: the outer 10 microns of enamel holds a higher concentration of fluoride.)

As the process of demineralization continues, the edges of the enamel crystal demineralize . . . that is, calcium and phosphate become dissociated in the small subsurface area.

Partially Demineralized Enamel Crystals

This process results in the development of an early lesion (begins 10-15 microns beneath the surface) which has a relatively intact surface layer that cannot be penetrated with a dental explorer. If the acid challenge continues, greater amounts of subsurface enamel will be demineralized (or as it is sometimes called "decalcified") and the lesion will progress deeper into the subsurface enamel layer.

Polarized-light micrograph (in water) of early enamel lesion (about half way through the enamel) showing the body of the lesion in brown with its advancing front and a blue surface zone at the enamel surface area as shown in the accompanying diagram.
(Image provided by:  Dr. James Wefel)

Early Lesion

The caries process is a dynamic situation which occurs with the substantial pH fluctuations which occur in the biofilm on the tooth. Kidd and Fejerskov6 describe this process and its histopathology and indicate the "Regular removal of the biofilm, preferably with a toothpaste containing fluoride, delays or even arrests lesion progression." The processes of demineralization and remineralization can occur simultaneously or alternately. The high resolution transmission electron microscope has been used to demonstrate how these crystals look in caries lesions.7 Very simply in crystallographic terms, crystal dissolution is demineralization and the restoration of partially dissolved crystals, growth of surviving crystals and the formation of new crystals within the carious lesion is remineralization. If net demineralization continues, eventually, the outer layer of enamel will become extensively undermined; with the clinical result being an area that is "sticky" or "soft" to the explorer coupled with visual evidence of demineralization. Larsen and Bruun8 describe this process in detail in their textbook chapter on "Caries Chemistry and Fluoride – Mechanisms of Action." They discuss the theory which claims that when " . . . fluoride is present in the aqueous phase around the tooth, in saliva and in plaque fluid, enamel solubility is low, which tends to prevent it from dissolving."

Advanced Lesion


Remineralization of the subsurface lesion occurs when the dissociated ions of calcium and phosphate recombine to form an even stronger crystal.  This reaction is enhanced in the presence of fluoride.

Thus, fluoride changes the remineralization process by acting as a mineral growth catalyst.  The action of fluoride accelerates the rebuilding of enamel and can stop or even reverse the progression of dental decay and, more importantly, makes enamel more resistant to acid demineralization then it was originally.

It is documented in the literature that the processes of remineralization and demineralization are similar, regardless of the surface on which they are occurring (enamel pits, fissures, smooth surfaces).  However, some surfaces tend to have higher incidence of lesion formation compared to others.  This is primarily a function of a combination of tooth morphology and accessibility for cleaning, with pit and fissure along with interproximal sites experiencing the highest rates of lesion formation.

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