Chemistry and Pathogenesis of Erosion

The challenge posed by erosive acids is much worse than that posed by a cariogenic challenge. Caries is caused by acids produced by plaque bacteria from sugars but plaque pH does not fall much below 4. Moreover, plaque contains calcium and phosphate ions, which reduce the impact of acid on mineral. In contrast, the pH of most erosive substances is less than 4 and often as low as 2.5. Also, erosive liquids contain little or no calcium or phosphate, so that the tooth mineral experiences the full impact of the acid. The main factors influencing erosive potential of a drink or foodstuff are:

• pH. Erosion rate increases steeply as pH falls.

• Movement of erosive solution in the mouth. Erosion rate is very slow in static solutions but increases rapidly if the solution is moving past the teeth, e.g. if a drink is ‘swished' round the mouth.

• Buffer capacity. Higher buffer capacity increases dissolution rate in highly erosive solutions but has less or no effect when erosion is slow. In vivo, well-buffered erosive solutions can better withstand neutralization by saliva, so present a longer-lived erosive challenge.

• Pellicle. Salivary pellicle provides a short-lived reduction of erosion, which varies considerably between individuals.

Because of the aggressive nature of the erosive challenge, therapeutic or preventive strategies developed against caries cannot be transferred directly to treatment of erosion. This applies particularly to use of fluoride. Whereas simple fluoride preparations are very effective under the relatively mild conditions of caries lesion formation, they have limited effect against erosion. New strategies – both in fluoride use and in other approaches – need to be developed. It may be that the most severe erosive challenges can overcome all preventive measures but an understanding of the chemistry of erosion is essential to developing methods to counter less aggressive, more everyday challenges.