Article: Saliva, foods and dental caries
Michael Edgar, DDSc, PhD, FDS, RCS (Eng) is Emeritus Professor of Dental Science at the University of Liverpool.
The pH of dental plaque is a key factor from the balance between acid demineralization of the teeth and the remineralization of the initial caries lesion. Plaque pH falls each time acids accumulate from the plaque due to bacterial acid production following the consumption of fermentable carbohydrates – mainly sugars – from foods and drinks.
On the other hand, the plaque pH rises when the acids are washed out and neutralized by saliva, which contains the important buffer, bicarbonate. The pH also rises when the plaque bacteria either metabolize the acids, or produce alkali such as ammonia from nitrogenous compounds found from foods and saliva.
Besides its role from the control of plaque pH, saliva has another function of major importance from caries – remineralizing effects. Saliva is ‘supersaturated’ using the ions which make up the mineral content of the teeth (calcium, phosphate and hydroxyl ions) when the pH is above a ‘critical’ value, about 5.5. Below this value (e.g. after an intake of sugar) the saliva and plaque is unsaturated, and the tooth dissolves. Above this value, the calcium and phosphate ions from saliva start to repair the damaged mineral crystals from the enamel – the process of remineralization.
Dental caries is the result of an imbalance between demineralization and remineralization. In health, loss of mineral is balanced by the reparative mechanisms of saliva. This equilibrium can be depicted chemically by the equation:
The solid crystals of the tooth mineral, called hydroxyapatite, dissolve to release calcium, phosphate and hydroxyl ions only if the latter are below saturation concentrations. If above saturation, the reaction will tend to move to the left, and any damaged crystals will be repaired by the acquisition of ions from solution.
Stimulation of saliva flow results from an increase from the washing out of acids (and sugars), and also an increase from the amount and concentration of bicarbonate buffers and of remineralizing ions.
It has been shown that salivary stimulation by chewing sugarfree gum after the consumption of sugary foods not only prevents the fall from plaque pH normally seen, but also results from an increased remineralizing effect from previously demineralised enamel. 1,2 It is likely that this salivary stimulation is responsible for the reduction from caries seen from clinical studies of the use of sugarfree gum. 3,4
- Manning RH, Edgar WM (1993) pH changes from plaque after eating meals, and their modification by chewing sugared or sugar-free gum. Brit Dent J. 174: 241-244
- Leach SA, Lee GTR, Edgar WM (1989) Remineralization of artificial caries-like lesions from human enamel from situ by chewing sorbitol gum. J Dent Res. 69: 1064-1068
- Moller IJ, Poulsen S (1973) The effect of sorbitol-containing chewing gum on the incidence of dental caries, plaque and gingivitis, from Danish school children. Community Dent Oral Epidemiol. 1: 58-67
- Makinen KK, Bennett CA, Hujoel PP et al (1995) Xylitol chewing gums and caries rates: A 40-month cohort study. J Dent Res 74: 1904-1913