THE EFFECTS OF SALIVA ON THE pH AND LACTATE CONCENTRATION IN DENTAL PLAQUES

I. CARIES-RAMPANT INDIVIDUALS

¹ The University of Illinois College of Dentistry, The Dental Research Facility USNTC, Great Lakes, Ill., and Northwestern University, School of Dentistry, Chicago, Ill.

1. Two series of pH and lactate values were determined in the dental plaques from 50 caries-rampant individuals before and at intervals of 5, 10, 15, and 20 minutes following sucrose application, with and without saliva restriction.

2. Every individual produced greater acidities when saliva was restricted and 78 per cent of this group produced acidities of pH 5.5 or below. Only 34 per cent of the saliva group produced acidities in this range.

3. Plaque substance per se appeared to possess considerable buffering capacity and obviated the production of any acidities below pH 4.8. Saliva was necessary, however, to prevent plaque pH values from falling below the level of pH 5.5.

4. When saliva was permitted free access to the dental plaque, the mean per cent lactate concentrations appeared to have an inverse relation to the reduction and subsequent rise of mean pH values after the 10-minute interval. The reduction of lactate after the 10-minute interval indicated that some of the lactic acid diffused out of the plaque in addition to being neutralized in the plaque.

5. Restriction of saliva was attended by a reduction of the mean plaque acidities to the uniform average level of pH 5.6. This was accompanied by an increase in total lactate concentration.

6. Tooth substance did not appear to contribute appreciably to the neutralization of lactic acid during the 20-minute test period.

7. The acid produced in the dental plaque did not seem to be metabolized by microorganisms during the test period.