Salivary Concentrations of Urea Released from a Chewing Gum Containing Urea and how These Affect the Urea Content of Gel–Stabilized Plaques and Their pH after Exposure to Sucrose

Abstract

The objectives were to: (1) determine the salivary concentrations of urea during 20 min chewing of a sugar–free gum containing 30 mg of urea; (2) measure the degree to which this urea would diffuse into a gel–stabilized plaque; (3) study the effect of the urea on the fall and subsequent rise in pH (Stephan curve) on exposure to 10% sucrose for 1 min; (4) model the measurements 2 and 3 mathematically. In point 1, the salivary urea concentration of the 12 subjects peaked at 47 mmol/l in the first 2 min of gum chewing, falling within 15 min to the unstimulated salivary concentration of 3.4 mmol/l. Recovery of urea from the saliva averaged 81.5%. ‘Plaques’ of 1% agarose or 67% dead bacteria in agarose accumulated urea from the saliva roughly as expected, whereas those plaques containing 8% live and 59% dead Streptococcus vestibularis showed negligible accumulation. Computer modelling showed this difference to be due to urease of live bacteria breaking down the urea as rapidly as it entered the plaque. Simulation of the effect of gum chewing subsequent to initiation of a Stephan curve in the latter type of plaque showed a rapid rise in pH but then a fall again on return to unstimulated conditions. This fall had not been seen in previous studies, with Streptococcus oralis, nor was it predicted by the computer modelling. Neither experimental simulation nor computer modelling suggested that chewing urea–containing gum before exposure to sucrose would have any effect on a subsequent Stephan curve. Thus chewing gum is only likely to inhibit caries when it is chewed after consumption of fermentable carbohydrate, rather than before.

Protein Buffering in Model Systems and in Whole Human Saliva

“…As SDS Page probable cannot provide high enough resolution to separate the different protein species that may be present in single protein band, further studies applying 2D electrophoresis will be necessary for unambiguous protein identification. In this study, the role of carbonic anhydrases and urease was neglected because both enzymes are found mainly in the enamel pellicle [9], [44] which was not included in the experiments.…”

The Effect of pH, Temperature and Plaque Thickness on the Hydrolysis of Monofluorophosphate in Experimental Dental Plaque

“…In a mouthrinse trial, 500 mmol/l urea raised plaque pH to 8.3 within 1 min, when MFP was rapidly hydrolysed [Schamschula et al, 1985], and urea chewing gum has a strong plaque pH-raising effect [Dawes and Dibdin, 2001]. However, the possibility that urea may inhibit alkaline phosphatase should be kept in mind [Seiffert et al, 1984].…”

Minimum intervention dentistry principles and objectives

“…35 CaviStat is now used as an additive in toothpastes as well as in mints. There have been numerous studies of chewing gums supplemented with urea, and it is now clear that these best inhibit caries when chewed after consumption of fermentable carbohydrate, not before, 36 with a rapid rise in plaque pH within the first minutes of chewing, 37 resulting in lower plaque acid production. Examples of urea enriched chewing gums include V6…”