Progressive Sorbitol Acidogenicity in Successive Oral Mixed Bacteria Incubations

Introduction: Sorbitol is widely used as a sugar substitute in many cariogenic food products to avoid cariogenicity. Still uncertain is whether sorbitol is non-cariogenic. Objective: Test whether sorbitol catabolized by the mixed bacteria found normally in the mouth are sufficiently acidogenic to be cariogenic and if repeated and lengthy sorbitol exposures could make it so. Method: The mixed bacteria salivary sediment system was used and highly acidogenic glucose was included for comparison. As earlier, bacterial sediment and saliva supernatant were obtained by whole saliva centrifugation at 1740g. Incubation mixtures were prepared with sediment at 16.7% (v/v), sorbitol or glucose at 28mM and saliva supernatant at 0 or 33.3% (v/v). Baseline was adjusted to pH 7.0 with filter-sterilized HCl or NaOH. Incubations were performed at 37ºC overnight in loosely capped sterile tubes. At 2, 4 and 21 hours, aliquots were withdrawn aseptically for pH measurement. A second incubation followed after washing the bacterial sediment with sterile deionized water and adding fresh sterile substrates with and without saliva. Third and sometimes fourth day incubations were done thereafter. Some comparison to other polyols was also done. Results: Sorbitol or glucose caused the pH to drop rapidly from neutrality and more slowly thereafter. pH decreased to about 5.0 with sorbitol, and near 4.0 with glucose. On the second day, the pH fell further with both sorbitol and glucose to below 5.0 with sorbitol and to 3.4 with glucose, and further still on days thereafter. Clearly, sorbitol enabled the oral mixed bacteria in successive incubations to decrease the pH low enough to cause mineral loss and tooth decay. The pH with glucose fell significantly lower, hence its greater acidogenicity. Saliva inhibited the pH decrease with sorbitol more than it did glucose. Conclusion: Sorbitol should be considered to be potentially cariogenic but less so than glucose.