The phrase “immunity to caries ” may lead to erroneous views. In neither enamel nor other hard tissues of a tooth are there any protecting factors that afford immunity in a biologic-bacteriologic sense. The terms resistance and irresistance to caries are preferable. In a mouth having high caries-resistance, a dental plaque is innocuous. The all important causative factor resides in the irresistance, not in the plaque.
Saliva is a possible source of acid production. Stagnating saliva yields, in sixty hours, a pH of 4.5. Similar results were obtained in bread-milk and milkcoffee-bread-sugar mixtures. The most important components for acid production in a dental plaque are the retained particles of food, which usually contain chemical substances and bacteria necessary for acid fermentation. Salivas from patients of high or low caries-resistance had the same acid-producing effects in artificial plaques. [Reported by Rudolf Jeanneret.]
Reference: Schw. Monat. Zahnh., 1927.