When I first studied the digestive system—which traditionally begins at the lips and ends at the anus—I was told that saliva was rich in calcium ions. This caused me to wonder over the years whether this imparted any benefit. For example, might it aid mineralisation of the teeth?
I’m particularly aware of the effects of calcium ions on my teeth given that there is always some tartar that needs to be removed every time I visit the dental hygienist. I’ve tended to blame my calcium-rich saliva. However, it transpires that I was wrong to do so. Firstly, it should be pointed out that, although the words tend to get used interchangeably, there is a difference between plaque and tartar. Plaque is a soft, sticky film of bacteria that adheres to the teeth but which can be removed with daily brushing and flossing. Tartar is plaque that has hardened over time, requiring professional dental cleaning for its removal.
Looking into this question more deeply, I find that saliva is not necessarily ‘rich’ in calcium ions. The calcium concentration in saliva is actually similar to or even lower than that of blood plasma. Nevertheless, what calcium there is in the saliva does aid mineralisation of the teeth. It is not the concentration of calcium in the saliva that seems to matter but rather the fact that the saliva is supersaturated with calcium and phosphate ions. These are the main components of tooth enamel. Thus, saliva provides a constant supply of these minerals to help repair and strengthen the teeth. In addition, the calcium and phosphate in saliva help to neutralise acids produced by oral bacteria. Without this neutralising effect, these acids would demineralise the tooth enamel, leading to cavities.
Salivary calcium concentration can become elevated and lead to the formation of stones in the salivary ducts. This is a process known as sialolithiasis. So too much calcium does not so much mean stronger teeth but potentially blocked salivary glands.
I always find it amusing how textbooks always point out that saliva is about 99.5% water. That makes saliva more aqueous than beer—but not at all more palatable to drink.
