Under acidic conditions the OH - ions turn to water and the phosphate ions to mono-, di-, and trihydrogen phosphates. Such conditions prevail at alkaline pH (pH>7). Hydroxyapatite only forms when enough hydroxyl (OH -) and phosphate (PO 4 3-) ions are present. juice, milk, formula) are some of the strategies that may help reduce the risk. 5 Good oral hygiene including twice daily brushing of teeth with fluoride-containing toothpaste, and minimising prolonged exposure of teeth to drinks with fermentable carbohydrates (e.g. Due to prolonged sucking on the baby bottle, even if only filled with water, the teeth become porous and typical caries on the upper front teeth develops. This happens for example in the so-called nursing bottle syndrome seen in infants. If our saliva was constantly diluted with water, the concentration of calcium phosphate would be insufficient and the tooth enamel would start to erode. These occupy the spaces freed up in the crystal lattice and thus prevent continuous corrosion of the enamel surface. To reverse this process, our saliva is saturated with calcium and phosphate ions. Although in hydroxyapatite the ions are bound very tightly, in water the crystal would steadily lose ions from the surface and shrink. Table salt for example quickly disintegrates in water into its constituent sodium and chloride ions. Source of building blocksīecause of its specific properties water can dissolve out ions from salt crystals. Additionally, it contains organic molecules, mainly collagen, and in the case of dentine also cellular projections from odontoblasts (cells that produce dentine). Hydroxyapatite is made from calcium, phosphate and hydroxyl ions. The hard matter of our teeth - enamel and dentine - consists of a very hard crystal called hydroxyapatite. The same holds for proteins, from which proteases in saliva cut individual amino acids, some of which may stimulate the “umami”-receptor (umami = savoury). The individual sugar units released then bind to “sweet” receptors, which relay the message to the brain that this is indeed nutritious food that is safe to swallow. Amylase, for example, helps the water molecules in our saliva to split the chemical bonds between the monosaccharides in starch. 4 Each enzyme accelerates a specific chemical reaction that would otherwise proceed too slowly for our purposes. To reveal the true nature of the food, our saliva contains digestive enzymes. This is why a starch molecule - although consisting of millions of single sugars (monosaccharides) - does not taste sweet. The portfolio of receptors on our taste buds can only bind small molecules and ions, but not large chains of molecules (polymers). More complex foods such as starch or protein, require further help from our saliva, before we can identify them as tasty. This function of saliva is brought about by its main component, water. Only after moisturising the lump with saliva are the individual sugar or salt molecules released and we taste sweet or salty. Differentiating between the two will be even more difficult the drier your tongue. As an experiment, close your eyes and have a lump of rock sugar or salt placed on your tongue. The taste buds lie hidden in deep, narrow vaults across our tongues that cannot be accessed by dry, lumpy aroma compounds. 2, 3 This is important for us not to choke on the food or let the oesophagus get damaged by rough food particles. Moreover, mucins bind large quantities of water and thus keep the bolus moist and soft. 1 This bolus is held together by long, thread-like molecules, the mucins, which get tangled up at their ends. During mastication the dry, crumbly or disintegrating food turns into a soft, cohesive lump, the “bolus”. Food and saliva Preventing us from choking on foodĪn important role of saliva during eating is based in its sliminess. Just as varied are the many functions, of which only a few major ones will be outlined below. The list of ingredients found so far in saliva is long, and growing. Blood plasma is used as the basis, from which the salivary glands extract some substances and add various others. The salivary glands in our mouth produce about 1-2 litres of saliva daily. The remaining one per cent, however, contains numerous substances important for digestion, dental health and control of microbial growth in the mouth. Our saliva is ninety-nine per cent water.
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