. Biology and human life. Biology. 132. The teeth and their care. One of the commonest causes of indigestion is found in decayed teeth. People with poor teeth get into the habit of swallowing the food without chewing it. Then they blame their stomachs or the cook for their miser- able feeling or even for the poor work they do. The structure of a human tooth is shown in Fig. 8i. The enamel is a hard protec- tive casing. Trouble with the teeth very frequently begins with the breaking of this enamel. The enamel can be cracked by sudden changes of temperature, or by grind- ing it against some hard
. Biology and human life. Biology. 132. The teeth and their care. One of the commonest causes of indigestion is found in decayed teeth. People with poor teeth get into the habit of swallowing the food without chewing it. Then they blame their stomachs or the cook for their miser- able feeling or even for the poor work they do. The structure of a human tooth is shown in Fig. 8i. The enamel is a hard protec- tive casing. Trouble with the teeth very frequently begins with the breaking of this enamel. The enamel can be cracked by sudden changes of temperature, or by grind- ing it against some hard sub- stance, as when you try to crack a nut with your teeth. Picking the teeth with a needle or some other hard body is also hkely to scratch the en- amel and thus to open the way for further damage. In the food that we eat there are many bacteria, of many kinds. In particles of food that cling to the teeth these bacteria begin their digestive activities (see Fig. 73). Some of the substances thus produced act upon the enamel, dissolving away this protective cover. Gradually a cavity becomes larger and deeper until it reaches the pulp and the nerve becomes exposed.^ ^In recent years it has been found that many serious disorders in various parts of the body may result from a sick condition of the teeth. Studies on patients and experiments with animals have shown that when the root of a tooth is abscessed (infected with certain kinds of bacteria), living bacteria and the poisons which they produce can be carried by the blood to remote parts of the body and there set up local but serious disturbances such as rheumatism of the joints, inflammation of the heart, kidney disease, or ulcers of the stomach. Fig. 81. Structure of mammalian teeth A, human grinding tooth, showing central pulp cavity (a), containing nerves and blood vessels and surrounded by dentine (b). The crown is covered with enamel (c), and the root with cement (d). B, gnawing tooth of rabbit, which grows from below as
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Keywords: ., bookcentury1900, bookdecade1920, bookpublishe, booksubjectbiology
