Anatomy, physiology and hygiene . ecay results. Fig. Vertical Section of Tooth. E, enamel. C, cementum. O 0, openings in roots for thepassage of nerves and blood-vessels into the pulp cavity,represented in figure bydarkened centre. 123. There are two sets of teeth: the temporary, ormilk teeth, of early childhood, twenty in number, thefirst appearing usually about the seventh month of 1 The hardness of the enamel varies in different persons. In some itis so soft, from a deficiency of phosphatic salts, that the teeth wear downalmost to the gums. 2 The pulp supplies nourishment to the tooth.
Anatomy, physiology and hygiene . ecay results. Fig. Vertical Section of Tooth. E, enamel. C, cementum. O 0, openings in roots for thepassage of nerves and blood-vessels into the pulp cavity,represented in figure bydarkened centre. 123. There are two sets of teeth: the temporary, ormilk teeth, of early childhood, twenty in number, thefirst appearing usually about the seventh month of 1 The hardness of the enamel varies in different persons. In some itis so soft, from a deficiency of phosphatic salts, that the teeth wear downalmost to the gums. 2 The pulp supplies nourishment to the tooth. When it dies, the toothloses its translucency and sensibility, and is discolored, and if it be atooth of the permanent set, is never replaced by a new one, or even bynew tooth-structure, but may retain its position in the jaw and do dutyfor years. 124 DIGESTION. life,1 the last about the twenty-fourth; and the perma-nent set of youth and adult life, thirty-two in number,the first appearing about the sixth year, the last, or wis-. M/2 \M Fig. 56. A diagram of two upper jaws, representing the location, arrangement, and time oferuption of the temporary and permanent teeth. The relation of the temporaryto the permanent teeth is indicated by their position, and by dotted lines con-necting them with the permanent teeth. The numerals represent, in oneinstance, the time of the appearance of the teeth in years; in the other, inmonths. I, incisor teeth. C, canine teeth. B, bicuspid teeth. M, molar teeth. dom teeth, about the twenty-fourth The perma-nent teeth originate near the roots of the temporary teeth,and, as they develop, press upon these roots and cause 1 From various causes, such as sickness, hereditary peculiarities, orlack of proper tooth-forming food, the appearance of the teeth may bedelayed till one year of age, or even longer. Babies are sometimes bornwith teeth. 2 The first permanent teeth appear behind the posterior milk molars,before any of the milk teeth are she
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