Any discussion of the teeth should explain in some detail the physiology behind the development of these organs. The upper and lower jawbones are formed in halves and unite in the center as their development progresses. In tiny grooves in the inside portion of the jaws are small “tooth germs” or buds. These buds form teeth which begin to calcify as early as the seventeenth week of prenatal life. All of the deciduous teeth and four permanent ones (the six-year molars) are undergoing calcification before the child is born. These permanent teeth begin to calcify about the twenty-fifth to the thirtieth week of embryonic life.
Although there are teeth present in the gums and bone of the jaw, a child is born almost always without any being visible. At about six months of age the front teeth begin to erupt. These are followed by the first deciduous molars. Next in order are the cuspids or “eye-teeth,” and finally at about two years of age the last deciduous molars appear.
One must bear in mind that while these baby teeth are erupting, beneath them in the bone the permanent ones are beginning to harden. When one year old the child begins to calcify other permanent teeth, the process continuing until he is about eighteen. The first permanent teeth to appear are the six-year molars which usually come while all of the baby teeth are still in position. As a result many of these are often mistaken for baby teeth, and no attention being paid to them by parents, are allowed to decay. Also at about six years of age the front deciduous teeth loosen and come out to be replaced by permanent teeth. The last to make their appearance are the third molars, called “wisdom teeth,” which erupt about the seventeenth to the twenty-first year. When all of the permanent ones have erupted the average mouth contains thirty-two teeth.
It can be readily understood that prenatal factors can easily affect the structural development of teeth, leaving their marks on the enamel organs of those which are formed before the child is born. There are several diseases, in fact, which can be diagnosed as hereditary only by the markings on the deciduous teeth.
A tooth is composed of four main structures. The visible portion of it is known as enamel, which is the hardest substance in the human body. It is mainly formed of inorganic salts. Beneath this covering of enamel is the main body of the tooth, called dentine. In its chemical composition dentine closely resembles bone, which has slightly more organic material in it than has dentine. Covering the root of a tooth, very much as the enamel covers the crown, there is a substance known as cementum. To this are attached fibers forming a covering similar to periosteum, overlying the surfaces of the bones, which holds the tooth in its bony socket. Inside of the tooth is the chamber called the “pulp chamber” which contains a small artery, vein, and nerve tissue. These are commonly called the “nerve.” It gives life to the tooth, and by means of the blood vessels supplies it with nourishment. When this pulp or “nerve” is removed or dies, we have what is termed a devitalized tooth, often referred to as a “dead” tooth.