Contents -SUBJECT INDEX -BIBLIOGRAPHIC RECORD -ILLUSTRATION INDEX

Henry Gray (1825–1861). Anatomy of the Human Body. 1918.

pages 1114

The dental formulæ may be represented as follows:

Deciduous Teeth. mol. can. in. in. can. mol. Upper jaw 2 1 2 2 1 2 Total 20 Lower jaw 2 1 2 2 1 2 Permanent Teeth. mol. pr.mol. can. in. in. can. pr.mol. mol. Upper jaw 3 2 1 2 2 1 2 3 Total 32 Lower jaw 3 2 1 2 2 1 2 3

General Characteristics.—Each tooth consists of three portions: the crown, projecting above the gum; the root, imbedded in the alveolus; and the neck, the constricted portion between the crown and root.

FIG. 998– Maxillæ at about one year. (Noyes.) (See enlarged image)

The roots of the teeth are firmly implanted in depressions within the alveoli; these depressions are lined with periosteum which invests the tooth as far as the neck. At the margins of the alveoli, the periosteum is continuous with the fibrous structure of the gums.

In consequence of the curve of the dental arch, terms such as anterior and posterior, as applied to the teeth, are misleading and confusing. Special terms are therefore used to indicate the different surfaces of a tooth: the surface directed toward the lips or cheek is known as the labial or buccal surface; that directed toward the tongue is described as the lingual surface; those surfaces which touch neighboring teeth are termed surfaces of contact. In the case of the incisor and canine teeth the surfaces of contact are medial and lateral; in the premolar and molar teeth they are anterior and posterior.

The superior dental arch is larger than the inferior, so that in the normal condition the teeth in the maxillæ slightly overlap those of the mandible both in front and at the sides. Since the upper central incisors are wider than the lower, the other teeth in the upper arch are thrown somewhat distally, and the two sets do