Anatomical Nomenclature for Direction and Position

Terms that denote direction and position are standardized in anatomical nomenclature so that all the positional descriptions of areas of the human body can be located by reference to specific planes and directions. In dentistry, these systems of reference can be used, for example, to fit a row of teeth into the geometry of the skull. To locate the position of parts of the body or organs, the human body can be divided into four principal planes and three main axes (Fig 1-3).

The median or symmetry plane divides the body into the right and left halves. The following adjectives are used to distinguish between the two halves of the body: dexter, dextra, dextrum = right; sinister, sinistra, sinistrum = left. A sagittal plane (sagitta = arrow), or paramedian plane, is a plane parallel to the median plane through the body. The median plane is therefore unique among the numerous sagittal planes.

The frontal plane (frons = forehead) is the plane parallel to the forehead and perpendicular to the median plane, which divides the body into the posterior (rear) and anterior (front) regions. The transverse plane is the horizontal plane that is perpendicular to the median and frontal planes and divides the body into the upper and lower regions.

The main axes run as follows:

Vertical axis: from top to bottom
Sagittal axis: from front to back
Transverse axis: from left to right

To locate the position of a tooth, directional names that relate to the anatomy of the tooth are used. For each tooth, a distinction is made between the visible area protruding into the oral cavity, the crown of the tooth (corona dentis), and the root (radix dentis), which is anchored in the jawbone. The transition between the crown and the root is known as the neck of the tooth (collum dentis, cervix dentis).The tip of the root (apex dentis) is the only part of the tooth that is perforated, and the perforation is known as the apical foramen (foramen apicis dentis).

The location of a particular tooth in relation to the head, the occlusion, and the other teeth is identified using directional terms in addition to other terms that specify a point within the body, head, occlusion, or tooth that lies in the specified direction. Common directional terms used in relation to the teeth and the dental arches include (Figs 1-4 and 1-5):

Vestibular, the area of the vestibule (vestibulum = space between cheeks and gingiva/teeth); directed toward the outside of the dental arch
Buccal, the cheek area (bucca = cheek); directed outward in the region of the posterior teeth
Labial: the lip area (labium = lip); directed outward in the region of the anterior teeth
Oral, the area in the mouth (os = mouth) facing the inside of the dental arch
Lingual: the tongue region (lingua = tongue)
Palatal: the palate area (palatum = palate)
Approximal: adjacent; toward the contact surface (ad = to, proximus = nearest)
Mesial: toward the midline of the dental arch (medium = middle, medial = toward the middle)
Distal: toward the back of the dental arch (distare = to be away from)
Occlusal, toward the chewing surface of the tooth (occludere = to close)
Masticatory, toward the chewing surface (mas-ticare = to chew)
Incisal: toward the cutting surface (incidere = to cut into)
Apical, toward the apex of the root (apex = tip)
Coronal: toward the crown of the tooth (corona dentis = crown)
Gingival: toward the soft tissues (gingiva)
Cervical: toward the neck of the tooth (cervix = neck)

General directional terms for the body and head region include:

Anterior: at the front (ante = before, in front of)
Basal: toward the base of the skull, downward (basis = floor of the skull)
Central: in the middle
Dorsal: toward the back (dorsum = back)
Frontal: toward the forehead, forward (frons = forehead)
Caudal: downward (cauda = tail)
Cranial: in an upward direction (cranium = skull)
Lateral: toward the side (latus = side)
Marginal: toward the edge (margo = margin)
Nasal: toward the nose (nasus = nose)
Occipital: toward the back of the head (occiput = back of head)
Peripheral: outlying, located in the periphery
Posterior, at the back (post = after/behind)
Sagittal: in the plane of the suture between the parietal bones of the skull or in a parallel plane (sagitta = arrow)
Temporal: toward the temple (tempus = temple)
Ventral: in a forward direction (venter = belly)

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