Anatomical terminology provides a standardized language for medical professionals to pinpoint exact locations. This system uses fixed points of reference, ensuring that descriptions of body parts are understood universally, regardless of the body’s current posture. The terms mesial and distal are specialized directional descriptors used to describe relative position within a structure.
Defining Mesial and Distal
Mesial and distal are opposing directional terms describing a point’s relative location along a longitudinal axis, referencing a central plane. Mesial refers to a position or direction that is closer to this central reference point, while distal refers to a position or direction that is further away.
This relationship is always comparative; a point can be mesial to one object and simultaneously distal to another object farther along the axis. The entire concept relies on defining a clear origin for the measurement. These terms are a specialized subset of anatomical language, primarily used when standard terms like medial and lateral are insufficient.
Use in General Anatomical Positioning
In general human anatomy, particularly when describing the torso and limbs, the primary directional terms used are proximal and distal. Proximal describes a position closer to the trunk of the body or the point of attachment of a limb, while distal describes a position farther away from that point of origin. For instance, the elbow is proximal to the wrist but distal to the shoulder joint.
The terms mesial and distal are not typically used for the primary axis of a limb or the trunk, where medial (closer to the body’s midline) and lateral are the standard descriptors. However, the concept of distal—meaning farther from the origin—is consistent with its specialized definition, such as the ankle being the most distal major joint in the leg relative to the hip.
Specific Application in Dentistry
The most common application of mesial and distal is within the field of dentistry. In this context, the central reference point is the median sagittal plane, or the midline of the face, which runs vertically between the two central incisors. Every tooth in the dental arch has five surfaces, and the two surfaces that touch adjacent teeth are the mesial and distal surfaces.
The mesial surface of a tooth is the side that faces toward the midline of the dental arch, or toward the front of the mouth. The distal surface is the side that faces away from the midline, or toward the back of the mouth. For nearly every tooth, its mesial surface is in contact with the distal surface of the tooth in front of it. The only exception is the pair of central incisors, where the mesial surfaces of the two teeth touch each other at the exact midline.
Understanding these surfaces is fundamental for diagnosis and treatment planning in dental care. For example, a dentist describing an area of decay might use the term “disto-occlusal” to specify a cavity located on the chewing surface and extending onto the distal surface of a molar. These surfaces, collectively known as the proximal surfaces, are particularly susceptible to dental caries because they are difficult to clean with a toothbrush alone.
Therefore, X-ray examinations, such as bitewings, are routinely used to check for lesions, or “proximal decay,” that often begin on the mesial or distal sides of the teeth. The last tooth in each arch, such as the wisdom tooth, only has a mesial surface that contacts the tooth in front of it; its back side is entirely distal and does not contact another tooth. The consistent use of mesial and distal ensures that any professional can interpret a patient’s chart and understand the exact location of a dental feature.