Macroscopic Structure of a Tooth
Anatomically, each tooth is divided into three clearly differentiable parts. The part projecting above the gingiva and directly participating in mastication is called the crown (corona dentis). The constricted region serving as the boundary between the crown and the root is designated as the neck of the tooth (cervix dentis). The part concealed within the jaw alveolus is the root of the tooth (radix dentis).
Inside each tooth lies a complex system of spaces known as the pulp cavity. It includes:
- Pulp chamber (cavitas coronae) — the expanded part of the space located inside the crown.
- Root canal (canalis radicis dentis) — the narrowed continuation of the cavity running through the entire root.
This entire internal system is filled with loose connective tissue — the dental pulp (pulpa dentis), which contains vessels and nerves.
Dental Tissues and Supporting Apparatus
From a histological standpoint, a tooth consists of three main hard tissues, each with a specific location:
- Enamel (enamelum) — covers the tooth crown externally, protecting it from external influences.
- Dentin (dentinum) — forms the bulk of the entire tooth, located beneath the enamel in the crown and beneath the cementum in the root region.
- Cementum (cementum) — covers the outer surface of the tooth root in a thin layer.
For secure fixation of the tooth in the jaw, the periodontium (periodontium) is present. It surrounds the tooth root, firmly attaching it to the alveolar wall, and plays a critical role in shock absorption and the uniform distribution of masticatory load.
Tooth Surfaces
In anatomy, for precise orientation, five surfaces of the tooth crown are distinguished based on their orientation within the oral cavity:
- Lingual surface (facies lingualis) — faces inward toward the oral cavity and the tongue.
- Vestibular surface (facies vestibularis) — faces outward toward the oral vestibule (lips or cheeks).
- Occlusal surface (facies occlusalis) — the masticatory surface that contacts opposing teeth of the opposite jaw.
- Contact surfaces (facing adjacent teeth in the arch): mesial (facies medialis), directed toward the center of the dental arch, and distal (facies distalis), directed away from the center.
Classification by Shape and Dentition
Depending on crown morphology and function, all teeth are divided into four groups:
- Incisors (dentes incisivi)
- Canines (dentes canini)
- Premolars (dentes premolares)
- Molars (dentes molares)
Based on eruption timing, two generations of teeth are distinguished: deciduous (dentes decidui) and permanent (dentes permanentes).
Deciduous Teeth
There are a total of 20 deciduous teeth — 10 on each of the upper and lower jaws. They begin to erupt around 6 months of age and finish by approximately 2 years. Their main differences from permanent teeth are:
- smaller overall size;
- crowns are visually wider and shorter;
- roots are shorter and thinner;
- premolars are entirely absent in the deciduous dentition.
The deciduous dental formula is traditionally written with Roman numerals (for one half of the jaw): V IV III II I | I II III IV V.
Permanent Teeth
An adult normally has 32 permanent teeth (16 on each jaw). Each jaw quadrant contains a strict set: 2 incisors, 1 canine, 2 premolars, and 3 molars.
In dentistry, a clinical formula is used where permanent teeth are designated by Arabic numerals from the center outward: 8 7 6 5 4 3 2 1 | 1 2 3 4 5 6 7 8. The FDI two-digit system is also widely applied, assigning a two-digit code to each tooth: the first digit indicates the jaw quadrant, and the second indicates the tooth position.