Macroscopic structure of the tooth
Anatomically, each tooth is divided into three clearly differentiable parts. The part protruding above the gingiva and directly participating in mastication is called the clinical crown (corona dentis). The narrowed area that serves as the boundary between the crown and the root is designated as the cervix of the tooth (cervix dentis). The part concealed within the dental 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 cavity (cavitas coronae) — the expanded portion 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 perspective, a tooth consists of three main hard tissues, each with its specific localization:
- Enamel (enamelum) — covers the crown of the tooth 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) exists. It surrounds the tooth root, firmly attaching it to the alveolar wall, and plays a crucial role in shock absorption and the even distribution of masticatory load.
Tooth surfaces
In anatomy, for precise orientation, five surfaces of the tooth crown are distinguished depending on their direction in the oral cavity:
- Lingual surface (facies lingualis) — faces inward toward the oral cavity and the tongue.
- Vestibular surface (facies vestibularis) — faces outward toward the vestibule of the mouth (towards the 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 same dental arch): mesial (facies medialis), directed closer to the center of the dental arch, and distal (facies distalis), directed away from the center.
Classification by shape and occlusion
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)
Depending on eruption times, two generations of teeth are distinguished: deciduous teeth (dentes decidui) and permanent teeth (dentes permanentes).
Deciduous teeth
There are a total of 20 deciduous teeth in the primary dentition — 10 on each of the upper and lower jaws. They begin to erupt between 6 months and finish around 2 years of age. Their main differences from permanent teeth are:
- smaller overall size;
- crowns appear wider and shorter;
- roots are shorter and thinner;
- premolars are completely absent in the primary dentition.
The deciduous dental formula is traditionally written in 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 half of the jaw contains a strict set: 2 incisors, 1 canine, 2 premolars, and 3 molars.
In dentistry, the 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 international system is also widely used, in which each tooth is assigned a two-digit code: the first digit indicates the jaw quadrant number, and the second indicates the tooth serial number.
Briefly: answers to topical questions
What quadrant numbers are used in the FDI system for permanent and deciduous teeth?
In the FDI two-digit international system, different quadrant numbers are used to designate permanent and deciduous teeth.
- Permanent teeth — designated by digits from 1 to 4 (1 — upper right jaw, 2 — upper left jaw, 3 — lower left jaw, 4 — lower right jaw).
- Deciduous teeth (dentes decidui) — designated by digits from 5 to 8.
Which nerves innervate the teeth of the upper jaw?
The teeth of the upper jaw are innervated by branches of the maxillary nerve (n. maxillaris), originating directly from it or from the infraorbital nerve (n. infraorbitalis).
- Posterior superior alveolar branches (nn. alveolares superiores posteriores) — arise from the maxillary nerve.
- Superior middle alveolar branch (ramus alveolaris superior medius) — innervates the upper premolars.
- Superior anterior alveolar branches (rami alveolares superiores anteriores) — innervate the incisors and canines.
These branches jointly participate in the formation of the superior dental plexus.
At what age do permanent teeth erupt?
The eruption of permanent teeth in humans occurs over a fairly wide age range. Humans experience only one set of teeth replacement during their lifetime. The process of replacing deciduous teeth with permanent ones begins at 6–7 years of age and finally concludes by 18–30 years. A total of 32 permanent teeth are formed — 16 on the upper and lower jaws.
How many roots do molars have?
The number of roots in molars depends on their location in the jaws.
- Maxillary molars — have 3 roots.
- Mandibular molars — have 2 roots (anterior and posterior, flattened in the anteroposterior direction).
An exception is the mandibular third molar (dens molaris tertius inferior), whose anatomy is variable: it can have one or more roots, which are often curved and fused together.
What structures are part of the periodontium?
The periodontium (the supporting apparatus of the tooth) is a morphofunctional complex of tissues surrounding the tooth. It includes the following structures:
- Gingiva — includes the gingival epithelium, sulcular epithelium, and junctional epithelium.
- Periodontal ligament — a dense connective tissue ligament that fills the periodontal space and anchors the tooth root.
- Alveolar bone is the wall of the dental alveolus of the jaw.
- Cementum (cementum) is the calcified tissue covering the roots and neck of the tooth.
Which arteries supply blood to the mandibular teeth?
Blood supply to the mandibular teeth is provided by branches of the inferior alveolar artery (a. alveolaris inferior). This artery enters the mandibular canal (canalis mandibulae) and gives off the following branches:
- Dental branches (rr. dentales) directly supply blood to the mandibular teeth.
- Peridental branches (rr. peridentales) supply blood to the alveoli and gingiva.
The inferior alveolar artery itself is a branch of the maxillary artery (a. maxillaris), which originates in its mandibular part (pars mandibularis).
To remember the set of teeth in one half of the dental arch for the permanent dentition, use the digital series 2-1-2-3 (2 incisors, 1 canine, 2 premolars, 3 molars).
Class and exam questions
What is the main difference in composition between deciduous and permanent teeth?
The deciduous dentition contains a total of 20 teeth and completely lacks premolars.
What is the name of the type of joint between the tooth and the jaw?
This type of joint is called gomphosis, and it is fixed by means of the periodontium.
Which tissue forms the bulk of the tooth?
The bulk of the tooth is formed by dentin (dentinum), which is located beneath the enamel and cementum.
What else to study on this topic
- Anatomical features of incisors and canines
- Differences between premolars and molars
- Topography of root canals in different tooth groups
- Principles of the FDI two-digit system
- Blood supply and innervation of the dental pulp
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