Crown (tooth)
In dentistry, the crown is the visible part of the tooth above the gingival margin and is an essential component of dental anatomy. Covered by enamel, the crown plays a crucial role in cutting, tearing, and grinding food. Its shape and structure vary depending on the type and function of the tooth, and differ between primary dentition and permanent dentition. The crown also contributes to facial aesthetics, speech, and oral health.
Anatomical crown vs clinical crown
The anatomical crown refers to the portion of the tooth covered by enamel, regardless of whether it is visible. The clinical crown is the part of the tooth that is visible in the mouth. In a healthy young adult, the gums typically follow the contour where enamel meets the root, so the clinical and anatomical crowns are similar in size. However, with age or periodontal disease, this may change.Terminology of tooth surfaces
To describe the location and orientation of the crown's surfaces, dental professionals use several standard terms.The surface of the tooth that faces the lips or cheeks is referred to as the facial surface. In anterior teeth, such as incisors and canines, this surface is more specifically known as the labial surface, while in posterior teeth, such as premolars and molars, it is termed the buccal surface.
The lingual surface is the side of the tooth that faces the tongue. In the upper jaw or maxillary arch, this surface may also be referred to as the palatal surface due to its proximity to the palate.
The occlusal surface is the chewing surface found on posterior teeth, whereas anterior teeth have an incisal edge, which is a sharp cutting edge used for biting.
The sides of a tooth that make contact with neighbouring teeth are called proximal surfaces. If the surface faces toward the midline of the dental arch, it is known as the mesial surface. Conversely, if it faces away from the midline, it is termed the distal surface.
Function of the tooth crown
The crown contributes to multiple functions, including mastication, speech, aesthetics, and protection of supporting oral structures. Incisors, positioned at the front of the mouth, have sharp edges for cutting food and aiding in speech. Canines have pointed cusps to tear food and support the bite. Premolars combine tearing and grinding functions, while molars, with their broad surfaces, are specialised for crushing and grinding food.Structure of the anatomical crown
The anatomical crown refers to the portion of a tooth covered by enamel, it includes three main layers: enamel, dentine, and the pulp chamber.Enamel
Enamel is the outermost and hardest tissue in the human body. It consists of approximately 96% inorganic material, primarily in the form of carbonated hydroxyapatite crystals, with the remainder composed of organic matrix and water. Its main function is to protect the underlying dentine and aid in food breakdown through mastication.Enamel is formed during amelogenesis, a two-stage process beginning with the secretion of an organic matrix by ameloblasts near the dentinoenamel junction. Once mineralisation reaches 96%, enamel formation is complete, and no further deposition occurs due to the degeneration of ameloblasts.
At the microscopic level, enamel has a complex structure composed of enamel rods and interrod enamel, arranged in a prism-like pattern which contributes to its density and mechanical strength.
Dentine
Dentine lies beneath the enamel and forms the bulk of the anatomical crown. It supports the enamel and protects the innermost pulp chamber. Composed of 70% inorganic material, 20% organic matrix, and 10% water, dentine is resilient and capable of absorbing functional stresses.The structure of dentine includes dentinal tubules that extend from the enamel-dentine junction to the pulp. These tubules are surrounded by peritubular and intertubular dentine, contributing to its mechanical properties and sensitivity.
Pulp chamber
The pulp chamber is the innermost part of the anatomical crown and contains blood vessels, nerves, lymphatics, and odontoblasts. It plays a role in dentine formation, nutrient delivery, and pain response.Though mainly associated with root canal treatments, the pulp chamber's position within the crown is important in clinical practice. Several anatomical "laws" have been described to aid in locating the pulp chamber during restorative or endodontic procedures:
- Law of centrality: The pulp chamber is always located in the centre of the tooth at the level of the cementoenamel junction.
- Law of concentricity: At the CEJ level, the pulp chamber walls are concentric to the external surface of the crown.
- Law of the CEJ: The CEJ is the most consistent landmark for locating the pulp chamber.
Differences between primary and permanent crowns
Primary teeth differ from permanent teeth in several anatomical and structural ways. The crowns of primary teeth are generally shorter and broader, with a thinner layer of enamel, making them more susceptible to wear. This enamel also gives them a whiter appearance compared to permanent teeth. In anterior teeth, mamelons, small bumps on the incisal edge of newly erupted permanent incisors, are absent in the primary dentition. The cervical ridges are more pronounced, particularly in molars, and the crowns are more bulbous with a distinct cervical constriction.
Structurally, the roots of primary teeth are thinner and more widely spread, with short or absent root trunks. These adaptations facilitate natural exfoliation as the underlying permanent teeth erupt.
Functionally and morphologically, primary molars have narrower occlusal tables and flatter buccal and lingual surfaces, whereas anterior primary teeth are proportionally wider mesiodistally compared to their crown height. These distinctions are important during dental assessments and restorative procedures.
Morphological variation across tooth types
Incisors
In the permanent dentition, maxillary central incisors have broad, rectangular crowns with a straight incisal edge. Newly erupted incisors often display three mamelons, which wear down with time. The lingual surface contains a distinct cingulum bordered by mesial distal marginal ridges, enclosing a shallow lingual fossa. Maxillary lateral incisors are smaller, with rounded incisal angles and a deeper lingual fossa that may include developmental grooves. Mandibular central incisors are the smallest teeth and exhibit a symmetrical crown with a straight incisal edge and smooth lingual surface. Mandibular lateral incisors are slightly larger and possess a distally sloping incisal edge.Primary maxillary central incisors have crowns wider mesiodistally than inciso-cervically, a feature not found in any other tooth. They lack mamelons and display a prominent cingulum and marginal ridges with a deeper lingual fossa. Primary lateral incisors are smaller with more rounded incisal angles. In the mandible, primary central incisors are symmetrical with a tapered crown and smooth lingual surface, while lateral incisors are slightly larger with a distally sloped incisal edge.
Canines
Permanent maxillary canines are characterised by a prominent labial ridge, a well-developed cingulum, and a pronounced pointed cusp. The crown appears diamond-shaped from the incisal view, with strong mesial and distal slopes. The lingual anatomy includes a central ridge flanked by shallow fossae and prominent marginal ridges. Mandibular canines are narrower mesiodistally, with a less prominent cingulum and smoother lingual surface. Their crowns are generally flatter and less pointed than those of maxillary canines.In the primary dentition, maxillary canines maxillary canines have prominent, sharp cusps with longer mesial slopes. The crown is constricted cervically and appears more bulbous.
Premolars
Maxillary premolars usually have two cusps–buccal and lingual. The first premolars show sharp buccal cusp and a smaller lingual cusp separated by a central groove. They often exhibit a pronounced buccal ridge and occlusal sulcus. The second premolars are smaller with cusps of more equal height and display more supplemental grooves on the occlusal surface.Mandibular first premolars have a dominant buccal cusp and a much smaller lingual cusp, often giving the appearance of a single cusp. The crown tapers sharply towards the lingual side. Second premolars typically have two lingual cusps and a broader, square, or round occlusal table. Their occlusal groove pattern may vary from Y, H, to U shapes.
Molars
Maxillary first permanent molars have four main cusps, and sometimes a fifth cusp known as the cusp of Carabelli. The occlusal surface typically has a rhomboidal shape and includes a distinct oblique ridge connecting the mesiopalatal and distobuccal cusps. Second maxillary molars are smaller, and the distopalatal cusp may be reduced or absent, giving rise to a heart-shaped occlusal form. Third molars are highly variable in anatomy, often smaller and more rounded, with numerous accessory grooves and ridges.Mandibular first molars have five cusps and a pentagonal occlusal outline. They include three buccal and two lingual cusps, separated by distinct grooves. The mesiobuccal cusp is typically the largest. Second molars have four cusps of nearly equal size and a rectangular occlusal outline, with grooves forming a cross pattern. Third molars exhibit significant anatomical variation and often have wrinkled occlusal surfaces due to supplemental grooves.
Primary molars differ in shape and size from permanent molars. Maxillary first molars have a prominent mesiopalatal cusp and a smooth buccal surface with minimal grooves. Second molars resemble permanent maxillary first molars and include a cusp of Carabelli. Mandibular first molars are unique in shape and do not resemble any permanent teeth, featuring a strong mesial marginal ridge and pronounced curvature at the cervical third. Second mandibular molars resemble the permanent mandibular first molars but are smaller in all dimensions.