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Cusp (anatomy)
Cusp (anatomy)
Cusp (anatomy)
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Cusp
The teeth of the right side of the mouth, shown contacting the teeth in the opposing jaw with their cusp tips
Details
Identifiers
Latincuspis dentis
TA98A05.1.03.010
TA2925
FMA56481
Anatomical terminology
1. Tooth
2. Enamel
3. Dentin
4. Dental pulp
5. cameral pulp
6. root pulp
7. Cementum
8. Crown
9. Cusp
10. Sulcus
11. Neck
12. Root
13. Furcation
14. Root apex
15. Apical foramen
16. Gingival sulcus
17. Periodontium
18. Gingiva
19. free or interdental
20. marginal
21. alveolar
22. Periodontal ligament
23. Alveolar bone
24. Vessels and nerves
25. dental
26. periodontal
27. alveolar through channel

A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth. The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has two cusps, is also known as the bicuspid valve, and the tricuspid valve has three cusps.

In humans

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A cusp is an occlusal or incisal eminence on a tooth. Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps. In certain populations the maxillary molars, especially first molars, will possess a fifth cusp situated on the mesiolingual cusp known as the Cusp of Carabelli.

One other variation of the upper first premolar is the 'Uto-Aztecan' upper premolar. It is a bulge on the buccal cusp that is only found in Native American Indians, with highest frequencies of occurrence in Arizona. The name is not a dental term; it comes from a regional linguistic division of Native American Indian language groups.

Cusps on the molars of therian mammals

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See also: Glossary of mammalian dental topography
Right upper molar showing the four main upper molars cusps

There are four main cusps found on the molars of the upper dentition of therian mammals.

Hypocone

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The hypocone is found on the distal lingual side of the tooth. It fits into the grooves of the lower dentition and is an adaptation for the overall grinding and tearing of foods using the occlusal (chewing side) of the tooth surface during occlusion or mastication (chewing). Its strength is due to the thickness of the enamel which differs among species of hominids. The hypocone appears to have evolved independently more than twenty times in different mammal groups during the Cenozoic period.[1]

Metacone

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The metacone is a cusp on the molars of the upper dentition in hominids. It is found at the buccal distal area of the tooth. The crests between the cusps are adaptations for slicing food during occlusion or mastication (chewing).

Paracone

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The anterior of the three cusps of a primitive upper molar that in higher forms is the principal anterior and outside cusp.

Protocone

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The protocone is founding the molars of the upper dentition in Placental and Marsupial vertebrates.[2] It is found at the mesiolingual area of the tooth. The crests between the cusps are adaptations for slicing food during occlusion or mastication (chewing).

See also

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References

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Bibliography

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cusp (anatomy)

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from Grokipedia
In anatomy, a cusp is a pointed or rounded eminence or projection, most notably appearing as an elevation on the occlusal surface of a or as a thin, leaflike segment of a that facilitates unidirectional blood flow. These structures vary in form and function depending on their location but share a role in mechanical processes such as mastication or valve closure. In dental anatomy, cusps are key components of the tooth crown, forming during odontogenesis in the bell stage of tooth development where the enamel knot signals the differentiation of odontoblasts and ameloblasts to create these projections. Canine teeth typically feature a single prominent cusp, premolars have two, and molars possess four or more, enabling efficient grinding and shearing of food during mastication. These cusps are covered by enamel and supported by underlying , with their size, shape, and arrangement contributing to occlusal harmony and overall dental function. In cardiac anatomy, cusps are the triangular leaflets of the semilunar valves—the aortic and pulmonic valves—each normally comprising three cusps separated by commissures and featuring a central nodule of Arantius for enhanced sealing during . These cusps consist of layered , including a collagen-rich fibrosa for structural integrity, a proteoglycan-filled spongiosa to absorb , and elastic ventricularis fibers for recoil, ensuring competent closure to prevent regurgitation. The geometry of these cusps, such as effective height (typically 9–10 mm in adults), is critical for competence and is influenced by their attachment within the aortic or pulmonary . Abnormalities in cusp number or form, like bicuspid aortic valves, can lead to dysfunction and require surgical consideration.

Dental cusps

Definition and morphology

In dental anatomy, a cusp is a pointed or rounded eminence on the occlusal or incisal surface of a , forming a key component of that aids in mastication. Cusps are pyramidal elevations with a cusp tip at the peak, covered by enamel and supported by underlying , varying in size, shape, and number depending on the tooth type. For instance, cusps on posterior teeth are broader and more rounded for grinding, while those on are sharper for tearing. Cusps develop during odontogenesis in the bell stage of tooth formation, where the enamel knot—a signaling center in the dental —initiates cusp patterning by directing the differentiation of odontoblasts and ameloblasts. Mineralization begins at the cusp tips and progresses cervically toward the root. Morphologically, cusps consist of an outer enamel layer (approximately 96% mineralized ), a core (about 70% mineral), and proximity to the pulp chamber, which provides vascular and neurosensory support. Cusp ridges and inclined planes extend from the tip, forming the occlusal anatomy that interdigitates with opposing teeth.

Functions in mastication

Dental cusps play a central biomechanical in mastication by facilitating the grinding, tearing, and shearing of through precise occlusal contacts. During the cycle, cusps interdigitate with opposing teeth's fossae and ridges, enabling efficient breakdown of the food bolus as the moves toward maximum intercuspation. This arrangement allows cuspal inclines to pass across one another, creating shear forces that pulverize tougher food particles while minimizing slippage. Cusps are classified occlusally into supporting and guiding types, each contributing distinctly to masticatory efficiency. Supporting cusps, such as the lingual cusps of maxillary posterior teeth and buccal cusps of mandibular posterior teeth, bear vertical forces during centric occlusion, maintaining the vertical dimension and providing stability through broad, rounded tips that contact flat opposing surfaces. In contrast, guiding cusps, exemplified by the buccal cusps of maxillary posterior teeth and lingual cusps of mandibular posterior teeth, facilitate lateral and protrusive excursions by directing mandibular movements and aiding in shearing actions during non-centric positions. This classification ensures even force distribution in centric occlusion while allowing disocclusion of posterior teeth during excursions to reduce lateral stresses. Beyond direct , cusps contribute to overall stability by promoting proper alignment and optimal force transmission along the long axes of teeth, which prevents uneven wear and structural overload. They also provide sensory feedback through mechanoreceptors in the periodontal ligaments, relaying occlusal contact information to the to modulate positioning, muscle activity, and efficiency. Pathologically, cusp fractures or excessive wear—often resulting from trauma, parafunctional habits like , or weakened enamel—can lead to sensitivity, altered occlusion, and , potentially causing temporomandibular disorders. In , such damage necessitates cusp coverage with materials like amalgam or composites to restore function and prevent further complications.

Cusps in human dentition

In human dentition, cusps are primarily found on posterior teeth, with their number and configuration varying by tooth type to support functions such as piercing, crushing, and grinding. Canines typically feature a single prominent cusp that aids in tearing and piercing , while premolars generally have two cusps—a larger buccal cusp and a smaller lingual cusp—facilitating initial crushing of particles. Molars exhibit more complex arrangements, with four to five cusps arranged to enhance grinding efficiency during mastication.
Tooth TypeTypical Number of CuspsKey Cusp PositionsExample Tooth
Canines1Single apical cuspMaxillary/mandibular canine
Premolars2Buccal and lingual
Molars4–5Mesiobuccal, distobuccal, mesiolingual, distolingual (plus accessory in some)Mandibular first molar (5 cusps)
The mandibular first molar, for instance, possesses five main cusps: the mesiobuccal, distobuccal, mesiolingual, distolingual, and distal (hypoconulid), often separated by a Y-shaped groove pattern that defines its occlusal surface. In contrast, the maxillary first molar typically has five cusps, including the four primary ones plus the accessory on the mesiolingual aspect of the mesiopalatal cusp, which varies in size from a small groove to a distinct . Variations in cusp morphology occur across populations and can manifest as anomalies. The is a rare developmental anomaly presenting as a protruding, talon-like structure on the lingual surface of incisors or , potentially extending to the incisal edge and complicating occlusion or hygiene. appears as an accessory cusp-like on the occlusal surface of , more prevalent in Asian populations and prone to pulp exposure if fractured. Ethnic-specific traits include the Uto-Aztecan premolar bulge, a distobuccal and enlargement of the buccal cusp on the , observed at higher frequencies in Native American groups. Clinically, cusp alignment influences orthodontic treatments, where malocclusions involving cusp interferences may require adjustments to achieve proper bite harmony. In , variations like accessory cusps necessitate customized restorations to restore occlusal function and prevent uneven wear. Cusp development can also be affected by , a condition resulting in thin or pitted enamel on cuspal surfaces, often linked to nutritional deficiencies or genetic factors, increasing susceptibility to caries and requiring preventive interventions.

Cusps in therian mammal molars

Therian mammals, encompassing both placental (eutherians) and marsupial (metatherians) lineages, exhibit tribosphenic dentition as a defining feature of their molars, characterized by a primitive four-cusp pattern on the upper molars that facilitates a transverse chewing motion for efficient shearing and grinding of food. This pattern consists of the protocone (mesiolingual cusp for primary grinding), paracone (mesiobuccal cusp for initial shearing), metacone (distobuccal cusp for tearing and secondary shearing), and hypocone (distolingual cusp that enhances grinding surfaces). The opposing lower molars feature a trigonid with protoconid, paraconid, and metaconid cusps, along with a talonid basin, allowing precise occlusion that supports versatile mastication. Originating in Early Cretaceous therian ancestors around 125-100 million years ago, this dentition marked a key innovation enabling the diversification of therians from earlier mammaliaforms. The hypocone, absent in the primitive triangular upper molar, evolved through the expansion of a posterior cingulum and appeared independently more than 20 times during the era, particularly in lineages adapting to folivorous diets. In herbivorous therians such as ungulates, the hypocone is often enlarged, forming a quadrate occlusal surface that promotes thorough pulverization of fibrous vegetation, as seen in the bunodont or lophodont molars of and perissodactyls. Conversely, carnivorous therians like felids and canids exhibit reduced or modified cusps, with emphasis on pairs (e.g., paracone-metaconid) for slicing , leading to sectorial rather than grinding-dominant morphology. Fossil evidence from Purgatorius-like stem placentals in the early (around 66 million years ago) reveals well-developed tribosphenic molars with all four upper cusps, indicating rapid post-Cretaceous-Paleogene boundary radiation from precursors. Compared to non-therian mammals such as monotremes, therian molars differ fundamentally: monotremes possess a more primitive, V-shaped cusp arrangement without a distinct hypocone or true tribosphenic occlusion, limiting their chewing to simple puncture-crush actions rather than transverse shear. This therian-specific pattern played a pivotal role in dietary specialization, allowing adaptations from insectivory in basal forms to extreme herbivory or carnivory, and correlating with higher species diversity in hypocone-bearing clades.

Cardiac cusps

Definition and morphology

In cardiac anatomy, cusps are thin, flexible leaflets or flaps that form the primary components of the semilunar heart valves, serving to prevent retrograde blood flow during the . These structures are essential for unidirectional blood propulsion, with semilunar valves (aortic and pulmonary) featuring three cusps each. Morphologically, cardiac cusps consist of a core of rich in and fibers, overlaid by a continuous endothelial lining that minimizes thrombogenicity and facilitates smooth blood flow. Semilunar cusps are typically thinner and crescent-shaped, with nodular thickenings known as nodules of Arantius at the midpoint of their free edges to enhance coaptation and sealing. Cardiac cusps originate developmentally from , which form through epithelial-to-mesenchymal transition in the atrioventricular canal and outflow tract during embryogenesis around weeks 4-6 of . These cushions remodel into mature valve leaflets via , deposition, and cellular proliferation. A notable congenital variation is the , where fusion of two semilunar cusps occurs, affecting 1-2% of the population and predisposing to or regurgitation later in life. In gross anatomy, the base of each cusp attaches to the fibrous skeletal annuli surrounding the valve orifices, providing structural support and electrical insulation between chambers. The free edges of opposing cusps meet to form coaptation zones, ensuring competent valve closure under pressure gradients.

Functions in circulation

Cardiac valve cusps, also known as leaflets, primarily function to maintain unidirectional blood flow through the heart by passively opening and closing in response to pressure gradients generated during the cardiac cycle. During ventricular systole, semilunar cusps open to permit ejection; conversely, in diastole, semilunar cusps close to prevent regurgitation of blood back into the ventricles. This passive mechanism relies on the cusps' coaptation, where their edges meet to form a tight seal. Biomechanically, the cusps respond to hydrodynamic forces that drive their motion and ensure efficient circulation. In semilunar valves, blood flow creates vortices within the sinuses of Valsalva, which fill the cusps and promote rapid closure while minimizing turbulence and energy dissipation during the transition from systole to diastole. Cusp inversion occurs under these forces, allowing the leaflets to evert slightly during opening and recoil via elastin fibers to restore shape, thereby reducing shear stress on the endothelium and optimizing flow profiles. This design contributes to low-resistance passage of blood, with peak velocities in healthy valves typically around 1-1.35 m/s for semilunar types, preventing excessive energy loss. The cusps' roles are critical to overall heart performance, as they ensure complete ventricular ejection during —ejecting approximately 70 mL of per beat in adults—and maintaining at about 5 L/min at rest. Dysfunction, such as incomplete coaptation or stiffening, leads to valvular insufficiency (regurgitation fractions up to 60% in severe cases), (with transvalvular pressure gradients exceeding 40 mmHg), or turbulent flow producing audible murmurs. These impairments compromise hemodynamic efficiency and can precipitate if untreated. Adaptively, cardiac cusps remodel in response to hemodynamic stress through extracellular matrix reorganization by valve interstitial cells, aligning fibers to withstand cyclic pressures up to 120 mmHg. However, with aging, progressive —often involving osteoblast-like phenotypes—reduces cusp flexibility, leading to thickening and impaired motion that exacerbates risk, particularly in the after age 65.

Structure in specific heart valves

The , located at the outflow tract of the right ventricle into the , is composed of three semilunar cusps: the anterior, left, and right. These cusps are relatively thin and flexible, consisting of four histological layers—the thin arterialis facing the artery, the dense fibrosa of , the spongiosa rich in proteoglycans, and the elastic ventricularis—allowing rapid opening and closure. They are supported by the sinuses of Valsalva, which form dilations or pockets between the cusps and the arterial wall, aiding in preventing cusp adhesion during and facilitating coronary blood flow. The , situated at the base of the left leading to the , includes three semilunar cusps: the right coronary, left coronary, and non-coronary. The right and left coronary cusps contain the ostia of the respective within their associated sinuses of Valsalva, ensuring perfusion of the during when the cusps are closed. Composed primarily of collagen-rich membranes anchored to a fibrous ring, these cusps are particularly susceptible to , a degenerative process that accelerates with age and can lead to or regurgitation, especially in structurally abnormal variants. A notable structural variation is the anomaly, a congenital condition where the has only two cusps instead of three, resulting in a potentially narrowed or obstructed opening that impairs blood flow. This anomaly affects 1-2% of the and often involves fusion of two cusps, increasing the risk of early and associated complications. Racial differences in cusp dimensions and related aortic root measurements have been observed; for example, with exhibit smaller aortic annulus (2.1 ± 0.4 cm vs. 2.4 ± 0.4 cm), sinuses of Valsalva (3.1 ± 0.6 cm vs. 3.4 ± 0.7 cm), and (3.2 ± 0.5 cm vs. 3.5 ± 0.7 cm) dimensions compared to Caucasians, despite comparable valve morphology and higher prevalence of risk factors like . In contrast, Asian individuals with more frequently present with right-noncoronary cusp fusion and larger overall aortic dimensions than Europeans.

References

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