biology

Glossary of mammalian dental topography

Glossary of mammalian dental topography is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Glossary of mammalian dental topography rather than just read about it. In short: Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology.

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Reference excerpt

Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn in 1907 and is, although with many variations, the one that continues today.

Suffixes Tooth structures bear suffixes in order to note the type of structure they are and whether they are present in the upper or lower molars.

The suffix "-cones /-conids" (upper molar/lower molar) is added to the main cusps: Paracone, Metacone, Protocone and Hypocone on the upper molar, and Paraconid, Metaconid, Protoconid, Hypoconid and Entoconid on the lower molar. This name is used for both bunodont and selenodont molars, that is, as many for "buno" pillar-like cusps as for "selenes" crescent-like cusps. The suffix "-conule /-conulid" (upper molar/lower molar) is added to the secondary cusps. For example, Metaconule, Hypoconulid. The suffix "-style/-stylid" (upper molar/lower molar) is added to the peripheral cusps that are found in the cornices or cingulus of the tooth. These cusps are traditionally named according to their proximity to the main cusps, although some anatomists prefer to name them according to their position on the tooth. The suffix "-loph/-lophid" (upper molar/lower molar) is added to the crests that join cusps together. They include in the name one the cusps involved. For example, the hypolophid is the ridge that unites the hypoconid with the entoconid. These ridges often have secondary ridges: the secondary crest of the ectoloph is called crista; antecrochet to that of the protoloph, and crochet to that of the metaloph. The suffix "-crista / -cristid" (upper molar / lower molar) is used for the ridges that come out of the cusps but do not connect them with other cusps. It is also used to name the edges of selenes. To the structures in the lingual part of the molar, the prefix "ento-" ("internal") is often added, while those of the lingual part are added the prefix "ecto-" ("external"). the mesial part of the molar is often added the prefix "pre-" (from "previous") while those of the distal part are added the prefix "post-" ("posterior"). The mesial part is that which is towards the incisors. The suffix "-flexus / -flexid" (upper molar / lower molar) is used for the open valleys in the occlusal surfaces of the hypsodont teeth. When this valleys are enclosed, they are called fossetes/fossetids (upper molar / lower molar). Sometimes they are used also for the folds of the teeth, although the proper name for the folds is sulcus (pl. sulci). The cusp prefixes "para-", "meta-", "proto-", "hypo-", etc., are related to the succession and position of the cusps according to the ancient tritubercular theory of the evolution of molars from Cope and Osborn. Although this theory has lost its validity, they continue to use the names for the description of the molars. The prefix "proto" referred to the original cusp which would be homologous to a single cusp tooth according to Osborn, and would be the first cusp to appear not only in evolution but in development. This was criticized early by studies of embryology where it was shown that the first cusp in the embryonic development of the upper molars was the paracone. Later this was shown to be variable and the first cusp to appear in ontogeny would not be related to the evolution of the tooth.

Major features The positions of tooth features are described along four directions: mesial (forwards, towards the chin), distal (backwards, towards the jaw joint), lingual (inwards, towards the tongue), and buccal or labial (outwards, towards the cheek).

Upper teeth Therians (marsupials and placentals) ancestrally have roughly triangular upper molars, with the apex pointing lingually (inwards) and the flat edge positioned labially (outwards). This fundamental three-pointed structure is sometimes called the trigon. Three major cusps are almost always present:

Protocone: A major cusp at the lingual apex of the upper molar. In mammals with tribosphenic teeth, the protocone slides into the talonid basin on the lower teeth in order to grind and crush food. Often the largest cusp in the upper molar, though some insectivorous mammals reduce it substantially. Paracone: A major cusp outwards from the protocone and in front of the metacone. Metacone: A major cusp outwards from the protocone and behind the paracone. Other common features include:

Stylar shelf: A shelf or offset surface along the outer edge of the tooth. Often bears minor cusps (stylar cusps or conules). Parastyle: A forward extension of the stylar shelf which juts out at the mesiolabial (front outer) corner of the tooth, in front of and outwards from the paracone. May bear one or more minor cusps (including the stylocone, which is observed in some extinct mammals). Metastyle: A rearward extension of the stylar shelf which juts out at the distolabial (rear outer) corner of the tooth, behind and outwards from the metacone. May bear one or more minor cusps. Mesostyle: A cusp at the midpoint of the stylar shelf. Ectoflexus: A notch at the midpoint of the stylar shelf. Paraconule / Protoconule: A minor cusp on the front edge of the tooth, between the protocone and paracone. Metaconule: A minor cusp on the rear edge of the tooth, between the protocone and metacone. Hypocone: A fourth major cusp which only becomes widespread in placentals. It develops at the distolingual (rear inner) corner of the tooth, behind the protocone and inwards from the metacone. Mammals with a large hypocone (such as humans) have upper molars with four cusps set in a quadrate (square-shaped) arrangement rather than a triangular form. Many marsupials and artiodactyls have an enlarged metaconule which serves the same role as the hypocone and is occasionally labelled as a hypocone, despite being derived from a different part of the tooth.

Lower teeth Therians ancestrally have lower molars which are longer from front-to-back than from side-to-side. Five to six cusps are most common. The trigonid region at the front part of the molar is triangular, with three large cusps:

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Illustrations

Worked examples

Example 1 — a first encounter with Glossary of mammalian dental topography

Start with the simplest possible case. Write down what Glossary of mammalian dental topography claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Glossary of mammalian dental topography before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Glossary of mammalian dental topography ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Glossary of mammalian dental topography

In research: Glossary of mammalian dental topography appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Glossary of mammalian dental topography in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Glossary of mammalian dental topography is common in secondary-school and first-year university syllabi. It links to neighbouring topics Glossaries of zoology, Mammal anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Glossary of mammalian dental topography outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

What is Glossary of mammalian dental topography in simple terms?

Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology.

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Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Glossary of mammalian dental topography?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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