tooth

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Upper central incisors
Lower left premolar and molar
Lower wisdom tooth

The tooth (plural teeth ), Latin and technical language dens , is a hard structure in the oral cavity of vertebrates. The teeth are used to grasp, chop and grind food. They developed in vertebrates according to the form-function principle. In humans, there are also the functions of sound formation (especially the dental sounds ) and social functions.

etymology

The word Zahn comes from Middle High German zan (t) from Old High German zan (d) and, like Latin dens, belongs to the Indo-European word root (e) don / dnt- ( Urm . * Tanþ- , * tunþ- , Latin dens , Greek ὀδούς ( odoús ), ved. dánt- etc. 'teeth', of indogerman. * h 1 dont- * h 1 DNT , to active participle * h 1 ed- 'apple').

Development history

In terms of developmental history, teeth are ectodermal hard structures (derivatives of the outer skin that have migrated into the mouth) that arise through induction of the underlying mesenchyme of the neural crest . The ectoderm provides the hard enamel, the mesenchyme the remaining components of the teeth such as dentin , cement and the tooth-supporting structures. In their entirety, they are called teeth . They occur for the first time in the jaw mouths ( fish and terrestrial vertebrates ). They developed from the simple skin teeth of ancient fish. The scaly teeth fused to form hard structures with basal bone mass, dentine crown and inner pulp cavity . In mammals (Mammalia) they represent the modified remainder of the ectodermal exoskeletons of older vertebrates in the phylogenetic sense . Primarily toothless are the jawless ( Agnatha ), which have become extinct except for the lampreys and hagfish . The turtles , birds and the mammals (monotremata, egg-laying mammals) have become secondary toothless . In contrast to other vertebrates (fish, amphibians, birds), mammals use their teeth not only to grasp, but also to chew food.

Real and fake teeth

Cross-section through the fossil, rootless tusk of a mammoth

In the animal kingdom a distinction is made between real and fake teeth.

  1. The real teeth consist of enamel (enamelum), dentin and cement as well as the pulp (tooth pulp). They are also called dentin teeth because the dentin is the main component (see heterodontic teeth).
  2. The hard substances enamel, dentin and cement are absent from the false teeth . They are mostly horn teeth , such as those found in the throat and esophagus of leatherback turtles . Primitive rootless teeth come in fish , amphibians and reptiles , and are all the basic type of teeth. You can take the form of slightly pointed, conical have cone teeth, edgy or more jagged in fish to in sharks plaster teeth in snakes fangs reshuffled can be (see homodontic dentition).

Vulgo “false teeth” is also used to describe various types of dentures in humans.

Types of teeth

According to the time of the breakthrough, the size and the shape, a distinction is made in mammals:

  • Milk teeth ( Dentes decidui - Latin literally: sloping) and
  • Permanent teeth ( Dentes permanentes - permanent) after changing teeth .

According to the position in the dentition one differentiates:

  • Incisors ( Dentes incisivi , Incisivi - incisive),
  • Canines ( Dentes canini , Canini - canine ),
  • Anterior teeth ( dentes premolares , premolars ) and
  • Molars ( Dentes molar , molars ).

Incisors and canines form the so-called front teeth in humans - 3 per quadrant, pre-grinding teeth and molars the 5 molars.

In the other classes, numerous other forms of teeth find how the Sägezahngebisse of sharks or "rasp" cog Dentures in bloodsucking lamprey .

According to the crown height , mammals distinguish between low and high crowned teeth. Teeth with a high crown are further divided into those with a late closing root and rootless teeth with a non-closing root and unlimited growth. Renewed teeth are also found in fish , amphibians and reptiles .

Structure of the tooth

1. Tooth 2. Tooth enamel 3. Dentin (dentin) 4. Pulp cavity with pulp 5. Crown pulp 6. Root pulp 7. Root cement 8. Tooth crown 9. Cusps 10. Fissure 11. Tooth neck 12. Tooth root 13. Bifurcation 14. Root tip 15. Foramen apical 16th gingival sulcus 17, attachment apparatus 18 gums 19 oral or vestibular marginal 20 21 22 alveolar ligament with Sharpey's fibers 23. alveolar bone (the fine yellow line is the lamina dura ). 24. Vessels and nerves: 25. Pulp 26. Periodontium 27. Mandibular canal .

Every (real) tooth consists of the tooth crown (Corona dentis), the tooth neck (Cervix dentis, more rarely: Collum dentis) and the tooth root (Radix dentis) and is made up of several layers. In a healthy tooth, you can only see the enamel , which covers the dentine inside like a glaze . The dentin in turn surrounds the pulp . The root is surrounded by tooth cement (cementum) and the periodontal membrane up to the neck of the tooth .

Tooth enamel (enamelum)

Tooth enamel ( Latin : enamelum ) is the hardest substance in the human body with a Vickers hardness of 250 to 550 and a compressive strength of 300 to 450 MPa. Its modulus of elasticity is 50,000-85,000 MPa (Körber, 1995). Tooth enamel is made up of enamel-forming cells called adamantoblasts (also called ameloblasts ). It consists of 95 percent hydroxyapatite (Ca 5 (PO 4 ) 3 OH), a crystalline material, the main parts of which are calcium and phosphate . Tooth enamel is slightly permeable to water-soluble substances, for example its components calcium and phosphate, as well as fluorides . With the help of fluorides, the hydroxyapatite is converted into the harder fluoroapatite (Ca 5 (PO 4 ) 3 (F)). This is why they are used to harden the enamel in toothpastes . Acids, on the other hand, can damage the tooth because they dissolve the calcium and phosphate from the tooth enamel and thus soften it (see tooth decay ).

Dentin

The dentin lies beneath the enamel. It represents the bulk of the tooth. Like enamel, the hard substance of dentin consists of calcium and phosphate, but only two thirds, the rest is protein and water , which is why dentin is softer and more susceptible to tooth decay than tooth enamel. The dentin is sensitive to pain. Heat, cold and contact stimuli lead to fluid movements in the dentinal tubules (which can reach to the surface in the area of ​​the tooth neck). This irritates the Tomes fibers , cell processes of the odontoblasts (dentin-forming cells). The odontoblasts are connected to free nerve endings that transmit the stimulus to the central nervous system as a pain sensation.

Dentin is much more elastic than tooth enamel (modulus of elasticity 15,000–20,000 MPa) because it has a significantly higher proportion of organic matter. The Vickers hardness of the dentin is 60–70 and the compressive strength is 200–350 MPa (Körber, 1995).

Tooth pulp (pulp)

The dentin in turn encloses the inner part of the tooth, the pulp (tooth pulp), which is permeated by blood vessels and nerve fibers and which nourishes the tooth. The nerve fibers of the maxillary teeth come from the infraorbital nerve , those of the mandibular teeth from the inferior alveolar nerve . The tooth has no lymphatic drainage system - one of the reasons why pulpitis ("tooth nerve inflammation") cannot heal again.

Root cement (cementum)

In the root area, the dentin is covered by the root cement ( neutr. ), ( Latin : cementum , more rarely: substantia ossea dentis ), the third hard tooth substance next to the tooth enamel and dentin. The root cement, which encloses the root dentine as a thin layer, is the outer shell of the tooth in the area of ​​the tooth root and "walls" it in the jaw. However, the connection to the jawbone , in which each tooth is suspended in its tooth socket (alveolus), has a certain elasticity (see tooth support apparatus ).

The porous surface structure of the tooth root becomes visible under the electron microscope . The finest nerve extensions coat the porous surface of the root. The temperature and touch sensitivity of receding gums originate from these nerve branches.

The structure and hardness of the root cement are similar to human bones (compressive strength 15 kg / mm², tensile strength 10 kg / mm²). It is already part of the tooth support system, as the periodontal fibers attach to it, which anchor the teeth in the alveolus in a mobile manner (Hellwig et al., 1999b).

Tooth Fixation

Arrows mark a light line, the lamina dura

As periodontal ligament (Syn .: periodontal) the connective tissue of the gums is called. These Sharpey fibers , collagen fiber bundles belonging to the periosteum, which are attached to the basic bone substance, form the connection to the root cement of the tooth. The tooth is resiliently attached to them and bridges the gap a few tenths of a millimeter wide (periodontal gap) between the tooth cement of the tooth root and the bony wall of the tooth socket (alveolus), the lamina dura . At the neck of the tooth, the periodontal gap is sealed by the supraalveolar fiber apparatus (formerly known as the circular ligament ).

Tooth formation and change

Tooth enamel is created from the ectoderm , the rest of the tooth and the tooth-supporting structure from the mesoderm . In the 5th week of development (in humans) the ectoderm proliferates , which grows deeper and forms the tooth bar there. Ectodermal and mesodermal interactions cause the ectoderm to form the epithelial enamel organs and, in the immediate vicinity, the mesenchyme to form the dental papilla. The first attachment of a tooth is called the tooth bud .

The Theriodontia ("animal teeth") are land vertebrates from the group of therapsids ("mammal-like reptiles"). They include three more highly developed, mainly carnivorous, groups. From one of them, the cynodontia , the mammals emerged.

Most mammals have a one-time change of teeth ( diphyodontia ). First, milk teeth are created ( lacteal dentition ), which are later replaced by the "second" or permanent teeth ( permanent dentition ). The molars (large molars ) have no milk tooth predecessors, they only arise in the permanent set of teeth.

In fish , amphibians and reptiles , the teeth can be replaced by new ones over and over again ( polyphyodontics ) . Are known for this z. B. the zebrafish and the " revolver bite " of the sharks .

Human dentition

The permanent teeth in humans. Right branch of the lower jaw

Humans normally have a total of 32 permanent teeth (including wisdom teeth ), but one or more teeth can also be missing : Hypodontia . More rarely, there is an excess of teeth: hyperdontia . The deciduous dentition comprises 20 deciduous teeth, 5 per quadrant. All teeth in human dentition are teeth with a tooth root. Incisor and canine teeth form the front teeth , premoling and molar teeth form the side teeth (colloquially: molars ).

Tooth names

Human teeth (computer graphics) - view horizontally from outside + vertically from inside

In dentistry, human teeth are clearly identified by different tooth schemes. The FDI scheme of the Fédération Dentaire Internationale has been established internationally since 1970 . Each tooth is given a designation consisting of two digits. The first digit indicates the quadrant in which the tooth is located. The second digit is the numbering of the teeth from the center backwards.

Tooth features

Human teeth have unique tooth characteristics . These make it possible to determine which position the tooth has assumed in the dentition based on the shape of the tooth.

  • The angle feature , the curvature feature and the root feature can be used to determine whether the tooth belongs to the right or left half of the jaw.
  • The crown alignment provides information on whether the tooth belongs to the lower or upper jaw.
  • There is also the tooth neck feature , which is assessed from the vestibular point of view. The most apical point of the labial tooth neck is shifted distally. This feature occurs in front teeth, especially the two central incisors. Furthermore, the lower front teeth often have an indentation, the furrow feature, distally in the root area . This concavity allows the lower incisors to be assigned to the corresponding side.

Andrews defines perfect occlusion by 6 "keys":

  • Molar relation: the distobuccal cusp of the upper first molar ( six-year molar ) is in contact with the mesiobuccal cusp of the lower second molar and the mesiobuccal cusp of the upper first molar occluded with the fossa between the mesial (towards the middle; "front") and middle buccal cusps of the lower first molar. The mesiopalatal cusp of the upper first molar is in contact with the central fossa of the lower first molar.
  • Crown angulation (mesiodistal angulation ): The roots of the teeth are inclined distally (to the rear).
  • Crown inclination (buccolingual torque): The incisors have a vestibular crown torque, the upper canines, premolars and molars have a constant palatal crown torque and the lower canines, premolars and molars have a lingual crown torque that increases from anterior to posterior.
  • Missing tooth rotations.
  • Tight contact points between the teeth.
  • The occlusion curve of all teeth is flat or has only a slight Spee curve .

Orthodontic Features

The values programmed into straight wire brackets in the first, second and third order are statistical averages. Andrews used the following reference values ​​for their determination:

  • The longitudinal axis of the clinical crown: In all teeth, with the exception of the molars, this denotes the ridge that protrudes furthest on the vestibular surface. In the molars, the mesio-buccal groove forms the longitudinal axis of the crown.
  • The longitudinal axis point (LA point) / facial axis point (FA point): The LA point or FA point denotes the center of the crown longitudinal axis between the gingiva and the incisal edge or the cusp tips.

According to Andrews, the center of the bracket base should be positioned on the LA point and the bracket wings should be positioned parallel to the longitudinal axis of the crown.

Diseases and important forms of treatment

The Dentistry ( Stomatology ) deals with the diseases of the teeth ( dental disease ) and its human therapy. Periodontal diseases are the subject of periodontics . Inflammation that starts from the teeth is called odontogenic infection .

Dental caries (tooth decay) is the most common disease affecting teeth and humans, which has been detectable since prehistoric times . In Germany only about one percent of adults are caries-free, so they have naturally healthy teeth. The efforts by means of group prophylaxis and individual prophylaxis lead to ever better dental health, especially of children and adolescents, which is measured using the DMFT index . Diseases of the periodontium (see gums , periodontitis ) are also common. A rare clinical picture is tuberculosis of the teeth, in which mostly bronchogenic spreading can lead to the development of tuberculous tooth granulomas. Oral, mostly overlooked findings are found in 1.4% of those suffering from tuberculosis

For thousands of years include dental fillings (commonly known as " seals "), few dental crowns and maxillofacial surgery to health care of civilized nations.

If larger gaps arise due to extractions that have become necessary, a dental prosthesis (“third teeth”) or a bridge is often used. Since the 1990s, it has also been possible to use dental implants that are used to fix dentures .

Oral hygiene , which dentists offer to keep teeth healthy , is also of growing importance . Regular dental care can prevent many diseases.

Dental abnormalities

A tooth anomaly is the deformity of teeth. The most common form is the dens invaginatus , which is also known as dens in dente . It is a developmental disorder that results from the invagination of the enamel epithelium, which occurs before the tooth starts to mineralize. Starting from the foramen caecum or the tip of the cusp, the enamel epithelium is inverted to different depths.

The intussusception occurs both in the deciduous dentition and in the permanent dentition. Most often the upper lateral incisor (tooth 12 or tooth 22) is affected.

The anomaly of the dens invaginatus is predominantly made according to the Oehlers classification.

  • I. Type: The enamel indentation ends as a blind sack in the tooth crown.
  • Type II: The intussusception extends to the root of the tooth and can occasionally communicate with the pulp.
  • Type III: The intussusception ends as a second apical foramen (entry opening of the pulp at the end of the tooth root ) in the periapical tissue or laterally in the periodontal ligament.

Taurodontics can occur very rarely .

consequences

Aesthetic impairments are in the foreground , especially in the presence of a dens invaginatus in the anterior region. Functionally, such a tooth can be more susceptible to carious lesions due to the predilection point at the invagination. Due to the greater extension of the tooth can lead to breakthrough disturbances come. Systemically , this anomaly has no further consequences.

Artificial teeth

Color scale for selecting a standardized tooth color for artificial teeth

In ancient times people tried to treat toothlessness with prosthetic teeth made of bone, ivory, wood, pebbles, animal or human teeth. Ceramic teeth were used at the turn of the 18th and 19th centuries. Developed century and held as dentures until 1933, when by Otto Röhm , the Plexiglas (PMMA) was invented. Since then, the plastic teeth have been further developed and are made of PMMA or composites . The industrially processed plastics try to meet numerous criteria in the manufacture of teeth. This includes:

In the broadest sense, artificial teeth also include artificial tooth crowns .

Implants are artificial tooth roots on which artificial crowns or denture teeth are attached.

See also

Portal: Dentistry  - Overview of Wikipedia content on dentistry

literature

  • Placido Micheloni: Il mondo dei denti e la sua storia. I-II, Rome 1976/77.
  • Franz-Viktor Salomon: teeth. In: Franz-Viktor Salomon et al. (Hrsg.): Anatomie für die Tiermedizin. Enke-Verlag, Stuttgart 2004, ISBN 3-8304-1007-7 , pp. 251-264.

swell

Web links

Commons : Teeth  - collection of pictures, videos and audio files
Wiktionary: Zahn  - explanations of meanings, word origins, synonyms, translations
  • Healthy teeth - kindergesundheit-info.de: independent information service from the Federal Center for Health Education (BZgA)

Individual evidence

  1. ^ Friedrich Kluge , Alfred Götze : Etymological dictionary of the German language . 20th ed., Ed. by Walther Mitzka , De Gruyter, Berlin / New York 1967; Reprint (“21st unchanged edition”) ibid 1975, ISBN 3-11-005709-3 , p. 872.
  2. ↑ Dagmar Wodtko et al. a .: nouns in the Indo-European lexicon. Winter, Heidelberg 2008, p. 210.
  3. ^ Rüdiger Wehner, Walter Gehring: Zoologie. 23rd edition. Thieme Verlag, 1995.
  4. ↑ Keith L. Moore, E. Lütjen-Drecoll: Embryology. 3. Edition. Schattauer Verlag 1990. (German translation of The developing Human, Clinically oriented Embryology. 4th edition. WB Saunders, 1988)
  5. ↑ Milton Hildebrand, George E. Goslow: Comparative Anatomy of the Vertebrates. Springer Verlag, 2004, ISBN 3-540-00757-1 . (German translation of Analysis of Vertebrate Structure. 5th edition. John Wiley & Sons)
  6. ↑ a b c Jörg Bark: Quantification of dentine abrasion on human teeth. (PDF; 2.2 MB) Dissertation . LMU, 2006.
  7. ↑ Chemistry and Morphology of Bone. (PDF; 186 kB) Dissertation. Martin Luther University Halle-Wittenberg, 2003.
  8. ↑ A. Benninghoff, D. Drenckhahn (Ed.): Anatomie - Macroscopic Anatomy, Histology, Embryology, Cell Biology. 17th, revised edition. Volume 1, Urban & Fischer, Munich / Jena 2008, pp. 607f.
  9. ↑ JR Strube, M. Stern: Curriculum Prosthetics. Volume I, Quintessenz Verlag, 2011, ISBN 978-3-86867-026-4 , pp. 32-33.
  10. ^ LF Andrews: The six keys to normal occlusion. In: Am J Orthod. 62, 1972, pp. 296-309.
  11. ↑ Ärzteverlag, breakthrough mode in mixed dentition ( memento of April 9, 2014 in the Internet Archive ) (PDF; 215 kB)
  12. ^ LF Andrews: The straight-wire appliance. Explained and compared. In: J Clin Orthod. 10, 1976, pp. 174-195.
  13. ↑ See for example Jörg Orschiedt : Dental diseases. In: Alfred Czarnetzki (Hrsg.): Mute witnesses of their suffering. Diseases and Treatment Before the Medical Revolution. Attempto Verlag, Tübingen 1996, ISBN 3-89308-258-1 , pp. 111-137.
  14. ↑ 35 Caries-free in one boat ( Memento from February 27, 2009 in the Internet Archive )
  15. ↑ Ravikran Orgole: Textbook of Oral Medicine, Oral Diagnosis and Oral Radiology, Elsevier Health Sciences, 2014, p. 215
  16. ↑ SK Kannan, TPN Bharadwaj: Dens in dente (Dens invaginatus). Report of two unilateral and one bilateral case. In: Indian J Dent Res. 14, 2003, pp. 125-129.
  17. ↑ M. Hülsmann: Dens invaginatus: aetiology, classification, prevalence, diagnosis and treatment considerations. In: Int Endodont J. 30, 1997, pp. 79-90.
  18. ^ FAC Oehlers: Dens invaginatus (dilated composite odontome), I: variation of the invagination process and associated anterior crown forms and pathogenesis. In: Oral Surg Oral Med Oral Pathol. 10, 1957, pp. 1204-1218.
  19. ↑ A. Hintze: Endodontic treatment of type II dens invaginatus (PDF; 111 kB).
  20. ^ RL Engelmeier: The history and development of posterior denture teeth - introduction, part I. In: J Prosthodont. 12, 2003, pp. 219-226.