incisor
The incisors ( Latin Dentes incisivi , shortened only Incisivi , Singular Dens incisivus to incidere 'cut in') are the teeth that are used to bite off food. They are relatively sharp and lie in the front of the jaw .
Human incisors
Humans have two central incisors (teeth 11, 21, 31 and 41 ) and two lateral incisors (teeth 12, 22, 32 and 42 ) in the upper and lower jaw . The incisors belong together with the canines to the "front teeth", with a shovel-shaped or chisel-shaped crown shape.
Cutting edge
A cutting edge (incisal edge) is understood to be the end of the incisors with which a shearing movement can be carried out. For this reason, the upper incisors are more ventral (front) than the lower incisors. The tooth enamel is distinctly transparent in the area of the incisal edge due to the lack of underlaid dentin.
Mamelon
In the area of the incisal edges there are slight indentations after the tooth eruption. Central incisors usually have two notches, which result in three small cusps on the edge (mamelon, French : nipple ), the two lateral incisors two mamelons. A single groove can often be seen on the canine teeth. Over the years, these cusps disappear at a young age, because the incisal enamel edge wears out due to abrasion , creating a straight cutting edge. In the case of a so-called open bite , the mamelons can still be recognizable in adulthood due to a lack of abrasion.
Crown anatomy
The central incisors usually have a mesial and distal edge bulge, as well as a central bulge on the oral (inner) surface. Lateral incisors normally only have the two marginal ridges. The front teeth have an angular feature . The incisal edge merges mesially at a more acute angle to the approximal surface than distally, with the distal crown corner being more rounded than the mesial crown corner.
Tooth color
The tooth color is largely determined by the dentin , which shimmers through the relatively colorless and transparent tooth enamel . The thickness of this enamel layer is responsible for the weakening of the intensity of the dentin color. The tooth is made up of dozens of shades of color.
Mammals
In various mammals , the incisors have undergone changes in the course of evolution . Thus, the upper incisors form elephants the tusks of animals. The incisors of rodents have incisors. Ruminants have no incisors in the upper jaw , the dental plate serves as a counter bearing for the incisors of the lower jaw .
Almost all predatory species have six small incisors each in the upper and lower jaw. The few exceptions are the sloth bear , which has only two incisors in each half of the upper jaw so that it can suck up insects through the gap, and the sea otter, which only has four incisors in the lower jaw.
Web links
Individual evidence
- ↑ a b c Hans H. Schulz: Modeling and anatomy of the tooth crown . Verlag Neuer Merkur GmbH, 1997, ISBN 978-3-929360-14-1 , pp. 21-35.
- ↑ McLean JW: The science and art of dental ceramics. Vol 1: The nature of dental ceramics and their clinical use. Chicago: Quintessence Publishing Co Inc. (1979)
- ↑ Muia PJ: The four-dimensional tooth shade system. Quintessenz, Berlin 1982
- ↑ PT Marshall, Hughues: The Physiology of Mammals and Other Vertebrates: A Text Book for High Schools and Colleges . Springer-Verlag, October 5, 2013, ISBN 978-3-0348-5963-9 , p. 57–.