Tooth (animal)

Teeth in animals vary greatly. Some animals, such as turtles and tortoises, are toothless. Other animals, such as sharks, may go through many teeth in their lifetime. The multiple replacement of teeth is known as polyphedont. Since the appearance of teeth reflects their function, the animal's diet may correspond to types of teeth. For example, carnassials are teeth in carnivores used for slicing food. Elephants' tusks are specialized incisors for digging food up and fighting.

Some of elephant teeth are similar to those in manatees. Mandibular molars of manatees develop separately from the jaw and are encased in a bony shell separated by soft tissue. Also, walrus tusks are canine teeth that grow continuously throughout life. [ [http://www.uic.edu/classes/orla/orla312/CANINES.htm The Permanent Canine Teeth] , hosted on the University of Illinois at Chicago website. Page accessed February 5, 2007.]

Other differences to human teeth can exist in diseases and anatomy. In dogs, the teeth are less likely than humans to form dental caries because of the very high pH of dog saliva, which prevents enamel from demineralizing. [Chris C. Pinney, "The Illustrated Veterinary Guide for Dogs, Cats, Birds, and Exotic Pets" (Blue Ridge Summit, PA: TAB Books, 1992), p. 187.] In Aardvarks, teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata.

Reptiles

The teeth of reptiles are replaced constantly during their life. Juvenile crocodilians replace teeth with larger ones at a rate as high as 1 new tooth per socket every month. Once adult, tooth replacement rates can slow to two years and even longer. Over all, crocodilians may use 3,000 teeth from birth to death. New teeth are created within old teeth.

Whales

Toothed whales is a suborder of the cetaceans characterized by having teeth. The teeth differ considerably between the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, which is a tooth containing millions of sensory pathways and used for sensing during feeding, navigation and mating. It is the most neurologically complex tooth known. Beaked whales are almost toothless, with only bizarre teeth found in males. These teeth may be used for feeding but also for demonstrating aggression and showmanship.

Rabbit

Rabbits and other Lagomorphs usually shed their deciduous teeth before (or very shortly after) their birth, and are usually born with their permanent teeth. [ [http://www.peteducation.com/article.cfm?cls=18&cat=1798&articleid=3078 Dental Anatomy & Care for Rabbits and Rodents ] ] The teeth of rabbits complement their diet, which consist of a wide range of vegetation. Since many of the foods are abrasive enough to cause attrition, rabbit teeth grow continuously throughout life. [Brown, Susan. [http://www.rabbit.org/chapters/san-diego/health/dental_disease.html Rabbit Dental Diseases] , hosted on the [http://www.rabbit.org/chapters/san-diego/ San Diego Chapter of the House Rabbit Society] . Page accessed April 9, 2007.] Rabbits have a total of 6 incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. There are no canines. Three to four millimeters of tooth is worn away by incisors every week, whereas the posterior teeth require a month to wear away the same amount. [Ryšavy, Robin. [http://www.mohrskc.org/hrswebpg23.html The Missouri House Rabbit Society] , hosted by the [http://www.mohrskc.org/index.html Kansas City Missouri House Rabbit Society] . Page accessed April 9, 2007.]

Rodent

Rodents' incisors grow continuously throughout their lives, a process known as aradicular. Unlike humans whose ameloblasts die after tooth development, rodents continually produce enamel and must wear down their teeth by gnawing on various materials. [Caceci, Thomas. "Veterinary Histology" with subtitle "Digestive System: Oral Cavity" found [http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab17/Lab17.htm here] .] These teeth are used for cutting wood, biting through the skin of fruit, or for defense. The teeth have enamel on the outside and exposed dentin on the inside, so they self-sharpen during gnawing. On the other hand, continually growing molars are found in some rodent species, such as the sibling vole and the guinea pig. [Tummers M and Thesleff I. Root or crown: a developmental choice orchestrated by the differential regulation of the epithelial stem cell niche in the tooth of two rodent species. Development (2003). 130(6):1049-57.] [AM Hunt. A description of the molar teeth and investing tissues of normal guinea pigs. J Dent Res. (1959) 38(2):216-31.] There is variation in the dentition of the rodents, but generally, rodents lack canines and premolars, and have a space between their incisors and molars, called the diastema region.

Horse

Horse teeth can be used to estimate the animal's age. At five years of age a horse has between 36 and 44 teeth. By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth. All horses have twelve premolars, twelve molars, and twelve incisors. After eight years, the age of a horse can only be conjectured. Dishonest dealers sometimes "bishop" the teeth of old horses, that is scoop them out, to imitate the mark: but this can be known by the absence of the white edge of enamel which always surrounds the real mark, by the shape of the teeth, and other marks of age about the animal. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing.

Some horses have a form of premolars called wolf teeth. Wolf teeth are small peg-like teeth in horses and other equidae, and they do not have any precursors. They may be knocked out by the bit if particularly loose and can certainly be extracted accidentally, either partially or whole, when routine equine dentistry is performed. In size they are extremely variable from being only 3 mm in diameter to having roots up to 2 cm long. In a small number of cases they may be "molarized" with a distinct irregular rim of enamel. It is impossible to gauge the size of the root from an examination of the crown except to say that if the crown is mobile it is very unlikely that there is a large intact root.

Also, a horse may have 4 or 5 canine teeth between the molars and incisors. Generally all male horses have four canines. However, few female horses have canines. A horse's incisors, premolars, and molars continuously grow throughout the animal's life, to provide new material as the grinding surface is worn down from eating. A young adult will have teeth which are 4.5-5 inches long. The enamel and dentin layers are intertwined with each other. [Encarta article found [http://encarta.msn.com/text_761561931__1/Teeth.html here] and Randall-Bowman, whose link can be found [http://rev.tamu.edu/stories/04/041504-6.html here] ] Problems that can develop in horse teeth include hooks, step mouth, wave mouth, and shear mouth.

For nomenclature, the modified triadan system is of good help.

References