Tooth eruption is a process in
tooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
in which the
teethTeeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums...
enter the
mouthThe mouth, buccal cavity, or oral cavity is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva...
and become visible. It is currently believed that the
periodontal ligamentThe periodontal ligament, commonly abbreviated as the PDL is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
s play an important role in tooth eruption.
PrimaryDeciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during...
(baby) teeth erupt into the mouth from around 6 months until 2 years of age. These teeth are the only ones in the mouth until a person is about 6 years old. At that time, the first
permanentPermanent teeth are the second set of teeth formed in humans. There are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.The first...
tooth erupts and begins a time in which there is a combination of primary and permanent teeth.
Tooth eruption is a process in
tooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
in which the
teethTeeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums...
enter the
mouthThe mouth, buccal cavity, or oral cavity is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva...
and become visible. It is currently believed that the
periodontal ligamentThe periodontal ligament, commonly abbreviated as the PDL is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
s play an important role in tooth eruption.
PrimaryDeciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during...
(baby) teeth erupt into the mouth from around 6 months until 2 years of age. These teeth are the only ones in the mouth until a person is about 6 years old. At that time, the first
permanentPermanent teeth are the second set of teeth formed in humans. There are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.The first...
tooth erupts and begins a time in which there is a combination of primary and permanent teeth. This stage, known as the mixed stage, lasts until the last primary tooth is lost. Then, the remaining permanent teeth erupt into the mouth.
Theories
Although researchers agree that tooth eruption is a complex process, there is little agreement on the identity of the mechanism that controls eruption. There have been many
theoriesThe term theory has two broad sets of meanings, one used in the empirical sciences and the other used in philosophy, mathematics, logic, and across other fields in the humanities. There is considerable difference and even dispute across academic disciplines as to the proper usages of the term...
over time that have been eventually disproven. One of the theories is that the tooth is pushed upward into the mouth by the growth of the tooth's root. Others advocated that a tooth is pushed upward by the growth of the bone around the tooth. In addition, some believed teeth were pushed upward by vascular pressure or by an anatomical feature called the cushioned hammock. The cushioned hammock theory, first proposed by Harry Sicher, was taught widely from the 1930s to the 1950s. This theory postulated that a
ligamentIn anatomy, the term ligament is used to denote three different types of structures:# Fibrous tissue that connects bones to other bones. They are sometimes called "articular ligaments", "fibrous ligaments", or "true ligaments"....
below a tooth, which Sicher observed under a microscope on a histologic slide, was responsible for eruption. Later, the "ligament" Sicher observed was determined to be merely an artifact created in the process of preparing the slide.
The most widely held current theory is that while several forces might be involved in eruption, the periodontal ligaments provide the main impetus for the process. Theorists hypothesize that the periodontal ligaments promote eruption through the shrinking and cross-linking of their collagen fibers and the contraction of their fibroblasts.
Timeline
Although tooth eruption occurs at different times for different people, a general eruption timeline exists. Typically, humans have 20 primary teeth and 32 permanent teeth. Tooth eruption has three stages. The first, known as primary
dentitionDentition is the development of teeth and their arrangement in the mouth.All mammals except the monotremes, the xenarthrans, the pangolins, and the cetaceans have up to four distinct types of teeth, with a maximum number for each. These are the incisor , the canine, the premolar, and the molar ...
stage, occurs when only primary teeth are visible. Once the first permanent tooth erupts into the mouth, the teeth are in the mixed (or transitional) dentition. After the last primary tooth falls out of the mouth, the teeth are in the permanent dentition.
Primary teeth
Primary dentition starts on the arrival of the
mandibular central incisorThe mandibular central incisor is the tooth located on the jaw, adjacent to the midline of the face. It is mesial from both mandibular lateral incisors. As with all incisors, its function includes shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
s, usually at eight months, and lasts until the first permanent molars appear in the mouth, usually at six years. The primary teeth typically erupt in the following order: (1) central
incisorIncisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
, (2) lateral incisor, (3) first molar, (4)
canineIn mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
, and (5) second molar. As a general rule, four teeth erupt for every six months of life, mandibular teeth erupt before maxillary teeth, and teeth erupt sooner in females than males. During primary dentition, the tooth buds of permanent teeth develop below the primary teeth, close to the palate or tongue.
Mixed stage
Mixed dentition starts when the first permanent molar appears in the mouth, usually at six years, and lasts until the last primary tooth is lost, usually at eleven or twelve years. Permanent teeth in the maxilla erupt in a different order from permanent teeth on the mandible. Maxillary teeth erupt in the following order: (1)
first molarThe maxillary first molar is the tooth located laterally from both the maxillary second premolars of the mouth but mesial from both maxillary second molars. The function of this molar is similar to that of all molars in regard to grinding being the principle action during mastication, commonly...
(2)
central incisorThe maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication . There are...
, (3)
lateral incisorThe maxillary lateral incisor is the tooth located distally from both maxillary central incisors of the mouth and mesially from both maxillary canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
, (4)
first premolarThe maxillary first premolar is the tooth located laterally from both the maxillary canines of the mouth but mesial from both maxillary second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication, commonly known...
, (5)
second premolarThe maxillary second premolar is the tooth located laterally from both the maxillary first premolars of the mouth but mesial from both maxillary first molars. The function of this premolar is similar to that of first molars in regard to grinding being the principle action during mastication,...
, (6)
canineThe maxillary canine is the tooth located laterally from both maxillary lateral incisors of the mouth but mesial from both maxillary first premolars...
, (7)
second molarThe maxillary second molar is the tooth located distally from both the maxillary first molars of the mouth but mesial from both maxillary third molars. This is true only in permanent teeth. In deciduous teeth, the maxillary second molar is the last tooth in the mouth and does not have a third...
, and (8)
third molarThe maxillary third molar is the third molar located laterally from both the maxillary second molars of the mouth with no tooth posterior to it in permanent teeth. In deciduous teeth, there is no maxillary third molar...
. Mandibular teeth erupt in the following order: (1)
first molarThe mandibular first molar or six-year molar is the tooth located distally from both the mandibular second premolars of the mouth but mesial from both mandibular second molars...
(2)
central incisorThe mandibular central incisor is the tooth located on the jaw, adjacent to the midline of the face. It is mesial from both mandibular lateral incisors. As with all incisors, its function includes shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
, (3)
lateral incisorThe mandibular lateral incisor is the tooth located distally from both mandibular central incisors of the mouth and mesially from both mandibular canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on...
, (4)
canineThe mandibular canine is the tooth located distally from both mandibular lateral incisors of the mouth but mesially from both mandibular first premolars...
, (5)
first premolarThe mandibular first premolar is the tooth located laterally from both the mandibular canines of the mouth but mesial from both mandibular second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication, commonly...
, (6)
second premolarThe mandibular second premolar is the tooth located distally from both the mandibular first premolars of the mouth but mesial from both mandibular first molars. The function of this premolar is assist the mandibular first molar during mastication, commonly known as chewing...
, (7)
second molarThe mandibular second molar is the tooth located distally from both the mandibular first molars of the mouth but mesial from both mandibular third molars. This is true only in permanent teeth...
, and (8)
third molarThe mandibular third molar is the third molar located distally from both the mandibular second molars of the mouth with no tooth posterior to it in permanent teeth. In deciduous teeth, there is no mandibular third molar...
. Since there are no premolars in the primary dentition, the primary molars are replaced by permanent premolars. If any primary teeth are lost before permanent teeth are ready to replace them, some posterior teeth may drift forward and cause space to be lost in the mouth. This may cause crowding and/or misplacement once the permanent teeth erupt, which is usually referred to as
malocclusionA malocclusion is a misalignment of teeth and/or incorrect relation between the teeth of the two dental arches. The upper arch is called the maxilla and the lower is called the mandible.-Presentation:...
.
OrthodonticsOrthodontics is a specialty of dentistry that is concerned with the study and treatment of malocclusions , which may be a result of tooth irregularity, disproportionate jaw relationships, or both...
may be required in such circumstances for an individual to achieve a straight set of teeth.
Permanent teeth
The permanent dentition begins when the last primary tooth is lost, usually at 11 to 12 years, and lasts for the rest of a person's life or until all of the teeth are lost (
edentulismEdentulism is the condition of being toothless to at least some degree; it is the result of tooth loss. Loss of some teeth results in partial edentulism, while loss of all teeth results in complete edentulism....
). During this stage, third molars (also called "wisdom teeth") are frequently
extractedA dental extraction is the removal of a tooth from the mouth. Extractions are performed for a wide variety of reasons, including tooth decay that has destroyed enough tooth structure to prevent restoration...
because of decay, pain or impactions. The main reasons for
tooth lossTooth loss is when one or more teeth come loose and fall out. Tooth loss is normal for deciduous teeth , when they are replaced by a person's adult teeth. Otherwise, losing teeth is undesirable and is the result of injury or disease, such as mouth trauma, tooth injury, tooth decay, and gum disease...
are decay or
periodontal diseasePeriodontitis refers to a number of inflammatory diseases affecting the periodontium — that is, the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of...
.