Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth, are the first set of teeth in the growth and development of humans and other diphyodonts, which include most mammals but not elephants, kangaroos, or manatees, which are polyphyodonts. Deciduous teeth develop during the embryonic stage of development and erupt (break through the gums and become visible in the mouth) during infancy. They are usually lost and replaced by permanent teeth, but in the absence of their permanent replacements, they can remain functional for many years into adulthood.
Development
Formation
Primary teeth start to form during the embryonic phase of human life. The development of primary teeth starts at the sixth week of tooth development as the dental lamina. This process starts at the midline and then spreads back into the posterior region. By the time the embryo is eight weeks old, there are ten buds on the upper and lower arches that will eventually become the primary (deciduous) dentition. These teeth will continue to form until they erupt in the mouth. In the primary dentition, there are a total of twenty teeth: five per quadrant and ten per arch. The eruption of these teeth ("teething") typically begins around the age of six months and continues until 25–33 months of age during the primary dentition period. Usually, the first teeth seen in the mouth are the mandibular central incisors and the last are the maxillary second molars.
The primary teeth are made up of central incisors, lateral incisors, canines, first molars, and second molars; there is one in each quadrant, making a total of four of each tooth. All of these are gradually replaced by similarly named permanent counterparts except for the primary first and second molars; they are replaced by premolars.
thumb|left|Bottom teeth of a seven-year-old, showing primary teeth (left), a lost primary tooth and visible [[dental alveolus|socket (middle), and a fully erupted permanent tooth (right)]]
{| class="wikitable"
|+Teething ages, by tooth
! Tooth
! Upper
! Lower
|-
|Central incisors
|8–12 months
|6–10 months
|-
|Lateral incisors
|9–13 months
|10–16 months
|-
|First molars
|13–19 months
|14–18 months
|-
|Canine teeth
|16–22 months
|17–23 months
|-
|Second molars
|25–33 months
|23–31 months
|}
{| class="wikitable"
|+Exfoliation ages, by tooth
Function
Primary teeth are essential in the development of the mouth. The primary teeth maintain the arch length within the jaw, the bone and the permanent teeth replacements develop from the same tooth germs as the primary teeth. The primary teeth provide guidance for the eruption pathway of the permanent teeth. Also the muscles of the jaw and the formation of the jaw bones depend on the primary teeth to maintain proper spacing for permanent teeth. The roots of primary teeth provide a pathway for the permanent teeth to erupt. The primary teeth are important for the development of the child's speech, for the child's smile and play a role in chewing of food, although children who have had their primary teeth removed (usually as a result of dental caries or dental injuries) can still eat and chew to a certain extent.
Caries in deciduous teeth
Dental caries, also known as tooth decay and cavities, is one of the most prevalent chronic diseases among children worldwide. This oral condition involves bacterial infection which demineralizes and destroys tooth tissues. In primary dentition, extensive tooth decay is the most common dental disease. An extensive carious lesion affects at least half of a tooth and possibly involves the pulp.
Treatment for caries
Tooth decay in primary teeth tends to progress quite quickly and often reaches the pulp of the tooth. In cases of extensive tooth decay, the pulp must be treated to maintain the health of the tooth and its supporting tissues. In pulp therapy, areas of decay and infected pulp tissue are removed, then the pulp is sealed with medicaments,
Direct pulp capping (DPC) is a treatment performed when a pin-point or small pulp exposure of 1mm or less occurs after removal of carious tooth material (dentin) excavation. The pulp is covered with a medicament. This technique has limited use when pulp is exposed due to injury but is generally not accepted for managing carious pulp exposures in primary teeth, as it has been shown to have limited success. Medicaments used in DPC include calcium hydroxide and alternates such as mineral trioxide aggregate (MTA).
Medicaments used in pulp treatment
After direct pulp capping, it is unclear whether any one medicament is superior.
After pulpotomy, MTA is the most effective medicament and formocresol is also effective. Both are more effective than calcium hydroxide, which is more likely to fail.
Various cultures have customs relating to the loss of deciduous teeth. In English-speaking countries, the tooth fairy is a popular childhood fiction that a fairy rewards children when their baby teeth fall out. Children typically place a tooth under their pillow at night or on a bedside table. The fairy is said to take the tooth and replace it with money or small gifts while they sleep. In some parts of Australia, Sweden and Norway, the children put the tooth in a glass of water. In medieval Scandinavia there was a similar tradition, surviving to the present day in Iceland, of , a gift to a child when it cuts its first tooth. In Nigeria, the Igbo in a similar custom expect a visiting relative or guest to make a gift or donation to an infant upon the visitor's sighting of the infant's deciduous teeth.
Hausa culture has it that a child with a fallen tooth should not let a lizard see the toothless gum because if a lizard does see it, no tooth will grow in its place.
Other traditions are associated with mice or other rodents because of their sharp, everlasting teeth. The character Ratón Pérez appears in the tale of The Vain Little Mouse. A Ratoncito Pérez was used by Colgate in marketing toothpaste in Venezuela and Spain. In Italy, the Tooth Fairy () is also often replaced by a small mouse (), or by Saint Apollonia, patron saint of tooth complaints. In France and in French-speaking Belgium, this character is called . From parts of lowland Scotland comes a tradition similar to the fairy mouse: a white fairy rat who purchases the teeth with coins. In Afrikaans speaking families in South Africa, children leave their teeth in a shoe so that the Tandemuis (Tooth Mouse) can replace the teeth with money.
Several traditions concern throwing the shed teeth. In Turkey, Cyprus, and Greece, children traditionally throw their fallen baby teeth onto the roof of their house while making a wish. Similarly, in some Asian countries, such as India, Korea, Nepal, the Philippines, and Vietnam, when a child loses a tooth, the usual custom is that they should throw it onto the roof if it came from the lower jaw, or into the space beneath the floor if it came from the upper jaw. While doing this, the child shouts a request for the tooth to be replaced with the tooth of a mouse. This tradition is based on the fact that the teeth of mice grow for their entire lives, a characteristic of all rodents.
In Japan, a different variation calls for lost upper teeth to be thrown straight down to the ground and lower teeth straight up into the air or onto the roof of a house; the idea is that incoming teeth will grow in straight. Some parts of China follow a similar tradition by throwing the teeth from the lower jaw onto the roof and burying the teeth from the upper jaw underground, as a symbol of urging the permanent teeth to grow faster towards the right direction.
In Sri Lanka, tradition is to throw the baby teeth onto the roof or a tree in the presence of an Indian palm squirrel. The child then tells the squirrel to take the old tooth in return for a new one.
In some parts of India, young children offer their discarded baby teeth to the sun, sometimes wrapped in a tiny rag of cotton turf. In the Assam state of India, children throw their baby teeth to the roof of their house and urge a mouse to take it, to exchange with its teeth (permanent ones). Something similar occurs in the Dominican Republic where children will throw their baby teeth to the roof of a house with a thatched roof and ask a mouse to take it and replace it with a new (permanent) tooth (but not its own).
The tradition of throwing a baby tooth up into the sky to the sun playfully asking for a better tooth to replace it is common in Middle Eastern countries (including Iraq, Jordan, Egypt and Sudan). It may originate in a pre-Islamic offering and certainly dates back to at least the 13th century, when Izz bin Hibat Allah Al Hadid mentions it.
In 17th and again in 19th century Britain, lost teeth were commonly burnt to destroy them. This was partly for religious reasons connected with the Last Judgement and partly for fear of what might happen if an animal got them. A rhyme might be said as a blessing:
<poem style="margin-left:2em">
Old tooth, new tooth
Pray God send me a new tooth
</poem>
In 1949, a Spike Jones novelty Christmas song All I Want for Christmas Is My Two Front Teeth became Billboard number-one single. The song was written in 1944 by Donald Yetter Gardner, who wrote it while teaching music at public schools in Smithtown, New York. He asked his second grade class what they wanted for Christmas, and noticed that almost all of the students had at least one front tooth missing as they answered in a lisp. Gardner wrote the song in 30 minutes. In a 1995 interview, Gardner said, "I was amazed at the way that silly little song was picked up by the whole country."