Humans are diphyodont, meaning that they develop two sets of teeth in a lifetime. The first set of teeth, the deciduous teeth are also called the milk, primary, temporary, or baby teeth. These teeth begin to develop before birth, start to appear in the mouth between the ages of 6 months to 2 1/2 years and usually start to fall out when a kid is around 6 years old. They are replaced by a set of permanent teeth, which are also called secondary or adult teeth.
Gums and supporting structures, medically known as Periodontium.
The tooth is a structure formed by the combination of different kinds of tissues. Each tissue is formed by different cell types that work in a well co- ordinated and co-dependent way. The tooth goes through the following phases of development, named on the basis of the peculiarities of the stage of development.
In every stage the various cells contribute to the formation of different tissues of the tooth in coordination with each other. The different tissues with their respective cells of formation are as follows:
The tooth root is formed by a combination of the dentin and cementum formed by odontoblasts and cementocytes respectively. The tooth development is completed after its the eruption.
The milk / primary teeth are the first set of teeth in humans and many mammals. They start to form in the embryo phase during pregnancy. The development initiates in the sixth week as dental lamina. The process starts at the midline and then spreads back into the posterior region. By the time of eight weeks, there are ten areas on the upper and lower arches that will eventually become deciduous dentition. These teeth continue to form until they erupt in the mouth.
The milk teeth usually start erupting from the 6th month of age and by the time a child is 3 years old, he or she has a set of 20 deciduous teeth, 10 in the lower and 10 in the upper jaw. Each jaw has four incisors, two canines and four molars.
The deciduous teeth help the permanent teeth erupt in their normal positions; most of the permanent teeth form just beneath the roots of the deciduous teeth. When a deciduous tooth is preparing to fall out, its root begins to dissolve. This root has completely dissolved by the time the permanent tooth below it is ready to erupt.
The eruption of the permanent teeth begins even before the first primary sheds. The first permanent teeth to appear in the oral cavity, by the age of 6 years, is mandibular first permanent molar.
From ages 6 to 9, the incisors and first molars start to appear. Between ages 10 and 12, the first and second premolars, as well as the canines, erupt. From 11 to 13, the second molars erupt. The phase during which permanent teeth develop usually lasts for about 15 years as the jaw steadily grows into its adult form.
The wisdom teeth (third molars) erupt between the ages of 17 and 21. Sometimes there is no room in a person's mouth for all the permanent teeth. If this happens, the wisdom teeth may get stuck (or impacted) beneath the gum and may need to be removed. Overcrowding of the teeth is one of the reasons people get braces during their teenage years.
Both the dentitions have same teeth except the morphological changes and the absence of premolars in the primary dentition. The types of teeth are:
The teeth are arranged in the form of an arc, explaining the term dental arch. To understand this, the arch can be divided into two identical halves from the midline. The first tooth beginning from the front is the central incisor, followed by lateral incisor, canine, first premolar, second premolar, 1st and then the 2nd molar and 3rd molar.
Thus a dental formula is used to describe the arrangement in each quadrant (half of each arch, thus there are 4 quadrants making the upper and lower arches). Dental Formula - 2 1 2 3
The deciduous dentition does not have the premolars nor the wisdom teeth, thus reducing the number to 20. So the dental formula can be given as 2 1 2 Any discrepancy in the tooth arrangement can lead to problems along with maintenance of the oral hygiene.
The tooth is a mineralised entity. It can be divide into two portions; the coronal structure or the crown i.e. the visible portion of the tooth, and the radicular or the root portion that is covered by the gingiva or the gums. Basically the tooth consists of four type of tissues; enamel, dentin, pulp and cementum. The difference in crown and root of the tooth lies in the fact that enamel is the outer covering of the crown while cementum covers the root. The second layer is the dentin and the pulp forming the core respectively.
Enamel - It is the hardest tissue in the human body, covering the crown of the tooth. It is highly mineralised tissue as 96% of it’s content is mineral organic content and water comprising the rest.
Dentin - A hard yellow substance, dentin makes up most of the tooth. It is the dentin that gives the tooth its slightly yellowish tint. Any injury to the dentin is sure to cause you pain.
Cementum - Cementum covers the root and holds the tooth in place within the jawbone. Cementum is as hard as bone but not as hard as enamel.
Pulp - The pulp is the innermost portion of the tooth. Unlike the other parts of the tooth, the pulp is soft. It is made of connective tissue, nerves, and blood vessels, which nourish the tooth. Blood vessels and nerves enter the root through a small hole at the very bottom of the tooth called the apical foramen.
