Developmental abnormalities of teeth

Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. A developmental disturbance means an abnormality where the pathology starts in the embryonic stage of human life, before the formation of the dentition. The development of teeth is regulated by genes, but the genetic program is very sensitive to disturbances in the environment such as exposure to infection or toxic chemicals, including drugs. So, numerous genetic and environmental factors may cause abnormalities in tooth development.

Disorders of teeth development may be prenatal or postnatal in origin and may be inherited or acquired. All developmental abnormalities of teeth can be classified into:

• Anomalies of number

• Anomalies of size

• Anomalies of shape

• Anomalies of structure

• Anomalies of color

Anomalies of number

Anomalies of number are represented by anodontia, hypodontia, hyperdontia.

Anodontia is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. Hypodontia is the condition at which the patient has missing teeth as a result of their failure to develop. Hypodontia describes a situation where the patient is missing up to 6 teeth, excluding the 3rd molars. Hyperdontia is an oral condition characterized by having an excess number of teeth. The standard number of primary teeth is 20 and the standard number of permanent teeth is 32. A person who develops more than 20 primary teeth or more than 32 permanent teeth has hyperdontia. The additional teeth are referred to as supernumerary teeth.

Anomalies of size

Anomalies of size are represented by microdontia and macrodontia. Microdontia is a condition in which the teeth appear smaller than normal teeth. Microdontia can occur on all teeth or just a few teeth. Macrodontia is a condition in which the teeth appear larger than normal.

Anomalies of shape

Anomalies of shape include germination, fusion, concrescence, dilacerations, enamel pearl, talon cusp, taurodontism, supernumerary roots.

Tooth gemination is a dental phenomenon when two teeth develop from one tooth bud and, as a result, the patient has an extra tooth, in contrast to fusion. Fusion is a rare dental case characterized by the complete bonding of two adjacent teeth due to irregular growth. Concrescence is a condition of teeth where the cementum overlying the roots of at least two teeth join together. The cause can sometimes be attributed to trauma or crowding of teeth. An enamel pearl is a condition of teeth where enamel is found on locations where enamel is not supposed to be, such as on a root surface. They are found usually in the area between roots of molars. Enamel pearls are not common in teeth with a single root. A talon cusp, also known as an "eagle's talon", is an extra cusp on an anterior tooth. Taurodontism can be defined as a change in tooth shape characterized by an enlarged pulp chamber, apical displacement of the pulpal floor, and no constriction at the level of the cemento-enamel junction. A supernumerary root is a condition found in teeth there may be a larger number of roots than expected. The most common teeth affected are mandibular canines, premolars, and molars, especially third molars. Dilaceration is the anomaly in the tooth shape and its structure and it refers to a sharp bend in the tooth which can be in the crown portion or in the root, making sharp angles at the junction of the crown and root.

Anomalies of structure

Anomalies of structure can be divided into disturbances in structure of enamel (enamel hypoplasia, enamel hypocalcification, amelogenesis imperfecta, dental fluorosis), dentin (dentin dysplasia, dentinogenesis imperfecta, dentin hypocalcification) and cementum (hypercementosis).

Enamel hypoplasia is the defect of the teeth in which the tooth enamel is hard but thin and deficient in amount. This is caused by defective enamel matrix formation with a deficiency in the cementing substance. Enamel hypocalcification is a defect of tooth enamel in which normal amounts of enamel are produced but are hypomineralized. In this defect the enamel is softer than normal. Amelogenesis imperfecta presents with abnormal formation of the enamel or external layer of teeth. Enamel is composed mostly of mineral, which is formed and regulated by the proteins in it. Amelogenesis imperfecta is due to the malfunction of the proteins in the enamel. Dental fluorosis is a developmental disturbance of dental enamel caused by excessive exposure to high concentrations of fluoride during tooth development. Dentin dysplasia is a genetic disorder of teeth characterized by presence of normal enamel but atypical dentin with abnormal pulpal morphology. Dentinogenesis imperfecta is a genetic disorder of tooth development. This condition causes teeth to be discolored (most often a blue-gray or yellow-brown color) and translucent. Hypercementosis is characterized by the excessive buildup of normal cementum on the roots of one or more teeth.

Anomalies of color

Abnormal tooth color is any color other than the white to yellowish-white of normal teeth. The change in color may affect the entire tooth, or just appear as spots or lines in the tooth enamel. Your genes influence your tooth color. Other things that can affect tooth color include: congenital diseases, environmental factors, infections. Inherited diseases may affect the thickness of enamel or the calcium or protein content of the enamel, which can cause color changes. Metabolic diseases may cause changes in tooth color and shape. Drugs and medications either taken by the mother while pregnant or by the child during the time of tooth development can cause changes in both the color and hardness of the enamel.

Ex. 16. Find in the text the equivalents for the following words and word-combinations:

Формування зубного ряду, рідкісне генетичне захворювання, суміжні зуби, скупченість зубів, поверхня кореня, один корінь, більша кількість коренів, гострі кути, недостатня кількість, зовнішні шари зубів, зміни кольору.

Ex. 17. Answer the following questions:

1. What is tooth development? 2. What are the causes of tooth development? 3. What categories can all developmental abnormalities of teeth be classified into? 4. What disease is characterized by the congenital absence of all teeth? 5. What is the difference between hypodontia and hyperdontia? 6. What is the difference between microdontia and macrodontia? 7. What anomalies of enamel structure can you name? 8. What is the difference between germination and fusion? 9. What factors can affect tooth color?

Ex. 18. Insert the missing prepositions (at, in, of):

Disorders ___ development of teeth may be due to abnormalities ___ the differentiation of the dental lamina and the tooth germs, causing anomalies __ the number, size, and form ___ teeth (abnormalities of morphodifferentiation) or to abnormalities __ the formation ___ the dental hard tissues resulting in disturbances ___ tooth structure (abnormalities of histodifferentiation). Abnormalities of histodifferentiation occur ___ a later stage in development than abnormalities of morphodifferentiation; in some disorders both stages ___ differentiation are abnormal.

Ex. 19. Insert the missing words given below:

A disruption during tooth ________ may affect the enamel. Generally such a __________ is referred to as hypoplasia (insufficient and/or irregular quantity of ________). Tetracycline can _____ enamel hypoplasia when taken during _________ or by an infant or young _______ during tooth development. Tetracycline should not be _____ during pregnancy or by children ages 8 and under. In addition, Vitamin D _______ during tooth development and calcification results in enamel and ________ hypoplasia. The enamel is poorly calcified and may fail to ______ at all in some areas.

Disruption, development, cause, enamel, used, pregnancy, child, deficiency, dentin, form

Ex.20. Read and retell the following text: