Text II. Facial clefts

Aberrations in embryonic facial development lead to a wide variety of defects. Although any step may be impaired, defects of primary and secondary palate development are most common.

Most cases of clefts of the lip with or without associated cleft palate appear to form a group etiologically different from clefts involving only the secondary palate. For example, when more than one child in family has facial clefts, the clefts are almost always found to belong only to one group.

There is some evidence that underdevelopment (small size) of the medial or lateral nasal prominences is involved in primary palate clefting, so the contact at the site of fusion is either prevented or inadequate. Other data present the evidence that many cases of cleft lip result from a combination that together reduce the mesenchyme in the primary palate at the point of fusion by an amount sufficient to prevent normal contact and fusion. About two thirds of patients with clefts of the primary palate also have clefts of the secondary palate. Studies of experimental animals suggest that excessive separation of jaw segments as a result of the primary palate cleft prevents the palatal shelves from contacting after elevation. The degree of clefting is highly variable. Clefts may be either bilateral or unilateral and complete or incomplete. Most of this variation results from differing degrees of fusion.

Clefts involving only the second palate constitute the second most frequent facial malformation in humans (after clefts involving the primary palate). Cleft palate can also be produced in experimental animals with a wide variety of chemical agents or other manipulations affecting the embryo. Usually, such agents retard or prevent shelf elevation. In other cases, although elevation occurs, the shelves are too small to make contact. There are also some proofs that the state develops after the application of some environmental agents.

Less frequently, other types of facial clefting are observed. In most instances they can be explained by failure of fusion between facial prominences of reduced size, and similar clefts can be produced experimentally. Examples include failure of merging and fusion between the maxillary prominence and the lateral nasal prominence, leading to oblique facial clefts, or failure of merging of the maxillary prominence and mandibular arch, leading to lateral facial clefts (macrostomia). Other rare facial malformations (including oblique facial clefts) may also result from abnormal pressures or fusions with folds in the fetal (e.g., amniotic) membranes.

Text III. Oral structures anomalies in ancient times

The known types of developmental disorders manifested in teeth and bone can be represented in samples from antiquity.

The discovery of the oldest evidence of a human hereditary genetic disorder has been announced by researchers at the Hebrew University of Jerusalem. The authors of an article in the June issue of the Journal of Human Evolution detail the finding of a disease known as amelogenesis imperfecta in the teeth of a fossil found in archaeological excavations in Ethiopia. The fossil is dated as 1.5 million years old and is from a two-year-old Homo erectus child. Homo erectus was a precursor of modern man. According to Dr.Zilberman, this is the first recorded evidence from such an early prehistoric period of a hereditary disorder in which the specific genes responsible have been identified. Undoubtedly, he said, there are other hereditary diseases that have come down to us from prehistoric ancestors and which are yet to be discovered in fossil remains.

Amelogenesis imperfecta is a hereditary disorder that manifests itself in tooth enamel that is abnormal in structure, low in mineral content and hence subject to rapid wear and chipping. The Hebrew University researchers confirmed the clear presence of the disease in the fossil sample through x-ray and scanning electron microscope analyses. The disease appears relatively rarely today (one in 14,000 people in Israel, one in 8,000 in the U.S.). It is much more common in one area of Sweden (one in 700).

Enamel hypoplastic defects were found in the teeth of Pithecanthropus.

Manifestations of disturbances in tooth number include anodontia (absence) and supernumerary teeth (additional). Partial anodontia was noted throughout the various periods and cultures to the present day. In the Neolithic culture, particularly in Europe, there was an increased frequency of absence of third molars at a level which made that state relatively common.

Anthropologists from Medical Research University of Johannesburg, South Africa, reported the data that the maxillary dental arch of a partial cranium of an adult specimen of Australopithecus robustus shows the presence of a supernumerary tooth between the right first and second incisors. The fossil specimen is considered, on the basis of associated fauna, to be approximately 1.7 million year old.

A high occurrence of supernumerary or extra teeth was revealed in the remnants dating back to the Gallo-Roman period and Middle Ages.

Speaking

Choose any of the oral structures anomalies to dwell on. Speak on the frequency of its occurrence, predisposing factors, possible complications and prognosis.

Unit VIII. Human habits as a cause of the oral structures

disturbances.

Lead-in

In every organ and tissue in the body, nature provides a wide margin of safety. The teeth and their supporting tissues are no exceptions. There are many cases when teeth become victims of excessive use and even of abuse far beyond any margins of safety. There are oral habits and, sometimes, neglect in which the use of the teeth causes a structural or functional anomaly.

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