Development and anatomy of the teeth and jaws

The period of histogenesis of dental tissues begins with the 4th month of intrauterine life. During the formation of hard dental tissues, organic matter is first formed, and then its mineralization occurs, clearly defined on radiographs. Three periods are distinguished in the process of growth and formation of the dental apparatus.

The first period from the birth of the child to 5-6 years (before the eruption of permanent teeth). At birth, the spongy substance of the jaws has a delicate, finely looped character, in each jaw there are 18 follicles (10 milk and 8 permanent).

The tooth follicle is presented as a rounded lesion of bone tissue, surrounded on the periphery by a closing cortical plate. The tooth is visible on radiographs only after mineralization, which begins with the appearance of point calcifications along the cutting edge or in the area of tubercles, gradually merging and forming the contour of the crown.

Teething in girls occurs somewhat earlier. Lower baby teeth usually erupt 1-2 months earlier than similar upper teeth. Rickets, chronic dyspeptic disorders, acute infections, endocrine changes (thyroid gland, pituitary gland diseases), nutritional disorders, hypovitaminosis affect the timing of teething.

If the eruption of teeth is delayed, only an X-ray examination makes it possible to determine the presence or absence of rudiments and the nature of their formation, taking into account the age of the child.

On radiographs, two stages of root formation (both deciduous and permanent) are distinguished: the stage of unformed and the stage of unclosed apex. In the stage of unformed apex, the radiograph shows an unevenly wide root canal, funnel-shaped widened at the root apex and narrowing towards the tooth cavity. At the apex of the tooth with a wide apical opening, the growth zone is visible in the form of a rounded focus of bone rarefaction, surrounded on the periphery by the cortical plate of the socket.

The stage of the unclosed apex is observed at the roots of teeth that are completing their formation. The unevenly wide root canal gradually narrows in the direction from the cavity of the tooth to the apex. At the apex of the tooth, the apical opening is clearly visible, which is usually not determined in formed teeth. The periodontal gap at the apex of the tooth is somewhat widened.

The second period begins at the age of 6-7 years with the replacement of temporary teeth with permanent ones. Upon completion of crown formation, the rudiment of the permanent tooth begins to shift to the edge of the alveolar process. After the crown formation is complete, approximately 5 years pass until the permanent tooth is fully erupted. Eruption is preceded by physiological resorption of the roots of the primary teeth (the roots are shortened, "eaten away").

On radiographs during this period, the teeth and rudiments are arranged in three rows: temporary teeth in the dental arch and rudiments of permanent teeth in two rows. The rudiments of canines are located separately: on the upper jaw - under the lower orbital edge, on the lower jaw - above the cortical layer of the lower edge. The first lower molars erupt first. If the lower central incisors erupt first, this is considered a possible variant of the norm.

In the third period, at the age of 12-13 years, permanent teeth are found in the dental row, the roots of which are formed to varying degrees.

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