Development and anatomy of teeth and jaws

The period of histogenesis of dental tissues begins with the 4th month of intrauterine life. When forming hard tooth tissues, an organic substance is first formed, and then its mineralization, clearly defined on X-ray patterns, occurs. In the process of growth and formation of the dentoalveolar apparatus, three periods are distinguished.

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

The follicle of the tooth is presented in the form of a focus of rarefaction of bone tissue of rounded shape, surrounded by a circumscribing cortical plate around the periphery. The tooth is visible on radiographs only after mineralization, beginning with the appearance of point calcifications along the cutting edge or in the region of the hillocks that gradually merge and form the contour of the crown.

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

With a delay in teething, only an X-ray study 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.

X-ray patterns distinguish two stages of the formation of roots (both dairy and permanent): the stage of unformed and the stage of the uncovered apex. In the stage of the unformed tip, an unevenly wide root canal is defined on the roentgenogram, funnel-shaped widened at the apex of the root and tapering toward the cavity of the tooth. At the apex of the tooth with a wide apical opening, there is a growth zone in the form of a focus of dilatation of bone tissue of rounded shape, surrounded on the periphery by the cortical plate of the socket.

The stage of the uncovered apex is observed at the roots of the teeth that complete their formation. The uneven width of the root canal gradually narrows in the direction from the tooth cavity to the apex. At the apex of the tooth, the apical opening is clearly visible, which is not usually detected in the formed teeth. The periodontal cleft at the apex of the tooth is somewhat enlarged.

The second period begins at the age of 6-7 years with the replacement of temporary teeth with permanent teeth. After the completion of the crown formation, the rudiment of the permanent tooth begins to shift to the edge of the alveolar process. After the end of the crown formation before the full eruption of the permanent tooth takes about 5 years. The eruption is preceded by a physiological resorption of the roots of the baby teeth (the roots are shortened, "eaten").

On the radiographs during this period, the teeth and rudiments are arranged in three rows: temporary teeth in the dental arch and in two rows of the rudiments of permanent teeth. Separately located the rudiments of canines: on the upper jaw - under the lower-vertebral margin, in the lower - above the cortical layer of the lower margin. Earlier all the first lower molars erupt. If the bottom central incisors are pricked first, then this is considered as a possible variant of the norm.

In the third period, at the age of 12-13 years, in the dentition there are permanent teeth, the roots of which are formed in different degrees.

[1], [2], [3]