Baby teeth: eruption and their loss

Milk teeth erupt after birth in a specific sequence.

Teeth originate from a double germ: from the epithelium and the underlying mesenchyme. Enamel develops from the epithelial germ, and dentin from the mesenchyme. Teeth formation begins by the end of the 2nd month of intrauterine development. After the dental plate has formed, protrusions appear in it, from which enamel crowns are formed. The crowns of baby teeth (at the 11th week) appear first, followed by permanent teeth.

The milk teeth of the same name on each half of the jaw erupt simultaneously. The lower teeth, as a rule, erupt earlier than the upper ones. The only exception is the lateral incisors - the upper teeth appear earlier than the lower ones.

Stages of formation of milk teeth

Teeth	Calcification		Teething, months		Loss, years
	Beginning, months of pregnancy	The end, months of life	Upper jaw	Lower jaw	Upper jaw	Lower jaw
Incisors
Central	5	18-24	6-8	5-7	7-8	6-7
Lateral	5	18-24	8-11	7-10	8-9	7-8
Fangs	6	30-36	16-20	16-20	11-12	11-12
Molars:
The first	5	24-30	10-16	10-16	10-11	10-12
Second	6	36	20-30	20-30	10-12	11-13

Timing of eruption of primary teeth (months) (according to S. Horowitz and E. Hixon, 1966)

Jaw	Teeth	Very early	Early 10%	Normal 30%	Normal 50%	Later 90%
Lower	Central incisor	4	5	6	7.8	11
Upper	Central incisor	5	6	8	9.6	12
Upper	Lateral incisor	6	7	10	11.5	15
Lower	Lateral incisor	6	7	11	12.4	18
Upper	Molar first	8	10	13	15.1	20
Lower	Molar first	8	10	14	15.7	20
Lower	Fang	8	11	16	18.2	24
Upper	Fang	8	11	17	18.3	24
Lower	Molar 2	8	13	24	26.0	31
Upper	Molar 2	8	13	24	26.2	31

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Milk teeth and bite formation

There are at least two periods in the existence of an already formed, i.e. completed, milk bite. According to A. I. Betelman, the first period often coincides with the age of 2 1/2-3 1/2 years and is characterized by:

• close-set teeth with no spaces between them;
• absence of tooth wear;
• the location of the distal surfaces of the upper and lower dental arches in the same frontal plane;
• orthognathic bite.

The first period can be considered young, or initial, in the biological existence of the milk bite.

The second period is, accordingly, the final one and falls on the age from 3 1/2 to 6 years. It is characterized by:

• the appearance of interdental spaces, or distances, called in dentistry diastemas (between incisors) or tremas (between other teeth); their width on the upper jaw is naturally greater than on the lower;
• clear signs of tooth wear;
• misalignment in the frontal plane of the teeth of the lower and upper rows;
• transition of orthognathic bite to straight bite.

The differences in the characteristics of the two periods can also be used to judge the biological age of children of early and pre-school age. The second sub-period of the primary bite illustrates the intensive preparation of the dental complex for the eruption of permanent teeth, the width of which is significantly greater than that of the primary bite. The emergence of tremas reflects the intensity of jaw growth.

When analyzing the condition of the milk bite in children, it should be borne in mind that the absence of physiological diastemas and tremas by the age of 6 years signals insufficient growth of the jaws and the child's unpreparedness for the eruption of permanent teeth. In such cases, the child is consulted by a pediatric orthodontist; in some cases, there are indications for surgical treatment.

In physiological conditions, the abrasion of baby teeth is one of the manifestations of the approaching change of bite. It should be ensured by intensifying the use of teeth in the chewing process. For this purpose, it is necessary to introduce such products as raw vegetables and fruits, black coarse bread, etc. into the diet of children.

The biological role of the primary dentition is extremely important. Due to such an intermediate stage of dentition, wide opportunities for extended modeling of the dental system, the articulation system and the facial skull as a whole arise. With the appearance of a primary tooth, space is fixed for the subsequent permanent tooth, the active use of primary teeth during chewing provides a stimulus for the growth of the jaws, for the maximum extension of the period of the second dentition, which should occur only at a certain stage of growth of the jaws and facial skull. Premature loss of a primary tooth or its extraction contributes to the premature eruption of a permanent tooth, desynchronization of the growth of individual sections of the jaw, creates unfavorable conditions for the eruption of neighboring teeth, and therefore, deterioration of the conditions for their long-term healthy functioning. The formation of sound articulation and speech largely depends on the primary dentition. If the primary dentition is insufficient, the reproduction of 10-18 sound components of speech is impaired. Milk bite is also of great importance for the development of the child's personality and facial features. The latter is largely determined by the role of bite and chewing force in the development of the tone and mass of the facial muscles and its ligamentous apparatus.

The period of retention of baby teeth and the appearance of permanent teeth is called the period of mixed dentition. When baby teeth are replaced by permanent teeth (mixed dentition), 3-4 months usually pass after the loss of a baby tooth and before the eruption of a permanent tooth. The first permanent teeth erupt at about 5 years of age. They are usually the first molars. Then the sequence of appearance of permanent teeth is approximately the same as when baby teeth appear. After the replacement of baby teeth by permanent teeth, the second molars appear at about 11 years of age. Third molars ("wisdom teeth") erupt at the age of 17-25 years, and sometimes later. In girls, teeth eruption occurs somewhat ahead of boys. For an approximate estimate of the number of permanent teeth, regardless of gender, you can use the formula

X = 4n - 20, where X is the number of permanent teeth; n is the number of years the child is old.

The formation of both primary and permanent dentition in children is an important indicator of the level of biological maturation of the child. Therefore, the concept of "dental age" is used in assessing the biological maturity of children. Of particular importance is the determination of dental age in assessing the degree of maturity of pre-school and primary school children, when other criteria are more difficult to use.

Normal sequence of eruption of permanent teeth in children (no R. Lo and R. Moyers, 1953)

Number	Lower jaw	Number	Upper jaw
1	First molar	2	First molar
3	Central incisor	5	Central incisor
4	Lateral incisor	6	Lateral incisor
7	Fang	8	First premolar
9	First premolar	10	Second premolar
11	Second premolar	12	Fang
13	Second molar	14	Second molar

Assessment of the level of age development by "dental age". Number of permanent teeth

Age, years	Floor	Slow development	Average rate of development	Accelerated development
5.5	Boys	0	0-3	More than 3
	Girls	0	0-4	More than 4
6	Boys	0	1-5	More than 5
	Girls	0	1-6	More than 6
6.5	Boys	0-2	3-8	More than 8
	Girls	0-2	3-9	More than 9
7	Boys	Less than 5	5-10	More than 10
	Girls	Less than 6	6-11	More than 11
7.5	Boys	Less than 8	8-12	More than 12
	Girls	Less than 8	8-13	More than 13

Age patterns of teeth eruption. Development of the formula of permanent occlusion in children (permanent occlusion)

Age, years	Girls	Boys
6	61 16 61 16 621 126	6 6 61 16 621 126
7	621 126 621 126	621 126 621 126
8	621 126 65421 12456	621 126 6421 1246
9	64321 12346 654321 123456	64321 12346 654321 123456
10	654321 123456 7654321 1234567	654321 123456 654321 123456
11	7654321 1234567 7654321 1234567	7654321 1234567 7654321 1234567
12	7654321 1234567	7654321 1234567

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Examination of baby teeth

When examining the facial part of the skull, attention is paid to the features of the position of the upper and lower jaw, the features of the bite, the number of teeth and their condition. The main pathological signs are changes in the bite and teeth:

• hypo- or oligodontia;
• premature eruption or delayed eruption of teeth;
• protruding incisors, persistent diastemas;
• enamel dysplasia, early caries;
• upper and lower jaws - upper micrognathia, upper prognathia; lower retrognathia, micrognathia or agnathia (micrognathia), lower prognathia.

Deformation of the bones of the base of the skull leads to a sunken bridge of the nose and exophthalmos, a decrease in the transverse dimensions of the upper jaw with the formation of a high Gothic palate. The front part of the upper jaw protrudes forward, while the lower jaw moves back, which is called prognathism. This position of the jaws subsequently leads to the formation of an incorrect bite.

When examining baby teeth, it is necessary to determine their number on the upper and lower jaws, the ratio of baby and permanent teeth, their shape, direction of growth, integrity and color of the enamel.

During the examination, you can focus on some distinctive features of the teeth of the milk and permanent bite. Milk teeth are characterized by the following properties:

• smaller sizes;
• bluish-white color (permanent ones have a yellowish color);
• more vertical arrangement;
• a pronounced sign of curvature;
• clear boundary between the crown and the root of the incisors;
• abrasion of cutting and chewing surfaces;
• some looseness.

Quite a lot of difficulty arises when trying to distinguish the second primary molar from the first permanent molar, but the distinction can be made easier by taking into account that the second primary molar is in fifth place, and the first permanent molar is in sixth place.

The approximate number of due baby teeth can be determined by the formula n - 4, where n is the child's age in months. Discrepancies in the timing of teeth eruption, usually a delay, are most often associated with nutritional characteristics, often with rickets.

Diseases of permanent and milk teeth

Premature eruption of teeth or their presence from birth is much less common and is not a diagnostic sign of the disease. Anomalies in the development of baby teeth include supernumerary teeth (the appearance of extra teeth), congenital absence, incorrect growth direction (teeth can be pushed out of the dental arch, rotated around their axis, significantly moved apart). Barrel-shaped deformation of the upper incisors with a crescent-shaped notch of the cutting edge (Hutchinson's incisors) is one of the signs of congenital syphilis.

Some diseases accompanied by disturbance of mineral and protein metabolism, suffered by a child during the period of dental calcification, can lead to enamel hypoplasia. Milk teeth lose their natural shine and become covered with depressions of various sizes and shapes. An unusual enamel color (yellow, brown, pink, amber) can be caused by hereditary diseases or complications of drug treatment.

Caries is a common disease of baby teeth, which has a significant impact on the child's health. The importance of poor dental hygiene and nutritional disorders in the origin of early and widespread caries in children has been confirmed.

The main etiologic factor of caries is the interaction between carbohydrates in food and bacteria of the oral mucosa, primarily Streptococcus mutans, located on the surface of tooth enamel. Organic acids, which arise during the fermentation of carbohydrates in food deposited on the surface of teeth or in the interdental spaces by microorganisms, demineralize tooth enamel, make deep tooth structures accessible to the microbial inflammatory process with the formation of cavities, destruction of the pulp, and perhaps even for penetration into the alveolar part of the bone with the formation of an abscess there. Caries of a baby tooth has an extremely negative effect on the development of a permanent bite. Multiple caries of baby teeth is a very significant risk for the development and long-term functioning of permanent teeth. In addition, the accumulation of active and virulent bacteria in caries foci can lead to lymphogenous infection of the membranes of the heart and its valve apparatus. Even a focal infection of a limited carious process is a source of bacterial sensitization, leading to the development of a rheumatic process, systemic vasculitis, glomerulonephritis and other potentially serious diseases.

There are some special forms of caries in children that occur by similar mechanisms, but intensified, due to special circumstances. These include caries and often a changed bite in children who were fed uncontrolled feeding with sweet mixtures, juices or tea. Often this is just a bottle (a horn with a nipple), left with the child during the hours of night or daytime sleep. Here, the constant leakage of sweet mixture into some part of the oral cavity, low activity of saliva secretion and swallowing during sleep are triggered. This leads to local damage to the teeth, most often the incisors of the upper jaw, by the same bacterial-acidotic mechanism. A peculiar and often severe clinical picture of caries can be observed in children with gastroesophageal reflux or simply habitual regurgitation. The entry of acidified gastric contents into the oral cavity can lead to independent acidic destruction of enamel, which is later superimposed by the action of bacteria.

Prevention of early caries of baby teeth is a whole chapter of preventive pediatrics. It includes monitoring the nutrition of a pregnant woman during the period of teeth formation. There are recommendations for additional introduction of fluoride into the child's nutrition, starting from the age of 6 months.

Daily Fluoride Dose (mg) Based on Fluoride Content in Drinking Water and Age of Children (American Academy of Pediatrics)

Age	Fluoride concentration in water
	Less than 0.3	0.3-0.6	More than 0.6
6 months - 3 years	0.25	0	0
3-6 years	0.5	0.25	0
6-16 years	1.0	0.5	0

Widespread promotion and use of fluoride toothpastes for the prevention of dental caries in children has its negative consequences - the lack of a strict technique for brushing teeth, the pleasant taste of the paste create conditions for children to frequently swallow small amounts of it. This amount is quite sufficient for the widespread occurrence of fluorosis in recent years - a toxic excess of fluoride, the main negative manifestation of which is tooth decay. Therefore, for young children, it is more rational to use toothpastes that do not contain fluoride.

Prevention of dental caries in children is not limited to the problems of fluoride and calcium balance. It includes adherence to the principles of a complete nutritional balance across a wide range of vitamins and salts, limiting simple carbohydrates with high cariogenicity (sucrose), using fruit juices with added water, limiting carbonated drinks, enriching the diet with complex carbohydrates, and adequate mechanical load on the jaws.

Common diseases of the gums and teeth are gingivitis and periodontitis. The former are caused almost exclusively by the accumulation of plaque in the oral cavity, consisting of pieces of food and bacteria, due to poor oral hygiene. Clinically, this is expressed by reddening of the mucous membrane at the edges of the gums and swelling of the interdental papillae. The alveolar bone structures are never involved in the process.

Periodontitis is recognized by the involvement of the connective tissue structures (ligaments) and bones adjacent to the tooth in the infectious process. This process always leads to irreversible changes with tissue destruction. In this case, a significant role is attributed to anaerobic streptococci and actinomycetes. Since bone destruction usually occurs below the gum edge, X-ray examination of the jaw in the suspected affected area has to be used for diagnosis.

Premature loss of baby teeth can be caused by different, but always serious reasons. These include poisoning with salts or mercury vapor, radiation therapy of neoplasms, severe forms of acatalasia, hypophosphatasia, diabetes mellitus, leukemia, histiocytosis, immunodeficiency states. Baby teeth can fall out due to scurvy (hypovitaminosis C).

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