Introduction to the pediatric dentistry. Anathomical- morphological and X-ray features of teeth – jaw system at children in different age-old periods
A pediatric dentistry is one of the most difficult disciplines. It studies the dentistry diseases based on knowledges from age-old ones anatomical – functional features of child, its development in аntе -, intra -, and postnatal periods of life.
Child’s population makes the considerable particle of population of our country that is why the sphere of help touches the most perspective part of society. Level of dents diseases at children extraordinarily high. Sickly state of cavity to the mouth badly influences on psychological and physical status of child. From a toothache, discomfort in the cavity of mouth, from inferiority of dental row a child renounces meal, badly chews her. Teeth which are not treating always are the source of infection, allergy, and lower resistance of organism on the whole. Sick temporal teeth are reason 85% heavy festering – inflammatory processes result in teeth – jaws deformations.
Complication of work of child’s doctor – dentistry consists in that he must take into account not only symptomatic of disease but also anatomical- physiology features of child’s organism in a certain period of development. To set a diagnosis and to choose the method of treatment, a doctor must owot only by basic dentistry manipulations but also to have knowledge from pediatrics about the periods of growth and development of child, feature of its functional state.
Our object, propedeutic of therapeutic pediatric dentistry enables to the students to lay hands on certain skills of treatment of teeth and his complications decay on phantoms. Knowledges purchased thus, you use in the process of work directly with patients. On phantoms models and remote teeth students meet with the basic periods of development and resorbtion of roots of baby teeth, by the periods of forming of roots of the second teeth at children, and also seize by basic manipulations from preparing and stopping of carious defects of teeth, conduct endodontic interference in teeth with the different stages of their development.
DEVELOPMENT OF TEETH-JAWS SYSTEM AT CHILDREN
A primary oral cavity at an embryo has the appearance of narrow crack which is limited by five sprouts of branchial arcs. The overhead edge of mouth crack is formed by an odd frontal sprout and located on sides from him by supramaxillary sprouts — the appendix first branchial arc. The lower edge of mouth crack is limited by two lower- jaw sprouts which also are derivative the first branchial arc. Transferred sprouts not only limit a mouth crack but also form the walls of mouth cavity — future cavity of mouth.
Teeth are derivative mucus shell of oral cavity of embryo. Enamel organs develop from the epithelium of mucus shell, and from a mesenchyma, which is under an epithelium is dentine, pulp, cement, hard and soft fabrics circumferential a tooth (parodontium).
The odontogeny passes in three stages: the embryos of teeth are formed in the first; differentiation of dental embryos passes in the second, in the third is formation of teeth.
In the first stage, on 7-8 week of embryo development, on the overhead and lower surfaces of cavity of mouth there is the bulge of epithelium is dental plate lamina enamelare, which grows in an inferior mesenchyma. On turned to the lip or cheek of surface of dental plate due to subsequent excrescence of epithelium form tube educations which grow afterwards into the enamel organs of temporal teeth are formed. In every dental plate is formed for 10 educations which answer the embryos of temporal teeth. On a 10th week in enamel organs, submerging into their wall, a mesenchyma, which forms dental baby’s dummies papillae dentales, grows in. To the end of 3rd month of development enamel organs move away from a dental plate, but keep with her connection by mediocrity of epithelial bunch are necks of enamel organ. Round an enamel organ due to the compression of mesenchyma a dental sac saccus dentalis, which near basis of dental embryo meets with a dental papilla, is formed.
Both the embryos of teeth and fabrics circumferential they change in the second stage. There is stratification of homogeneous mews of enamel organ on separate layers. Pulp appears in a center, and on periphery is layer of internal enamel mews which give beginning of ameloblasts, that form enamel. Part of mews of pulp, which adjoins to the layer of ameloblasts, makes the intermediate layer of enamel organ.
At the same time there is the process of differentiation of dental papilla. It is multiplied in sizes and is grown in deeper in an enamel organ. Vessels and nervous fibres fit for a papilla. On the 4th month of embryo development of neck of enamel organs germinate by a mesenchyma and resolve. Dental embryos hereupon move away from a dental plate which also germinates by a mesenchyma and loses connection with the epithelium of oral cavity.
It is saved and is grown back departments and free edges of dental plates which in future grow into the singed organs of the second teeth. Round dental embryos in the mesenchyma of jaws appear and grow bones cross-beams which form the walls of dental teeth ridges.
In the third stage of odontogeny, which begins from the end of 4th month of embryo period, there is the histogenesis of fabrics, a dentine, enamel and endodontium, appears.
Mineralization of fabrics begins at the end of 5th month. Complete Mineralization does not take place, and there is the layer of don’t calcify dentine in the inside of tooth.
Development of root is carried out in a postembrionale period. The lower department of enamel organ proliferes grows into a root epithelial vagina radicalis epithelialis, which consists of two rows of mews — external and internal. A root epithelial vagina deeply grows in an inferior mesenchyma and engulfs its area which the root of tooth will appear from. Mesenchymal mews which got in an epithelial vagina grow into odonthoblasts, which form the dentine of root of tooth. As soon as the dentine of root will be formed, root epithelial vagina germinating by a mesenchyma, resolves, as a result the mesenchymal mews of dental sac directly run into the dentine of root and grow into tsementhoblasts, which form cement on-the-spot root of tooth. Part of mews, which surrounds the root of tooth, gives beginning to development of fabrics to periodont.
The second teeth appear also from dental plates. The embryos of first permanent molar appear on the 6th month of intranatal development. The embryos of chisels, dog-teeth appear on the 8th month of development. Dental plates grow at the same time; on their edges the enamel organs of premolar are mortgaged. Subsequent stages of forming similar with described for temporal teeth.
The certain degree of forming of different groups of teeth answers every term of antenatal and postnatal period.
How the results of researches (Vinogradova T.F.) testify at the term of pregnancy 18-19 weeks (4,5 months) evidently signs of mineralization of cutting edge and surfaces of crowns of chisels on 1/3. Also there is mineralization of mesiobuccal knolls of first molar.
Mineralization of chisels lasts in 24-25 weeks (6 months), almost fully mineralizate cutting edge of canine; the hearths of mineralization of tongue–medial knoll of first molars appear. The follicle of first permanent molar begins to appear.
Mineralization of chisels and dog-teeth proceeds in 26 weeks (7 months), mineralization of medial knolls of first molars is almost closed; the follicle of sixth tooth is multiplied.
Mineralization of incisives and canines proceeds in 32 weeks (8 months), the size of follicle of sixth tooth is multiplied; the embryos of chisels and dog-teeth of the second teeth appear.
In 36 weeks of pregnancy (9 months) calcified all surfaces of chisels, the process of mineralization spreads on the approcsimal surface of first temporal molar. The bulk of crown of first permanent molar is formed after birth of child.
– At first the rudiments of the second teeth baby and lie in general teethridges, afterwards between them bone partition is formed. In an interval from 6 to 12 years, when baby teeth are replaced permanent, an osteoclast destroys bone partition and root of baby tooth. Under the action of pressure, that grows in pulp of the second teeth as a result of strengthening of synthetic activity of localisated there fibroblasts, the crown of the tooth cuts through above the surface of alveolar sprouts, replacing a baby tooth. The last before the fall consists only of crown and overhead part of root. The terms of the cutting through second teeth are resulted on a fig. 4.3, 4.4, 11.21, 11, 22, tables.
Bones teethridges develop simultaneously with development of overhead and lower jaws. Thus bone fabric of supramaxilla appears directly from a mesenchyma, and the stage of formation of cartilaginous rudiment proceeds to development of cartilage bone (cartilage of Mekkel). We will mark that a cartilaginous model is not transformed directly in a bone, and is subject to degeneration. Round tailings of cartilage of Mekkel from two bones rudiments the bone of lower jaw develops as a result of direct bone genesis. The back-end of lower jaw enters into connection with a temporal bone and with participation of fibro cartilage forms a temporal-jaw joint. During all embryo period a lower jaw is built from two bones rudiments the ends of which are united between itself by a fibro cartilage.
At violation of odontogenesis there are the anomalies of terms of cutting through (including presence of teeth which were not cut through), anomalies of form and placing of teeth, and also defect of fabrics of tooth. To the anomalies of placing supraoccusia (overhead teeth do not achieve a closing surface), infraocclusion (lower teeth do not achieve an occlusal surface), torsi versos (turn of tooth about the axis), transpositions (mutual change of position of neighboring teeth), placing of teeth belongs out of dental arc (lip-cheek, linguistic-palatal and others like that), anomalous position (in a nasal cavity, to the gaymores bosom and others like that), accumulation of teeth, odontoplerosis (supernumerary teeth), diminishing of amount of teeth or their complete absence (adonti). Defects of fabrics of tooth: fluorosis (insufficiency of fluorine and calcium), giperplasia of enamel.
A dental embryo on an X-rays looks as light oval form. It is limited by the line of compact bone which surrounds an embryo.
Mineralization shows up as dense darkening. At first calcified cutting edge groups of frontal teeth and humps of masticatory teeth.
Afterwards the process of mineralization spreads on other parts of crown. Forming of root of tooth comes after it.
Сutting through temporal teeth begins on 6-8 month of life of child and is closed to 2,5-3 years. Lower central incisives cut through the first, afterwards are their antagonists, and then are lateral incisives. To 10-12 months all 8 incisives cut through. First temporal molar appears in 2-3 months, after them are canine, second molar cuts through the last.
A stabilizing period comes after the period of stabilization. It is a period forming of functional valuable temporal bite. With 6-7 years replacement of temporal bite is begun on permanent. To it growth precedes embryos of the second teeth and physiology resorbtion of roots of temporal teeth (tables. 2). This period lasts on the average to 12 years and is named the period of variable bite. First permanent molar which does not have temporal predecessors cuts through at first. Then teeth are replaced in the same sequence in which cut through.
The period of growth and forming of their roots comes after the cutting through second teeth. This period lasts on the average 3-4,5 years.
After mineralization of cutting edge or masticatory surface of crown X-ray the cavity of tooth begins to appear as a light area in the center of crown. Near basis the cavity of tooth meets with the area of mineralization, which shows itself the projection of area of growth. As far as growth of tooth and his calcination a sprout area diminishes gradually. In future with appearance of bifurcation the contours of cavity of tooth are designed and forming of roots begins.
During forming of crown of the tooth a follicle has the rounded form. With beginning of development of neck of tooth he begins to stretch in the direction of root. The process of education to periodont goes along with beginning of development of root.
On a X-ray the unformed root evidently as two parallel strips which take beginning near basis of crown of the tooth, where the widest part of root, then in direction opposite to the crown, gradually narrow and end with sharp part.
A root-canal in a lower department meets with the area of light, which has the rounded form with clear contours. This is a sprout area. This area diminishes as far as forming of root and disappears in the stage of the unclosed apex, and the in her place yet some time evidently extended periodontal crack.
In the process of forming of apex of root distinguish three stages: stage of the unformed apex of root, stage of the unclosed apex of root, and stage of the fully formed apex.
X-ray picture of the unformed apex of root there is such: the walls of root are located parallel, a width them diminishes gradually. A periodontal crack on all draught has an identical width. Near an apex she meets with the area of growth.
In the stage of the unclosed apex of wall of root have the same structure, as well as in the stage of the unformed apex, differ from her by the greater thickness of walls. On an X-ray expressly evidently projection of the apex opening. In the stage of the formed apex of root of area of growth it is not, some time the extended periodontal crack is saved, the apex opening is closed.
Temporal teeth on an X-ray differ from permanent to those, that they less sizes, with short roots. The roots of molars considerably to go away. Cavity of tooth and root-canals, especially in the group of frontal teeth, considerably wider, than in permanent.
Since 6-7 years there is replacement of temporal bite on permanent. Physiology resorbtion of roots of temporal teeth precedes to it. As a result of pressure of embryo of the second teeth the area of enhanceable vascularisation appears on surrounding fabrics. She is rich on an osteoclast and resorbtions is named.
X-ray the process of resorbtion shows up as follows. The follicles of the second teeth have clear contours and are disposed in a direct closeness to the roots of temporal teeth. This closeness as far as progress of resorbtion of root becomes yet greater. Resorbtion of roots of temporal teeth concerns by correlation with the embryos of the second teeth.
From data of Vinogradova T.F., in default of teeth-jaws anomalies children have three as physiology resorbtion of roots of temporal teeth:
— The first type is even resorbtion of all roots, which begins in the area of apexes and spreads on a vertical line. Roots are resorbtions evenly. Phenomena of resorbtion in the area of bifurcation minimum.
— Second type — resorbtion of one root which the nearest is disposed to the embryo of the second teeth prevails next to partial resorbtion of roots and area of bifurcation
— Third type — resorbtion of area of bifurcation prevails. At this type resorbtion can be saved morphological full value of apical part of root. Area of bifurcation oftenresorbtiones so that there is connection with crown pulp.
Next to physiology pathological resorbtion of roots can develop under act of different reasons (as a result of inflammations, new formations). Pathological resorbtion is carried out by the multinuclear giant mews of inflammatory exsudate. Processes of formation of bone here minimum and fall behind from resorbtion. In this connection at pathologicalresorbtion of base X-ray destruction and absence of bone fabric is a sign between the roots of temporal teeth and round them. The process of pathological resorbtion can spread on the follicle of the second teeth, causing premature resorbtion of bone shell of follicle and cutting through second teeth. In the process of embryo of the second teeth violation of safety of cortical plate is the sign of in drawing basic X-ray round him.
Histologic slide of tooth in cap stage.
The first signs of an arrangement of cells in the tooth bud occur in the cap stage. A small group of ectomesenchymal cells stops producing extracellularsubstances, which results in an aggregation of these cells called the dental papilla. At this point, the tooth bud grows around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes the enamel (or dental) organ. A condensation of ectomesenchymal cells called the dental follicle surrounds the enamel organ and limits the dental papilla. Eventually, the enamel organ will produce enamel, the dental papilla will produce dentin and pulp, and the dental follicle will produce all the supporting structures of a tooth.
Bell stage
The bell stage is known for the histodifferentiation and morphodifferentiation that takes place. The dental organ is bell-shaped during this stage, and the majority of its cells are called stellate reticulum because of their star-shaped appearance. The bell stage is divided into the early bell stage and the late bell stage. Cells on the periphery of the enamel organ separate into three important layers. Cuboidal cells on the periphery of the dental organ are known as outer enamel epithelium. The columnar cells of the enamel organ adjacent to the dental papilla are known as inner enamel epithelium. The cells between the inner enamel epithelium and the stellate reticulum form a layer known as the stratum intermedium. The rim of the dental organ where the outer and inner enamel epithelium join is called the cervical loop. In summary, the layers in order of innermost to outermost consist of dentine, enamel (formed by inner enamel epithelium, or ‘ameloblasts’, as they move outwards/upwards), inner enamel epithelium and stratum intermedium (specialised stratified cells that support the synthetic activity of the inner enamel epithelium) What follows is part of the initial ‘enamel organ’, the middle of which is made up of stellate reticulum cells. This is all encased by the outer enamel epithelium layer.
Other events occur during the bell stage. The dental lamina disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity; the two will not join again until the final eruption of the tooth into the mouth.
The adjacent layer of cells in the dental papilla suddenly increases in size and differentiates into odontoblasts, which are the cells that form dentin.[11] Researchers believe that the odontoblasts would not form if it were not for the changes occurring in the inner enamel epithelium. As the changes to the inner enamel epithelium and the formation of odontoblasts continue from the tips of the cusps, the odontoblasts secrete a substance, an organic matrix, into their immediate surrounding. The organic matrix contains the material needed for dentin formation. As odontoblasts deposit organic matrix, they migrate toward the center of the dental papilla. Thus, unlike enamel, dentin starts forming in the surface closest to the outside of the tooth and proceeds inward. Cytoplasmic extensions are left behind as the odontoblasts move inward. The unique, tubular microscopic appearance of dentin is a result of the formation of dentin around these extensions.[1]
After dentin formation begins, the cells of the inner enamel epithelium secrete an organic matrix against the dentin. This matrix immediately mineralizes and becomes the tooth’s enamel. Outside the dentin are ameloblasts, which are cells that continue the process of enamel formation; therefore, enamel formation moves outwards, adding new material to the outer surface of the developing tooth.
Enamel
Enamel formation is called amelogenesis and occurs in the crown stage of tooth development. “Reciprocal induction” governs the relationship between the formation of dentin and enamel; dentin formation must always occur before enamel formation. Generally, enamel formation occurs in two stages: the secretory and maturation stages.[12] Proteins and an organic matrix form a partially mineralized enamel in the secretory stage; the maturation stage completes enamel mineralization.
In the secretory stage, ameloblasts release enamel proteins that contribute to the enamel matrix, which is then partially mineralized by the enzyme alkaline phosphatase. The appearance of this mineralized tissue, which occurs usually around the third or fourth month of pregnancy, marks the first appearance of enamel in the body. Ameloblasts deposit enamel at the location of what become cusps of teeth alongside dentin. Enamel formation then continues outward, away from the center of the tooth.
In the maturation stage, the ameloblasts transport some of the substances used in enamel formation out of the enamel. Thus, the function of ameloblasts changes from enamel production, as occurs in the secretory stage, to transportation of substances. Most of the materials transported by ameloblasts in this stage are proteins used to complete mineralization. The important proteins involved are amelogenins,ameloblastins, enamelins, and tuftelins. By the end of this stage, the enamel has completed its mineralization.
Dentin
Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development. The formation of dentin must always occur before the formation of enamel. The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin.
Odontoblasts, the dentin-forming cells, differentiate from cells of the dental papilla. They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth. The organic matrix contains collagen fibers with large diameters (0.1–0.2 μm in diameter).[15] The odontoblasts begin to move toward the center of the tooth, forming an extension called the odontoblast process. Thus, dentin formation proceeds toward the inside of the tooth. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix. This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick.
Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause collagen to be secreted in smaller amounts, which results in more tightly arranged, heterogeneous nucleation that is used for mineralization. Other materials (such as lipids, phosphoproteins, and phospholipids) are also secreted.
Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth. This development continues throughout life and accounts for the smaller areas of pulp found in older individuals. Tertiary dentin, also known as reparative dentin, forms in reaction to stimuli, such as attrition or dental caries.
Tooth development is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans. For human teeth to have a healthy oralenvironment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth weeks in utero, and permanent teeth begin to form in the twentieth week in utero.[1]If teeth do not start to develop at or near these times, they will not develop at all.
A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first branchial arch that is necessary for the development of teeth. The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth and is organized into three parts: the enamel organ, thedental papilla and the dental follicle.
The enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium. These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. The growth of cervical loop cells into the deeper tissues forms Hertwig’s Epithelial Root Sheath, which determines the root shape of the tooth. The dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells. Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth. The dental follicle gives rise to three important entities:cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum.
Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth. This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages.
