The center of development of medical education the tashkent medical academy



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THE REPUBLIC OF UZBEKISTAN MINISTRY OF HEALTH

THE CENTER OF DEVELOPMENT OF MEDICAL EDUCATION

THE TASHKENT MEDICAL ACADEMY

Chair of histology and medical biology


Subject ______histology _______________

THEME: «DEVELOPMENT AND REPLACEMENT OF TEETH»
Methodical recommendation

(For students of higher medical schools)

Tashkent – 2011

METHODICAL RECOMMENDATION

FOR PRACTICAL LESSON ON THE THEME:
«DEVELOPMENT AND REPLACEMENT OF TEETH»




For stomatologic faculty

Lesson № 3 III semestre


Theme: «DEVELOPMENT AND REPLACEMENT OF TEETH »

1. Histology and Medical biology department.

Facilities: histologic preparations, microscopes, atlases, slides, computer.

2. Duration of studying of the theme - 3 hours.

3. Aim:

- To generate knowledge of sources and stages of development of teeth, to acquire skills of definition on micropreparation of structural components of teeth and tissues surrounding them in the different development periods.


Purpose

The student should know:

1. Sources of development of teeth

2. Stages of development of teeth

3. The teething mechanism

4. Development features and a secondary dentition

The student should have practical skills: defining in micropreparations the stages of teeth development, to indicate structure of a dental germ and surrounding tissues, the cells producing an enamel and dentine, to distinguish on electron microphotographs ameloblasts and odontoblasts.
4. Motivation

During the development of teeth sometimes there are observed various anomalies. Age periods of teething in children serve as an index of their general physical development. Anomalies of teeth development may be bound to endocrine impairments, genetical defects, chronic diseases, avitaminosis, etc. Knowledge on morphofunctional features of development of an oral cavity and, in particular, teeth, differences in development of milk (deciduous) and permanent teeth, their teething periods are necessary for pediatrists, stomatologists for definition of proper tactics in diagnosting and treatment at teeth diseases and anomalies of their development in children.



5. Intersubject and intrasubject correlations

The obtained knowledge can be used in surgical and therapeutic stomatology, pediatrics.


6. Content of the lesson

6.1. A theoretical part

Items for consideration

1. Sources of development of teeth tissues. En enamel organ originates from the oral cavity epithelium, then form an enamel. A tooth papilla (a dentine and pulp source) and a tooth saccule (a cement and periodontium source) originate from the mesenchyma.

2. The periods of teeth development

1) An anlage of dental germs: on 6th week of embryogenesis the oral cavity epithelium grows down wards into mesenchyma (dental lamina) which enlarges and form of a tooth bud (8th week).

2) Formation of an enamel organ: the tooth bud acquires shape "a little cup", then a "bell" one by the end of 4th month. In an enamel organ there are three layers of cells: internal - cuboidal shaped adjacent to a tooth papilla, high columnarc - precursors of the ameloblasts forming an enamel; the intermedial layer - a layer made up of flattened cells, forms a pulp of the enamel organ, contains cambial cells for replenishing of preameloblasts. The pulp of the enamel organ is a network of cells with processes, it is formed owing to secretion of the fluid containing glycosoamino-glycans and proteins by its cells. Desmosomes bind these cells with each other, and also with that of external and internal layers of an enamel organ; the external layer consist of cuboidal cells, with small quantity of organelles, afterwards partially degenerating, participate in development of the tooth root, forming together with inner cells the epithelial root (Hertvig) vagina, orienting growth of the tooth root. By the end of 3th month the tooth plate (dental lamina) are desintegrated and a germ of tooth becomes separated from an oral cavity epithelium. Under a basement membrane of preameloblasts there is located the mesenchimal tooth papilla which peripheric cells become preodontoblasts - precursors of the odontoblasts producing a dentine. Other cells are not differentiated. Round a dental germ there are aggregations of mesenchimal cells - a tooth saccule around which a network of capillaries is developed.

3) A differentiation of dental germs (a histogenesis of tooth tissues: preodontoblasts are differentiated in odontoblasts which start producing dentine (dentinogenesis). Odontoblasts are polar cells with well educed organelles, with a branched process on the apical part. The process is located in a dentine and elongates while thickening. Odontoblasts synthesize and secrete collagen I type, glycoproteins, phosphoproteins (specific proteins of a dentine – phosphorins), proteoglykans, glycosoaminoglykans, calcium-binding proteins - osteocalcin and оsteonectin. The dentine mineralization takes place gradually. On the odontoblasts surface there remains a non calcificated stria of the dentine (a predentin). At first there is formed the covering dentine – an external layer, then the parapulpar one. The dentine calcification begins at the end of 5th months of an embryogenesis. In a dentine there are found so-called growth lines (Ebner) – as result of frequency of the dentine formation.

Amelogenesis. Three stages: 1) secretion and a primary mineralization (depositions of hydroxyapatite crystals, containing a lot of organic substances); 2) maturing and the secondary mineralization (the further calcification and decreasing of the larger part of the organic matrix); 3) definitive maturing of an enamel (end of a mineralization after eruption of a tooth). Ameloblasts - are differentiated from preameloblasts after the beginning of predentin secretion by odontoblasts, change the polarity (inversion), it is a high columnzr cell with numerous organellae, containing process in its apical part (Thoms’s). Secretory granules are accumulated in a process. Specific proteins of the enamel are enamelins and amelogenins (not collagenic). Secretion starts at a dental germ apex between dentine and an apical surface of ameloblasts, and then down wards to the neck. Unlike a dentine it undergoes mineralization quickly. The enamel structure is cellular: there are distinguished enamel prisms and an interprismatic enamel. Growth of enamel prisms has cyclic character, therefore striations are visible in the enamel, there are also growth lines (Retzius), the calcification is bound to its frequency. Periods after maturation of the enamel ameloblasts together with external epithelium of the enamel organ and the remnants of the enamel organ pulp form the secondary cuticle of the enamel providing protective role at a tooth eruption.

4) The tooth root formation occurs in the postembryonal period. From cells of external and internal layers of epithelium of the enamel organ in the neck zone there grows in wards mesenchyma two-layer cylindrical cellular rod located between the tooth papilla and a tooth saccule (Gertvig’s a root vagina). The root dentine is deposited along the edge of a root vagina which is gradually destroyed, but from it small islets of it are preserved (Malasse islets). Some internal cells of root vagina can be differentiated in ameloblasts and produce small droplets of the enamel which are located in the periodontium («enamel pearls»).

Cementogenesis - cement formation. The cells of a tooth saccule contacting with to dentine are differentiated in to cementoblasts - cuboidal cells with numerous organellae. They produce an organic matrix of cement (collagenic fibers and the ground substance) which deposited over the root dentine. Further there takes place mineralization (deposit of hydroxyapatite crystals) and simultaneous by formation of a new layer of the organic matrix. Cementoblasts imbedded in cement transform into cementocytes (analogic to the development of an osseus tissue). First there forms noncellular cement (primary), and after a teeth eruption – cellular one (secondary). The cellular cement contains its own collagenic fibers and the fibers penetrating from a periodontium.

Periodontium formation. From the external layer of a tooth saccule there are differentiated fibroblasts producing collagenic fibers and the ground substance. Collagenic fibers grow from two sides – from cement and an alveolar bone ones (thicker and branched) towards each other and conjugate. Collagenic fibers bundles are disposed at an angle to the tooth root. After a tooth eruption bundles of collagenic fibers are thickened.

Development of a tooth pulp originates from a tooth papilla. Its differentiation begins from an apex. Blood vessels grow into a papilla before the appearance of odontoblasts, nerve fibers grow in before the beginning of dentine formation. Peripheral cells of a papilla are differentiated in to odontoblasts. The central part of a papilla transforms in to a loose connective tissue. The basic cells of a pulp are fibroblasts secreting intercellular substance (collagen I and III types, glycosoaminoglycans, etc.).

Blood vessels grows simultaneously: in the centre there expand arterioles and venules, on periphery - a capillary network (capillaries 1 and 2).



3. The teething is a process of moving of a place of an anlage and development in a jaw before crown eruption in an oral cavity.

The tooth moves nearer the surface an oral cavity epithelium, destroying a connective tissue above a crown, the reduced enamel epithelium merges with an oral cavity epithelium, over a crown extends, degenerates and the crown breaks in an oral cavity.

The basic mechanisms of a teething: 1) the theory of growth of a tooth root,

2) the hydrostatic pressure theory, 3) the theory of rearrangement of an osteal tissue of a tooth alveole, 4) the theory of draught of a periodontium.



4. A Replacement of teeth. In process of growth of a permanent tooth it puts pressure upon an alveolar bone of a milk tooth in which descends resorbtion. Then as a result of proceeding pressure, the milk tooth root is destroyed. Its place occupies a permanemt tooth, the milk tooth crown is pushed out. Process of resorbtion of milk tooth is undulating: periods of the enhanced disintegration are replaced by rest periods. The replacement of teeth ends by 12 years.
6.2. An analytical part.

Situation tasks

1. At development of a milk teeth (in a histogenesis), first of all there develops a

dentine. What cells participate in its formation? What embryonal germ are they

originated from?

2. In the period of the tooth root formation there develops a cement. What

cells participate in its development? What embryonal source are they originated

from?

3. On micropreparation of a sagittal section of the embryon head there is found the



germ of a tooth, having hat shaped or cap one. It consists of similar epithelial

cells, and mesenchyma in its depth. A germ of tooth is connected with an

epithelium of the oral cavity by a dental lamina. At what period of

development of the tooth germ has such a structure? What germinal layer is it

originated from? Formation of which type of tooth tissue will it participate in?

4. By the time of a birth edges of the enamel organ expand and form the

epithelial vagina (Gertvig’s). What cells does it consist of and their significance

in the development a tooth?

5. In the dental germ in the histogenesis there are found high, columnar cells, one

type of which have basal poles directed to the tooth papilla, others - to the

outer enamel epithelium and to mesenchyma of the tooth saccule. How these

cells are called, what their role in the development of tooth tissues?


6.3. A practical part

1. Studying of tissue specimens under a microscope and sketching them in albums.

2. Studying of electron microphotographs, drawings and schemes.
Preparation № 1. Development of a tooth - inicial stage: formation of the tooth lamina and the tooth bud. H & E.

Fig. 1. An embryo Mandible. Dental germ formation. H & E.

1 - an oral cavity epithelium, 2 - a dental lamina, 3 – the developping enamel organ, 4 - a tooth papilla, 5 - a tooth saccule, 6 - a wall of an osseus alveolus.

The preparation demonstrates section of the oral cavity, the lover part of the developing tongue, and a lower jaw (mandible). The oral cavity is lined by an epithelium from which into the underlying mesenchyma grows in the cellular rod (dental lamina). The dental lamina proceeds to the dental germ at the initial stage of the enamel organ formation. The tooth papilla and tooth saccule are formed of the mesenchyma. Around the dental germ there is seen the developing bone of the tooth alveolus in the form of anastomosing osseus trabeculi. On its surface there are osteoblasts and osteoclasts, and inside - osteocytes. Small blood vessels are visible in a mesenchyma.

Sketch the specimen and designate. Fig. 1 and in Almazov I.V., Sutulov's atlas fig. 429 see.



Preparation № 2. Development of tooth: formation of the enamel organ.

H & E.

Fig. 2. An enamel organ.

1 - a stratified epithelium, 2 - a dental lamina, 3 – outer enamel cells, 4 - a pulp of an enamel organ, 5 - inner enamel cells, 6 – the intermedial layer of an enamel organ, 7 - a tooth papilla, 8 - a tooth saccule, 9 - a wall of an osteal alveolus, 10 - a mesenchyma.


The preparation of an embryo jaw in the frontal section. At lower magnification the stratified epithelium of an oral cavity is visible. An epithelial rod (a dental lamina) growing down wards from it forms an enamel organ. It has the shape of an inverted cup or a cap. There are distinguished 3 layers of cells: 1) internal - the future ameloblasts producing an enamel; 2) intermedial - a pulp of an enamel organ, which consists of the star like cells connecting with each other by processes. Later on the enamel cuticle is formed of this layer; 3) an external layer which is reduced at a tooth erruption.

The dental papilla developed from mesenchimal cells and having a convex shape adjoins to the internal layer of the enamel organ. Further the dental pulp is developed in to a tooth papilla and in its peripheral part odontoblasts are differentiated (the cells producing dentine). Around the dental germ mesenchyma becomes condensed and forming a tooth saccule from which cement and a periodontium further are formed later. On the preparation it is also possible to see the permanent germ of tooth symmetrically located being can be at other stages of development. Around a dental germ there are seen osteal trabeculi of the developing osteal tooth alveoli and blood vessels among the mesenchimal cells.

Find and show all described structures on the preparation. Sketch and designate. Fig. 2 and in Almazov I.V., Sutulov's atlas fig. 430 see.
Preparation № 3. Development of tooth: a dental germ differentiation:

dentine and enamel formation. Preparation of an embryon jaw. H & E.

Fig. 3. A stage of a a tooth histogenesis of. H & E.

1 - enameloblasts, 2 - an enamel, 3 – a mineralized dentine, 4 - a predentin, 5 - odontoblasts,

6 – blood vessels, 7 - a tooth papilla, 8 - a pulp of an enamel organ, 9 - external enamel cells,

10 - a tooth saccule.


At lower magnification find the developing tooth on the longitudinal section. The oral cavity epithelium lying on the top is visible. The dental lamina is absent. It indicates that the dental germ has already separated from the epithelium. From above in the germ of a tooth there is visible the violet layer of cells (ameloblasts), under which - a thin layer of an enamel of lilac or violet colour. is visible. Beneath the enamel there is seen the wide dentine layer of red colour, and under it lies a layer of the odontoblasts producing the dentine. The enamel and a dentine grow towards each other. In the centre of a tooth from the tooth papilla there develops the loose connective tissue of the dental pulp and blood vessels. At every side of a tooth light strips (the remnants of a pulp of the enamel organ) are visible. Around the tooth a dental saccule is located and development of the osteal alveolus proceeds. On some preparations near this tooth it is possible to see a permanent tooth germ being at initial stage of development or only its dental lamina.

Sketch the specimen and designate.

Fig. 3,4 and in Almazov I.V., Sutulov L.S.’s atlas fig. 431 see.
Fig. 4. A preparation № 3 - formation of a dentine and an enamel at higher

magnification. H & E.


Studying electon microphotographs, drawings and schemes.

Fig. 1-4. Preparations.

Fig.5. Development and eruption of both milk and permanent teeth and formation of their alveoli - a scheme.

Fig. 6. Formation of a tooth bud at an early stage of tooth development at a 8th weeks old embryon – a scheme.

Fig. 7.The beginning of formation of a dental germ - a scheme.

Fig. 8. Formation of an enamel organ - a scheme.

Fig. 9. Formation of the dental hard tissues - a scheme.

Fig.10. Subsequent stages of a dentinogenesis - a scheme.

Fig.11. Enamel and dentine secretion - a scheme.

Fig.12. An amelogenesis - the scheme.

Fig.13. Subsequent stages of formation of a tooth root. An induction of a differentiation of the peripheric cells of a tooth papilla in odontoblasts by the epithelial vaginal cells of the root.

Fig.14. An apical part of the developing dental root.

Fig.15. Subsequent stages (1-4) of development of a periodontium - a scheme.

Fig.16. Changes of tissues at tooth erruption.

Fig. 17. Resorption of the root of a milk tooth - a scheme.
10. Questions for control:

1. Formation of an enamel organ.

2. What is formed at the dental germ stage?

3. What is the tooth papilla, what is it developed it form?

4. A source of origination and structure of ameloblasts.

5. A source of origination and a structure of odontoblasts.

6. Describe the structure of a milk tooth apex in the process of histogenesis.

7. How is a milk tooth root developped?

8. How does a tooth undergo a mineralization?

9. What is the differens in the development of milk and permanent teeth?

10. How is the cement formed?

11. How does a tooth errupt?

Prepare following questions independently:

1. Replacement of milk teeth by permanent ones.

2. Teething theories.

11. The recommended literature

The basic

1. Histology / under the editorship of J.I.Afanasiev, N.A.Jurina. М, Medicine, 1989.

2. Afanasiev J.I., Yurina N.A. Histology, М, 1989, 2004.

3. Зуфаров K.A.histology (uz.), Tashkent, 1991.

4. Zufarov K.A. Gistologiya.(uz) Toshkent. 2005.

5. Zufarov K.A., etc. Gistology practical work (uz). Т, Medicine, 1976.

6. Almazov I.V., Sutulov L.S.’s the Atlas on histology and a embryology. М, 1978.

7. Yeliseyev V. G, etc. The Atlas microscopic and ultramicroscopic structure of cells, tissues and organs. М, Medicine, 1970.

8. A practical work on histology, cytology and embryology. М, 1989.
The additional

1. The Atlas-textbook on histology. The computer program under the editorship of

S.L.Кuznezov, etc. М. 1999.

2. Histology (introduction in a pathology) under the editorship of Ulumbekov E.G.,

Chelyshev J.A. М, 1997.

3. Histology, cytology and an embryology. The atlas (under the editorship of

O.V.Volkova, J.K.Eletskiy).

4. A management on histology. Under the editorship of R.K.Danilov, I.L.Bykov and I.A.Odintsov. Т.1 and 2. S.-Peterburg, 2001.

5. Laboratory researches at the rate of histology, cytologies and embryology. Under Ed. Prof. J.I.Afanasiev. М, 1990.

6. Bikov V.L.Gistology and an embryology of an oral cavity of the human. М, 1998.

7. Ham А.W., Cormack D.H. Gistology in 5 volumes. Transfer with English М, 1982-83.

8. Gartner L.P., Hiatt J.L. Color Atlas of Histology. - Baltimore. 1990.

9. Stevens A., Love J.S. Human Histology, 2nd edit - L.e.a.: Mosby, 1997.

10. Educational resources on histology on the Internet:



www.histol chuvashia. com.; don hist.from ru.com.; medmir.ru; histology narod.ru; www.rezko.ru



Рис.5. Развитие и прорезывание временного и постоянного зубов и формирование их альвеол – схема.




Рис.6. Образование зубной почки на ранней стадии развития зуба у 8-недельногоэмбриона – схема.

ЭВР — эпителий выстилки полости рта; ЩГБ — щечно-губная борозда; ВПЛ — вестибулярная пластинка; ЗПЛ — зубная пластинка; ЗПО — зубная почка; М — мезенхима.



Рис.7. Начало формирования зубного зачатка – схема.

ЭВР — эпителий выстилки полости рта; ЩГБ — щечно-губная борозда; ВПЛ - вестибулярная пластинка; ФЭО — формирующийся эмалевый орган; ЗС - зубной сосочек; ЗМ — зубной мешочек; М — мезенхима.





Рис.8. Образование эмалевого органа – схема.

ЭВР—эпителий выстилки полости рта; ЭПЗ— закладка постоянного зуба; ШЭО — шейка эмалевого органа; НЭК— наружные эмалевые клетки; ВЭК — внутренние эмалевые клетки; ПРС — промежуточный слой (эмалевого органа); ПЭО — пульпа эмалевого органа; ШП — шеечная петля: ЗС — зубной .сосо­чек ; ЗМ — зубной мешочек.



Рис.9. Образование твердых тканей зуба – схема. .

ЭБЛ — энамелобласты; Э — эмаль; ОБЛ— одонтобласты; Д — дентин; НЭК — наружные эмалевые клетки; ПЭО — пульпа эмалевого органа; ПРС — проме­жуточный слой (эмалевого органа); ЖВ — эпителиальное (гертвиговское) кор­невое влагалище; ЭД — эпителиальная диафрагма; ЗМ — зубной мешочек; ЗС — зубной сосочек; КРС — кровеносные сосуды.



Рис.10. Последовательные стадии дентиногенеза – схема.





Рис.11. Секреция эмали и дентина - схема.

ОБЛ — одонтобласты; ПОБЛ— преодонтобласты; ПРД — предентин; Д — ден­тин; ПЭБЛ — преэнамелобласти; ЭБЛ — энамелобласты; Э — эмаль; ПРС — промежуточный слой эмалевого органа; ПЭО — пульпа эмалевого органа; НЭЭ — наружный эмалевый эпителий; КАП - капилляр; ЗМ — зубной ме­шочек.





Рис.12. Амелогенез – схема.
а — образование начальной (беспризменной) эмали; б—начало образования при-зменной эмали одонтобластами, сформировавшими отростки Томса; в — срез, парал­лельный поверхности образующейся эмали на стадии, соответствующей изображен­ной на рисунке б (уровень среза показан на рисунке б горизонтальной линией); г — активное образование призменной эмали энамелобластами. Стрелка — направ­ление смещения энамелобластов. НЭ — начальная (беспризменная) эмаль; ЭБЛ — энамелобласты; ПРС — промежуточный слой эмалевого органа; ПЭ — призменная эмаль; ОТ — отросток Томса; МЭ — межпризменная эмаль; ЭП — эмалевая призма.


Рис.13. ПОСЛЕДОВАТЕЛЬНЫЕ СТАДИИ ОБРАЗОВАНИЯ КОРНЯ ЗУБА. ИНДУКЦИЯ ДИФФЕРЕНЦИРОВКИ ПЕРИФЕРИЧЕСКИХ КЛЕТОК ЗУБНОГО СОСОЧКА В ОДОНТОБЛАСТЫ КЛЕТКАМИ ЭПИТЕЛИАЛЬНОГО КОРНЕВОГО ВЛАГАЛИЩА



Рис.14. Апикальная часть развивающегося корня зуба: разрушение эпителиального корневого влагалища с образованием эпителиальных остатков Малассе, дифференцировка цементобластов, выработка ими начальных слоев цемента, развитие периодонтальной связки и зубной альвеолы из мезенхимы зубного мешочка.
ОБЛ – одонтобласты, Д – дентин, ПРД – предентин, Ц – цемент, ЦБЛ – цементобласты, ЭД – эпителиальная диафрагма, ДОБЛ – дифференцирующиеся одонтобласты, ЭОМ –эпителиальные остатки Малассе, ЗС – зубной сосочек, КРС – кровеносный сосуд,

ЗМ – зубной мешочек, РЗА – развивающаяся зубная альвеола, РПО – развивающийся периодонт, ФБЛ – фибробласт





Рис.15. Последовательные стадии (1-4) развития периодонта – схема.




Рис.16. Изменения тканей при прорезывании зуба





Рис.17. Резорбция корня временного зуба – схема.





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