VISCERA An organ is a part of the human body and it serves as an instrument for adaptation of the organism to the environment. The organ has a definite, inherent only by it, shape, structure, function, development, and, position in the human body. The vital activity of an organ occurs under the direct effect of the nervous system and in correlation with the endocrine glands activity.
Organs consist of different tissues, one or more of which prevail and determine its specific structure and function. Some organs are made up of many structures, which are similar in organization and are themselves formed of several tissues (e.g. the nephron in the kidney or the acinus in the lungs). They were named morpho-functional units of organs.
Some functions cannot be accomplished only by one organ. That is why, a complex of organs form systems. The system of organs is a collection of homogeneous organs which have a common plan of structure, function, development, and they are connected to each other anatomically and topographically.
Some systems, for instance, the bony system is a set of bones with common structure, functions, and development.
There are organs and systems of organs that differ in structure and development but they are united for the performance of a common function. Such functional collection of heterogeneous organs, form an apparatus.
The endocrine apparatus consists of endocrine glands, which differ in their structure and development, but are united by a common function.
The motor apparatus, the sensory organs, and the nervous system form the group of organs of animal life because the function of movement and nervous activity are inherent only in animals and are almost absent in plants.
The organs (viscera or splanchna) are concerned with metabolism. The sex organs are an exception to this, they are concerned with reproduction. All these processes are also inherent in plants and that is why the viscera are also called (organs of vegetative life). The separate grouping of organs of vegetative life, from those of animal life is justified not only because they differ in function, but they also differ in their development.
Though lodged in the body cavities, the visceral systems communicate, nonetheless, with the external environment. The organs of vegetative life in higher vertebrates and human are represented by three tubes communicating with the external environment by means of openings.
The alimentary canal communicates with the external environment by means of two orifices and entrance orifice through which the food is ingested and the exit orifice through which the wastes are discharged. The respiratory system has a single orifice that serves both the inspiration and expiration of air. The exit orifice of the urogenital system is located in the lower part of the body in front of the alimentary canal opening.
General notions concerning norm, variants and abnormalities of viscera
In the process of phylo- and ontogenesis the human body becomes adapted to the environment and a definite equilibrium was established between the human organism and the environmental conditions.
The human body has definite morphological and functional features and due to them the equilibrium was established and was designated as a norm.
The norm is not something fixed and unchangeable, it is diverse and represented by many structural variants which together constitute the organism's variability, caused by both hereditary and environmental factors. In man are encountered a lot of variants of norm.
An anomaly or abnormality is a deviation from the norm, and it is manifested to different degrees. Some anomalies do not disturb the function of organs (situs viscerus inversus, or dextrocardia). Other abnormalities are attended by impaired function of the organ or even of the entire organism, they are called monstrosities or teratisms such as: cleft palate, acardia (absence of the heart), acrania (absence of the skull), the last two are incompatible with life.
Viscera and constitutional types of the human body
The size, shape and position of the organs and vessels depend on constitutional type.
In asthenic type the viscera are smaller and have a lower position as they were ptotic. The lungs are longer, because the thoracic cage is longer. The heart has a vertical position and the aorta is narrow. The stomach has almost a vertical position as well as the loops of the small intestine. The liver, spleen, pancreas and the kidney are small.
In hypersthenic type the heart is relatively large and has almost a horizontal position and the aorta is large. The lungs are short. The stomach has a transverse position as well as the loops of the small intestine. The liver, spleen, pancreas and the kidney are large.
The normosthenictype is an intermediate between the hypersthenic and asthenic type, and the organs have an intermediate position according to the characteristics accounted above.
Structure of the internal organs
By their structure all the internal organs are divided into two groups: tubular organs and parenchymatous organs.
The wall of the tubular organs has a common structure, consisting of few layers:
The mucous coat (tunica mucosa).
The submucous layer (tela submucosa).
The muscular coat (tunica muscularis).
The serous coat (tunica serosa), or the adventitious coat (tunica adventitia).
Fig. 1. Structure of a tubular organ
on a transverse cross–section. 1 – tunica serosa;
2 – tunica muscularis (stratum
3 – tunica muscularis (stratum circulare);
4 – tella submucosa;
5 – tunica mucosa;
6 – plicae circulares;
7– villi intestinales.
1. The mucous coat, tunica mucosa consists of:
lamina epithelialis mucosae, epithelial lining of the mucosa. The epithelium of the mucous coat differs according to the segments of the alimentary tract. The epithelium has a protective role.
lamina propria mucosae forms the connective-tissue foundation of the mucosa. It consists of loose fibrous connective tissue, which contains lymph nodules, glands, lymph and blood capillaries, nerves. The glands of the mucosa are divided into unicellular glands (located between the epithelial cells) and multicellular glands (located in the mucosa and tela submucosa).
At the boundary with the submucous layer is located the lamina muscularis mucosae, represented by a thin layer of smooth muscle fibers. Under contraction of the lamina muscularis the mucous coat forms folds.
2. The submucous layer, tela submucosa consists of connective tissue and within this layer are located glands, lymph and blood vessels, lymph nodules. Due to the presence of the submucous layer the mucous coat forms folds. The folds can be: circular, longitudinal, semilunar, or to be chaotically arranged to form a network.
3. The muscular coat,tunica muscularis usually consists of two layers of muscle fibers. In the initial and ending parts of the alimentary tract the muscle fibers are striated, but in the middle part of the alimentary canal the muscle cells are smooth.
Usually the internal layer of muscle is circular, and the external is longitudinal, but there are some exceptions (e.g. the muscular coat of the stomach consists of three layers of muscle fibers: external-longitudinal, middle-circular and internal oblique layer). Contractions of the muscular fibers are peristaltic in character and spread toward the distal end of the intestine. The circular layer constricts the lumen of the intestine and forms sphincters along the alimentary canal.
4. The serous coat, tunica serosa is the external coat for the most organs of the abdominal cavity and it was named peritoneum. It consists of loose fibrous connective tissue having a protective role for organs that it invests. The serous coat of the lungs was named pleura and the serous coat of the heart is the pericardium. The organs that are not covered outside by serous membrane are invested by adventitious coat, tunicaadventitia.
The parenchymatousorgans consist of parenchyma and stroma. These organs possess a hilum through which the vessels and nerves enter or leave the organ. The parenchymatous organs usually consist of lobes, segments and lobules. They perform specific functions that cannot be assured by other organs (e.g. exchange of gases, discharge of metabolic wastes, production of hormones and enzymes etc.).
Fig. 2. Structure of a parenchymatous
organ. 1 –connective tissue septa;
2 – the capsule;
3 – the epithelial bodies (corpuscles);
4 – the medullar substance;
5 – the cortical substance;
6 – the lobules.
The parenchyma is formed of high specialized elements that assure specific functions of organs.
The stroma consists of connective tissue that sustains the parenchyma, gives off interlobar, interlobular septa and leads the vessels and nerves within the organ. The stroma is like a soft skeleton of an organ.
Each organ has a well determined location in the body and for describing its location a physician uses the term topography. The topography of an organ is described taking into considerations the following terms:
Skeletotopy– position of an organ towards the skeleton.
Sintopy – position of an organ towards neighbouring organs.
Holotopy – position of an organ towards a cavity (thoracic, abdominal etc.).
DIGESTIVE SYSTEM – GENERAL CHARACTERIZATION, COMPONENTS, AND FUNCTIONAL ROLE
The digestive system, systema digestorium is a complex of organs which provides mechanical and chemical treatment of food, absorption of the treated nutrients, and excretion of undigested remnants of the food. The digestive system performs detoxification of noxious substances; as well it synthesizes biologic active substances such as hormones, enzymes, vitamins etc.
Organs of the digestive system are located in the regions of the head, neck, thoracic, abdominal and pelvic cavities. The whole length of the alimentary canal is about 8-10m and it consists of oral cavity, pharynx, esophagus, stomach, small intestine and large intestine.
Fig. 3. Organs of the digestive system. 1 – palatum durum;
2 – glandula parotidea;
3 – palatum molle;
4 – cavitas pharyngis;
5 – lingua;
6 – oesophagus;
7 – gaster;
8 – pancreas;
9 – ductus pancreaticus;
10 – flexura duodenojejunalis;
11 – flexura coli sinistra;
12 – jejunum;
13 – colon descendens;
14 – colon transversum;
15 – colon sigmoideum;
16 – m. sphincter ani externus;
17 – rectum;
18 – ileum;
19 – appendix vermiformis;
20 – caecum;
21 – valva ileocaecalis;
22 – colon ascendens;
23 – flexura coli dextra,
24 – duodenum;
25 – vesica fellea;
26 – hepar;
27 – ductus choledochus;
28 – m. sphincter pylori;
29 – glandula submandibularis;
30 – glandula sublingualis;
31 – labium inferius;
32 – cavitas oris;
33 – labium superius;
34 – dentes.
Functionally related to the alimentary canal are annexed glands such as salivary glands that are annexed to the oral cavity; the liver and the pancreas are annexed to the small intestine (duodenum).
The digestive system is divided into three parts:
ingestion part that includes the oral cavity with organs located in it, the pharynx and esophagus;
digestive part that comprises the stomach and the small intestine,
ejective part that consists of large intestine.
The most complicated anatomical structures are distinguished at the boundary between these parts, and they constitute the morphological substrate of the antireflux device, due to which is regulated the movement of the content of the alimentary canal into a single craniocaudal direction, maintaining the specific chemical composition and flora characteristic to each segment of the alimentary canal.
THE ORAL CAVITY
In the oral cavity the ingested food is changed by the mechanical action of teeth and by the chemical activity of saliva into an alimentary bolus that in the process of deglutition is swallowed into the pharynx.
The oral cavity, cavitas oris is located in the inferior part of the face and it constitutes the initial part of the alimentary canal. It is formed of bony and soft structures. The oral cavity is involved in digestion, respiration, phonation, mimicry and articulated speech. It connects with external environment by means of the oral orifice, rima oris and with the pharynx it communicates by means of the fauces, isthmus faucium. Oral cavity is divided into the vestibule of the mouth and cavity of the mouth proper, cavitas oris propria.
In the vestibule of the mouth opposite to the second upper molar on the mucous of the cheeks is located the papilla of the parotid duct, here opens the duct of the parotid gland, Stenon's duct. As well in the vestibule of the mouth open the small ducts of the buccal, labial and vestibular glands. The vestibule of the oral cavity extends posteriorly until the pterygomandibular fold that appears when the mouth is largely opened. The vestibule of the mouth connects with the oral cavity proper by means of interdental spaces and retromolar space, located behind the last molar. This space is used to feed the patient in spastic contraction of muscles of mastication, by introducing a probe through this space.
The oral cavity proper extends from the teeth anterolaterally to the entry into the pharynx posteriorly.
It is bounded:
Above - by the palate (hard and soft palate).
Below – by the diaphragm of the mouth and the tongue.
On the both lateral sides – by the teeth and gums.
Behind – by the fauces, isthmus faucium.
When the mouth is closed the tongue comes in contact with the palate and the oral cavity appears as a slit-like space between them.
The lips and the cheeks
The lips, labia oris are two muscular folds, highly mobile, whose principal function is associated with speech. They are formed by the orbicularis oris muscle and associated connective tissue, and are covered with soft, pliable skin. Between the outer skin and the mucous membrane of the oral cavity is a transition zone called the vermilion, which is reddish-brown in color because of blood vessels close to the surface. When the mucosa continues from the lips towards the gums two mucous folds form:
Frenulum labii superior
Frenulum labii inferior
In the submucous coat of the lips labial glands are located and their ducts open into the vestibule of the mouth.
Between lips there is a horizontal fissure called rima oris. At the angles of the oral fissure the lips fuse by means of comissures, commissura labiorum. On the midline of the external surface of the upper lip there is a longitudinal depression called strainer, filtrum.
The cheeks, buccae are formed by buccinator muscle, and they assist in manipulating food in the oral cavity. Outside the cheeks are covered by skin and inside by mucosa, lined with stratified squamous epithelium. Between buccinator muscle and the skin there is a fat tissue called corpusadiposum buccae (it is well developed in infants and helps to decrease the pressure on the part of the atmosphere during sucking).
The tongue, lingua is a muscular organ located in the oral cavity. The tongue is the organ of taste. As an organ of the digestive system it participates in mastication and deglutition. It has an important role in phonation and articulated speech.
Three parts are distinguished in the tongue:
The body, corpus linguae
The tip, apex
The root, radix linguae (it attaches the tongue to the mandible and to the hyoid bone).
Fig. 5. Dorsal surface of the tongue. 1 – rima glottidis;
Topographically the tongue can be divided into two parts:
Oral part (placed in the oral cavity proper);
Pharyngeal part (faces the pharynx).
The tongue is covered by mucous membrane. Its dorsal surface is called the back, dorsum linguae. The body of the tongue is separated from the root by terminal sulcus, in the middle of which the foramen caecum is placed. In front of the terminal sulcus are placed vallate (walled) papillae, papillae vallatae.
Two borders right and left are distinguished in the tongue. On the midline of the tongue passes the median sulcus of the tongue, to which within the tongue corresponds the septum of the tongue, septumlinguae.
Three folds of the mucous membrane are distinguished on the root of the tongue the medianglosso-epiglotic and two lateralglosso-epiglotic or (pharyngoepiglotic) folds, and two depressions, valleculae epigloticae are bounded by these folds.
On the root of the tongue is located the lingual tonsil. It consists of an aggregation of lymphoid structures (lymph nodes, or follicles). These lymphoid structures penetrate the mucous membrane and reach the superficial layer of the laminapropria mucosae. In the middle part of the each follicle there is a crypt, which opens into the environment by a pin-full orifice. In the crypt open the ducts of the posterior lingual glands. The ensemble of lingual follicles constitutes the lingual tonsil.
NB: The lingual, the pharyngeal, two tube and two palatine tonsils form the Waldeyer-Pirogov's lymphoepithelial ring.
On the dorsal surface of the tongue are numerous small elevations called papillae and they give the tongue a roughened surface that aids the handling of food.
Papillae of the tongue:
The tongue papillae posses taste buds that can distinguish sweet, salty, sour and bitter sensations, excepting the filiform and conical papillae, which do not possess taste buds, performing just a mechanical function during mastication.
The inferior surface of the tongue is free just in its anterior part. The posterior part is occupied by the muscles. On the midline of the inferior surface of the tongue from the tip to the body stretches a mucous fold, named frenulum linguae. On the both sides of the frenulum can be seen the sublingual caruncula, and laterally from it stretches the sublingual fold, plica sublingualis, on which open the small ducts of the sublingual salivary gland. As well the right and left plica fimbriatae can be distinguished when the tongue is arisen.
The internal structure of the tongue consists of a muscular bulk, which is divided into two symmetric halves by a longitudinal fibrous septum. The muscles of the tongue are divided into two groups:
Extrinsic, or skeletal muscles of the tongue
Intrinsic, or proper muscles of the tongue
The intrinsic muscles of the tongue are muscles which do not have insertion on bones and are embedded within the tongue.
Superior longitudinal muscle arises from the depth of the root of the tongue, the lesser horns of the hyoid bone and from the epiglottis, and ends on the tip of the tongue. During contraction it arises the tip of the tongue and shortens the tongue.
Inferior longitudinal muscle begins on the root of the tongue and ends on the tip. It turns down the tip of the tongue and shortens the tongue.
Transverse muscle begins from the septum of the tongue and ends on its margins. This muscle arises the dorsum of the tongue and narrows the tongue.
Vertical muscle is located between the mucosa of the tongue and its inferior surface. It flattens the tongue.
According to their structure and action the muscles of the tongue are divided into three groups:
Muscles arising on the derivatives of the first visceral arch (on the mandible): the genioglossus muscle and the vertical muscle of the tongue.
Muscles arising on the derivatives of the second visceral arch (on the styloid process and lesser horns of the hyoid bone): the styloglossus muscle, the superior and inferior longitudinal muscles.
Muscles arising on the derivatives of the third visceral arch (or first branchial arch). This group of muscles originates on the body and greater horns of the hyoid bone): hyoglossus and the transverse muscle of the tongue and the palatoglossus muscle.
The extrinsic (skeletal) muscles of the tongue have their origin on the bones of the facial skeleton and they insert on the tongue. These muscles are called extrinsic muscles of the tongue:
Genioglossus muscle has its origin on the spine of the mandible and inserts in the thickness of the tongue. This muscle pulls the tongue anterior and down.
Hyoglossus muscle has its origin on the hyoid bone and insertion on the lateral parts of the tongue. This muscle arises the tongue posteriorly and upright.
Styloglossus muscle has its origin on the styloid bone and inserts in the thickness of the tongue.
Development of the face and oral cavity
On the 4 week of embryonic development the primary gut, which derives from endoderm is closed on both its ends. The cranial end is closed by pharyngeal membrane and the caudal one by the anorectal membrane.
At the end of the first month of embryonic life a pouch (Rathke's pouch) forms as a protrusion towards the brain. It invaginates and reaches the pharyngeal membrane that consists of two layers, being located between the oral pit and the primary gut.
Layers of the pharyngeal membrane
The outer layer is of ectodermal origin
The inner layer is of entodermal origin
On the 4-5 week the pharyngeal membrane ruptures and the cavity of the primary oral pit communicates with the cavity of the primary gut.
Development of the face
The face is formed by three swellings, which are derivatives of the pharyngeal arch (I arch).
The frontonasal process (unpaired);
Maxillary process (paired);
Mandibular process (paired).
The mandibular processes fuse on the midline to form the mandible and corresponding to it parts of the face.
From the maxillary process develops the maxilla with the palate and the corresponding soft tissues of the face and the lateral segments of the upper lip.
On the midline between the two maxillary processes, which do not fuse, is interposed the frontonasal process and it joins the maxillary processes to form the upper wall of the oral cavity.
From the frontonasal process develop the nasal septum, the incisive part of the hard palate and the middle part of the upper lip (the strainer).
Between the internal surfaces of the maxillary processes forms a palatine plate, which grows toward the median plane. At first the right and left palatine plates do not fuse and a cleft forms between them, but later they fuse to each other to form the palate.
The maxillary and mandibular processes on each side fuse to form the angles of the mouth. If they fail to unite it results in macrostomia (very large oral orifice, rima oris). If they fuse very close, then it results in microstomia (very small oral orifice).
Failure of fusion of the frontonasal process with the maxillary processes results in hare-lip, labium leporinum.
Cleft palate results as a failure of fusion of the palatine plates. Cleft lip and cleft palate are distinct malformations which often occur together.
Age specific features of the oral cavity organs
In new-born the oral cavity is of small size. The vestibule of the mouth is bounded by the gingival margin (there are no teeth). The lips are thick, their mucous membrane is covered by papillae and on the internal surface of the lips there are transverse folds. The intermediate part of the lips is narrow, but the orbicular muscle is well developed.
The hard palate is flat and it is situated at the level of the pharyngeal fornix. The soft palate is short and has a horizontal position. The velum palatinum does not touch the posterior wall of the pharynx and due to this fact the child can freely breathe during sucking. The mucous membrane of the hard palate is pour in glands and its transverse ridges are weakly seen.
The tongue in new-born is wide, short, thick and hardly mobile. It fills the entire oral cavity. The papillae of the tongue and the lingual tonsil are not well developed.
During eruption of the teeth the alveolar processes grow in size.
The palatine tonsils in new-born are small but well seen, because the palatine arches are slightly developed. The maximal development of the palatine tonsil is accounted at the age of 16.
Development of the tongue and its abnormalities
The oral part of the tongue appears in embryo at approximately 4 weeks in form of two lateral and one median lingual swellings (buds). They originate from the first pharyngeal arch. The lateral tongue buds overgrow the median tongue bud and fuse on the midline, to form the median sulcus, to which within the tongue corresponds the septum of the tongue.
The pharyngeal part of the tongue forms from a second median swelling, the hypobranchial eminence, that derives from the mesoderm of the second, third and fourth arches.
At the boundary between the oral and pharyngeal parts of the tongue forms a ventral invagination of epithelium, called thyroglossal duct, from which the thyroid gland develops. On the dorsal surface of the tongue, as a remnant of the thyroglossal duct remains the foramen caecum linguae.
Ankyloglossia (tongue-tie) occurs when the frenulum of the tongue extends to the tip of the tongue, and the tongue is not freed from the floor of the mouth.
Bifurcated tongue occurs when there is a failure of fusion of the tongue buds.
Persistence of the thyroglossal duct when instead of the foramen caecum linguae the tongue is united with the thyroid gland by the hypoglossal duct.
Examination on alive person of the oral cavity
The most common methods of examination of the oral cavity are:
Inspection (oroscopy and bucopharyngoscopy)
For a most detailed examination are used special instruments such as frontal mirror, a lamp, a spatula, wide medical hooks for the dilatation of the oral cavity, stomatological mirror and laryngoscopical mirror.
Under inspection of the oral cavity can be mentioned: the shape, position and colour of the organs which are placed in the oral cavity.
The teeth are located on the alveolar processes of the maxilla and of the mandible.
In adult man there are 32 permanent teeth. The teeth carry out the following functions:
Perform mechanical treatment of food during mastication.
Have a phonetic role for the articulation of speech.
Determine the physiognomy (the form of the face).
Every tooth consists of:
A crown, corona dentis
A neck,colum dentis
A root,radix dentis
The crown is elevated above the gum, the neck is the narrowed part of the tooth and the root slits in the dental alveolus. The root ends by an apex, apex radicis dentis, on which is seen a small orifice, the apical foramen. Vessels and nerves enter the tooth through this foramen.
Inside the tooth crown there is a cavity, cavum dentis, but inside the root a canal forms, canalis radicis dentis. The canal opens at the apex by means of foramen apicis dentis. The cavity of the tooth is filled with the tooth pulp, pulpa dentis, which is rich in vessels and nerves. The tooth roots fuse tightly with the surface of the alveoli by means of alveolar periosteum(periodontium) and the joining of the tooth is called gomphosis.
NB: The tooth, the gums, the alveolar wall and the periodontium form the dental organ.
The hard material of the tooth consists of:
Dentine, dentinum encloses the tooth cavity.
Enamel,enamelum covers outside the crown.
Cement cementum covers outside theroot.
Fig. 6. Structure of the tooth (scheme).
I – corona dentis;
II – cervix dentis;
III – radix dentis;
IV – foramen apicis dentis.
1 – enamelum;
2 – dentinum;
3 – cavitas dentis;
4 – gingiva;
5 – periodontium;
6 –gingival fibers;
7 – desmodontium;
8 – canalis radicis dentis;
9 – os alveolare;
10 – pulpa dentis.
The crowns of the teeth are placed above the gums and form two dental rows:
The upper, or maxillary row
The lower, or mandibular row
Each row accounts 16 teeth, which are arranged in the form of an arch. On every tooth five surfaces are distinguished:
Facies vestibularis faces the vestibule of the mouth and for the anterior teeth it is called facies labialis, while for the posterior is called facies buccalis.
Facies lingualis faces the oral cavity proper.
Facies contactus (there are two in number) and they are the surfaces that come in contact (they are called facies mesialis and facies distalis).
Facies occlusalis or masticating surface is the surfaces for the dental occlusion with the opposite row of teeth.
Fig. 7. External shape of the teeth
1 – facies vestibularis;
2 – facies lingualis;
3 – corona dentis;
4 – cervix dentis;
5 – apex radicis dentis;
6 – radix dentis;
7 – cuspis dentalis;
8 – apex cuspidis;
9 – facies contactus;
10 – cristae triangulares;
11 – crista transversalis;
12 – crista marginalis;
13 – tuberculum dentis;
14 – cingulum.
The teeth are classified according to the terms of eruption, location, shape, number of cusps and number of roots.
According to the terms of eruption:
Deciduous teeth, dentes decidui
Permanent teeth, dentes permanentes. The third molar is termed dens serotinus.
According to the shape the teeth are divided into:
According to the number of roots:
According two the number of cusps (tubercles) on the occlusal surface:
The permanent teeth replace the deciduous teeth. The teeth of an adult are divided into incisors, canines, premolars and molars.
Incisors, dentes incisivi are eight in number, four on each jaw. They have a crown, shaped like a cutting chisel. The crown of the upper incisors is twice wider then that of the lower incisors. Each tooth has a single root, which on lower incisors is flattened from the sides. The apex of the root deviates laterally. The incisors cut the food to the needed size.
Canines, dentes canines are four in number, two on each jaw. Their crown has two cutting edges, which meet at an angle. A tubercle is seen on the lingual surface of the crown. The canines have a single long root, flattened and grooved on its sides. The canines tear the food.
Premolars, dentes premolares are eight in number, four on each jaw. The first premolar is located mesially (medially) and the second distally. The crown is oval shaped. A specific feature of the premolars is the presence on the masticating surface of the crown of two occlusal cusps and due to this fact premolars are called as well bicuspid teeth. One cusp is vestibular and another is lingual. The root of the premolars is a single one and is flattened anteroposteriorly. The upper first premolar usually has a bifurcated root. The premolars crush the food.
Molars, dentes molares are twelve in number, six on each jaw. The molars are smaller in order from front to back (the first molar is the largest one). The crown of molars is cuboid by shape and the masticating surface is more or less square and has from three to five cusps. The first lower molar usually has five cusps ant the fifth cusp was named Carabelli's tubercle. The upper molars have three roots one lingual and two buccal, while the lower molars have an anterior and a posterior root. The molars grind the food.
Fig. 8. The permanent teeth and their
roots (lateral view). 1 – dens caninus superior;
2 – dens incisivus superior lateralis;
3 – dens incisivus superior medialis;
4 – facies vestibularis;
5 – dens incisivus inferior medialis;
6 – dens incisivus inferior lateralis;
7 – dens caninus inferior;
8 – dentes premolares;
9 – foramen mentale;
10 – dentes molares;
11 – canalis mandibulae;
12 – facies vestibularis;
13 – dentes molares;
14 – sinus maxilaris;
15 – dentes premolares.
Variants of dental occlusion
The dental occlusion (bite) can be physiological and pathological. According to the relations of the upper anterior teeth to the lower anterior teeth there are two variants of physiological occlusion:
Scissor-like bite – psalidodontia when the cutting edges of the upper anterior teeth overlap the cutting edges of the lower anterior teeth. It is the most common type of dental occlusion, encountered in 79.6% of individuals.
Tong-like bite – labidodontia when the cutting edges of the upper anterior teeth meet the cutting edges of the lower anterior teeth. It is less frequently encountered then the first type (characteristic for children in attrition of the teeth and in the elderly).
As variants of normal dental occlusion are considered the progenia, when the upper teeth are located in front of the lower, and another variant is the orthognathia, when the upper and lower teeth come in contact with their cutting edges.
Pathological types of dental occlusion
Stegodontia, roof-like when the upper incisors protrude forward and cover the lower incisors like a slope of a roof.
Hiatodontia, gap-like, when a gap remains between the upper and lower anterior teeth.
Opistodontia, when the upper anterior teeth are behind the lower anterior teeth.
Dental formula for the permanent teeth expresses the number of teeth, their arrangement and location on the upper and lower jaw.
The dental formula for the permanent teeth:
This dental formula expresses arrangement of teeth on both halves of the maxilla and mandible – 2 (incisors), 1 (canine), 2 (premolars), 3 (molars).
This dental formula expresses the order of teeth beginning with the first incisor (1), second incisor (2), canine (3), first premolar (4), second premolar (5), first molar (6), second molar (7), third molar (8).
Order and time of eruption of the permanent teeth
First molar – 6-7 years
Medial incisors – 8 years
Lateral incisors – 9 years
First premolar – 10 years
Canines – 11-13 years
Second premolars – 11-15 years
Second molars – 13-16 years
Third molars – 18- 30 years
Structural peculiarities of the deciduous teeth
The deciduous teeth are twenty in number: 8 incisors, 4 canines, 0 premolars, 8 molars. The deciduous teeth have the same shape and arrangement as the permanent teeth. The enamel of the deciduous teeth is of white-blue colour, but that of the permanent teeth is of white-yellowish colour. The roots of the deciduous teeth are shorter and the space between the roots of the molars is larger, then in permanent teeth, because between the roots of the deciduous teeth are arranged the germs of permanent teeth.
Order and time of eruption of the deciduous teeth
Medial incisors – 6-8 months
Lateral incisors – 7-9 months
First molars – 12-15 months
Canines – 16-20 months
Second molar – 20-24 months
Fig. 9. The deciduous teeth. 1 – the temporary dentition.
Development of teeth in man begins on the seventh week of embryogenesis. The teeth develop from ectoderm and mesenchyma.
Dental lamina develops from the oral epithelium (ectoderm) as a downgrowth into the underlying mesenchyma. It gives rise to the tooth buds, which develop into enamel organs.
Enamel organs are derived from ectoderm. These organs develop first for the 20 deciduous teeth, then for 32 permanent teeth. They give rise to ameloblasts, which produce enamel.
The mesenchymal tissue of the dental papilla gives rise to the odontoblasts (which produce predentin and dentin) and as well the dental pulp derives from the mesenchyma.
The dental sac is formed by a condensation of mesenchyma that surrounds the dental papilla. This sac gives rise to the cementoblasts (which produce cementum) and to the periodontal ligaments.
Abnormalities of position
The adjacent teeth may exchange their position; a tooth may be set on the hard palate, outside the dental arch, in the vestibule of the mouth, in the maxillary sinus, or even in the nasal cavity.
Abnormalities of number
The absence of the upper lateral incisors or second premolars occurs more frequently then other number dental abnormalities.
Abnormalities of shape of the crown and root
The roots can be elongated, shorten or curved at different angles. The molars can have more roots than usual number. The cusps can vary in number (to be more or less then usually).
Defective enamel formation (amelogenesis imperfecta) is an autosomal dominant trait.
Defective dentine formation (dentinogenesis imperfecta) is an autosomal dominant trait.
Discoloration of teeth is caused by the administration of tetracycline, which strains and affects the enamel of both deciduous and permanent teeth.
X-ray anatomy of the teeth
X-ray examination of the teeth is made intraorally or on extraoral panoramic radiographs. The radiographs clearly demonstrate all the anatomical details of the tooth with area of low density at the site of dental cavity. A narrow band of low density which corresponds to the pericementum is noticeable on the periphery of that part of the tooth, which is embedded in the dental alveolus.
THE salivary glands
The salivary glands are classified according to their structure, topography, size and secret.
According to their structure the salivary glands are divided into:
According to their topography:
According to their volume (size):
Small glands: labial, molar, palatine, buccal and lingual glands.
Large glands: parotid gland, submandibular and sublingual glands.
According to the produced secret the salivary glands are divided into:
Three pairs of large salivary glands are distinguished:
The ducts of the salivary glands open into the oral cavity proper, or into the vestibule of the mouth.
THE parotid gland
The parotid salivary gland,glandula parotidea is the largest salivary gland and it is located on the lateral side of the face, in front and below the auricle of the ear and in the retromandibular fossa. In front of the parotid gland lies the masseter muscle.
The gland has a lobular structure and it is covered by the parotid fascia. It is a compound acinous (alveolar) gland. Its duct, ductus parotideus, Stenon's duct has 5-6 cm in length and arises on the anterior border of the gland. The duct passes under the surface of the masseter muscle and piercing the buccinator muscle opens into the vestibule of the mouth opposite to the second upper molar, at the level of the papilla parotidea, which is located on the internal surface of the check. The parotid gland produces a serous secret.
The submandibular salivary gland is a compound alveolar-tubular (acino-tubular) gland by structure. It is located in the submandibular fossa of the submandibular triangle. It is covered outside by a thin capsule. The submandibular gland has an irregular structure. It weighs about 4g and it has in length about 4cm. It comes in contact with the mandible, with the digastric, mylohyoid and hyoglossus muscles, and it is pierced by the branches of the facial nerve.
By secretion it is a mixed (seromucous) gland. Its duct, Wharton's duct, opens into the oral cavity proper at the level of the caruncula sublingualis.
THE sublingual gland
The sublingual salivary gland is located over the mylohyoid muscle on the floor of the oral cavity. It is covered by the mucous membrane of the oral cavity and a sublingual fold is formed between the tongue and inner surface of the mandible.
By structure it is an alveolar-tubular gland, and by secretion it is a mixed gland, with prevalence of mucous secretion.
From the sublingual gland arise about 18-20 small ducts, Rivinus' ducts, which open along the sublingual fold, plica sublingualis.
The main duct of the sublingual gland, Bartholin'sduct opens on the caruncula sublingualis separately, or together with the duct of the submandibular gland.
THE small salivary glands
In the mucous membrane of the vestibule of the mouth and oral cavity proper are located a lot of small glands which produce saliva. These glands are named according to their location.
Labial glands – are located in the mucous membrane of the lips.
Buccal and molar glands – are located in the mucous membrane of the cheeks.
Palatine glands – are located in the mucous membrane of the hard and soft palate.
Lingual glands – in the mucous membrane of the tongue.
According to the character of the secretion these glands can be serous, mucous and mixed.