The jaw of each person has its own structure, which is individual. The beauty of the profile of its owner depends on how "correctly built" it is. In addition to the aesthetic function, they perform many others, for example, they provide a person with the opportunity to chew food, swallow, without them the crown of nature's creation would not be able not only to talk, but also to breathe.
Researchers have noticed that the jaws of each person have their own structure and are arranged in such a way that they are very similar to the jaws of mammals, that is, they are not intended to chew raw meat. In more detail, you can examine and study the structure of the human jaw from the photo in the dentist's office. In dentistry, its anatomy is divided into paired and unpaired.
Upper jaw (right)
As you know, only the upper jaws of a person are paired, and the lower ones are unpaired. The anatomy and structure of the lower and upper jaw of a person are different, from the photo it can be seen, placed in dental clinics. The upper part is quite multifunctional, each of its sections, even the smallest, has its own task. The jaw is located in the center and is connected to all bones, with its participation the walls of the human eye sockets, the nasal cavity and the mouth are also formed.
It weighs very little, despite its impressive volume, the whole point is that it has a cavity.
Also, the human jaw has a body and four processes, which are called palatine, alveolar, zygomatic, frontal. Each of them has its own direction, for example, the frontal is looking up, the alveolar is facing down, the palatine is medially, and the zygomatic is laterally. The process, called the frontal, also connects to the bone of the same name. The upper jaw has three surfaces, in addition to the front, namely the nasal, orbital, infratemporal.
Anatomy of the upper jaw
The upper jaw connects to the bones of the skull in a motionless manner. The anatomy of the lower jaw is unlike the upper one in that it is very mobile. An interesting fact noted among scientists is the force with which the jaws of humans and animals such as dogs, sharks or wolves clench, researchers argue that human performance is much lower than those of the listed predators.
Its surface has a concave shape, at the bottom there is a process called alveolar. On them are the cells intended for the roots of the teeth, which are separated by partitions.
Alveolar ridge
Interestingly, one of the highest places is assigned to the canines. Its center is a depression located at the opening called the infraorbital. Next, the muscle that is responsible for lifting the corner belonging to the mouth originates. The size of this depression can be from two to six millimeters.
The part of the jaw, called the frontal one, makes the transition to the outer one. Its boundary can be called the nasal notch. The surface of the human jaw, called the infratemporal, has a tubercle. It is separated by a process called the zygomatic. It has, most often, a convex shape, it has four holes for the alveoli, which keep the way to the large molars. Through these holes there is access to the nerves, and inside there is a sinus, which has a mucous membrane and an exit into the nasal cavity.
The palatine canal is provided with a wall that looks like a groove. That surface of the jaw, called the nasal surface, flows into the upper one. The processes belonging to her are connected to the cheekbone bone, thereby forming a rather powerful support that allows you to withstand the chewing process.
An interesting fact noticed by scientists is that the upper jaw of a person can be of such forms as: narrow and high or low and wide. According to the first form, we can say that the person's face is slightly narrowed and somewhat oblong, and according to the second, that the human face is somewhat wide.
Infraorbital foramen
The lacrimal notch and bone represent the medial edge, near which the infraorbital groove is located, which passes into the canal of the same name. The hillock located there is represented by openings and pits that open the way to blood vessels and nerves.
One of its constituent elements are also plates that reduce access to paths called airways. Further, there is an air cavity.
Anthropological researchers studying the structure of the human skull and other remains can easily determine the age, belonging to a particular race and the intellectual level of its owner by the anatomy of the jaw apparatus.
Anatomy and structure of the lower human jaw
The structure of the lower jaw differs from the upper one in that the larger arch is basal. The jaw itself has a body and two processes. Her body has two parts. A distinctive feature of the lower jaw is that it is very mobile, has a large number of roughness, tuberosities, and muscles responsible for the chewing process are attached to it.
The chin protrusion is located on its surface from the outside. He is the owner of a tubercle called the chin and the hole in which the roots of the teeth are located, and behind him there is a line ending with a branch. It contains hillocks, called alveolar, there should be sixteen of them in total and they are separated by partitions.
structure of the lower human jaw
The lower jaw has a chin spine located on the surface of its body. It can be single or bifurcated. One of its edges is provided with a fossa, which is called digastric, and it connects to the muscle of the same name. Slightly above them are the submandibular hyoid fossa.
In the canal of the lower jaw, there are blood vessels and nerves; it passes through an opening called the chin. One of its sides is equipped with a tuberosity, called the chewing, and the other is pterygoid, which serves to fix the muscle of the same name. A furrow passes along it, which is called the sublingual, sometimes transforming into a canal. Holes for nerves are also located here. In addition, there is a compact bone, which is responsible for the function of movement, which can be performed in different planes, cartilage and a joint with ligaments are also located here, which allow it to be advanced and directed in different directions.
More detailed advice on the structure and anatomical features of the human jaw, including your own, can be obtained at the reception of a competent highly qualified dentist by contacting a dental clinic.
In fact, the structure and anatomical features of the jaw of each person are very individual, even for an experienced specialist it is very difficult to identify any problem and violations in this area, but it is possible with the help of modern equipment and the latest technological developments that almost all dental clinics have today. ...
The jaws are the basis of the facial skeleton. Not only the beauty of the profile depends on their anatomical structure, but also the functional capabilities important for life. They provide chewing, swallowing, breathing, speaking, forming sensory cavities, and more. According to human anatomy, the upper jaw is paired and the lower jaw is unpaired.
The structure of the upper jaw
The structure of the human upper jaw implies the presence of four processes:
- palatine;
- alveolar;
- zygomatic;
- frontal.
Human jaws.
There are four surfaces on the body of the upper jaw:
- front;
- infratemporal;
- nasal;
- orbital.
Unlike the lower, in the anatomy of the upper jaw, the joints with the rest of the bones of the skull are motionless. The anterior surface is concave, and below it passes into the alveolar process. On the alveolar processes, the upper jaw has cells with partitions, where the roots of the teeth are located. The most significant elevation is provided for the canine.
In the center of this part of the jaw is the so-called "canine fossa" - a depression next to the infraorbital opening through which the infraorbital nerve and artery pass. The anterior part smoothly passes into the outer, its medial border is the nasal notch.
The upper jaw has a tubercle, which is located on the infratemporal surface. It is separated from the anterior zygomatic process. This part is often convex. It contains small alveolar openings that lead to the alveolar canals.
In the body of the upper jaw is the airway - the maxillary sinus, which opens into the nasal cavity. It is covered with a mucous membrane. Its bottom is located near the tops of the roots of such teeth: the first and second molars, as well as the second premolar. On the nasal surface is the ridge of the inferior turbinate.
Chewing muscles.
The frontal process is connected to the frontal bone, and the place of attachment of the nasal concha is indicated by a ridge on the medial surface. The palatine groove passes along the nasal surface, which is the wall of the palatine canal.
The nasal surface passes into the upper one with the right and left palatine processes. They, in turn, join in the anterior part of the hard palate, forming the bottom of the nasal cavity and the skeleton of the palate. The nasal surface also has an opening for communication between the nasal cavity and the maxillary sinus.
The zygomatic process connects to the zygomatic bone, forming a thick support with it, which is loaded when chewing.
The upper jaw also includes the orbital, or upper, surface. It is the lower wall of the orbital orbit. Outside, it smoothly passes into the zygomatic process. The infraorbital edge is connected to the frontal process, along which the lacrimal ridge stretches.
The orbital orbit.
The lacrimal notch is located at the medial edge. It includes the lacrimal bone. Near the posterior edge of the orbital surface of the upper jaw, the infraorbital groove originates. The posterior and lower edges form the orbital fissure, in which the infraorbital groove is located. In the forward direction, it gradually passes into the infraorbital canal. Describing an arc, it opens at the front.
The outer-lateral surface is turned towards the wing-palatine and infratemporal fossa. In the posterior lower region there is a tubercle of the upper jaw. This part is dotted with small holes through which nerves and blood vessels pass to the teeth.
The upper jaw is formed from light, thin plates that limit the airways. Inside the body is the largest among the adventitious - the air cavity. Together with this airiness, human anatomy is designed for high loads. Therefore, buttresses are formed on thin plates - denser areas that provide bone strength.
Mandibular anatomy
The structure of the lower jaw involves a body and two processes (branches). Unlike the upper one, the largest arch in it is basal, and the smallest is the dental arch. The body consists of two halves: the base and the alveolar part. In the first year of life, they are combined into one bone. The height of each half is greater than the thickness.
Chewing muscles are attached to its surface, so there are many bumpy areas and roughness on it. It is the only part of the facial skull that has the ability to move.
On the outer surface, the lower jaw has a chin protrusion. Outside of it, the chin tubercle protrudes, on top and outside of which there is the chin foramen. It corresponds to the placement of the roots of the second small teeth. Behind this hole, an oblique line is directed upward, which becomes the front edge of the branch. There are alveolar eminences on it.
On the alveolar arch, the anatomy provides sixteen alveoli for the teeth. They are separated from each other by interalveolar septa.
Alveoli for teeth.
On the inner surface of the body, the lower jaw has a chin spine. It can be either single or bifurcated. At the lower edge is the digastric fossa, where the digastric muscle is attached. The maxillary-hyoid lines run on the later areas. Above it, the sublingual fossa is attached, and a little lower - the submandibular fossa.
The lower jaw is also "equipped" with a hole and a kind of restriction - a tongue. Deep into the hole in the thickness of the spongy substance there is a channel with vessels and nerves. On the surface, it exits through the chin hole. From it passes the maxillary-hyoid groove, and a little higher - the mandibular ridge.
On the outside there is a chewing tuberosity, which takes a position in the corner. On the inside of the chewing tuberosity, there is a pterygoid tuberosity. The medial pterygoid muscle is attached to it. The hyoid groove runs down and forward along the pterygoid tuberosity.
Sometimes it turns into a canal, hiding behind a bone plate. The chin protrusion is located on the external tuberosity in the symphis area. This part grows together with the chin bones, which are involved in the formation of this protrusion. On the side of it is the chin foramen through which the chin nerves and vessels exit.
At the upper end of the branch there are two processes: the coronary and posterior. The temporal muscle is attached to the coronary muscle, and the posterior muscle ends with a head, which has an articular surface in the form of an ellipse. She is involved in the formation of the temporomandibular joint.
The lower jaw consists of a copact bone. It belongs to the unpaired type and has the ability to move both vertically and horizontally due to the anatomy of this joint.
Temporomandibular joint structure
The lower jaw, with its head and articular tubercle, as well as the scaly part, forms the temporomandibular joint. The axes of the cushion-shaped heads converge in front of the occipital foramen. The fossa consists of two parts: intracapsular and extracapsular. The first is in front of the stony-scaly crack, and the second is behind it.
The first, as its name suggests, is enclosed in a capsule. It extends to the tubercle of the joint and reaches its anterior edge. The surface of the temporal joint is covered with connective cartilage, and in its cavity there is an articular disc - a fibrous cartilaginous plate.
The anatomy of the temporomandibular joint has the following ligaments:
- lateral;
- medial.
The lateral ligament begins at the base of the zygomatic process. Then it goes to the posterior and outer surface of the neck of the lower jaw. Part of the bundles is located in the capsule of the temporomandibular joint. The medial ligament begins near the inner edge of the articular surface and runs along the ventral surface.
There are also ligaments that are not associated with the capsule, but belong to the temporomandibular joint: awl and wedge-mandibular ligament.
The upper surface of the disc of the temporomandibular joint is adjacent to the articular tubercle, and the lower - to the head of the lower jaw. It divides the joint into two sections, each cavity of which is lined with an upper and lower synovial membrane. The tendon bundles of the lateral pterygoid muscle are attached to the inner edge of the disc.
The temporomandibular joint is a block joint. Thanks to its movements, it is possible to raise and lower, advance and shift to the sides of the lower jaw of a person.
Mandibula, unpaired, forms the lower facial section. In the bone, a body and two processes are distinguished, called branches (go from the posterior end of the body upwards).
The body, the corpus, is formed from two halves connected along the midline (chin symphysis, symphysis mentalis), which grow together into one bone in the first year of life. Each half is curved outwardly with a convexity. Its height is greater than its thickness. On the body, the lower edge is distinguished - the base of the lower jaw, basis mandibulae, and the upper - the alveolar part, pars alveolaris.
On the outer surface of the body, in its middle parts, there is a small chin protrusion, protuberantia mentalis, outside of which the chin tubercle, tuberculum mentale, immediately protrudes. Above and outwardly from this tubercle lies the chin foramen, foramen mentale (the place where the vessels and nerve exit). This hole corresponds to the position of the root of the second small molar. An oblique line, linea obliqua, which passes into the anterior edge of the branch of the lower jaw, is directed upward from the chin foramen.
The development of the alveolar part depends on the teeth contained in it.
This part is thinned and contains the alveolar eminences, juga alveolaria. At the top, it is bounded by an arcuate free edge - the alveolar arch, arcus alveolaris. In the alveolar arch there are 16 (8 on each side) dental alveoli, alveoli dentales, separated from one another by interalveolar septa, septa interalveolaria.
On the inner surface of the body of the lower jaw, near the midline, there is a single or bifurcated chin spine, spina mentalis (the place where the chin-hyoid and chin-lingual muscles begin). At its lower edge there is a depression - a digastric fossa, fossa digastrica, an attachment trace. On the lateral sections of the inner surface on each side and towards the branch of the lower jaw, the maxillary-hyoid line, linea mylohyoidea, runs obliquely (here the maxillary-hyoid muscle and the maxillopharyngeal part of the upper pharyngeal constrictor begin).
Above the jaw-hyoid line, closer to the sublingual spine, there is a sublingual fossa, fovea sublingualis, - the trace of the adjacent sublingual gland, and below and posterior to this line - often a weakly expressed submandibular fossa, fovea submandibularis, a trace of the adjoining submandibular gland.
The branch of the lower jaw, ramus mandibulae, is a wide bony plate that rises from the posterior end of the lower jaw body up and obliquely backward, forming with the lower edge of the body mandibular angle, angulus mandibulae.
On the outer surface of the branch, in the area of the corner, there is a rough surface - chewing tuberosity, tuberositas masseterica, a trace of attachment of the muscle of the same name. On the inner side, respectively, of the chewing tuberosity, there is less roughness - pterygoid tuberosity, tuberositas pterygoidea, a trace of attachment of the medial pterygoid muscle.
In the middle of the inner surface of the branch there is mandibular opening, foramen mandibulae, limited from the inside and in front by a small bony protrusion - the tongue of the lower jaw, lingula mandibulae. This hole leads into the canal of the lower jaw, canalis mandibulae, in which the vessels and nerves pass. The canal lies in the thickness of the cancellous bone. On the front surface of the body of the lower jaw, it has an outlet - the chin opening, foramen mentale.
From the opening of the lower jaw downward and forward, along the upper border of the pterygoid tuberosity, passes the maxillary-sublingual groove, sulcus mylohyoideus (a trace of the occurrence of the vessels and nerves of the same name). Sometimes this groove or part of it is covered by a bone plate, turning into a canal. Slightly higher and anterior to the opening of the lower jaw is the mandibular ridge, torus mandibularis.
At the upper end of the branch of the lower jaw, there are two processes that are separated by the notch of the lower jaw, incisura mandibulae. The anterior, coronoid, process, processus coronoideus, often has a roughness on the inner surface due to the attachment of the temporal muscle. The posterior, condylar, process, processus condylaris, ends with the head of the lower jaw, caput mandibulae. The latter has an elliptical articular surface that participates together with the temporal bone of the skull in the formation
The human jaw is a large bony structure of the facial part of the skull, consisting of two unpaired parts (upper and lower), different in structure and function.
The upper jaw (in Latin - maxilla) occupies a central place among the bones of the facial section of the human skull. This bone structure is complex and has a number of vital functions.
INTERESTING: With the development of labor activity, ancient people transferred part of the grasping functions from the jaw to their hands. As a result, the size of this bone structure has decreased significantly.
Functions and purpose
The maxilla has a number of important functions. Below is a description of some of them:
- Form-building. Forms the nasal and ocular cavities, the septum between the mouth and nose.
- Aesthetic. The size and shape of this bone will determine the oval of the face, the fit of the cheekbones, and the appearance of a person.
- Respiratory. Forms an extensive maxillary sinus, in which the inhaled air is humidified and heated.
- Chewing... The teeth located on the jaw provide chewing of the consumed food.
- Swallowing... The muscles and ligaments involved in the process of swallowing food (including the tongue) are anchored here.
- Sound generating. Together with the lower jaw and airways, it takes part in the formation of various sounds. When this bone structure is damaged, the person's diction is disturbed.
IMPORTANT! A person makes about 1.4 thousand chewing movements per day. When chewing bread, the jaw is under pressure of 15 kg, of fried meat - 25 kg, maximum pressure - 72 kg
Structural features
The upper jaw bone has a complex structure. It consists of several segments and processes, shown in the following picture.
Below we will consider how the body of the jawbone is arranged, of how many interconnected surfaces it consists of.
Jaw body
Front surface, located under the infraorbital margin, has a slightly curved shape. On it you can see the infraorbital foramen and canine fossa.
Rear surface consists of a tubercle and several alveolar openings for nerves and blood vessels. Near the tubercle is the palatine groove.
Orbital surface consists of a lacrimal notch and an infraorbital groove, passing into the infraorbital canal.
Nasal surface and the anterior surface are isolated from each other by the nasal notch. The main part of the nasal surface consists of the maxillary cleft.
REFERENCE: Fixed upper jawbone is stronger than movable lower jaw. Together with other bone structures of the skull, it protects the brain from injury and bruises.
Scions
Palatine process occupies a significant area of hard tissues of the palate. With the second process, located on the opposite side, it is connected with a median suture.
Frontal process with its upper side it is attached to the nasal region of the frontal bone, the front to the new bone, and the back to the lacrimal bone. The lower edge of the process is connected to the body of the jaw. On the process there is a lacrimal groove and an ethmoid crest.
Zygomatic process begins at the outer upper corner of the body and has a lateral location. The upper part of the zygomatic process is adjacent to the frontal bone.
Alveolar ridge Is a bone formation with a complex structure. It includes walls, dental alveoli, interdental and inter-root bone septa.
Hillocks
The infratemporal part of the jaw is convex. Its most prominent area is called the "maxillary tubercle" (in Latin - tuber maxillae). At the base of the tubercle there are alveolar openings for blood vessels and nerves. The oblique head of the pterygoid lateral muscle is attached to the maxillary tubercle.
In international practice, the following abbreviations are used to designate mounds: PNA (according to the French nomenclature), BNA (according to the Basel nomenclature) and JNA (according to the Jena nomenclature).
Features of blood supply
The jaw internal artery is responsible for the blood supply, or rather, its four branches:
- posterior superior alveolar;
- infraorbital;
- descending palatine;
- nasopalatine (see the following diagram).
The following table shows which sites the listed vessels supply blood to.
Blood supply to the upper jaw bone
The venous network, which is responsible for the outflow of blood, does not always repeat the pattern of the supplying vessels. It is represented in parallel by the outgoing veins and venous plexuses. From the pterygopalatine node, blood enters the jaw vein, and from there into the external jugular vein. From the plexus of the alveolar process, it enters the facial vein, and then into the internal jugular vein.
Teeth
When studying the anatomy of the human upper jaw, one should dwell on the structure of the teeth in more detail. This bone structure contains incisors, canines, premolars and molars.
Below is a brief description of the structure of the teeth of a normal, healthy upper jaw of a person.
Teeth located on the upper jaw of a person
| Tooth name | Tooth shape | Number of tubercles | Root structure |
| Central incisor | Chisel | 3 | Single, conical |
| Side cutter | Chisel | 3 | Flattened from center to edge |
| Fang | Pointed | 1 | Single, powerful |
| First premolar | Prismatic | 2 | How many tubercles, so many roots |
| Second premolar | Prismatic | 2 | Consu-shaped, compressed in front and back |
| First molar | Rectangular | 4 | With three branches |
| Second molar | Cubic | 4 | With three branches |
| Third molar | Cubic | 4 | Short, powerful |
Despite the fact that teeth differ in types (types) and shapes of crowns and roots, their internal structure is the same.
Diseases and pathologies of the upper jaw
Inflammatory processes in the oral cavity can provoke the appearance of cysts on the human jaw - hollow tumors filled with fluid. Cysts are treated in several ways, but surgery is considered the most successful. More information about the treatment of cysts can be found in the article
Inflammation of the bones can lead to osteitis, periostitis, or osteomyelitis, the characteristics of which are summarized in the following table.
Inflammatory diseases of the human maxillary bone
Periostitis can occur in fibrous, purulent or serous forms, and osteomyelitis in acute or chronic forms. The listed diseases can cause odontogenic sinusitis - a disease associated with the penetration of infection into the maxillary sinuses.
Among the malignant formations of this bone structure, tumors of epithelial origin predominate.
Lower jaw
The lower jaw (in Latin - mandibula) is a movable unpaired bone located in the lower part of the facial part of the skull. In the course of evolution, this bone was formed from the first branchial (mandibular) arch of the horseshoe shape, which it retains to this day (see the following diagram).
INTERESTING. The pressure coefficient during the compression of the jaws in humans is 60 times less than that of a dog, 300 times less than that of a wolf, and 1600 times less than that of a shark
Functions
The lower jaw bone performs the same functions as the upper one. She is involved in chewing food, swallowing, breathing, making sound and distributing the load on the teeth.
To chew food, a person has to close the dentition, and to swallow it and produce sound, open them. In this case, a person can move the lower jaw in six directions: up and down, back and forth and to the sides.
The anatomical shape of this bone formation determines the attractiveness of the human face. A wide, protruding jaw makes a person's face coarser, and a thin, elongated one - narrow and effeminate.
REFERENCE. Scientists believe that the human lower jawbone has much in common with the bony formations of ruminants. Therefore, it is more convenient for a person to chew soft plant foods than coarse meat foods.
Structural features
The lower jaw of an adult is formed from a body and two processes. The rough surface of this bone formation is surrounded by well-developed muscles. The body of the jawbone consists of the inner and outer surfaces.
The inside of the bone
The central element of the inner part is the chin spine (bone spine), in which two large muscles are attached: the chin-lingual and chin-hypoglossal. Under the spine is the digastric fossa, a little higher - the hyoid fossa and the maxillary-hyoid line.
Under the jaw-hyoid line, you can see the submandibular fossa - this is a trace from the submandibular salivary gland.
REFERENCE... In newborn babies, the lower jaw bone consists of two separate parts connected by an epithelium. These halves grow together by the end of the first - the beginning of the second year of the child's life.
Outside bone
The chin protrusion is located on the outer part of the bone, and the alveolar eminences are slightly higher. The chin angle ranges from 46 to 85 degrees. Teeth are fixed on the front upper part of the bone formation.
At the chin protrusion, the chin tubercles are located, behind them is a small hole (ø ≈ 1.5-5 mm) for the vessels and nerves. In the background, the uvula, neck and two processes are visible: condylar, coronary.
Teeth
Human lower jaw anatomy studies not only bones, but also teeth. A normally developed jaw accommodates 8 pairs of teeth, including incisors, canines, premolars and molars. The teeth of the upper and lower jaw are similar in name, but differ in structure.
A brief description of the lower teeth is presented in the following table.
Human lower teeth
| Tooth name | Tooth shape | Number of tubercles | Root structure |
| Central incisor | Convex outside, concave inside | 3 | Very small, flat |
| Side cutter | Narrow chisel | 3 | Flat, grooved |
| Fang | Diamond-shaped, narrow | 1 | Flat, tilted inward |
| First premolar | Rounded | 2 | |
| Second premolar | Rounded | 2 | Single, flat, grooved |
| First molar | Cubic | 5 | |
| Second molar | Cubic | 4 | Double, the back is shorter than the front |
| Third molar | Cubic | 4 | Double, slightly rounded |
Over the past millennium, the human jaw has decreased by 1 cm. Therefore, you cannot argue with anatomy. Therefore, people have to go to the dentist to remove "extra" teeth.
Features of blood supply
Several arteries are involved in the blood supply to the lower part of the jaw, forming large-looped and dense small-looped networks. Blood flows to the teeth through the inferior alveolar artery, to the lower side of the body and the inner surface of the angle - along the external jaw, to the chin plate - along the lingual, to the articular process - along the internal jaw, to the coronoid process - along the artery of the masseter muscle.
Branches
The lower jaw has two branches that smoothly merge into the condylar and coronal processes. The shape of these branches is purely individual, as evidenced by the following figure.
The front of the branches transforms into an oblique line on the outside of the jaw. Medially, it reaches the posterior alveoli. The back of the branches connects to the base of the jaw. On the outer surface of the branches, you can notice a chewing tuberosity, on the inner surface - a pterygoid tuberosity.
The branches are turned inward, so the distance between their outer points is less than the distance between the condylar processes of the branches. The width of a person's face depends on the size between the branches.
Major diseases and pathologies
. It can be open or closed. The most common causes of fracture are impacts and falls from great heights. A person with a broken jaw cannot chew food.
. Its most common cause is a blow to the jaw when a person's mouth was open. In case of dislocation, the mouth remains ajar, it is impossible to close it with a hand. Treatment consists in repositioning the articular surface.
In contact with
Lower jaw (mandibula) unpaired, horseshoe-shaped, the only movable of. It consists of two symmetrical halves, which grow together completely by the end of the 1st year of life. In each half, a body and a branch are distinguished. A dense bony protrusion forms at the junction of both halves in old age.
In the body (corpus mandibulae) distinguish between the base (basis) and the alveolar part (pars alveolaris)... The body of the jaw is curved, its outer surface is convex, and the inner surface is concave. At the base of the body, the surfaces merge into one another, in the alveolar part they are separated by alveoli. The right and left halves of the body converge at an angle, individually different, forming a basal arch. The shape of the basal arch is one of the main features that characterize the shape of the lower jaw. To characterize the basal arch, the latitudinal-longitudinal index is used (the ratio of the distance between the corners of the lower jaw to the distance from the middle of the chin to the middle of the line connecting the corners of the lower jaw). There are jaws with a short and wide basal arch (index 153-175), with a long and narrow (index 116-132) and with an intermediate shape. The height of the jaw body is greatest in the area of the incisors, the smallest - at the level of the 8th tooth. The thickness of the jaw body is greatest in the area of the molars, and the smallest in the area of the premolars. The cross-sectional shape of the jaw body is not the same in different areas, which is due to the number and position of the roots of the teeth. In the area of the front teeth, it approaches triangular with the base facing down. In the areas of the body corresponding to the large molars, it is close in shape to a triangle with the base facing upward (Fig. 1-12).
BUT - view from above: 1 - the head of the lower jaw; 2 - pterygoid fossa; 3 - coronoid process; 4 - mandibular pocket; 5 - molars; 6 - the body of the lower jaw; 7 - premolars; 8 - canine; 9 - incisors; 10 - chin tubercle; 11 - chin protrusion; 12 - interalveolar septa; 13 - dental alveoli; 14 - chin opening; 15 - inter-root partitions; 16 - the angle of the lower jaw; 17 - the outer wall of the alveoli; 18 - oblique line; 19 - the inner wall of the alveoli; 20 - posterior molar fossa; 21 - buccal crest; 22 - notch of the lower jaw; 23 - the tongue of the lower jaw; 24 - the neck of the lower jaw. ; B - back view: 1 - incisors; 2 - canine; 3 - premolars; 4 - molars; 5 - coronoid process; 6 - condylar process; 7 - the tongue of the lower jaw; 8 - jaw-hyoid groove; 9 - jaw-hyoid line; 10 - submandibular fossa; 11 - pterygoid tuberosity; 12 - digastric fossa; 13 - chin spine; 14 - hypoglossal fossa; 15 - the angle of the lower jaw; 16 - the canal of the lower jaw; 17 - the neck of the lower jaw.
... IN - inside view: 1 - buccal crest; 2 - temporal crest; 3 - notch of the lower jaw; 4 - the head of the lower jaw; 5 - the neck of the lower jaw; 6 - the tongue of the lower jaw; 7 - opening of the lower jaw; 8 - jaw-hyoid groove; 9 - mandibular roller; 10 - pterygoid tuberosity; 11 - jaw-hyoid line; 12 - the angle of the lower jaw; 13 - submandibular fossa; 14 - hypoglossal fossa; 15 - digastric fossa; 16 - compact substance of the lower jaw; 17 - spongy substance of the lower jaw; 18 - incisors; 19 - canine; 20 - premolars; 21 - molars
In the middle of the outer surface of the jaw body there is a chin protrusion (protuberantia mentalis), which is a characteristic feature of modern humans and determines the formation of the chin. The angle of the chin in relation to the horizontal plane in a modern person ranges from 46 to 85 °. On both sides of the chin protrusion, closer to the base of the jaw, are the chin tubercles (tubercula mentalia). Outside of them is the chin foramen (foramen mentale), which is the outlet of the mandibular canal. Through the chin opening, the vessels and nerves of the same name go out. Most often, this hole is located at the level of the 5th tooth, but it can be displaced anteriorly to the 4th tooth, and posteriorly to the gap between the 5th and 6th teeth. The size of the chin hole ranges from 1.5 to 5 mm, its shape is oval or round, sometimes it is double. The chin foramen is removed from the base of the jaw by 10-19 mm, on the edentulous jaws of adults with atrophied alveolar part - closer to the upper edge of the jaw.
In the lateral areas of the body of the lower jaw there is an obliquely located roller - an oblique line (linea obliqua), the anterior end of which corresponds to the level of the 5-6th tooth, and the posterior end, without sharp boundaries, passes to the anterior edge of the lower jaw branch.
On the inner surface of the jaw body, near the midline, there is a bone thorn, sometimes double, - the chin spine (spina mentalis). This place is the beginning of the sublingual and sublingual muscles. Below and lateral to the chin spine, the digastric fossa (fossa digastrica) is defined, in which the digastric muscle begins. Above the digastric fossa there is a sloping depression - the fovea sublingualis - a trace from the adjacent sublingual salivary gland. Further posteriorly, the maxillary-hyoid line (linea mylohyoidea) is visible, on which the upper pharyngeal constrictor and the maxillary-hyoid muscle begin. The maxillary-hyoid line runs between the digastric and hyoid fossa at the level of the 5-6th tooth and ends on the inner surface of the jaw branch. Under the maxillary-hyoid line at the level of the 5-7th tooth there is a submandibular fossa (fovea submandibularis) - a trace from the submandibular salivary gland located in this place.
Alveolar part of the jaw body contains 8 dental alveoli on each side. The alveoli are separated from each other by interalveolar septa (septa interalveolaria). The walls of the alveoli facing the lips and cheeks are called vestibular, and the walls facing the tongue are called lingual. On the surface of the body, the alveoli correspond to alveolar elevations (juga alveolaria), which are especially well pronounced at the level of the canine and the 1st premolar. Between the alveoli of the incisors and the chin protrusion there is an undercutting depression (impressio subincisiva). The shape, depth and width of the alveoli, the thickness of their walls for teeth of different groups are different. The alveoli of the incisors (especially the central ones) are compressed from the sides, their bottom is displaced to the vestibular compact plate, so the thickness of the lingual wall of the alveoli is greater than that of the vestibular one. The alveoli of the canine and especially of the premolars are rounded, the lingual wall is thicker than the vestibular wall. The deepest alveoli of the canine and 2nd premolar. Their walls are thicker than the alveoli of the incisors. Alveoli of molars are distinguished by the presence of inter-root septa. In the alveoli of the first two molars, there is one septum separating the anterior and posterior chambers for the corresponding roots. The alveoli of the third molar is varied in shape and number of partitions, which is associated with the inconstancy of the shape of this tooth. Most often, the alveolus is conical, without septa, but it can have one or sometimes two septa. The walls of the molar alveoli are thickened due to the oblique and maxillary-hyoid lines. This strengthens the lower molars and prevents them from loosening in the bucco-lingual direction during transverse lateral chewing movements.
The area behind the third molar is triangular in shape and is called the fovea retromolaris. Laterally from this fossa, on the outer plate of the alveolar part, there is a mandibular pocket (recessus mandibulae), which stretches from the 2-3rd molar to the coronoid process (Fig. 1-13).
Fig. 1-13. The structure of the lower jaw, outer surface (scheme according to V.P. Vorobiev ), part of the dense bone substance of the outer plate is removed: 1 - condylar process; 2 - coronoid process; 3 - opening of the lower jaw; 4 - the tongue of the lower jaw; 5 - buccal crest; 6 - posterior molar fossa; 7 - incisors; 8 - alveolar eminences; 9 - chin elevation; 10 - canine; 11 - premolars; 12 - roots of teeth; 13 - the canal of the lower jaw; 14 - the angle of the lower jaw; 15 - chewing tuberosity; 16 - notch of the lower jaw; 17 - the tongue of the lower jaw (outside view); 18 - molars
The structure of the alveoli of the lower jaw similar to the structure of the alveoli of the upper jaw. The wall of the upper third consists of two layers: solid and compact plates (inner and outer). In the area of the bottom and lower third of the alveolus, there is a spongy substance under the hard plate.
In the spongy substance of the body of the lower jaw there is a canal of the lower jaw (canalis mandibulae), through which vessels and nerves pass. The canal begins with the foramen mandibulae on the inner surface of the branch and ends with the chin foramen on the outer surface of the body. The canal has an arcuate direction with a bulge facing down and forward, lies closest to the bottom of the alveoli of the 2-3rd molar and passes between the chambers for their roots. Small tubules depart from the canal, in which vessels and nerves pass to the roots of the teeth; they open at the bottom of the alveoli. Medially from the chin foramen, the mandibular canal continues in the form of a small tubule to the midline and gives off lateral branches along this length to the bottom of the alveoli of the anterior teeth.
The branch of the lower jaw (ramus mandibulae) has an outer and inner surface, anterior and posterior edges, which pass, respectively, into the coronal process (processus coronoideus) and into the condylar process (processus condylaris). These processes are separated by the notch of the lower jaw (incisura mandibulae). The coronoid process serves for the attachment of the temporal muscle, the condyle for education. The shape of the branch of the lower jaw is individually different (Fig. 1-14).
Fig. 1-14. , bottom view: A - wide and short; B - narrow and long
Condylar process has a head (caput mandibulae) with an articular surface for connection with the mandibular fossa of the temporal bone and a neck (collum mandibulae). On the anteromedial surface of the neck of the condylar process, there is a pterygoid fossa (fovea pterygoidea) - the place of attachment of the external pterygoid muscle.
The head of the articular process flattened and occupies a position in which the axes drawn through the largest size of both heads intersect at the foramen magnum at an angle of 120-178 °, open anteriorly. The shape and position of the head are individually different and depend on the working conditions of the temporomandibular joint and the state of its components. Deviations leading to a change in the volume and direction of movement in the joint change the shape and position of the articular heads.
The anterior edge of the branch of the lower jaw laterally passes on the outer surface of the jaw body into an oblique line, and medially reaches the posterior alveoli, thus limiting the posterior molar fossa. The medial part of the ridge, formed at the place of transition of the anterior edge into the walls of the posterior alveoli, stands out under the name of the buccal crest (crista buccinatoria), from which the buccal muscle begins.
Rear edge of the branch passes into the base of the jaw, forming an angle (angulus mandibulae), the value of which ranges from 110 to 145 ° (usually 122-133 °) and changes throughout life. In newborns, it is close to 150 °, decreases in adults with preserved teeth and maximum chewing load, and increases again in old people with complete loss of teeth (Fig. 1-15).
The outer surface of the branch contains a chewing tuberosity (tuberositas masseterica), which occupies most of the branch and angle of the jaw and is the place of attachment of the masseter muscle. On the inner surface of the branch in the area of the corner and adjacent sections there is a pterygoid tuberosity (tuberositas pterygoidea) - the place of attachment of the medial pterygoid muscle. On the same surface, in the middle, there is an opening of the lower jaw (foramen mandibulae), which is covered in front and above by an inconsistently pronounced bony protrusion - a tongue (lingula mandibulae). Above and in front of the uvula is the mandibular ridge (torus mandibularis) - the place of attachment of two ligaments: the jaw-pterygoid and the jaw-wedge-shaped.
Branches of the lower jaw usually turned outward, so that the distance between the condylar processes of the right and left branches is greater than the distance between the outer points of the corners of the jaw. It can be distinguished as extreme forms of the jaw with maximally and minimally deployed branches. The degree of divergence of the branches depends on the shape of the upper half of the face. With a wide upper half of the face, the branches of the lower jaw are less developed than with a narrow upper half of the face. The smallest branch width, which usually falls in the middle of its height, ranges from 23 to 40 mm (usually 29-34 mm). The width and depth of the jaw notch are also individually different: the width of the notch is from 26 to 43 mm (more often 32-37 mm), the depth is from 7 to 21 mm (more often 12-16 mm). In people with a wide upper half of the face, the jaw is usually the widest notch and vice versa.
Biomechanics of the lower jaw
The forces that compress the teeth create more stress in the posterior branches of the branches. Self-preservation of living bone under these conditions consists in changing the position of the branches, i.e. the angle of the jaw must change; this happens from childhood through maturity to old age. The optimal conditions for stress resistance are to change the value of the jaw angle to 60-70 °. These values are obtained by changing the "external" angle: between the plane of the base and the rear edge of the branch (see Fig. 1-15).
Overall strength of the lower jaw when compressed under static conditions, it is about 400 kgf, less than the strength of the upper jaw by 20%. This suggests that arbitrary loads during clenching of the teeth cannot damage the upper jaw, which is rigidly connected to the cerebral section of the skull. Thus, the lower jaw acts as a natural sensor, a "probe", allowing the ability to gnaw, destroy with teeth, even break, but only the lower jaw, preventing damage to the upper one. These indicators should be taken into account when prosthetics.
One of the characteristics of the compact bone substance is the indicator of its microhardness, which is determined by special methods by various devices and is 250-356 HB (according to Brinell). A greater indicator is noted in the area of the sixth tooth, which indicates its special role in the dentition.
Fig. 1-15. Change in the value of the "external" angle of the lower jaw of a person in connection with his age and the presence of teeth
The microhardness of the compact substance of the lower jaw ranges from 250 to 356 HB in the area of the 6th tooth.
In conclusion, let us point out the general structure of the organ. So, the branches of the jaw are not parallel to each other. Their planes are wider at the top than at the bottom. Convergence is about 18 °. In addition, their front edges are located closer to each other than the back ones, by almost a centimeter. The base triangle, connecting the apices of the angles and the symphysis of the jaw, is almost equilateral. The right and left sides are not mirrored, but only similar. Ranges of size and design options are based on gender, age, race and individual characteristics.
Materials used: Anatomy, physiology and biomechanics of the dentition: Ed. L.L. Kolesnikova, S.D. Arutyunova, I. Yu. Lebedenko, V.P. Degtyarev. - M.: GEOTAR-Media, 2009
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