Vertical movement of the lower jaw. Radiographic determination of the angle of the sagittal articular path
Biomechanics of the lower jaw. Sagittal movements of the lower jaw. Sagittal incisal and articular pathways, their characteristics.
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 should change; this happens from childhood through maturity to old age. The optimal conditions for resistance to stress are to change the value of the jaw angle to 60-70 °. These values \u200b\u200bare obtained by changing the "external" angle: between the plane of the base and the rear edge of the branch.
The total strength of the lower jaw during compression under static conditions 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 with the cerebral section of the skull. Thus, the lower jaw acts as a natural sensor, a “probe”, allowing the possibility of gnawing, destroying with teeth, even breaking, 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 \u200b\u200bthe sixth tooth, which indicates its special role in the dentition. The microhardness of the compact substance of the lower jaw ranges from 250 to 356 HB in the area of \u200b\u200bthe 6th tooth.
In conclusion, let us point out general structure organ. So, the branches of the jaw are not parallel to each other. Their planes are wider at the top than at the bottom. The convergence is about 18 °. In addition, their front edges are located closer to each other than the rear ones by almost a centimeter. The base triangle connecting the apices of the angles and the symphysis of the jaw is almost equilateral. Right and left side mirrored not corresponding, but only similar. Ranges of size and design options are based on gender, age, race and individual characteristics.
With sagittal movements, the lower jaw moves forward and backward. It moves forward due to bilateral contraction of the external pterygoid muscles attached to the articular head and bursa. The distance that the head can travel forward and downward along the articular tubercle is 0.75-1 cm. However, during the act of chewing, the articular path is only 2-3 mm. As for the dentition, the forward movement of the lower jaw is impeded by the upper frontal teeth, which usually overlap the lower frontal ones by 2-3 mm. This overlap is overcome as follows: Incisal edges lower teeth slide along the palatine surfaces of the upper teeth until they meet the cutting edges of the upper teeth. Due to the fact that the palatal surfaces of the upper teeth are an inclined plane, the lower jaw, moving along this inclined plane, simultaneously moves not only forward, but also downward, and, thus, the lower jaw moves forward. With sagittal movements (forward and backward), as well as with vertical ones, the articular head rotates and slides. These movements differ from each other only in that with vertical movements rotation prevails, and with sagittal ones - sliding.
with sagittal movements, movements occur in both joints: in the articular and dental. You can mentally draw a plane in the mesio-distal direction through the buccal tubercles of the lower first premolars and the distal tubercles of the lower wisdom teeth (and if the latter are not there, then through the distal tubercles of the lower
second molars). This plane in orthopedic dentistry is called occlusal, or prosthetic.
The sagittal incisal path is the path of movement of the lower incisors along the palatal surface of the upper incisors when the lower jaw moves from the central occlusion to the anterior one.
JOINT WAY - the path of the articular head along the slope of the articular tubercle. SAGITTAL JOINT PATH - the path taken by the articular head of the lower jaw when it is displaced forward and downward along the posterior slope of the articular tubercle.
SAGITTAL CUTTING PATH - the path made by the incisors of the lower jaw along the palatal surface of the upper incisors when the lower jaw moves from the central occlusion to the anterior one.
Articular path
During the advancement of the lower jaw forward, the opening of the upper and lower jaws in the area of \u200b\u200bthe molars is provided by the articular way when the lower jaw is moved forward. It depends on the bending angle of the articular tubercle. During lateral movements, the opening of the upper and lower jaws in the region of the molars on the non-working side is ensured by a non-working articular path. It depends on the angle of bending of the articular tubercle and the angle of inclination of the mesial wall of the glenoid fossa on the non-working side.
Incisal path
The incisal path, when the lower jaw moves forward and to the side, constitutes the anterior guiding component of its movements and ensures the opening of the posterior teeth during these movements. The group working guide function ensures the opening of the teeth on the non-working side during working movements.
Biomechanics of the lower jaw. Transversal movements of the lower jaw. Transversal incisal and articular pathways, their characteristics.
Biomechanics is the application of the laws of mechanics to living organisms, especially to their locomotor systems. In dentistry, the biomechanics of the masticatory apparatus considers the interaction of the dentition and the temporomandibular joint (TMJ) during movements of the lower jaw due to the function of the masticatory muscles. Transversal movementscharacterized by certain changes
occlusal contacts of teeth. As the lower jaw blends to the right and left, the teeth describe curves that intersect at an obtuse angle. The further the tooth is from the articular head, the dumber the angle.
Changes in the relationship of the chewing teeth during lateral excursions of the jaw are of considerable interest. With lateral movements of the jaw, it is customary to distinguish between two sides: working and balancing. On the working side, the teeth are set against each other by the same named tubercles, and on the balancing side they are opposite, that is, the cheek lower tubercles are set against the palatine.
Transversal movement is therefore not a simple but a complex phenomenon. As a result of the complex action of the chewing muscles, both heads can simultaneously move forward or backward, but it never happens that one moves forward, while the position of the other remains unchanged in the glenoid fossa. Therefore, the imaginary center around which the head moves on the balancing side is never actually located in the head on the working side, but is always located between both heads or outside the heads, i.e., according to some authors, there is a functional, not anatomical center ...
These are the changes in the position of the articular head during transversal movement of the lower jaw in the joint. With transversal movements, changes also occur in the relationship between the dentition: the lower jaw alternately moves in one direction or the other. As a result, curved lines appear, which, crossing, form corners. The imaginary angle formed when the central incisors move is called the gothic angle, or the angle of the transversal incisor path.
It is on average 120 °. At the same time, due to the movement of the lower jaw towards the working side, changes occur in the relationship of the chewing teeth.
On the balancing side, dissimilar tubercles are closed (the lower buccal ones are closed with the upper palatine ones), and on the working side, the homonymous tubercles are closed (buccal - with the buccal and lingual - with the palatine).
Transversal articular path- path of the articular head of the balancing side inward and downward.
The angle of the transversal articular path (Bennett angle) is the angle projected onto the horizontal plane between purely anterior and maximum lateral movements of the articular head of the balancing side (mean value 17 °).
Bennett movement- lateral movement of the lower jaw. The articular head of the working side is displaced laterally (outward). The articular head of the balancing side at the very beginning of the movement can make a transversal movement inward (by 1-3 mm) - "initial lateral
movement "(immediate sideshift), and then - movement down, inward and forward. In others
in some cases, at the beginning of Bennett's movement, a movement downward, inward and forward (progressive sideshift) is carried out immediately.
Incisal guides for sagittal and transversal movements of the lower jaw.
Transversal incisal path- the path of the lower incisors along the palatal surface of the upper incisors when the lower jaw moves from the central occlusion to the lateral one.
The angle between the transversal incisal paths to the right and left (mean value 110 °).
Algorithm for constructing a prosthetic plane with a non-fixed interalveolar height on the example of a patient with complete loss of teeth. Making wax bases with bite rollers. The method of making wax bases with bite rolls with edentulous jaws, name the size of the bite rolls (height and width) in the anterior and lateral section on the upper and lower jaw.
Determination of the occlusal height of the lower third of the face.
Biomechanics of the lower jaw should be considered from the point of view of the functions of the dentition: chewing, swallowing, speech, etc. The movement of the lower jaw occurs as a result of a complex interaction of the masticatory muscles, TMJ and teeth, coordinated and controlled by the central nervous system. Reflex and voluntary movements of the lower jaw are regulated by the neuromuscular apparatus and are carried out sequentially. Initial movements, such as biting off and placing a piece of food in the mouth, are arbitrary. The subsequent rhythmic chewing and swallowing occurs unconsciously. The lower jaw moves in three directions: vertical, sagittal and transversal. Any movement of the lower jaw occurs with the simultaneous sliding and rotation of its heads.
The scheme of translational movements of the heads of the lower jaw forward and downward
The temporomandibular joint provides a distal fixed position of the lower jaw in relation to the upper and creates guide planes for its movement forward, sideways and downward within the limits of movement. In the absence of contact between the teeth, the movements of the lower jaw are guided by the articulating surfaces of the joints and proprioceptive neuromuscular mechanisms. Stable vertical and distal interaction of the lower jaw with the upper jaw is ensured by the intertubercular contact of the antagonist teeth. The cusps of the teeth also form guiding planes for the forward and lateral movement of the lower jaw within the contact between the teeth. When the lower jaw moves and the teeth are in contact, the chewing surfaces of the teeth direct the movement and the joints play a passive role.
Vertical movements that characterize the opening of the mouth are carried out with active bilateral contraction of the muscles going from the lower jaw to the hyoid bone, as well as due to the gravity of the jaw itself.
Lower jaw movements when opening the mouth
There are three phases in opening the mouth: insignificant, significant, maximum. The amplitude of the vertical movement of the lower jaw is 4-5 cm. When the mouth is closed, the lower jaw is lifted by the simultaneous contraction of the muscles that lift the lower jaw. At the same time, in the temporomandibular joint, the heads of the lower jaw rotate together with the disc around their own axis, then down and forward along the slope of the articular tubercles to the apex when opening the mouth and in the opposite order when closing.
Sagittal movements of the lower jaw characterize the forward movement of the lower jaw, i.e. a complex of movements in the sagittal plane within the boundaries of the displacement of the inter-incisal point.
The forward movement of the lower jaw is carried out by bilateral contraction of the lateral pterygoid muscles, partly of the temporal and medial pterygoid muscles. The movement of the mandibular head can be divided into two phases. In the first, the disc, together with the head, slides over the surface of the articular tubercle. In the second phase, a hinge movement of the head about its own transverse axis passing through the head is attached to the slide of the head. The distance that the head of the lower jaw travels when it moves forward is called the sagittal articular path. It is on average 7-10 mm. The angle formed by the intersection of the line of the sagittal articular path with the occlusal plane is called the angle of the sagittal articular path. Depending on the severity of the articular tubercle and tubercles of the lateral teeth, this angle changes, but on average (according to Gizi) it is 33 °.
Biomechanics of the lower jaw when moving from the central occlusion to the anterior:
O-O1 - sagittal articular path, M-M1 - sagittal molar path, P-P1 - sagittal incisal path; 1 - angle of the sagittal articular path, 2 - angle of the sagittal incisal path, 3 - dissociation (deocclusion between the molars)
Sagittal Occlusal Curve (Spee Curve) runs from the upper third of the distal slope of the lower canine to the distal buccal cusp of the last lower molar.
With the extension of the lower jaw, due to the presence of the sagittal occlusal curve, multiple interdental contacts arise, providing a harmonious occlusal relationship between the dentition. The sagittal occlusal curve compensates for the roughness of the occlusal surfaces of the teeth and is therefore called a compensatory curve. Simplified, the mechanism of movement of the lower jaw is as follows: when moving forward, the head of the condylar process moves forward and down the slope of the articular tubercle, while the teeth of the lower jaw also move forward and downward. However, meeting with the complex relief of the occlusal surface of the upper teeth, they form continuous contact with them until the time when the separation of the dentition occurs due to the height of the central incisors. It should be noted that during sagittal movement, the central lower incisors slide along the palatal surface of the upper ones, passing the sagittal incisal path. The angle formed by the incisal path vector and the occlusal plane. Depending on the elevation of the tubercles of the central incisors, this angle changes, but on average it is 40-50 °. Thus, the harmonious interaction between the tubercles of the chewing teeth, the incisal and articular pathways ensures the preservation of the contact of the teeth during the extension of the lower jaw. If you do not take into account the curvature of the sagittal compensatory occlusal curve in the manufacture of removable and not removable dentures, there is an overload of the articular discs, which will inevitably lead to TMJ disease.
The ratio of the sagittal articular and sagittal incisal pathways
Transversal (lateral) movements of the lower jaw are carried out as a result of a predominantly unilateral contraction of the lateral pterygoid muscle. When the lower jaw moves to the right, the left lateral pterygoid muscle contracts and vice versa. In this case, the head of the lower jaw on the working side (offset side) rotates around the vertical axis. On the opposite balancing side (the side of the contracted muscle), the head of the lower jaw slides along with the disc along the articular surface of the tubercle downward, forward and somewhat inward, making a lateral articular path. The angle formed between the lines of the sagittal and transversal articular pathway is called the angle of the transversal articular pathway. In the literature, it is known as “ bennett's corner»And is equal, on average, 17 °. Transversal movements are characterized by certain changes in the position of the teeth. The curves of the lateral displacement of the anterior teeth at the inter-incisal point intersect at an obtuse angle. This angle is called the Gothic or the angle of the transversal incisal path.... It determines the scope of the incisors during lateral movements of the lower jaw and is equal to an average of 100-110 °.
Lateral movement of the lower jaw (Gothic angle - 110 ° and Bennett angle - 17 °)
This data is necessary for programming the articular mechanisms of devices that simulate the movements of the lower jaw. On the working side, the lateral teeth are set relative to each other by the same tubercles; on the balancing side, the teeth are in an open state.
The nature of the occlusion of the chewing teeth with left lateral occlusion: a - balancing and b - working side
It is known that the chewing teeth of the upper jaw have an axis inclination towards the buccal side, and lower teeth - into the lingual. Thus, a transversal occlusal curve is formed connecting the buccal and lingual tubercles of the chewing teeth of one side with the tubercles of the same name on the other side.
In literature transversal occlusal curve occurs under the name of the Wilson curve and has a radius of curvature of 95 mm. As noted above, with lateral movements of the lower jaw, the condylar process on the balancing side moves forward, downward and inward, while changing the plane of inclination of the jaw. In this case, the antagonist teeth are in continuous contact, the opening of the dentition occurs only at the moment of contact of the canines. This type of release is called "canine guidance". If the canines and premolars remain in contact on the working side at the moment of opening the molars, this type of opening is called "canine-premolar guidance". In the manufacture of fixed prostheses, it is necessary to establish what type of opening is typical for a given patient. This can be done by focusing on the opposite side and the height of the canines. If this is not possible, it is necessary to make a prosthesis with canine-premolar guidance. Thus, overloading of the periodontal tissues and articular discs can be avoided. Compliance with the radius of curvature of the transversal occlusal curve will help to avoid the occurrence of supercontacts in the chewing group of teeth during lateral movements of the lower jaw.
The central relationship of the jaws is the starting point of all movements of the lower jaw and is characterized by the uppermost position of the articular heads and the tubercular contact of the posterior teeth.
Opening the mouth (A) from the position of the central ratio (B) and central occlusion (C)
The sliding of the teeth (within 1 mm) from the position of the central relation to the central occlusion is directed forward and upward in the sagittal plane, it is otherwise called "sliding in the center".
The movement of the mandible from the central ratio (A) to the central occlusion (B)
When the teeth are closed in the central occlusion, the palatine tubercles of the upper teeth contact the central fossa or marginal protrusions of the lower molars and premolars of the same name. The buccal tubercles of the lower teeth are in contact with the central fossa or marginal protrusions of the upper molars and premolars of the same name. The buccal tubercles of the lower teeth and the palatine of the upper ones are called "supporting" or "retaining", the lingual tubercles of the lower teeth and the buccal tubercles of the upper teeth are called "guiding" or "protective" (protect the tongue or cheek from biting).
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The functional purpose of the tubercles:
1 - the buccal tubercle of the upper molar - protective;
2 - palatine tubercle of the upper molar - supporting;
3 - the buccal tubercle of the lower molar - protective;
4 - lingual tubercle of the lower molar - protective
When the teeth are closed in the central occlusion, the palatine tubercles of the upper teeth contact the central fossa or marginal protrusions of the lower molars and premolars of the same name. The buccal tubercles of the lower teeth are in contact with the central fossa or marginal protrusions of the upper molars and premolars of the same name. The buccal tubercles of the lower teeth and the palatine of the upper ones are called "supporting" or "retaining", the lingual tubercles of the lower teeth and the buccal tubercles of the upper teeth are called "guiding" or "protective" (protect the tongue or cheek from biting).
Percentage of support and guide cusps
During chewing movements, the lower jaw should slide freely along the occlusal surface of the upper jaw teeth, i.e. the tubercles should glide smoothly along the slopes of the antagonist teeth without disturbing the occlusal relationship. At the same time, they must be in close contact. On the occlusal surface of the first lower molars, the sagittal and transversal movements of the lower jaw are reflected by the location of the longitudinal and transverse fissures, which is called “ occlusal compass". This landmark is very important when modeling the occlusal surface of the teeth.
Occlusal Compass:
a, c - sagittal movements; b, e - transversal movements; d - combined movement
When the lower jaw moves forward, the guide tubercles of the chewing teeth of the upper jaw slide along the central fissure of the lower teeth. With lateral movements, sliding occurs along the fissure separating the posterior cheek and the median buccal tubercle of the lower molar. In the combined movement, sliding occurs along a diagonal fissure dividing the median buccal tubercle. " Occlusal compass»Is observed on all teeth of the lateral group.
An important factor in the biomechanics of the dentition is the height of the masticatory tooth tubercles. The value of the initial articular shift depends on this parameter. The fact is that with lateral movements of the lower jaw, the head on the working side, before starting the rotational movement, shifts outward, and the head on the balancing side shifts inward. This movement is carried out within 0-2 mm.
Initial articular displacement
The more gently sloping the slopes of the tubercles, the greater the initial articular shift. Thus, the free mobility of the dentition relative to each other is determined within the central occlusion. Therefore, when modeling artificial teeth, it is extremely important to observe the parameters of the tubercles and slopes of the slopes of the chewing teeth. Otherwise, there are disorders in the interaction of the elements of the TMJ, articular dysfunction develops.
Summing up, it is important to note that when manufacturing a full-fledged functional prosthesis, it is necessary to take into account five fundamental factors that determine the features of the articulation of the lower jaw:
1) the angle of inclination of the sagittal articular path;
2) the height of the tubercles of the chewing teeth;
3) sagittal occlusal curve;
4) the angle of inclination of the sagittal incisal path;
5) transversal occlusal curve.
In the literature, these factors are known as the "five of Hanau", after the name of the outstanding scientist who established this pattern.
Vertical movement of the lower jaw
correspond to opening and closing the mouth. For opening the mouth and introducing food into the mouth, it is characteristic that at this moment the selected optimal action option is triggered, depending on a visual analysis of the nature of the food and the size of the food lump. So, a sandwich, seeds are placed in a group of incisors, fruits, meat - closer to the canine, nuts - to the premolars.
Thus, when the mouth is opened, there is a spatial displacement of the entire lower jaw (Fig. 33).
Depending on the amplitude of opening the mouth, this or that movement prevails. With a slight opening of the mouth (whispering, quiet speech, drinking), rotation of the head around the transverse axis in the lower part of the joint prevails; with a more significant opening of the mouth (loud speech, biting off food), the sliding of the head and disc along the slope of the articular tubercle down and forward joins the rotational movement. With the maximum opening of the mouth, the articular discs and mandibular heads are set at the tops of the articular tubercles. Further movement of the articular heads is delayed by the tension of the muscular and ligamentous apparatus, and again only rotational or hinge movement remains.
The movement of the articular heads when opening the mouth can be traced by placing fingers in front of the ear tragus or inserting them into the external auditory canal. The mouth opening amplitude is strictly individual. On average, it is 4-5 cm. The dentition of the lower jaw describes a curve when opening the mouth, the center of which lies in the middle of the articular head (Fig. 34). Each tooth also describes a certain curve (Fig. 35).
Sagittal movements of the lower jaw.
The movement of the lower jaw forward is carried out mainly due to the bilateral contraction of the lateral pterygoid muscles and can be divided into two phases: in the first, the disc, together with the head of the lower jaw, slides along the articular surface of the tubercle, and then in the second phase, a hinge movement is added around the transverse axis passing through the heads. This movement is carried out simultaneously in both joints.
The distance that the articular head travels in this case is called the sagittal articular path. This path is characterized by a certain angle, which is formed by the intersection of a line that is a continuation of the sagittal articular path with the occlusal (prosthetic) plane. The latter is understood as a plane passing through the cutting edges of the first incisors of the lower jaw and the distal buccal tubercles of the last molars (Fig. 36). The angle of the sagittal articular path is individual and ranges from 20 to 40 °, but its average value, according to Gizi, is 33 °.
This combined nature of the movement of the lower jaw is found only in humans. The value of the angle depends on the slope, the degree of development of the articular tubercle and the amount of overlap of the upper anterior teeth of the lower anterior ones. With deep overlap, head rotation will prevail, with small overlap - sliding. With a straight bite, the movements will be mainly sliding. Advancement of the lower jaw forward with orthognathic occlusion is possible if the incisors of the lower jaw come out of the overlap, that is, the lower jaw must first descend. This movement is accompanied by the sliding of the lower incisors along the palatal surface of the upper ones until they close directly, that is, before the anterior occlusion. The path taken by the lower incisors is called the sagittal incisal path. When crossing it with occlusive (prosthetic)
the plane forms an angle called the angle of the sagittal incisal path (Fig. 37 and 33). 
It is also strictly individual, but, according to Gizi, it is within 40-50 °. Since during movement the mandibular articular head slides downward and forward, the posterior part of the lower jaw naturally drops downward and forward by the amount of incisal slip. Therefore, when lowering the lower jaw, a distance should form between chewing teethequal to the amount of incisal overlap.
11. Transversal movements of the lower jaw. The concept of the working and balancing sides. The phases of the chewing movements of the lower jaw.
Transversal (lateral) movements of the lower jaw result from unilateral contraction of the lateral pterygoid muscle. When moving to the right, the left lateral pterygoid muscle contracts, when moving to the left, the right one.
In transversal movement of the lower jaw, two sides are distinguished: working and balancing.
Laterotrusion(working movement) - movement of the lower jaw from the position of the central occlusion or the central ratio in the direction of the working side, at which its deviation outwards from the mid-sagittal plane occurs.
Working side (laterotrusion side) - the side in which the movement of the lower jaw is directed from the position of the central occlusion or central relation.
Mediotrusion(non-working movement) - movement of the lower jaw, in which it deviates to the mid-sagittal plane.
Non-working side(balancing, mediotrusive) - the side opposite (contralateral) to the working side when performing working movement.
On the working side, where the movement of the jaw is directed, the chewing antagonist teeth are set with the same tubercles, and on the opposite (balancing) side, with opposite ones. On the working side, the head remains in the fossa and rotates only around its vertical axis. On the balancing side, the head, together with the disc, slides along the surface of the articular tubercle down and forward, as well as inward, forming an angle with the initial direction of the sagittal articular pathway. This angle was first described by Bennett and is called the angle of the transversal articular path (ANGLE OF THE LATERAL JOINT PATH ( bennett's corner), which is 15-20 ° (Fig. 37). It is depicted as a projection of two straight lines onto the Frankfurt horizontal.
Figure: 38. Angle of the transversal articular path (Bennett movement).
Transversal movements are characterized by certain changes in the position of the teeth. If you graphically depict the curves of the movement of the teeth with alternate movement of the lower jaw to the right and to the left, then they intersect at an obtuse angle. The further from the head the tooth is, the greater the angle. The most obtuse angle is formed from the intersection of the curves formed by the movement of the central incisors. This angle is called GOTHIC or ANGLE OF TRANSVERSAL (LATERAL) CUTTING WAY and is equal on average 100 - 110 °. It determines the range of the incisors during lateral movements of the lower jaw (Fig. 39).
The Gothic angle recording is used to determine the central relationship of the jaws and central occlusion.
Fig. 39. Transversal incisal path.
Complete complex movements of the mandible can be illustrated with a diagram showing the movement in space of the midpoint between the central lower incisors. The volumetric image of the trajectory of this point, obtained by U. Posselt by superimposing lateral radiographs of the skull, clearly demonstrates the complexity of the movements of the lower jaw (Fig. 40).
Figure: 40. 3D image of a complex of functional movements
lower jaw according to U. Posselt.
When chewing, the lower jaw performs a cycle of movements, accompanied by the appearance of fast sliding contacts of the teeth of the working side. The maximum chewing forces are developed in the position of the central occlusion. There are four phases of chewing. In the first phase, the jaw drops and moves forward. In the second, the jaw is displaced to the side (lateral movement). In the third phase, the teeth are closed on the working side by the same tubercles, and on the balancing one - by the opposite ones. However, there may be no tooth contact on the balancing side, which depends on the severity of the transversal occlusal curves. In the fourth phase, the teeth return to the central occlusion position (Fig. 41).
Figure: 41. The cycle of chewing movements according to U. Posselt.
The shape of the chewing cycle can be different depending on the degree of overlap and inclination of the anterior teeth, the height of the tubercles of the chewing teeth, etc. In this regard, distinguish between horizontal and vertical forms of the chewing cycle (Fig. 42). The range of movements of the lower jaw required for the implementation of the chewing cycle, as a rule, is less than the range of all possible movements.
a - horizontal form of the chewing cycle; b - vertical form of the chewing cycle.
Figure: 42. Forms of the chewing cycle according to U. Posselt.
Gothic arc... When viewed from above on the movements of the lower jaw in the horizontal plane during its extending right and left lateral movements to the limit, the trajectory of the midpoint of the lower incisors resembles an arrowhead or an arc. The top of this arc corresponds to the position of the central relation. The sides of the arc correspond to the trajectory of rotation of the median point of the lower incisors around the vertical axes of the working articular heads during the right and left lateral movements of the lower jaw to the limit.
The relationship between the sagittal incisal and articular pathways and the nature of the occlusion has been studied by many authors. Bonneville, on the basis of his research, deduced the laws that are the basis for the construction of anatomical arithculators.
Bonneville's triangle- the ratio between the incisor point and the right and left heads of the temporomandibular joint. It is an equilateral triangle with a side length of about 10.5 cm. It is the base for articulators set to medium anatomical parameters.
Considering the movements of the lower jaw carried out by the muscles of the maxillofacial region, three groups of muscle movements can be distinguished:
Conscious movements - moving the lower jaw forward, deliberately opening the mouth;
Reflex movements - mandibular reflex, mouth opening reflex;
Rhythmic movements - chewing, articulation.
Chewing movements are complex and include movements of the jaws, chewing and facial muscles and tongue, soft tissues of the face. Lips, cheeks and tongue control the position of the food bolus in oral cavity and keeping it on the occlusal surface. The following phases of the chewing cycle are distinguished:
1. preparatory phase - the formation and preparation of the food lump for crushing.
2. grinding phase - crushing and grinding the food lump, mixing it with saliva on the working side (laterotrusion).
3. the final formation of the food lump before swallowing - mixing the food lump with saliva.
In all phases of the chewing cycle, the following movements are distinguished: group and working guiding functions, canine guidance.
Working guiding function(teeth-guided lateral movement of the lower jaw from the central occlusion position) - lateral movement of the lower jaw from the central occlusion position with closed teeth is directed by the contacting surfaces of these teeth on the working side. In natural dentition, two types of working guiding function are most often found: the "canine way" and the "group guiding function".
Group guiding function(one-sided protection) - contact of the buccal cusps of molars and premolars in lateral occlusion on the working sides. It occurs in 16.3% of cases.
Canine way- sliding of the apex or the distal-buccal slope of the lower canine of the working side along the palatine slope of the upper canine of the working side, when the muscles move the lower jaw to the working side. This forces the lower jaw to move sideways, forward and open the mouth. During a canine-guided working movement, the central and lateral incisors of the working side can simultaneously be in movable contact with the opposing central and lateral incisors. In a canine-guided working movement, the premolars and molars of the working side open while the lower jaw moves away from the central occlusion position. All teeth on the non-working side open during this movement. The canine pathway provides an anterior guidance component, and the articular pathway constitutes the distal guidance component and allows the teeth to open on the non-working side. The canine way is found in 57%.
Canine protection- contact of canines in lateral occlusion on the working sides.
Front guiding function(incisal path) - when the incisors and canines direct both the forward and working movements of the lower jaw, they constitute the anterior guiding component of its movements.
Group working guide function- the working guiding function of a group of teeth is carried out by all teeth of the working side. The cutting edges of the anterior teeth of the lower jaw slide along the palatal surfaces of the anterior teeth of the upper jaw. The buccal cusps of the lower premolars of the imolar slide along the palatine slopes of the buccal cusps of the upper premolars and molars.
Chewing phases:
1) the phase of gripping and cutting food, which is characterized by the sliding of the cutting edges of the lower frontal teeth along the palatal surface of the upper teeth to their marginal closure and back; in this phase, forward movement of the lower jaw predominates and, therefore, the teeth are set in the anterior occlusion;
2) the phase of crushing food, which is carried out by the vertical movement of the lower jaw and is characterized by the maximum contact of the teeth of both jaws; occlusion of the dentition in this phase is called central and is the initial and final moment of all chewing movements of the lower jaw;
3) the phase of grinding food, which is characterized by alternating movements of the lower jaw to the sides, and when the lower jaw moves in any direction on this side, the tubercles of the chewing teeth of the lower jaw will be in contact with the similar tubercles of the upper (buccal with buccal, palatine with lingual).
When prosthetics of large and complete dentition defects, in the presence of a generalized form of pathological abrasion, it is necessary to create dentition with strictly individual occlusal curvature corresponding to the angle of the sagittal articular path. According to the theory of Gysi and Hanau, multiple contacts between the dentition of the upper and lower jaws in the phase of chewing movements are possible only if they correspond to the slope and the shape of the articular tubercle. Hanau identifies 5 factors of the so-called articulations guint: 1) the slope of the articular path; 2) the depth of the compensation arc; 3) the inclination of the prosthetic plane; 4) the inclination of the upper incisors; 5) the height of the cusps of artificial teeth - which can change. These factors are of great importance to this day. A. Gerber draws attention to the fact that the chewing surface of the erupted permanent teeth is formed gradually, rubbing during operation and acquiring an "articular" shape in order to work in harmony with the jaw joints.
To determine the angle of the sagittal articular pathway, graphical recording of the movement of the lower jaw with the help of the facial arch is traditionally used extraorally. To secure the facial arch on the lower jaw, the doctor mounts a portable plate on the wax roller of the lower bite template. The transfer plate is designed so that two retaining pins protrude from the mouth (Fig. 1). The front bow is attached and fixed on these pins. The doctor determines the patient's lateral articular points (external auditory canals) and fixes the hinge axis. At these fixation points, the writing tips are adjusted (Fig. 2). The registration cards to be plotted are placed between the fixation points and the nibs. During the up and down movement of the lower jaw, the writing tips record the path of movement of the joints. The angle of inclination (deviation between the articular line and the nasal line) is measured using a protractor.
Figure: one. The transfer plate is mounted on the bite template
Figure: 2. Writing nibs are attached to a pivot shaft for graphical writing
However, this method has disadvantages: 1) it is not always possible to achieve reliable fixation of the bite template; 2) amortization of the mucous membrane of the alveolar process often gives a distortion of the true position of the bite template; 3) preliminary definition of intermediate bite is necessary; fixation to two mutually movable substances (the lower jaw and the projection of the articular head of the lower jaw) is not very convenient and does not contribute to the accuracy of the result.
Modification of the facial arch and technique for measuring the angle of the sagittal articular path
L.G. Spiridonov modified the facial arch to determine the angle of the sagittal articular path. His model was tested in practice by V.N. Kozhemyakin and I.N. Losev. It is a springy steel strip, slidingly reinforced in plastic clips (Fig. 3), which allows you to lengthen or shorten the arc, depending on the type of face. Due to its springy properties, the arc is tightly pressed against the face and, thus, is not associated with mobile substances.
Figure: 3. Modified face bow
The angle of the sagittal articular pathway is determined at the examination stage. The arch is oriented on the face with its upper edge along the nasal line (Fig. 4). A panoramic X-ray is then taken. It can be used to study the condition of the teeth, jaw bones and temporomandibular joints. To determine the angle of the sagittal articular path on the roentgenogram, a line is drawn along the articular surface of the articular tubercle of the temporal bone until it intersects with the upper surface of the shadow of the facial arch (a line can also be drawn along the shadow). The resulting angle (this is the angle of the sagittal articular path) is measured using a protractor (Fig. 5).
Figure: 4. The face bow is installed on the face
Figure: five. Determination of the angle of the sagittal articular path on the roentgenogram
The modified method of measurement described above is easy to use, affordable and does not require additional costs for the manufacture of models, a rigid base on the lower jaw with a bite template, installation of a portable plate and registration cards. The method provides maximum information about the condition of the dentition.
Literature
1. Sapozhnikov A.L. Articulation and prosthetics in dentistry. - Kiev: Health, 1984 .-- 94 p.
2. Khatova V.A. Diagnostics and treatment of functional occlusion disorders. - N. Novgorod, 1996 .-- 272 p.
3. Gerber A. // Dt. zahnarztliche Ztschr. —1966. —Bd 21, N1. — S. 28-39.
4. Gerber A. // Dt. Zahnarztliche Ztschr. — 1971. —Bd 26, N2. —S. 119-141.
5. Gysi A. // Hanbuch der Zahnhailkunde. —Bruhn, 1926. —Bd. 3. —S. 167-267.
6. Lehmann G. // Dental labor. - 1982. - V. 11, N 1575. - S. 10.
Modern dentistry. - 2007. - No. 3. - S. 53-54.
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The biomechanics of the TMJ studies the functional connection of the joint with the masticatory muscles and the dentition, which is carried out by the trigeminal nerve system. The temporomandibular joint creates guide planes for the movement of the mandible. The stable vertical and transversal position of the lower jaw is provided by occlusal contacts of the chewing teeth, which prevent the lower jaw from displacement, thus providing “occlusal protection” of the TMJ.
TMJ refers to joints of the "muscle type". The position of the lower jaw, as if suspended in a cradle of muscles and ligaments, depends on the coordinated function of the masticatory muscles.
Correlation of the activity of a large number of different muscles with various functions and ensuring complete synchronization of movements of both joints is carried out by complex constant reflex activity. The source of reflex impulses are the nerve sensory endings located in the periodontium, muscles, tendons, capsule and ligaments of the joint. Sensory information from the dentition, joint, periodontium, oral mucosa enter the cortical centers, and also through the sensitive nucleus of the trigeminal nerve into the motor nucleus, regulating the tone and degree of contraction of the masticatory muscles.
If, for example, there is a premature contact when teeth are closed, then the receptors of the periodontium of these teeth are irritated, the movements of the lower jaw change. In this case, the closing of the jaws occurs in such a way that this premature contact (supercontact) is excluded.
Direction of traction of the muscles attaching to the lower jaw:
- 1.temporal muscle;
- 2. external pterygoid muscle;
- 3. the actual chewing muscle;
- 4. internal pterygoid muscle;
- 5.maxillary-hyoid muscle;
- 6. digastric muscle;
The relationship of the main elements of the dento-facial system (periodontium, muscles, temporomandibular joint) with each other and with the central nervous system
Occlusal contacts of the dentition, stresses in the periodontium, arising from chewing, through the central nervous system program the work of the chewing muscles and TMJ. The main chewing load is concentrated in the area of \u200b\u200bocclusal working contacts, where the proprioceptive sensitivity of the periodontium regulates the degree of chewing pressure on the teeth. Muscle strength is directed distally, therefore, the more distal the food is located, the more favorable the work of the muscles and the greater the chewing pressure. Normally, the temporomandibular joint on both sides performs a uniform support function with a slight load in the forward and upward direction from the articular heads through the disc to the posterior slope of the articular tubercle.
The most important feature of the TMJ function is that, when chewing, the articular heads move in the vertical, sagittal and transversal planes.
The path of movement of the lower jaw in the sagittal plane and can be studied by the displacement of the lower point between the central lower incisors when opening and closing the mouth, as well as when the lower jaw is displaced from the central occlusion to the central ratio (sliding in the center).
The scheme of movements of the lower jaw (midpoint between the central incisors) in the sagittal plane (no Posselt):
1 - central ratio (posterior contact position - occlusal analogue of the central ratio); 2 - central, occlusion; 3 - anterior occlusion when placing the incisors "butt"; 3 - 4 - extreme anterior movement from anterior occlusion; 5 - maximum opening of the mouth - 5 cm; 1 - 6 - the arc of a purely articulated movement of the lower jaw from the central ratio when opening the mouth - by 2 cm; 6 - 5 - the movement of the maximum opening of the mouth with a combined rotational-translational displacement of the articular head; 0 - temporomandibular joint axis.
At the beginning of opening the mouth, a rotational movement of the heads occurs from the central ratio, while the midpoint of the central lower incisors describes an arc with a length of about 20 mm. Then the translational movements of the heads (together with the discs) begin forward and downward along the posterior slope of the articular tubercles until the articular heads are established opposite the tops of the articular tubercles. In this case, the midpoint of the lower incisors describes an arc up to 50 mm long. Further exorbitant opening of the mouth can also occur with a slight hinge movement of the articular heads, but this is extremely undesirable, since there is a risk of stretching the temporomandibular joint apparatus, dislocation of the head and disc. These pathological phenomena occur when the sequence of the hinge and translational movement of the articular heads is disrupted at the beginning of opening the mouth, for example, in the case when the opening of the mouth begins not with rotational, but with translational movements of the articular heads, which is often associated with hyperactivity of the external pterygoid muscles (for example, with the loss of lateral teeth).
When the mouth is closed, the movements normally occur in the reverse order: the articular heads move back and up to the base of the slopes of the articular tubercles. Closing of the mouth is completed due to the hinge movements of the articular heads until occlusal contacts appear. After reaching the initial contact of the chewing teeth (central ratio), the articular heads move forward and upward into the central occlusion. At the same time, they move 1-2 mm along the mid-sagittal plane, without lateral displacements with bilateral simultaneous contact of the slopes of the cusps of the lateral teeth. One-sided contact with "sliding in the center" is considered to be premature (occlusal interference), capable of deflecting the lower jaw when closing the mouth to the side.
The extension of the lower jaw forward with closed teeth from the central occlusion to the anterior one is carried out by contraction of the lateral pterygoid muscles on both sides. This movement is guided by the incisors. If the lower incisors in the central occlusion are in contact with the palatal surfaces of the upper incisors, the forward extension of the lower jaw from this position causes de-occlusion of the posterior teeth. The path that the lower incisors pass along the palatal surfaces of the upper incisors is the sagittal incisal path, and the angle between this path and the occlusal plane is the angle of the sagittal articular path (~ 60 °). With this movement, the articular heads move forward and downward along the slopes of the articular tubercles, making a sagittal articular path, and the angle between this path and the occlusal plane is called the angle of the sagittal articular path (~ 30 °). These angles and their individual determination for each patient are used to adjust the articulator. The occlusal plane runs from the median incisal point to the distal-buccal cusps of the second lower molars with intact dentition. In the absence, they are guided by the Camper horizontal, which is parallel to the occlusal plane and runs from the middle of the ear tragus to the outer edge of the wing of the nose. How to explain why the sagittal incisal angle is 2 times the articular sagittal angle?
If the angles are equal, then during the transition of the lower jaw from the central occlusion to the anterior occlusion, the articular head performs only sliding translational movements forward and downward along the slope of the articular tubercle while maintaining the contact of the lateral teeth. This is rarely the case.
Influence of equality 1 and difference 2 sagittal and incisal angles on the nature of movement of the articular heads and occlusal contacts of lateral teeth in the anterior occlusion:
- 1.with equal angles, translational movements in the joint are observed, contacts of the lateral teeth in the anterior occlusion (rarely found in the norm);
- 2. at different angles - combined movements - rotational and translational, there are no contacts of the lateral teeth in the anterior occlusion (often found in the norm). This shows the importance of the preservation and restoration of the sagittal incisal path for the TMJ in the manufacture of prostheses in the anterior region;
AND.sagittal articular path;
B.sagittal incisal path;
IN.the occlusal plane (between the midpoint of the central lower incisors and the distal-buccal cusps of the lower second molars);
G.Camper's horizontal.
In most cases, there is no equality of the above angles. Therefore, with the anterior occlusal movement of the lower jaw, combined translational-rotational movements of the articular heads occur in the joint. Along with the translational movements in the upper part of the joint, rotational (hinge) movements occur in the lower part of the joint. In this case, the lateral teeth are dissociated - a normal phenomenon with intact dentition.
When setting teeth with complete removable dentures, to create stabilization of the dentures during the chewing function, during the transition from central to anterior occlusion, it is necessary to create contact between the posterior teeth. This is achieved by properly positioning the teeth over the sphere in the articulator.
The path of movement of the lower jaw in the horizontal plane (movement forward, backward to the sides) can be represented as a "gothic angle".
Scheme of movements of the lower jaw in the horizontal plane (recording of the Gothic angle):
and.the top of the Gothic angle corresponds to the central ratio of the jaws (with tuberous contacts of the lateral teeth);
b.the point of central occlusion is located anteriorly from the apex of the Gothic angle by 0.5-1.5 mm (with fissure-tuberous contacts of the lateral teeth);
- 1.central occlusion;
- 2. the central ratio of the jaws;
- 3. movement of the lower jaw forward;
- 4., 5. lateral movements of the lower jaw.
It can be recorded using the intraoral method with a rigid pin of a functiograph (Khvatova V.A., 1993,1996). The essence of this method is that a pin is installed on the removable maxillary plate along the mid-sagittal plane, and a horizontal plate is placed on the mandibular plate. The sliding of the pin on the plate is recorded when the lower jaw moves backward, forward, right and left, and a Gothic angle is obtained. The apex of the Gothic angle corresponding to the position of the central occlusion is located 0.5-1.5 mm anterior to that corresponding to the central ratio of the jaws.
During lateral movement of the lower jaw from the central occlusion position, the articular head on the displacement side (laterotrusion side) rotates around its vertical axis in the corresponding glenoid fossa and also performs a lateral movement, which is called Bennett's movement. This lateral movement of the working articular head averages 1 mm and may have a small anterior or posterior component. The articular head on the opposite side (mediotrusion side) moves downward, forward and inward. The angle between this by moving the head and the sagittal plane is Bennett's angle (15-20 °). The greater the Bennett angle, the greater the amplitude of the lateral displacement of the articular head of the balancing side.
Since the glenoid fossa does not have a regular spherical shape, and there is free space between the inner pole of the head and the inner wall of the fossa, at the beginning of the movement of the articular head of the balancing side, transversal movement is possible, which is referred to as "initial (direct) lateral movement". These features of the lateral displacement of the articular head affect the nature of the occlusal contacts of the teeth of the working and balancing sides.
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