Function of the masticatory apparatus is changing states of chewing muscles, changing relationships of the elements of the temporomandibular joint and the changing relationships between the dental series. In describing the structural features of biomechanical masticatory system made all the information set out on separate functional phases. Although at the time the function is strictly isolated phases are observed. Direct processing of food in the mouth is done by a complex set of changing relationships between the elements of the temporomandibular joint, dental series of upper and lower jaw. This is achieved by movement of the lower jaw. Due to the movement of the lower jaw in the vertical and sagittal planes of the front teeth of both planes is captured a piece of food, the movement in the vertical and horizontal planes in finding food between teeth chewing produce crushing and grinding food. Muscle contractions of tongue and cheeks provided meal service in the space between the dental series. Chewing can take place normally only when the teeth of the lower jaw with her movements will be in contact with the corresponding teeth of the upper jaw. Therefore, chewing movements are determined not only by the features of the functional mechanism of the joint, but also the nature of the relationship of the teeth in various occlusions. Chewing movements of the lower jaw, like the movement, depending on where in the plane they happen to fall into sagittal, transversal and vertical.
The main components of the sagittal movements are:
1) slip joint drive with the articular head on the slope of the articular tubercle;
2) sliding lower front teeth on the upper surface and establishing them in the closing of the boundary;
3) sliding posterior mandibular teeth cusps medial facet of the antagonists and the establishment in the same contact, the buccal cusp of the lower teeth interlock with the buccal cusp of the upper teeth, and palatine - to palatal.
Thus, in the sagittal movement is moving in two joints - joints and dental. The path traversed articular head (with discs) called sagittal articulate way. It is characterized by an angle which is formed by the intersection of the plane with the slope of the articular tubercle of the occlusal plane, dubbed the sagittal angle of joint path. Occlusal plane is a plane drawn through the hills of the lower third molars and buccal cusp of the lower first molars. Sagittal angle joint path is strictly individual and, Gysi, averages 33-35 degrees. Path traversed by the incisors of the lower jaw on the palatal surfaces of the upper front teeth in the lower jaw forward the nomination, called the sagittal burin way. The slope of the upper front teeth is determined by the angle that is formed by the intersection of the plane with the inclination of the occlusal plane. He, too, is strictly individual, but it defines Gysi on average 40-50 degrees.
When transversal movements of the lower jaw movement occurs in the temporal and dental articulation, different on the two sides. Transversal motion are obtained by reducing the external pterygoid muscles on one side, when the head of the lower jaw on this side makes a whole not just the usual way down and forward, but also deviates somewhat inward, forming an angle with the original direction. This angle was first described and named by Bennett in his honor, on average, it is equal to 15-17 degrees. On the other side of the head is still in the hole, making a rotational movement around the vertical axis sovey. For example, if the lower jaw is moved to the right, on the left side of the head is moved down and forward, and inside, on the right side of the head is left in place, rotating around a vertical axis. The lower jaw moves in the opposite direction, balancing the party moves down and forward, and work - out. The same path followed by the teeth, that is, the curves move teeth on the working side are preferred transverse direction, and the hills on this side of the same name are in contact with the antagonists. The balancing of the teeth move forward and inward and become a bucco-palatine closure. When trasverzal movement takes place alternately moving the lower jaw in one direction and then the other side. If you draw the graph curves of tooth movement under these conditions, then they intersect to form obtuse angles. The farther away from the joint head is a tooth, the stupid angle. Most obtuse angle is obtained from the intersection formed the movement of the central incisors, and he is 100-110 degrees and defines the scope of incisors in sideways. This angle is known in the literature as the Gothic or transversal angle incisive way. Noting that the articular head of the contracting muscles on the side makes a lateral movement to form a fairly tight angle - 15-17 degrees, and that at this time the central incisors of the lower jaw make way, the angle of which is 100-110 degrees, establish that any other point located on a particular tooth on the side of the contracting muscles, makes moving with the angle more than 15-17 and less than 100-110 degrees.
Sagittal and transversal occlusal curves F. Spee (1890) first described the sagittal occlusal curve in posterior area on the lower dental arch. By Spee is morphologically expressed by the fact that the chewing surface of the teeth from premolar to the last molar forms sagittal concave curve. The deepest place in the curve represents the chewing surface of the first molar. The upper set of teeth in the area of the molars is also the sagittal curve, but not concave and convex, concave bottom that follows the curve. Spee says that this curve is a part of a circle with the center in the orbit. The continuation of this arc is along the front edge of the articular head. According to Monson (1918) sagittal occlusal curve is part of the sphere of which the center is located in the cranial cavity to "Krista Ghali." Medio-lateral curvature of the slope of the occlusal plane is called the curve of Wilson and transversal compensation curve. These distortions are a function of the degree of inclination of the lower back teeth in the side of the language and the back of the upper teeth to the side cheeks. Supporters of the compensation theory (Gysi, Schroeder) associated with the development of the sagittal curve anteroposterior movement of the lower jaw, and transversal compensatory curve - with lateral movements. They represent a compensation mechanism: to the lower jaw forward is always accompanied by its lowering and between the lateral teeth of the upper and lower jaw should see the light. However, this gap is compensated by the presence of the sagittal occlusal curve. The fact is that due to the curve three crowns of the lower molars are tilted forward, and the upper jaw rejected some years back. Thus, in the lower jaw and distal cusps YII YIII teeth are above the medial cusps and the maxillary medial cusps of the molars are lower than the distal. At movement of the mandible distal cusp of the lower teeth move forward and set against the anterior cusp of the upper molars and teeth, due to the difference in the level of hillocks on the upper and lower jaws are in contact with each other. Lower posterior crowns tilted medially, and the crown of the upper posterior teeth - outward. Therefore, in the lower jaw are the buccal cusps and the maxillary palatal cusps are lower. In sideways mandibular buccal cusps lower posterior teeth are set against the upper teeth and palate, due to different levels of hillocks, the teeth in contact with each other, offset between the molars.
Thus, all the supporters of the compensatory theory links the development of the sagittal curve anteroposterior movement, education transversal curve - with lateral movements, and these movements, in turn, depend on the steepness of the slope of the articular way. It should also be noted that the shape of the occlusal curve depends on two anatomical features: degree of concavity and posterior height of hillocks. Compensatory effect of the same at the lesser curvature of the occlusal surfaces with high hills or low hills and pronounced curves. Thus, when there are overlapping front teeth to eliminate gaps between the molars to the presence of high mounds or pronounced compensatory curves. Due compensation curve is, according to proponents of the theory of compensatory and multiple contact, chewing pressure is evenly distributed, resulting in increased activity of the masticatory apparatus, and dental apparatus lasts longer. Such a perfect bite, in which there are multiple contacts with various occlusions, called by different authors in different ways: some call it a balancing bite, other - functional occlusion, and others - compensated bite. In some cases, compensation curve provides for the nomination of the lower jaw forward contacts dentition only three points, one of which is located in the front, and two - on hills distal second or third molars.
This phenomenon was first described and named Bonneville trehpunktnogo contact Bonneville (subcompensated bite). Save contacts to individual teeth depends on the severity of their mounds, which, as already mentioned, should be regarded as a compensation mechanism in the physiology of movement. In the absence of compensatory curve and expressed posterior tubercles, of course, in the nomination of the lower jaw forward, is breaking the back teeth (decompensated bite).It turns gap wedge with a wide base posteriorly, the width of which depends on the size of the sagittal joint angles and incisive way. The greater the angle, the wider the base of the gap and vice versa. This gap is the deviation of the sagittal jaw movements from the physiological norm, overloading the front teeth while chewing. Thus, Bonneville and his supporters celebrate multiple and 3-points contact as a cardinal sign of physiological articulation dentition. A. J. Katz believed that the compensation theory is not justified because the sagittal occlusal curve is present in animals, in particular, herbivores have no articular tubercle and no rear intended movements of the lower jaw. He found also on the basis of clinical studies, in most cases, the sagittal and transversal movements have contact only the front teeth, and not in the posterior part, and the more rare multiple contact. In his view, the formation of the sagittal curve associated with the installation of the teeth of the upper and lower jaw tooth stable ranks. The functional features of the structure of dentition and jaws formed in physiological development as a result of adaptation to environmental conditions, in particular, to the nature of the food.