CHEWING (masticatio) — the initial phase of digestion consisting in crushing, grinding of food and its hashing with saliva under the influence of enzymes a cut occurs so-called oral digestion. I. P. Pavlov established reflex influence of process. on secretion of sialadens, secretory and motor functions of a stomach; process. also positively influences blood circulation and the general metabolism in an organism
. it is carried out by teeth due to reduction of masseters, with the participation of muscles of lips, cheeks and language. Masseters (see) provide the movements of a mandible; lips, cheeks and language hold food, move it to oral cavities, create a food lump.
At hit of food in an oral cavity there is an irritation of tactile, temperature and flavoring receptors of a mucous membrane from which nervous impulses are carried out on fibers of a trifacial to a myelencephalon where the center Zh is located. From there effector impulses go to the masseters providing various reflex movements of a mandible.
Food is bitten off with foreteeth, side teeth are opened at this time. Further food is passed by language to a chewing surface of premolar tooths and painters (fig. 1). At the same time medial rollers of buccal muscles (bunches of muscle fibers of big buccal muscles) nestle on teeth, forming so-called buccal pockets. Then chewing of food begins teeth. The crushed food gets to buccal pockets from where again is returned to chewing surfaces of teeth reduction of medial rollers of buccal muscles. This process can happen on the right or left side of dentitions or on both parties. The volume and degree of a razmelcheniye of food is defined by the receptors which are available in a mucous membrane. The crushed particles gather in a food lump, larger move to chewing surfaces of teeth again. Along with a razmelcheniye of food there is a treatment its saliva; mucin of saliva promotes formation of a slippery food lump which gets on a back of the tongue to the fillet formed here. At this time there is a reflex of swallowing; in process. there comes the pause, the food lump nestles language on a hard palate and forces the way for palatal handles then reduction of muscles of a throat it moves to a gullet (see. Swallowing ).
In time. the person has horizontal and vertical movements of a mandible. They can be presented in the form of the following one after another of trajectories with various direction. Giz (A. Gysi, 1908) displayed recurrence of chewing movements of a mandible in the form of the scheme (fig. 2). A starting point of these movements is the provision of the central occlusion; then three phases follow: the mandible falls and displaced forward and aside, further the jaw rises and hillocks of a chewing surface of side teeth on the service side come to contact with the hillocks of teeth antagonists of the same name; after that the jaw moves horizontally and teeth are again closed in the central occlusion (see. Articulation of teeth ).
The analysis of chewing movements of a mandible is made by a graphical method. Depending on a way of receiving record are called differently: written down by means of a mastikatsiograf (according to I. S. Rubinov, fig. 3) — mastikatsiogrammam, on an oscillograph — oscillograms. Records of process. consist of the wavy curve (fig. 4) following one after another. All complex of movements of a mandible connected with chewing of one portion of food carries the name of the chewing period and develops of five consecutive phases: 1 — rest; 2 — introductions of food to a mouth; 3 — an approximate phase; 4 — the main phase of chewing; 5 — phases of formation of a food lump and swallowing; except movements of a mandible, on a mastikatsiogramma or the oscillogram time of the chewing period is noted. Main phase Zh. consists of so-called chewing waves; each wave has the ascending part (curve A B raising — lowering of a mandible) and descending (descent of curve BV — raising of a jaw). The lower loops between waves are called loops of a smykaniye of dentitions. Each wave is characterized by height, size and a form of a corner between the ascending and descending parts. Waves can follow one after another rhythmically or with various intervals. The size and rhythm of chewing waves, a form of loops of a smykaniye, duration of separate phases, time of the chewing period depend on the size of a piece of food, its consistence, a type of a bite, the number of occlusal contacts of natural or false teeth, extent of fixing of a prosthesis, a condition of masseters and a temporal and mandibular joint, etc.
Record of movements of a mandible can be combined with an electromyography of masseters, such record is called an elektromiomastikatsiografiya. For studying of chewing movements of a mandible use also method X-ray cinematographies (see). Rentgenokimogramma formed a basis for drawing of the trajectories forming certain cycles. All cycles have the general initial point corresponding to the central occlusion, and their trajectories consist of vertical, side and perednezadny components.
Record of chewing movements of a mandible helps to study a condition of dentoalveolar system normal and at various deviations, such as anomalies bite (see), mobility of teeth, their increased erasability and also to estimate efficiency of orthopedic treatment, in particular a denture after loss of teeth.
Function Zh. changes with age that affects the nature of chewing movements of a mandible. After eruption of the first milk teeth these movements at the child are still poorly expressed, arrhythmic and often alternate with the sucking movements presented on mastikatsiogramma by straight lines. With increase in number of milk teeth the chewing movements of a mandible become more differentiated, amplitude of chewing waves increases, and they follow one after another with equal intervals. During change of milk painters chewing waves lose rhythm, loops of a smykaniye are located at various levels, the additional waves displaying the lateral grinding motions of a mandible disappear. After change of all milk teeth and formation of a constant bite that corresponds to age of 12 — 13 years, at intact dentitions and lack of any deviations of a mastikatsiogramma represent the consecutive alternation of all elements of chewing waves reflecting the normal chewing movements of a mandible. At advanced age amplitude of chewing waves decreases, they can become arrhythmic that is connected with weakening of a tone of chewing muscles and various disturbances in a condition of dentoalveolar system, and also with a design and quality of dentures, to-rymi elderly people use.
Dysfunction of chewing
the Most frequent causes of infringement of function Zh. anomalies of a bite, loss of teeth owing to caries and its complications or diseases of a parodont, secondary deformations of dentitions are. At intact dentitions and the correct bite pressure at. extends to tooth arches of both jaws. At defects of dentitions the same chewing pressure falls on smaller number of teeth, which test at the same time a functional overload that injures fabrics of a parodont and leads to deformations of dentitions and a bite: to an inclination of teeth towards defect, to change of level of an arrangement of teeth, decrease in a bite, osteanabrosis of an alveolar shoot, etc.
However B. N. Bynin, I. G. Lukomsky and many other authors spoke against substitution of small, especially unilateral defects of dentitions, meaning considerable compensatory opportunities of the chewing device.
So, according to B. N. Bynin and A. I. Betelman, using one party of dentitions, it is possible to provide full chewing of food since function Zh. undertake the remained teeth. E.g., loss of premolar tooths on one party does not lead to noticeable decrease in efficiency., and at loss of painters efficiency. goes down more considerably. After loss of all chewing teeth of people it is forced to chew foreteeth which can take only relative part in a razmelcheniya of food. In the beginning compensation of function Zh. it is reached by lengthening of time. Further in the absence of many teeth or after their total loss the use only of the crushed or liquid food is possible, at the same time time of its stay in an oral cavity is sharply reduced that breaks oral digestion. It negatively influences secretory and motive functions of a stomach: food it is long is late in a stomach therefore can arise hron, gastritis and other diseases of bodies of a digestive tract.
Above-named and some other authors believed that compensation of dysfunction. becomes difficult after decrease in efficiency of chewing (chewing power) by 40 — 50%. For determination of chewing power methods which share on static and dynamic are offered. Special tables in which for each tooth with a healthy parodont the coefficient defining extent of its participation in process is established concern to the first. depending on the size of its chewing surface and some other indicators.
Among domestic scientists such table was offered for the first time by N. I. Agapov (1927); the author takes the chewing power of intact dentitions of a top and bottom jaw (28 teeth) for 100%. Proceeding from it, a half of dentition on each jaw makes 25%; the upper side cutter is taken for unit of chewing power (see the table). During the determination of chewing power of dentitions across Agapov loss not only the absent tooth, but also his antagonist is considered.
Table. Chewing coefficients of teeth according to N. I. Agapov (1927)
Agapov's method idle time, it was applied in the past in dentoprosthetic offices at primary survey of patients to definition of indications to prosthetics. Continue to use this table at medical survey of the big contingents (e.g., youths of premilitary age and called up for military service) for the purpose of bystry selection of persons in need in a denture.
I. M. Oksman (1956) altered N. I. Agapov's table a little; at assessment of chewing power of the remained teeth, according to I. M. Oksman, also the condition of a parodont is considered. At patol, mobility of the first degree the value of teeth decreases on 1/4, at mobility of the second degree — on 1/2, and teeth with mobility of the third degree or with the destroyed crowns, not subject to treatment and sealing, are considered as absent. Besides, the eighth teeth (wisdom teeth) are considered: upper — as three units, lower — as four units.
V. Yu. Kurlyandsky (1953) suggested to write down dental health and their basic fabrics in the so-called odontoparodontogramma made on the basis of data gnatodinamometriya (see); at the same time the chewing power of teeth expressed in units is defined depending on degree of an atrophy of their holes (see. Parodontogramma ).
More precisely chewing power is defined by functional methods (so-called chewing tests). For the first time such method was described by Hristiansen (E. Christiansen) in 1923, then it is modified by many authors. The essence of a method is that investigated suggest to chew kernels of nut or almonds of the standard size or weight at a certain number of chewing movements or during certain time. The chewed weight is dried up on the water bath and sifted through a sieve with openings to dia. 2,4 mm. Insufficiently chewed particles which remained on a sieve weigh and calculate loss of efficiency. as a percentage; e.g., if allow to chew 5 g of nut, and the sieve residue is equal to 2 g, then 5: 2 = 100: x; x = 2*100/5 = 40, i.e. loss of efficiency. it is equal to 40%.
Functional methods of definition of a condition of dentoalveolar system and efficiency. (chewing tests, mastikatsiografiya, miomastikatsiografiya, etc.) are evident and objective. However functional trials are labor-consuming, and absence in stomatol, policlinics of offices of functional diagnosis where they shall be carried out, complicates implementation of these methods in broad practice; use them generally during the performance of scientific works and in educational process.
Dysfunctions., caused by lack of teeth, are eliminated by prosthetics. The small defects of dentitions limited to natural teeth are usually replaced with fixed bridge-like prostheses, more extensive — leaning (byugelny) or removable lamellar (see. Dentures ). Efficiency of prosthetics can be checked by chewing tests or the above described graphical methods. Studying mastikatsiogramm showed that fixing of a prosthesis and emergence in this regard of multiple occlusal contacts causes disturbance of a rhythm of chewing movements of a mandible in the beginning, and then in process of adaptation to a prosthesis there is their normalization. Prosthetics of toothless jaws allows to recover efficiency. substantially, and it reaches a maximum by the end of the first year of use of prostheses and keeps at this level on average up to 3 years; further degree of a razmelcheniye of food can remain sufficient due to lengthening of time.
Bibliography: Gavrilov E. I. and N. I Karpenko. Record of chewing movements of a mandible (oscillography), Stomatology, No. 5, page 69, 1962, bibliogr.; Kevesh L. E. and Kurlyand B. of X. A X-ray cinema research of kinematics of a mandible in the course of the act of chewing, in the same place, No. 4, page 47, 1968; Kostur B. K. Functional features of the chewing device of children and teenagers, L., 1972, bibliogr.; I. S. Fiziologiya's rubies and pathophysiology of chewing and swallowing, L., 1958, bibliogr.
E. I. Gavrilov.