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Russian Journal of Biomechanics
MASTICATION AS STIMULUS OF GROWTH, DEVELOPMENT AND FORMATION OF THE DENTOFACIAL SYSTEM
E.Y. Simanovskaya*, M.Ph. Bolotova*, M.Y. Nyashin**
* Perm State Medical Academy, 39, Kuybishev Street, 614600, Perm, Russia
** Perm State Technical University, 29a, Komsomolsky Prospect, 614600, Perm, Russia, e-mail: [email protected]
Abstract. In this paper, the influence of mastication on functioning of the dentofacial system is analyzed. Moreover, biomechanical relationship between functions of two frame units, namely, the osteomuscular unit in the region of a temporomandibular joint and the intermaxillary unit formed by the dental arches of the maxilla and the mandible as well as interdependence between their structure and functions are considered.
Key words: mastication, dentofacial system, tooth, temporomandibular joint, jawbone
Modern natural science has many evidences that a human being is a result of a long evolution. He bears both related similarities to animals and specific structural elements which developed in consequence of his adaptable activity.
Processes of transformation of the human organism in response to environmental changes are illustrated most clearly by the example of phylogenetic changes in anatomy of the cerebral and visceral craniua and the masticatory system (Figs. 1, 2). For example, with ascent from a fossil lemur to a human being gradual shortening of the jawbones, infraplacement of the facial bones, antedisplacement of the chin, development of the temporomandibular joints may be mentioned (Fig. 2).
As early as 1862, Folkman stated that bone tissue growth is caused by pressure. Wolf [5] pointed to the fact that bone structure varies with mechanical load. In 1919 lores suggested that pressure is the sole physiologic stimulus of bone growth. As for the maxillofacial system, Dovgyalo [7, 8] wrote that the structure of the face bones is dictated by the state of the dental arches.
Among the numerous functions performing by the masticatory apparatus of a human being, mastication plays a prominent part. Mechanical load arising during mastication may be considered as stimulus which generates movements at cell, tissue and organ levels and thus facilitates growth and development of the all masticatory apparatus. Consequently, forces developed by the masticatory muscles, occlusal forces are essential for facial skeleton architectonics.
Both literature data and our clinical observations make it possible to conclude that different motions during mastication are governed by specific laws, show succession and sequence, and functionally interconnect.
It is well known that teeth are implicated in mastication. Apart from these unique organs, there are adapted structures which act as units, locks, valves and provide food capture and holding, its mechanical and chemical treatment, formation of a food lump, movement of a
Fig. 1. Progressive mandible increase which contributed to development of formation of its joint with the maxilla: (a) a primitive bestial reptile (Scymnognathus); (b) a progressive primitive bestial reptile (Ihtidopsis), (c) a primitive mammal (Thylacinus cynocephalus) [6].
Fig. 2. Skulls of primates: (a) a fossil lemur; (b) a marmoset; (c) a chimpanzee; (d) a human being [6].
food lump from the oral cavity to the throat and then to the esophagus, take an active part in voice and speech formations, respiration, swallowing, facial expression, etc. [3-4].
Let us consider the points on biomechanical interaction of functions of two frame units, namely, the osteomuscular unit in the region of a temporomandibular joint and the intermaxillary unit formed by the dental arches of the maxilla and the mandible as well as interdependence between their structure and functions.
When observed in an age aspect, it is worthy of note that the mandible occupies the mesial position in the 3rd month of the intrauterine development and the distal position in the 5th or 6th month, the latter being kept during six months after the birth [11].
As Napadov [11] stated, a newborn produces first biomechanical stimulations of the face bones by reflex contractions of masticatory muscles, with the result that powerful stimulus of their growth acts.
With the advent of contact between deciduous incisors, a more powerful biomechanical factor appears; it is masticatory pressure increasing as occlusion forms. Occlusion formation is completed by 14-16 years, the maxilla's arch having a semielliptical shape, the mandible's arch having a parabolic shape.
a)
b)
c)
d)
e)
Fig. 3. Age changes of mandible of (a) a new-born child; (b) a three-year child; (c) a seven-year child; (d) a eighteen-year person; (e) thirty-year person [6].
Katz [9, 10] studied mandible architectonics and concluded that bone material is distributed according to masticatory load. The latter has a pronounced effect on jawbones growth, their geometry, in particular the angle of the newborn's mandible is obtuse, that of the grown person's mandible is near-right. Furthermore, a newborn has a barely perceptible tuberculum articulare, and hence has a near-flat mandibular fossa. Tuberculum articulare is evident in the 7th or 8th month children and is more conspicuous by the 7th or 8th year, i.e. by the time of secondary dentition.
It might be well to point out that the depth of the mandibular fossa is related directly to its height and inclination to its posterior surface. The newborn's mandibular fossa is near-flat due to as yet absence of teeth, and the old person's mandibular fossa is frequently also near-flat because of its atrophy as a result of teeth loss and so mechanical load reduction.
Normal occlusion is created by clenched jawbones, when the cutting edge of a lower incisor is against the palatal surface of an upper incisor and the crown tubercles of a masticatory tooth contact with corresponded crown sulci of the antagonists.
From the known information it may be deduced that the mandibular fossa's height is dictated by the age and occlusion. This fact confirms the existence of not only an intimate connection between growth, development, formation of the osteomuscular and intermaxillary units, but also their functional interrelationship throughout the whole human lifetime (Fig. 3).
The presence of genetic, anatomic and functional correlations between these units, their interaction during mastication permits the use of approach in which mastication force as
an integral characteristic of general condition of the masticatory apparatus is measured. The obtained data may be employed to estimate results of oral cavity sanation, treatment of parodontal deseases, traumatic injures of teeth and jawbones, orthodontic treatment, reparative operations in the face and jawbones regions, prosthetics.
The described interrelationship between the aforementioned units enables one to biomechanically investigate them, their interplay. The behaviour of the intermaxillary and dentoalveolar units under load was analyzed in the literature (see, for example, [1, 2, 12]).
At the present time a number of experiments is planned to thorough study of the above osteomuscular unit. Particular attention must be given to the temporomandibular joint disc which provides congruence and enables the mandible to move in different directions. It should be stressed that amplitudes of relative mandible movements are vastly greater than those of other bones movements. In addition, the bone lamina of the mandibular fossa is very thin, hence the temporomandibular joint disc assumes great importance as shock absorber, otherwise the mandible head might injure the bone lamina and collapse into the intracranial cavity.
Experimental study of the temporomandibular joint and especially its disc will provide insight into processes occurring in the osteomuscular unit and influence of mechanical load on its structure. A knowledge of the anatomy and morphology of the temporomandibular joint tissues will allow building of a correct biomechanical model of its functioning and its interrelationship with the other units, in particular with the intermaxillary unit. As a result new qualitative and quantitative results useful for both theory and practice may be obtained.
Acknowledgements
The authors acknowledge financial support from the INTAS (No 97-32158).
References
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ФУНКЦИЯ ЖЕВАНИЯ КАК СТИМУЛЯТОР ПРОЦЕССОВ РОСТА, РАЗВИТИЯ И ФОРМООБРАЗОВАНИЯ ЗУБОЧЕЛЮСТНО-ЛИЦЕВОЙ
ОБЛАСТИ
Е.Ю. Симановская, М.Ф. Болотова, М.Ю. Няшин (Пермь, Россия)
Процесс преобразований человеческого организма под влиянием изменений условий жизни, эволюции животного мира может быть проиллюстрирован на примере филогенетических преобразований и изменений архитектоники мозгового, лицевого черепа и жевательного аппарата.
Среди выполняемых жевательным аппаратом современного человека многочисленных функций ведущую роль играет жевание - двигательный акт, основанный на безусловных и условных пищевых рефлексах.
Силовая нагрузка, возникающая при жевании, может рассматриваться как стимул, генерирующий движения на клеточном, тканевом и органном уровнях и, таким образом, рост и развитие всей системы.
Следовательно, напряжение жевательных мышц, жевательное давление становятся важными факторами, влияющими на формообразование и архитектуру лицевого скелета.
Обращает на себя особое внимание, что в жевательном аппарате, помимо таких уникальных органов как зубы, имеются многочисленные приспособительные структуры, функционирующие по принципу блоков, затворов, клапанов. Можно выделить два основных костно-мышечных блока, обеспечивающих механическую переработку пищи, создающих каркасность и трансформирующих нагрузку, возникающую в процессе жевания: задний костно-суставной блок в области височно-нижнечелюстных сочленений и передний многозвеньевой зубоальвеолярный блок, сочленяющий зубные ряды верхней и нижней челюстей. В настоящей работе рассматривается вопрос о биомеханическом взаимодействии функций этих блоков. Библ. 12.
Ключевые слова: жевание, зубочелюстная система, зуб, височнонижнечелюстной сустав, челюсть
Received 12 February 2001
