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mise à jour du
6 mai 2004
Swed Dent J
2000; Suppl 143; 1-41
Integrated jaw and neck function in man. Studies of mandibular and head-neck movements during jaw opening-closing tasks
Zafar H
Bâillements et stomatologie


Relationship between the temporomandibular and the craniocervical regions
Clinical data : Temporomandibular disorders (TMD) is a collective term embracing a number of clinical. problems involving the Jaw muscles, the temporomandibular joints and associated structures. The term is synonymous with 'craniomandibular disorders' (CMD). TMD has been identified as a major cause of non-dental pain in the orofacial region and is considered to be a subclassification of musculoskeletal disorders. Common patient complaints include pain in the jaw, face, head, neck and ear regions.
Previous reports have demonstrated that neck symptoms are often present in patients with TMD. Notably, it has been shown that treatment of TMD by occlusal adjustment resulted in a significant decrease in the number of days on sick leave and theuse of medical services for head and neck symptoms. Furthermore, an interdisciplinary approach in this context, seems to be of advantage. Physical trauma to the headneck from a motor vehicle accident or sortie other type of head-neck trauma, may lead to whiplash associated disorders (WAD). TMD as a consequence of such trauma is a matter of controversy. The proponents of a relationship between headneck trauma and TMD generally advocate a direct injury to the temporomandibular joint as the cause of TMD symptoms. However, this view has its opponents. Some studies with magnetic resonance imaging (MRI) support a relation between head-neck trauma and TMJ damage, while others have not found such a relationship. Alternatively, neuromuscular factors have been proposed to explain mechanisms behind the development of TMD in association with WAD. Furthermore, the validity of studies that refute a relationship between neck injury and TMD has been questioned.
Anatomical and experimental data : Gross anatomy and the close proximity between the temporomandibular and the craniocervical regions binds them into a biomechanical linkage. The existence of neural connections between the trigeminal and the cervical sensorimotor systems is demonstrated in neuroanatomical studies and by neurophysiological evidence from studies in animals and in humans. Likewise, observations in man of co-activation of jaw and neck-shoulder muscles during jaw activities and of head movements duringjaw opening indicate the presence of neuromuscular connections between the jaw and neck regions. The earliest reflex found in the human embryo is the trigemino-neck reflex, which consists of contraction of neck muscles elicited by light touch of the perioral region. Recent observations on human fetal yawning, using ultrasonographic technique, revealed that mouth opening movement is preceded by extension of the head, and that closing of the mouth is followed by head flexion. Thus, previous studies in several species suggest a linkage between the jaw and neck regions. However, systematic studies of the integrated mandibular and head-neck behaviour during natural jaw function are generally lacking.
Mandibular movements : Jaw opening-closing, biting, chewing, swallowing, yawning and speech require unrestrained mandibular movements. Systematic analyses of mandibular movements have been a subject of considerable interest ever since the photographie recordings by Luce (1889), since the knowledge of mandibular movements provides a basis for the understanding of jaw function in clinical dentistry. Numerous methods have later been employed with the objective to record and analyse the movements of the mandible in relation to the cranium. As mentioned above, head movements during jaw opening was reported by Ferrein as early as 1748, but in subsequent studies head-neck movements associated with mandibular function have only been mentioned in the context of methodology for recording mandibular movements and has even been considered as a "problem" in recording of mandibular movements ).
Head-neck movements : The main body of knowledge of neck function is developed in conjuriction with studies of the visual and the vestibular systems. Valkenburg suggested that the spinal tract of the trigeminal nerve probably participates in reflex head movements in response to tactile and noxious stimuli from the trigeminal area to the nuclei subserving head and neck motion in the upper cervical cord. It bas been shown that afferent activity from the orofacial region bas a significant input to the head-neck motor control mechanisms. However, the role of the trigeminal sensory motor system in head-neck function is still generally ignored both in experimental and clinical studies. For example, in a recent comprehensive book on the head-neck sensory and motor systems, the role of the trigeminal system in neck function is not mentioned.
Understanding human movement : Movement is one of the definitions of life. In physics, a movement can be defined as the change of the position of a body relative to another body, or with respect to a coordinate system. The quest to understand the basics of human movement has a long history. According to western literature, the earliest known contributions to explain human and animal movements were made by Leonardo da Vinci (1452-1519) and Borelli (1608-1679). The mechanical principles by Newton (1642-1727) later became the basis for the discipline of biomechanics, which is the application of mechanical principles to biological tissue during movement and rest. Biological movement is the final outcome of the integrated actions of the nervous and musculoskeletal systems. The neuromuscular nature and control of these actions is denoted 'motor control'. Motor control encompasses actions to stabilize the body in space - postural and balance control - and to move body segments in space - locomotion. Understanding of such mechanisms, underlying unrestrained natural movements as well as the interactions between movements of different body segments, thus provides the basis for evaluation and treatment of movement disorders.
Tolls for evaluation of movements and movement control : Depending on the question under study, biological movements can either be studied by biomechanical or electromyographical techniques, or a combination of both. Biomechanical analyses of kinematic parameters, such as position, velocity, and acceleration, can give understanding about the mechanisms behind the control of movements of body segments. Movement recordings have been made with various techniques ever since Muybridge (1830-1904) made the first photographic recordings of freely moving humans and animals in 1887. The technological advances in such recording equipment over the last decades have made several high-resolution computer assisted movement recording systems commercially available, which enables quantitative analyses of large amounts of movement data, as a basis for evaluation of human motor performance.
Electromyographic (EMG) recordings yield information about the activation patterns of muscles during movement. Due to the intricate topographic and functional anatomy of the temporomandibular and the craniocervical regions, EMG examination aimed at evaluating their possible functional relations poses special methodological problems. The two regions contain numerous muscles and subportions of muscles, which are known to differ in motor unit and fibre type characteristics. Thus, in these regions the selection of appropriate muscles and hence the type and location of EMG electrodes, is particularly critical for obtaining adequate and representative neuromuscular activation patterns, as is generally the case in other intricate neuromuscular systems. Given these complicating anatomical, morphological and electrophysiological factors, it is likely that kinematic recordings can be a technique of choice for the study of joint temporomandibular and craniocervical motor behaviour.
Mandibular and head-neck movements during naturai jaw function : Detailed and systematic analyses of the nature of mandibular and head-neck movements during natural jaw function could provide insight in the control processes underlying a putative integrated function of the human temporomandibular and the craniocervical regions. Such studies are generally lacking. In addition, the knowledge from such studies may be used to develop clinical protocols for pre- and post-treatment evaluation of jaw and neck movement disorders.
This investigation was undertaken to test the hypothesis of a functional relationship between the human temporomandibular and craniocervical regions by analyses of mandibular and head-neck movements durinc., maximal jaw opening-closing tasks at fast and slow speed in healthy young adults and individuals suffering from both temporomandibular disorders and whiplash associated disorders (WAD group).
A consistent finding was parallel and coordinated head-neck- movements during both fast and slow jaw opening-closin- tasks. Jaw opening was always accompanied by head-neck extension and jaw closing by headneck flexion.
At the initiation of both fast and slow jav opening, the head in general started to move simultaneously with or before the mandible, reached the peak position simultaneously with before or after the mandible, and reached the end position after the mandible. The head most often attained maximum velocity after the mandible, and was mostly lagging behind the mandible along the entire jaw opening and closing phases.
A high degree of spatiotemporal consistency of mandibular and head-neck movement trajectories was found in short- and lon-term perspectives.
The head movement amplitude and the temporal coordination between mandibular and the head-neck movements werc speed related but not the movement trajectory patterns.
Compared with healthy subjects, the WAD group showed: smaller amplitudes for mandibular and head-neck movements, a different pattern of temporal coordination between the mandible and the head-neck, but a similar high degree of spatiotemporal consistency of mandibular and head-neck movement trajectories.
The results suggest that:
  •  a functional linkage exists between the human temporomandibular and craniocervical regions
  • head movements are an integral part of natural jaw opening-closing tasks. 
  • "functional jaw movements" comprise concomitant mandibular and headneck movements which involve the temporomandibular, the atlantooccipital and the cervical spine joints, caused by jointly activated jaw and neck muscles.
  • jaw and neck muscle actions are elicited and synchronised by neural commands in common for both the jaw and the neck motor systems, and that these commands are preprogrammed, particularly at fast speed. In the light of previous observations of concurrent jaw and head movements during foetal yawning, it is suggested that these motor programs are innate.
  • neural processes underlying integrated mandibular and head-neck function are invariant both in short and long term perspectives.
  • integrated jaw and neck function seems to be crucial for maintaining optimal positioning of the gape in natural jaw function.
  • injury to the head-neck, leading to whiplash associated disorders (WAD) may derange integrated jaw and neck motor control and therefore compromise natural jaw function.