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.
SUMMARY
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.
CONCLUSIONS
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.
