Interactions between the Craniomandibular System and Cervical Spine

Table of Contents

I. Acknowledgement

III. Abstract

1. Introduction

2. Theoretical background
2.1. Embryology
2.1.1. Biological development and evolution of the jaw, facial and cervical regions
2.1.1.1. The gill system
2.1.1.2. Differentiation of tissues in human gill arches
2.1.1.3. Gill arch innervation in humans
2.1.1.3.1. CMS and anterior CS region
2.1.1.3.2. Pinna and posterior CS region
2.2. Anatomy of the human temporomandibular joint
2.2.1. Neuroanatomical relationships between the CMS and the upper portion of the CS
2.2.1.1. The nervus trigeminus pathway
2.2.1.2. The area innervated by the nervus trigeminus
2.2.1.3. Nervus trigeminus convergences with other areas
2.2.1.4. Plexus cervicalis and its relationship to the upper CS
2.2.2. Musculature in the CMS region
2.2.2.1. The CMS musculature
2.2.2.1.1. "True" masticatory muscles
2.2.2.1.2. Suprahyoid musculature, musculi suprahyoidei
2.2.2.1.3. Mimic musculature in the oral region
2.2.2.2. Musculature in the CS region
2.2.2.2.1. Prevertebral, lateral and posterior cervical spinal musculature:
2.2.2.2.2. Suboccipital musculature
2.2.2.3. Functional interactions between the masticatory musculature and the anterior and posterior neck musculature.
2.2.3. Functional connections between the CMS, CS and shoulder girdle regions
2.2.3.1. Head posture
2.2.3.2. Mandibular posture

3. Empirical section
3.1. Investigations on neuronal interactions between areas innervated by the trigeminus and the innervation of the upper cervical areas.
3.1.1. Sensory neuronal interactions between the CMS and CS regions
3.1.2. Neuronal motor interactions between the CMS and CS regions
3.2. Craniomandibular dysfunction
3.2.1. Historical background for CMD
3.2.2. Definition and diagnostics for CMD
3.2.3. Overview of investigations in cases of functional impairment of the CMS.
3.3. Pathophysiology of the CMS and the upper CS region in humans
3.4. Biomechanical connections between the CCS and CMS

4. Aims of the current study and hypotheses

5. Material and methods
5.1. Definition of the exclusion criteria
5.2. Sample
5.3. Questionnaire and clinical investigation of the CS region
5.3.1. Questionnaire A: Sociodemographic data, pain assessment and measurement of the maximum opening of the mouth
5.3.2. Questionnaire B: Determination of the exclusion criteria (B1) and questioning of the subjects on subjectively perceived tension (B2)
5.4. Experimental design and measurements
5.4.1. Experimental design
5.4.2. Chronological sequence of the entire experimental design depicted using a flow chart
5.4.3. Description of an individual measurement
5.4.3.1. Introduction, fitting of the metal foil, warming up
5.4.3.2. Conduct of analysis of mobility in the CS
5.4.3.2.1. Preparations for the measurement
5.4.3.2.2. The CMS 70 P hardware
5.4.3.2.3. Experimental protocol using the CMS 70 P
5.4.3.2.4. Software

6. Results and interpretation
6.1. Demographic data
6.2. Intergroup comparison of demographic data
6.3. General evaluation of the raw data on baseline measurements
6.4. Evaluation of the baseline measurements for each group
6.5. Statistical analysis of measurements made under experimental conditions
6.6. Results from the questionnaires on subjective perception of tension
6.7. Evaluation of the hypotheses

7. Discussion
7.1. Discussion of the findings with reference to the theoretical and empirical research background and their clinical relevance
7.2. Discussion of errors
7.3. Comparisons with other studies

8. Conclusions
8.1. Study design
8.2. Results of the current investigation

9. References

Appendix A: Questionnaire A for a study of the maxillary joint

Appendix B: Raw data 1 from Questionnaire A and from the motion analysis of the upper CS with the Zebris-CMS 70 P device

Appendix C: Questionnaire B1: Acquisition of excluding criteria

Appendix D: Raw data 2 from Questionnaire B1

Appendix E: Questionnaire B2: Estimates from the subjects about the flexibility of the spine and the tension in the maxillary region

Appendix F: Raw data 3 from Questionnaire B2

Appendix G: Introduction and warming-up of the probationers in order to adapt the body for the measurement of the occlusion.

Appendix H: Instruction to the measurement of the mobility of the CS

Appendix I: List of figures

Appendix J: List of tables

I Acknowledgement

I would like to give many thanks Mrs. Dipl.-Psych. Astrid Becker-Woitag, Mrs. Sabine Plosteiner, Dr.-Ing. Walter Klemm, Dr. med. Martin Vogel and Sebastian Zang for their technical assistance. Many thanks to the dance team Funky Jam Take Three headed by Mr. Oliver Zschörner, too.

I confirm truthfully, that I myself have performed this study except the assistance already known by the promoter. All further aids have been made recognizable exactly and completely. All results taken without or with changes from publications of other authors are indicated.

St. Andreasberg, February 2007

III Abstract

This prospective, randomized, double-blind investigation evaluated the influence of a short-time artificial change of occlusion to the upper cervical spine mobility. Twenty 14-19 aged female dancers were investigated in a cross-over-design on head movement rotation in anteflexion with a three-dimensional ultrasonic measurement device, the Zebris 3D Motion Analyzer (CMS 70 P). A change of the occlusion was produced by positioning a 0.75mm foil of tin between premolar and first molar of the right side. Towards the theory of convergence of cervical and trigeminal nerves (Hülse et al., 1998, Schupp, 2001, Bartsch & Goadsby, 2003), the change of occlusion should enlarge tensions in the suboccipital muscles and consequently decrease the mobility of the upper spine. The results of this investigation are: There were no significant differences in measuring movements of the upper cervical spine in dependence of changes of the occlusion. Assessments of the probationers to the changes in tension or motion support these results.

1. Introduction

The connections between the mobility of the jaw region and that of the cervical spine have been the subject of research on many occasions in recent decades. For example, Ridder (1998) gives an overview of experiments conducted on animals by Japanese scientists in his monograph "Functional impairments in the jaw and tooth malalignment and their effects on the periphery of the body". In this monograph, he describes investigations (Guzay (1976), Maehara & Hashimoto (1998), Maehara & Azuma (1998), cited in Ridder (1998, S. 194-212)) that tested the effects of changes in the dental and jaw regions, and that persisted in the long-term, on the periphery of the body. In the quadrant theory, Guzay (1953) outlines that the centre of the movements of the jaw does not lie within the temporomandibular joint itself. He describes how the movements of the jaw occur around a region in the upper cervical spine, namely around the atlanto-axial joint. Based on this proposition, he declares (ibid.) that inadequate dental occlusion can result in spinal malalignment, leading to curvature of the body axis. Maehara (1999) tested the propositions put forward in the quadrant theory by shortening the right-hand teeth in rats. He subsequently observed scoliosis of the spine and variation in the size of the right and left eyes. In addition, he shortened the teeth in Beagle dogs. As a result, the dogs exhibited bad posture, changes to their fur, watery eyes and cataracts. Maehara & Hashimoto (1998) then also shortened some of the teeth in monkeys. They observed that the monkeys suffered from loss of fur, exhibited abnormal behaviour and that their tongues were bent. Following this, a stencil-like splint was fitted to the shortened teeth to restore the original tooth height. This resulted in growth of the monkeys' fur, normal behaviour and a straightening of the tongues. In a further experiment, Maehara & Azuma (1998) shortened the teeth in guinea pigs. The guinea pigs lost weight after two weeks. Weight loss was greater in these animals than in control animals that were starved. After one week, electro-cardiograms of the guinea pigs exhibited a negative T wave, indicating cardiac insufficiency. The researchers then also shortened the teeth in the control group, which resulted in the negative T wave being exhibited by all animals.

Based on these results, the question arises as to whether functional connections in the dental and jaw regions also exert effects on the periphery of the body in humans. Several publications indicate that this may be so.

For example, Stiesch-Scholz et al. (2004) also make connections between impairments to the craniomandibular system (CMS) and postural changes in the region of the cervical spine (CS) and shoulders. Rocabado (1983) demonstrated that pain in the CMS can be caused by changes to the cervical spine. Fink et al. (2003) induced functional restrictions in the region of the cervical spine as well as peripherally in the iliosacral joint through artificial unilateral changes to dental occlusion.

The biological development and evolution of the CMS also suggest systemic observation of the dental / jaw region may be appropriate. The neurological and biomechanical connections to adjacent areas can be illustrated based on its genesis (Moore & Persaud, 1996). The CMS, for example, serves the purpose of taking in food as well as obtaining specific information about our environment through tactile oral perception. There are also connections to the digestive tract, for the regulation of our wake state (attentiveness), as well as to the cervical spine for the "orientation" of our "tactile organ", the temporomandibular joint.

The biological development and evolution of the craniomandibular region will therefore be investigated first, in order to provide information on the theoretical and empirical background to this research. The neurological, functional as well as biomechanical and muscular relationships resulting from this will then be illustrated for adult humans and will form the basis of this research.

Functional relationships between the craniomandibular system and adjacent structures were therefore the subject of intensive research. However, the question has not yet been satisfactorily answered of whether a change in dental occlusion can affect the degree of mobility in the cervical spine, and if this is the case, how this occurs. A closer investigation of this question is the subject of this research.

More specifically, the current research project will investigate whether an artificially produced, short-term, unilateral impairment of dental occlusion also produces changes in the mobility of the cervical spine.

2.Theoretical background

This section will first provide an overview of the genesis of the human craniomandibular system. The aim is to illustrate the overlapping development of the neurological and functional relationships between the CMS and CS, as seen in human embryology. The discussion of its embryological development will be followed up with an anatomical overview of the CMS and CS in adults. This is where the important baseline information on the neuroanatomy, musculature and their functional relationships will be illustrated schematically.

The empirical section will present research that focuses on experimentation on neurological, muscular and functional interrelations between the CMS and CS and which forms the foundation for what has been discussed in the theoretical section.

Theory and empiricism form the background for the question being investigated here, namely, whether a unilateral impairment in occlusion (physiological occlusion) has any effect on the mobility of the CS.

2.1. Embryology

The comparison between the embryological development in humans and fish outlined in the following is designed to permit a better understanding of the development of the complex system of the head, jaw and neck region (Moore & Persaud, 1996). The basis for this comparison is provided by both the theories of descendence and natural selection (Darwin, 1860) that deal with the evolution of life. For example, in his theory of natural selection on the origin of the numerous different plant and animal species, Darwin (ibid.) suggests that over the course of the Earth's history, extant forms have evolved from ancestors with a more simple organization. The theory of descendence (Darwin, 1860) explains species turnover, whereby mutations, recombination, natural selection and isolation are the most important evolutionary factors. Based on these foundations, Haeckel (1894) later described the fundamental biogenetic law. Based on comparative anatomical and embryological investigations on humans and other animals, he illustrated the fact that an individual's development represents a short, condensed repetition of the phylogenetic history of the branch it belongs to.

2.1.1. Biological development and evolution of the jaw, facial and cervical regions

The following sections describe the developmental processes in the head-jaw-neck region that constitute the basis for the neurological and functional relationships.

2.1.1.1. The gill system

The structure and function of the human embryonic gill system is most easily understood from an evolutionary biological perspective. In fish and amphibians, the gill system develops into a respiratory apparatus for the exchange of oxygen and carbon dioxide between blood and water. The gill arches are the skeletal elements to which the gills, the actual respiratory organs, are attached. In human embryos, true gill arches are no longer developed (Moore & Persaud, 1996), such that the gills or branchial arches (brankhia [gk.], gills) can only be regarded as pharyngeal arches. By the end of human embryonic development, these organs have therefore either undergone a functional change, such as, for example, the development of the pharyngeal region of the neck from the pharyngeal arches, or, as is made clear from the example of the gills, the organs undergo involution.

The human gill system is therefore composed of gill arches, gill pouches, gill clefts and the gill membrane. Most of the craniomandibular system develops from the first and second of the total of four to six gill arches and therefore the focus here will be on these two gill arches.

2.1.1.2. Differentiation of tissues in human gill arches

The development of the gill arches commences in the fourth week with the migration of cells from the neural crest to the future head region and back of the neck. Therefore, the head region and back of the neck develop simultaneously (Moore & Persaud, 1996).

Two processes develop from the first gill or mandibular arch. The mandibular process forms the mandibula and the maxillar process the maxilla, the os zygomaticum as well as the pars squamosa of the os temporale. Both processes are therefore substantially involved in facial development. Additional skeletal elements derived from the mandibular arch are the malleus and incus of the middle ear as well as the ligamentum sphenomandibulare.

All tissues developed from the mandibular arch are supplied by the trigeminal nerve. Therefore, this nerve supplies the sensory innervation to most of the facial skin, as well as the motor innervation for the masticatory musculature as well as parts of the suprahyoid musculature (above the os hyoideum).

The second gill or hyoid arch forms the hyoid bone as well as adjacent sections of the cervical and laryngeal regions. The skeletal elements derived from this arch are the stapes in the middle ear, the processus styloideus of the os temporale, the lesser horn of the hyoid and the upper portion of the body of the hyoid. The ligamentum stylomandibulare is the only ligament that develops from this arch. The nervus fascialis is the nerve associated with the hyoid arch and supplies the motor innervation for the mimic facial musculature as well as further portions of the suprahyoid musculature.

Therefore, different tissues develop from each gill arch. An associated nerve, associated muscles, skeletal elements as well as ligaments develop. This clearly demonstrates the overlapping and interconnected nature of the system, which is based on the simultaneous development of the facial, neck and head regions. It combines the tasks of food intake and its onward transfer, oxygen and carbon dioxide transfer and perception.

Human perceptual performance through this system, however, is also reflected in evolution when fishes and humans are assessed comparatively. The oral region is of particular importance as a tactile organ in fish, as the extremities that take on this role in humans are not present in fish. Even so, human lips and the oral region are highly sensitive. For example, in the basic course on Particle Technology, part of Mechanical Engineering, students are taught that oral determination of particle sizes is highly accurate.

"An experienced artist and purchaser can determine the degree of fineness (of particles) by eye (60µm), between the fingers (30µm), with the tongue (20-25µm) and between the teeth (5µm)" (Beckmann (1780), Kelleher (1956) and personal communication from Prof. Dr. Weichert em., Dept. of Mechanical Engineering at the TU Clausthal).

It is therefore possible to differentiate between particles down to a size of 5 mm with the teeth.

In order to provide a more easily accessible overview, the innervated areas of the mandibular and hyoid arches and the overlapping development of nerves, associated musculature, skeletal elements and ligamentous structures described above are summarized in Table 1 (page 12)

Table 1. Illustration of the gill arches and the tissues derived from them (from Moore & Persaud, 1996, p. 222)

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1.1.1.1.1

2.1.1.3. Gill arch innervation in humans

As was inferred earlier, the overlapping innervation in the craniomandibular and CS regions is best illustrated from an embryological perspective (Moore & Persaud, 1996).

Two particular perspectives are of interest here:

one in reference to the anterior CS region including the oral cavity and the digestive tract and another in reference to the genesis of the pinna and thereby to the posterior CS region. Both these relationships will now be illustrated in more detail.

2.1.1.3.1. CMS and anterior CS region

The function of the CMS is complex. It cannot be restricted to a local function, but requires a more systemic approach. The close interconnections of the associated cranial nerve nuclei, the cranial nerves and the musculature they innervate can be envisaged through the overlapping function of the masticatory apparatus, tactile assessment of food, mechanical breakdown, swallowing and transfer to the digestive tract.

The nervus trigeminus thereby supplies both the sensory innervation to the face and portions of the anterior cervical region as well as the motor innervation to the masticatory musculature. The two lower branches of the nervus trigeminus also supply sensory innervation to the teeth and the palatine, lingual, oral and nasal mucosa. The nervus fascialis innervates the facial mimic musculature as well as portions of the suprahyoid musculature. The nervus glossopharyngeus, which develops from the third gill arch, supplies the musculus stylopharyngeus that elevates the pharynx during swallowing, among other muscles. The final cranial nerve discussed here is the nervus vagus which develops from the fourth to sixth gill arches and supplies the entire pharyngeal and laryngeal musculature as well as large portions of the digestive tract.

In summary, it is clear that the simultaneous and overlapping development from the gill system in the cervical region includes the face, the tongue, the lips, the jaw and teeth, the palate and the pharynx. This close relationship is particularly well illustrated by the overlapping neurological supply by the cranial nerves to the jaw and anterior cervical region listed above, which will be looked at in more detail in the section on "Neuroanatomical relationships between the CMS and the upper CS" (page 17).

2.1.1.3.2. Pinna and posterior CS region

The relationships between the posterior cervical and the jaw regions are best assessed by looking at the development of the pinna. The pinna (Moore & Persaud, 1996) initially develops in the upper cervical region. However, with growth of the mandible, the external ear migrates to the lateral portion of the cranium and ascends to the height of the eyes. Those portions of the pinna that are derived from the first gill arch are supplied by the first gill arch nerve (nervus mandibularis), while those portions that are derived from the second gill arch nerve are supplied by the cutaneous nerves from the plexus cervicalis (i.e. from the cervical spine). Particular mention must be made of the nervus occipitalis and the nervus auricularis. The cranial ascent of the ear results in a mixing of trigeminal and cervical sensory fibres (see Fig. 1, page 15 and Fig. 2, page 15).

Hülse et al (1998) also describes this connectedness and refers to it as "cervico-trigeminal convergence" (cervico-trigeminal synapse). The terminal regions of the trigeminus and the cervical afferences overlap at the level of the upper cervical segments in the superficial dorsal horn, such that it can be assumed that secondary neurons receive convergent input from cervical and trigeminal afferences. In particular, exteroceptive afferences from the cervical region reach the spinal trigeminus nucleus, such that a cervico-trigeminal convergence can also take place at this level.

Schupp (2001) confirms this and writes the following on the innervation of the temporomandibular joints in this context:

1. Pain stimuli from the back of the head and neck reach the spinal cord through the roots of C2-5, where they ascend and descend up to three segments in the tractus dorsolateralis and the substantia gelatinosa. A mixing with the nucleus spinalis nervi trigemini fibres occurs after entry into the dorsal horn. This connection between the upper cervical roots and the nucleus spinalis nervi trigemini ("cervico-trigeminal synapse") is regarded as the neuroanatomical substrate for the projection of pain from cervical to frontal regions. (…)
2. The temporomandibular joints are innervated by the nn. auriculotemporalis, massetericus, temporalis and the ganglia of the dorsal roots of C2-5. The nervus auriculotemporalis, originating from the posterior branch of the nervus mandibularis, splits into the rami temporales superficiales for the skin and the fascia of the temples and adjacent scalp. It not only sends branches into the temporomandibular joint, but also into the external ear canal and the tympanic membrane. (…)^[1]

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Figure 1: Pinna development. A: 6th week, B: 8th week, C: 10th week, D: 32nd week. The pinnae ascend from the cervical region to the lateral portion of the cranium during development. (from Moore & Persaud, 1996, p. 517)

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Figure 2: Trigeminal and cervical innervation of the head (taken from Wilkie, 1988)

According to Schupp (2001), dysfunctions or pathologies of the upper cervical region can thus cause pain to be projected into the head/facial area through the cervico-trigeminal convergence. The sensory innervation of the temporomandibular joints therefore delivers a construct to explain why diagnosis of patients with articular or disc problems in the CMS

does not just indicate local pain in the temporomandibular joint. Furthermore, patients report on pain in or around the auricular region that occasionally radiates into the facial region.

On a neurological basis, a reciprocal effect is therefore produced. It is therefore to be assumed that dysfunctions in the masticatory apparatus can be projected into the cervical spinal region, just as in reverse, dysfunctions in the upper portion of the CS can affect the masticatory apparatus.

The anatomy of the human jaw region that is relevant to this research will be illustrated in the following.

2.2. Anatomy of the human temporomandibular joint

The structures underlying the anatomy of the human temporomandibular joint will be described in three sections.

In the first section, a descriptive neuroanatomical overview will be given of the nervus trigeminus in humans, based on the illustration of the embryological development of the CMS and CS regions. This will be followed by an overview of areas of the CMS and CS regions innervated by the trigeminal as well as those areas supplied cervically. Those convergences of the trigeminus with fascial, vagal and glossopharyngeal nuclei as well as with the hypothalamus and thalamus that are relevant to this research will also be discussed.

In the second section, the function of the masticatory musculature and that of the anterior cervical region will be discussed. This will be followed by an illustration of the functional interactions between the masticatory musculature and the anterior and posterior cervical musculature.

In the third section, the functional relationships between the shoulder girdle and the cervical region, and the shoulder girdle and the jaw-head region, will be illustrated based on the musculature discussed previously and the existing neurology.

Following this, theory will be contrasted with empiricism. Research on topics that demonstrate the neurological and biomechanical relationships in the CMS and CS regions will be reviewed.

2.2.1. Neuroanatomical relationships between the CMS and the upper portion of the CS

The following section describes the neuroanatomical relationships between the CMS and the upper portion of the CS. Initially, the nervus trigeminus will be looked at in more detail, followed by the plexus cervicalis and its close relationship with the CMS.

First, an overview will be provided of the nervus trigeminus in which its pathway, the innervated area and the neurological convergences with other areas will be highlighted.

Finally, the area innervated by the plexus cervicalis will be illustrated and existing convergences between the cervical portion of the CS and the CMS will be highlighted.

2.2.1.1. The nervus trigeminus pathway

The nervus trigeminus originates from a relatively large topographical area of the brainstem, from the C2 up to the pons (Trepel, 1999). It is therefore the largest of the twelve cranial nerves. It carries sensory information, such as the supply to the face, as well as motor information, for example, the innervation of the masticatory musculature. The nerve cell bodies are clustered in so-called nuclei, whereby these nuclei are associated with different tasks (see section: The area innervated by the nervus trigeminus, page 18). Four different nuclei can be distinguished:

- nucleus motorius nervus trigeminus
- nucleus mesencephalicus nervus trigeminus
- nucleus pontis nervus trigeminus
- nucleus spinalis nervus trigeminus

The neurons that form the nervus trigeminus and originate from these nuclei emanate laterally from the pons (see Fig. 3, page 18). From there, they extend ventrally over the edge of the petrosal pyramid and then disappear under the dura. At this location, the nervus trigeminus forms a sensory ganglion (ganglion trigeminale) in a large pouch in the dura that contains the perikarya of the majority of the sensory cranial neurons. After this ganglion, it separates into three large branches:

- nervus ophtalmicus (V1)
- nervus maxillaris (V2)
- nervus mandibularis (V3)

V1 and V2 are purely sensory branches and leave the cranium by the (V1) fissura orbitalis superior and (V2) the foramen rotundum. Before leaving the cranium, both send out a branch to the meninges.

V3, the nervus mandibularis that leaves the cranium through the foramen ovale, plays a central role in the current study as it is the strongest branch and is also closely topographically associated with the temporomandibular joint (TMJ). After leaving the foramen ovale, the nervus mandibularis follows a pathway medial to the temporomandibular joint, whereby it is easily irritated by dysfunctions in the region of the temporomandibular joint.

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Figure 3: The pathways followed by the three branches of the nervus trigeminus (from Rohen (2000), p.204)

2.2.1.2. The area innervated by the nervus trigeminus

The four distinct nuclei from which the nervus trigeminus originates serve different functions. The nucleus motorius alone carries motor information. It innervates the masticatory musculature as well as the majority of the suprahyoid musculature. All other nervus trigeminus nuclei carry only sensory information. The nucleus mesencephalicus receives information on pain and temperature perception, pressure and tactile sensations in the facial area, and also innervates the teeth, masticatory musculature and the temporomandibular joint capsule proprioceptively. The nucleus pontis also processes pain and temperature as well as

pressure and tactile sensations. The nucleus spinalis is responsible purely for pain and temperature perception. The nucleus spinalis plays a key role in the current study due to its multiple interconnections to other areas. These convergences will therefore be looked at in more detail in the following (see section on convergences of the nervus trigeminus with other areas, page 19).

Table 2 provides a summary of the area innervated by the nervus trigeminus nuclei for easier comprehension.

Table 2. Somatomotor and somatosensory area innervated by the nervus trigeminus (summary adapted from Trepel, 1999)

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2.2.1.3. Nervus trigeminus convergences with other areas

The spinal tract and nucleus of the trigeminal nerve is of special interest in this discussion. The spinal tract descends through the medulla into the upper levels of the spinal cord and reaches as far down as the C2 level, with some parts extending as far as the C4 root level (Trepel, 1999). At these levels, the terminations of the trigeminal nucleus overlap with those of the upper cervical nerves (C1, C2, C3, especially the dorsal horn of C2, from which the greater occipital nerve originates). This occurs in the pars caudalis of the spinal nucleus and the dorsal horns of the upper cervical segments of the spinal cord, which are histologically so intimately linked that they cannot be differentiated. The term cervico-trigeminal nucleus has therefore been used to describe the combined nucleus (Hülse et al, 1998; Schupp, 2001; Bartsch & Goadsby, 2003).

Both these regions are primarily concerned with the transmission of pain. Any dysfunction or lesion in the upper cervical spine which causes local stimulation of pain receptors, can therefore, via the cervico-trigeminal nucleus, cause stimulation of trigeminal nerve endings at this level. Since the trigeminal nerve has such a wide sensory distribution over the face and scalp and particularly in the temporomandibular joint (TMJ), a portion of the craniomandibular system with which we are concerned here, pain may be reflexively produced by dysfunction or pathology in the TMJ. Pain will cause stimulation of pain-transmitting nerve endings of the trigeminal nerve, which relay into the spinal nucleus and via the connections described, possibly producing pain in the region of the upper cervical nerves, i.e. the neck and posterior scalp.

It has also been well established that pain fibres from cranial VII, IX, X (fascial, glossopharyngeal and vagus nerves) also synapse in the pars caudalis of the spinal nucleus (Gray, 1960; Gelb, 1985). The close connections between the CMS and CS observed on the basis of overlapping development from the gill arches within the framework of embryological development are therefore also present in adult humans.

This nucleus is, therefore, an important relay centre for pain impulses to many widespread areas of the body. The convergence of cervical and trigeminal nerves has been demonstrated anatomically (Hülse et al, 1998; Schupp, 2001; Bartsch & Goadsby, 2003). Many other authorities have also demonstrated the convergence physiologically by injection of saline solution into upper cervical soft tissues, or by direct electrical stimulation (Pinkham, 1985). In both cases, pain patterns were produced in the head in regions corresponding to areas supplied by the trigeminal nerve. Other trigeminal convergences with the pain processing centres in the thalamus have been determined by Bartsch & Goadsby (2003). Malick et al. (2000) also determined such convergences with the hypothalamus, which explain the vegetative side effects of pain in the region.

2.2.1.4. Plexus cervicalis and its relationship to the upper CS

Convergences between trigeminal and cervical information have now been determined by several authorities (Hülse et al, 1998; Schupp, 2001; Bartsch & Goadsby, 2003; Bartsch et al., 2002). Those structures innervated by the plexus cervicalis will be looked at in the following. These structures will be used to demonstrate that in addition to symptoms of pain in the CS region, dysfunctions in the craniomandibular system (CMS) can also provoke symptoms such as dizziness or tinnitus.

The plexus cervicalis supplies the suboccipital muscles with its C1 dorsal ramus and the ventral ramus supplies the atlanto-occipital joint. Its C2 and C3 ventral rami innervate the upper anterior vertebral muscles. The C2 dorsal ramus (greater occipital nerve) innervates the skin over the occiput and the posterior neck muscles, whilst the ventral ramus also supplies the atlanto-occipital joint, in addition to the prevertebral muscles, sternocleidomastoid (SCM) and trapezius.

The C3 dorsal ramus supplies the suboccipital skin, muscles and C2/3 facet joints, whilst the ventral ramus in association with C2, supplies the prevertebral muscles, SCM and trapezius.

C2 and C3 also supply the skin over the anterior aspect of the neck and the angle of the jaw (see Fig. 2: Trigeminal and cervical innervation of the head, p.15) The upper cervical nerves also supply the dura mater of the posterior cranial fossa and the vertebral artery.

These anatomical details make clear that irritation of these nerves can give rise to symptoms all over the head and neck. In addition to pain, symptoms such as dizziness may be produced by irritation of the nerves supplying the vertebral artery. This is a symptom common in craniomandibular dysfunction (CMD) due to irritation of the inner ear. For example, Plato & Kopp (1989) determined increased occurrence of dizziness and tinnitus in patients suffering from CMD. This example once again demonstrates the relationship between HWS and CMS, this time through the production of similar symptoms in the same areas, and not only through interaction of neural stimuli at the cervico-trigeminal nucleus.

Following this discussion of the CMS and CCS (craniocervical system) neural connections, an anatomical overview of the masticatory muscles and their functional relationships with the cervical spine will now be given.

2.2.2. Musculature in the CMS region

In the following, the function of the CMS musculature will first be discussed. Then the innervation and function of the CMS and CS musculature will be illustrated. This will be followed by an illustration of the functional interactions between the masticatory musculature and the anterior and posterior neck musculature.

2.2.2.1. The CMS musculature

Three muscle groups are important for mastication and will be described in more detail below. First the "true" masticatory muscles, then the suprahyoid musculature, musculi suprahyoidei, and finally the mimic musculature in the oral region:

2.2.2.1.1. "True" masticatory muscles

Mastication involves the action of the "true" masticatory muscles, the mm. masseter, temporalis, ptergoideus medialis and lateralis, which insert directly onto the mandible and can therefore exert the greatest power on the region of the head and temporomandibular joint (see Fig. 4, page 22).

These muscles are derived from the first gill arch and are innervated by the nervus trigeminus (V3).

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Figure 4: Masticatory muscles; M. masseter, M. temporalis, M. pterygoideus lateralis and medialis. From MacKinnon, Morris (2005/2), p. 83

2.2.2.1.2. Suprahyoid musculature, musculi suprahyoidei

The os hyoideum is centrally positioned in the ventral region of the neck. The hyoid bone is a small horseshoe-shaped bone with paired processes on either side, the cornua majora et minora. The hyoid bone is not articulated but is embedded in and held in place by the muscular slings of the supra- and infrahyoid musculature. The ligamentum stylohyoideum originates from the processus styloideus ossis temporalis and inserts into the cornu minus and therefore connects the hyoid with the temporal bone via ligaments.

The suprahyoid musculature includes the musculus geniohyoideus, mylohyoideus and the venter anterior of the digastricus. The musculus geniohyoideus is innervated by the rami anteriores of the first and second cervical nerves. The musculus mylohyoideus and the venter anterior of the musculus digastricus are supplied by a branch of the nervus mandibularis. The suprahyoid musculature provides the muscular structure for the base of the mouth. These muscles are therefore also referred to as mouth floor muscles.

During swallowing, these muscles and the pharnygeal musculature lift the hyoid bone and the larynx skeleton cranio-ventrally. The mouth floor muscles constitute an abutment for the tongue, such that it can be pressed against the palate. The mouth floor musculature also acts on the temporomandibular joint via the mandible when the hyoid bone is held in place by the infrahyoid musculature (see Fig. 5, page 24). In this case, the mouth floor muscles actively lower the mandible, whereby activity of the venter anterior musculus digastrici increases the more the mouth is opened.

2.2.2.1.3. Mimic musculature in the oral region

The mimic musculature in the oral region plays a minor role in mastication. It is important in food intake and speech, as well as for facial mimicry. The mimic musculature includes the mm. orbicularis oris, buccinator, zygomaticus major et minor, risorius, levator labii superioris, levator anguli oris, depressor anguli oris, depressor labii inferioris and mentalis. They are derived from the second gill arch and their motor innervation is provided by the nervus fascialis.

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^[1] Aurikularhöcker des 1. und 2. Kiemenbogens (eng. auricular hillock derived from the 1st and 2nd gill arch; 1. Kiemenfurche (eng. 1st gill cleft)