From: BMC Musculoskelet Disord. 2009 Mar 2;10:28

Temporomandibular disorders are musculoskeletal pain conditions characterised by pain and dysfunction in the jaw-face muscles and/or the temporomandibular joint. Musculoskeletal pain conditions occurring at various locations may share pathophysiological mechanisms. Co-morbidity between temporomandibular disorders, headaches and neck/shoulder pain has been reported in temporomandibular disorders patient samples as well as in samples drawn from the general population. Low back pain, one of the most common pain conditions in humans, has been associated with other pains such as neck pain and headaches, which has been interpreted as a tendency for symptoms to cluster in some individuals. The source of these patterns is not known, but neurobiological sensitization processes, genetically determined vulnerability and psychological factors are commonly given as possible explanations. Results of a 3-year prospective study showed a significantly increased risk of developing a new pain condition with presence of a pain condition at baseline. A more recent prospective study based on patients with non-painful temporomandibular disorders indicated a dose-response relationship between the number of pain sites at baseline (head, back, chest, stomach) and the risk of onset of dysfunctional temporomandibular disorders pain among women. Frequency of headaches was found to have a dose-response relationship with occurrence of musculoskeletal symptoms (e.g. pain in neck, shoulders and low back) in a Norwegian population.

The authors have recently shown that patients with long-term spinal pain (neck, shoulder and/or low back) significantly more often have signs and symptoms of temporomandibular disorders than do matched controls. The associations remained statistically significant also after exclusion of those who reported jaw pain. It is not known whether co-morbidity between temporomandibular disorders and neck pain, shoulder pain and/or low back pain occurs within the whole range of variation in symptom frequency and severity. Most analyses in this field have involved dichotomized samples, not taking variations of symptom severity into consideration. The aim of the present study was to test whether a reciprocal dose-response relation exists between frequency and severity of neck pain, shoulder pain and/or low back pain and temporomandibular disorders. The authors tested the following null hypotheses:

1. Occurrence of frequent temporomandibular disorders symptoms and headaches does not differ significantly between study groups with varying frequency and severity of neck pain, shoulder pain and/or low back pain.

2. Presence of frequent neck pain, shoulder pain and/or low back pain does not differ significantly between study groups with varying frequency and severity of temporomandibular disorders symptoms.

The operational definition of ’spinal pain’ was pain in the neck, shoulders and/or low back. Symptoms in the jaw-face region, head, neck, shoulder and low back regions were assessed by questionnaire. Presence of symptoms was stated for frequency (never; not now, but previously; once or twice a month; once or twice a week; several times a week; daily), duration (< 1 month; 1 month–1 year; 1–5 years; > 5 years) and intensity. The subjects were also asked to estimate the impact of jaw symptoms, headaches, neck-shoulder pain and low back pain on activities of daily living. Intensity and activities of daily living was assessed using the 11-point Numerical Rating Scale.

Presence and severity of temporomandibular disorders was evaluated for the separate symptoms and according to the Helkimo Anamnestic dysfunction Index. This classification grades the severity of symptoms in the jaw-face region into mild (i.e. temporomandibular joint sounds during opening and closing of the jaw and/or tiredness/stiffness in the jaws) or severe (i.e. pain, temporomandibular joint locking and/or difficulties in opening the mouth wide).

The present study showed a dose-response relation between frequency and severity of spinal pain and temporomandibular disorders. The pattern was evident in both directions, the prevalence of frequent temporomandibular disorders symptoms and headaches increasing with increasing frequency/severity of spinal pain, and the prevalence of frequent pain in the neck, shoulders and/or low back increasing with increasing frequency and severity of temporomandibular disorders symptoms. The test for trends showed significant dose-response associations in both directions. The two tested null hypotheses were therefore rejected.

The authors have previously shown that patients with long-term pain in the neck, shoulders and/or low back have a sevenfold risk of reporting pain and dysfunction in the jaw-face region and a fivefold risk of having clinical signs of temporomandibular disorders, compared with matched controls. This finding was recently supported in a cross-sectional analysis based on almost 30,000 adults in the USA, indicating a strong relationship between reported pain in the neck, shoulders and/or low back and jaw-face pain. The present study shows a stepwise positive correlation between severity of spinal pain and pain and dysfunction in the jaw-face region. This dose-response-like pattern should not be interpreted as a sign of exposure and outcome. However, it strengthens previous results of an association between temporomandibular disorders and spinal pain and may point to common underlying biological or psychological mechanisms. It should be emphasized that the results are derived from a cross-sectional study and do not show causality. Owing to the study design we have no information about the temporal sequence of the examined disorders, an essential element in assessing causality. Studies with a prospective design have indicated that presence of a pain condition increases the risk of contracting temporomadibular disorder pain. In a recent prospective study the risk for onset of facial pain, meeting research diagnostic criteria for temporomadibular disorders, was almost four times higher among adolescents with back pain at baseline, than among those without back pain. Papageorgiou et al. followed a cohort without low back pain at baseline and noted that musculoskeletal pain at other sites predicted future episodes of low back pain. These results are interesting, but so far there is no sufficient evidence to conclude that back pain precedes temporomandibular disorders, or vice versa. Psychological factors are often co-morbid with chronic pain conditions. The temporal sequence of pain and depression is however not clear. In a review addressing this question the majority of studies indicated that depression was a consequence rather than an antecedent of pain. Longitudinal studies on these issues are therefore warranted.

It has been suggested that generalized pain (i.e. fibromyalgia) is at one end of a continuum. Vierck presents temporomandibular pain as an example of a focal pain condition where the nociceptive sensory input may contribute to development of generalized hypersensitivity and related susceptibility to further load. In line with this hypothesis one experimental study reports signs of mechanical allodynia in the hindpaw following nociceptive stimuli applied to the masseter muscle of rats. Other experimental studies have shown that perceived muscle pain intensity and distribution is influenced by the stimulation rate (temporal summation) and the number of stimulated afferents (spatial summation). Temporal summation has been shown in temporomandibular disorders patients, as well as in other chronic pain conditions, suggesting a generalized hyperexcitability of the central nociceptive system. In a large population sample grouped with respect to frequency of reported headaches a dose-response pattern was demonstrated between headache frequency and 1-year prevalence of musculoskeletal symptoms (with locations including neck, shoulders, elbows, wrist/hands, chest/abdomen, upper back, low back, hips, knees, ankles/feet). The contribution of input from the craniofacial nervous system in spreading pain may therefore be of significance and more experimental and clinical studies are needed.

Recent studies have shown that genetic polymorphism, with influence on the metabolism of catecholamines, is highly associated with pain sensitivity and the risk for developing temporomandibular disorders. Central sensitization may be one possible explanation for co-morbidity between pain conditions at different locations, as well as presence of allodynia and hyperalgesia. Reflex connections between nociceptors and the fusimotor-muscle spindle system may also be involved in the pathophysiologic mechanisms related to pain and dysfunction.

The allocation of subjects in the present study to different pain in the neck, shoulders and/or low back groups was based on the participants’ reports of pain frequency in the questionnaire. For example, if a subject reported daily shoulder pain, but infrequent low back pain, the grouping was done according to the frequency of shoulder pain. Subjects who had been referred to a rehabilitation programme and who were on sick leave were considered to have more severe spinal pain than subjects with frequent pain but not on sick leave. Symptom description in self-report questionnaires may be a limitation in a strict dose-response discussion; however, frequency as well as intensity and duration of pain and dysfunction are important variables in health care seeking behaviour. Similarly, in this study, pain severity in the separate neck-shoulder pain and low back pain groups demonstrates stepwise increased mean values of reported pain intensity and impact on activities of daily living. In the sub-sample test with symptoms of temporomandibular disorders as independent variable, we included none of the patients from the rehabilitation center. The severity of the temporomandibular disorders symptoms is reflected by the reported interference of jaw symptoms with daily living. The formation of groups, aiming at discrete severity categories (dose), therefore seems valid also with regard to the mean intensity level and the impact of the symptoms on daily living.

The study shows a reciprocal positive dose-response pattern between frequency and severity of neck-shoulder pain and low back pain and temporomandibular disorders. The results indicate a strong co-morbidity between these two conditions, suggesting that they may share risk factors or that they may influence each other. The authors agree with the recently advocated view of a need for hypothesis-based studies on specific pain -pain co-morbidities, but also on pain-dysfunction co-morbidities. The present results are of significance for physicians and dentists, both of whom are expected to manage patients with pain and dysfunction. Collaboration as well as a costing system for cooperation in the diagnosis and management of the two conditions is warranted. Researchers of pain conditions should include the jaw-face region in their efforts to comprehend the pain patient’s case history.

From: World J Orthod. 2008 Winter;9(4):329-36

To test whether there is a relationship between head and neck posture and dentofacial morphology in patients with temporomandibular joint osteoarthritis or osteoarthrosis. The subjects consisted of 34 Japanese females with temporomandibular joint osteoarthritis or osteoarthrosis (aged 24.7 +/- 6.1 years). Six craniocervical angular measurements were constructed for head posture. Two angular and 6 linear measurements were constructed for the skeletal relationship, while 1 angular and 6 linear measurements were constructed for the dental relationship. Pearson correlation coefficients were calculated between head posture and dentofacial variables.

In the skeletal relationship, increased craniocervical angulations were significantly associated with a more posterior position of the maxilla, a decreased Frankfort to mandibular plane angle, decreased mandibular length, and a decreased lower facial height. In the dental relationship, increased craniocervical angulations were significantly associated with more posterior positions of the anterior teeth to the basal bone and decreased alveolar height of the anterior-posterior teeth. The hypothesis was rejected. These results suggest that an association may exist between head and neck posture and dentofacial morphology in patients with temporomandibular joint osteoarthritis or osteoarthrosis.

From: J Orofac Pain. 2009 Winter;23(1):28-37

To evaluate the relationships between gender, diagnosis, and severity of temporomandibular joint disorders with self-reports of the impact of temporomandibular joint disorders on the quality of life, eighty-three individuals seeking temporomandibular joint disorders treatment at the Dental School of Pontifical Catholic University Minas from May to August 2005 were evaluated by a single examiner who was trained and calibrated for diagnosis according to criteria of Axis I of the Research Diagnostic Criteria for temporomandibular joint disorders. The severity of temporomandibular joint disorders was established by the Temporomandibular Index and the impact on quality of life by the Oral Health Impact Profile. Complete data were available for 78 of the 83 initial patients and evaluated by the Mann-Whitney test and Spearman correlation analysis.

Except for one patient, all individuals showed some impact related to physical pain. Of the seven aspects evaluated on the Oral Health Impact Profile, women presented a greater impact than men only for functional limitations. Patients presenting with diagnoses of muscular disorders (group I) or osteoarthritis (group III) reported a greater impact than those without. The Spearman test demonstrated a significant correlation between impact on quality of life and severity of temporomandibular joint disorders. Orofacial pain had a great impact on the quality of life of individuals with temporomandibular joint disorders, without group difference between genders. The presence of muscular disorders (group I) and osteoarthritis (group III) was related to greater impact on quality of life, which was not observed for diagnoses of disc displacement (group II). A correlation between severity of temporomandibular joint disorders and impact on quality of life was clearly observed.

From: Gerodontology. 2008 Dec;25(4):251-7. Epub 2008 Feb 27

The relationship of bony changes in the condylar surfaces in articular disc displacement without reduction in temporomandibular joint was investigated using diagnostic imaging. The study also evaluated whether the bony changes in the condylar surfaces limit disc and condyle motion, and produce pathological joint sounds.

Thirty seven temporomandibular joints in 28 patients diagnosed with degenerative bony changes in the condylar surfaces radiographically and anterior disc displacement without reduction using magnetic resonance imaging (MRI) were studied. The bony changes were assessed by radiographic examination and classified into two types: pathological bone changes including erosion, osteophyte formation and deformity, and adaptive bone changes including flattening and concavity. MRI was performed on the temporomandibular joint to examine the configuration and position of the discs. Joint sounds in the temporomandibular joint were determined using electrovibratograghy with a joint vibration analysis.

The articular disc motion to the condyle in the pathological bone changes group was smaller than in the adaptive bone changes group irrespective of the configuration of the disc, even though there were no significant differences between the two types of bony changes in the disc position during jaw closing. The joint vibration analysis of the temporomandibular joint showed that joint sounds with a higher frequency were observed in the pathological bone changes group than in the adaptive bone changes group. High energy levels needed to produce the higher frequencies were observed only in the pathological bone changes group.

From: Swed Dent J. 2008;32(4):171-7

Eating requires mouth opening, biting, chewing and swallowing and should be performed without dysfunction or pain. Previous studies have shown that jaw opening and closing movements are the result of coordinated activation of both jaw and neck muscles, with simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. Consequently, it can be assumed that pain or dysfunction in any of the three joint systems involved could impair jaw activities. In fact, recent findings support this hypothesis by showing an association between neck injury and reduced amplitudes, speed and coordination of integrated jaw and neck movements.

This study investigated the possible association between neck injury and disturbed eating behaviour. Fifty Whiplash associated disorders patients with pain and dysfunction in the jaw and face region and 50 healthy age and sex matched controls without any history of neck injury participated in the study. All participants were assessed by a questionnaire, which contained 26 items about eating behaviour, jaw pain and dysfunction. For the whiplash associated disorders group there were significant differences in jaw pain and dysfunction and eating behaviour before and after the accident, but no significant differences between whiplash associated disorders before and healthy. The healthy and the whiplash associated disorders group before the accident reported no or few symptoms. The whiplash associated disorders patients after the accident reported pain and dysfunction during mouth opening, biting, chewing, swallowing and yawning and felt fatigue, stiffness and numbness in the jaw and face region. In addition, a majority also reported avoiding tough food and big pieces of food, and taking breaks during meals.

Altogether, these observations suggest an association between neck injury and disturbed jaw function and therefore impaired eating behaviour. A clinical implication is that examination of jaw function should be recommended as part of the assessment and rehabilitation of whiplash associated disorders patients.

From: J Electromyogr Kinesiol. 2008 Nov 26; [Epub ahead of print]

The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular joint disorders as compared to control subjects. Seventy-five full dentate, normo-occlusion, right handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side temporomandibular joint disorder, 25 presented with left side temporomandibular joint disorder and 25 pain free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with temporomandibular joint disorders as compared to control subjects (temporalis: 195.74+/-18.57 vs. 275.74+/-22.11; masseters: 151.09+/-17.37 vs. 283.29+/-31.87. An asymmetry index was calculated to determine ratios of right to left sided activation. Patients with right sided temporomandibular joint disorders demonstrated preferential use of their left sided muscles (asymmetry index -5.35+/-4.02) whereas patients with left sided temporomandibular joint disorder demonstrated preferential use of their right sided muscles (asymmetry index 6.95+/-2.82). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index may be a useful measure in discriminating patients with right vs. left sided temporomandibular joint disorders.

From: Int Arch Med. 2008 Oct 30;1(1):23 [Epub ahead of print]

This review explores the aetiology of temporomandibular disorders and discusses the controversies in variable treatment modalities. Pathologies of the temporomandibular joint (TMJ) and its’ associated muscles of mastication are jointly termed temporomandibular disorders (TMDs). TMDs present with a variety of symptoms which include pain in the joint and its surrounding area, jaw clicking, limited jaw opening and headaches. It is mainly reported by middle aged females who tend to recognize the symptoms more readily than males and therefore more commonly seek professional help. Several aetiological factors have been acknowledged including local trauma, bruxism, malocclusion, stress and psychiatric illnesses. The Research Diagnostic Criteria of the Temporomandibular Disorders (RDC/TMD) is advanced to other criteria as it takes into consideration the socio-psychological status of the patient. Several treatment modalities have been recommended including homecare practices, splint therapy, occlusal readjustment, analgesics and the use of psychotropic medication; as well as surgery, supplementary therapy and cognitive behavioural therapy. Although splint therapy and occlusal readjustment have been extensively used, there is no evidence to suggest that they can be curative; a number of evidence-based trials have concluded that these appliances should not be suggested as part of the routine care. Surgery, except in very rare cases, is discouraged since it is the most invasive alternative; recent studies have shown healthier outcome with cognitive behavioural therapy.

From: Cranio. 2008 Apr;26(2):104-17

The objective of this investigation was to test the hypothesis that alteration of the occlusions of patients suffering from temporomandibular disorders (TMD) to one that is neuromuscularly, rather than anatomically based, would result in reduction or resolution of symptoms that characterize the TMD condition. This hypothesis was proven correct in the present study, where 313 patients with TMD symptoms were examined for neuromuscular dysfunction, using several electronic instruments before and after treatment intervention. Such instrumentation enabled electromyographic (EMG) measurement of the activities of the masticatory muscles during rest and in function, tracking and assessment of various movements of the mandible, and listening for noises made by the TMJ during movement of the mandible. Ultra low frequency and low amplitude, transcutaneous electrical neural stimulation (TENS) of the mandibular division of the trigeminal nerve (V) was used to relax the masticatory muscles and to facilitate location of a physiological rest position for the mandible. TENS also made it possible to select positions of the mandible that were most relaxed above and anterior to the rest position when the mandible was moved in an arc that began at rest position. Once identified, the neuromuscular occlusal position was recorded in the form of a bite registration, which was subsequently used to fabricate a removable mandibular orthotic appliance that could be worn continuously by the patient. Such a device facilitated retention and stabilization of the mandible in its new-found physiological position, which was confirmed by follow up testing. Three months of full-time appliance usage showed that the new therapeutic positions achieved remained intact and were associated with improved resting and functioning activities of the masticatory muscles. Patients reported overwhelming symptom relief, including reduction of headaches and other pain symptoms. Experts consider relief of symptoms as the gold standard for assessment of effectiveness of TMD treatment. It is evident that this outcome has been achieved in this study and that taking patients from a less to a more physiological state is an effective means for reducing or eliminating TMD symptoms, especially those related to pain, most notably, headaches.

From: Int J Oral Maxillofac Surg. 2008 Jun;37(6):529-34. Epub 2008 Apr 28

The aim of this study was to investigate temporomandibular joint (TMJ) pain and magnetic resonance imaging characteristics in 104 TMJs with and 58 without degenerative changes of the condyle, such as osteophytes, erosion, avascular necrosis, subcondral cyst and intra-articular loose bodies. TMJ images were also assessed for flattening, retropositioning and hypomobility of condyle and disc displacement. Comparison of the TMJ side-related data showed a significant relationship between disc displacement without reduction and the presence of degenerative bony changes. Flattening, retropositioning and hypomobility of condyle showed no significant difference in relation to the presence or absence of degenerative bony changes. Retropositioning of the condyle was significantly associated to disc displacement, while condylar hypomobility was significantly more frequent in TMJ. Independent of the presence or type of DD, TMJ pain was more frequent in the presence of degenerative bony changes. When considering only disc displacement with reduction, TMJ pain was significantly associated to a degenerative condition. When there were no degenerative bony changes, TMJ pain was significantly more frequent in disc displacement without reduction. Despite the present findings, the absence of symptoms in some patients with condylar bony changes suggests that the diagnosis of osteoarthritis should be established by evaluation of magnetic resonance images in association with clinical examination.

From: Minerva Stomatol. 2008 Sep;57(9):399-411.

The aim of this study was to determine if stomatognathic functions correlate with alterations in walking function, that are detectable through the analysis of walking. The study enrolled 24 Caucasian adult females, asymptomatic for temporomandibular and muscular disorders and 20 Caucasian adult females with temporomandibular joint disorders (TMDs). The analysis of walking was performed under three different experimental conditions: 1) mandibular rest position; 2) habitual dental occlusion; 3) cotton rolls between the upper and the lower dental arches.

The mean pressure during walking, the percentage of loading on the left and the right feet and the loading surface were recorded as posturographic parameters. Generally, no difference was found in any of these parameters in the mean pressure during walking in the different considered conditions; only when two cotton rolls were positioned between the dental arches the load pressure was found to be significantly higher in the TMD patients than in the control subjects. In addition, in the same condition, TMD subjects showed a significantly smaller loading surface than control subjects, both under the right and the left feet.

TMDs seem to be associated to detectable alterations of the walking function.