How muscle relaxation and laterotrusion resolve open locks of the temporomandibular joint. Forward dynamic 3D-modeling of the human masticatory system

Patients with symptomatic hypermobility of the temporomandibular joint report problems with the closing movement of their jaw. Some are even unable to close their mouth opening wide (open lock). Clinical experience suggests that relaxing the jaw muscles or performing a jaw movement to one side (laterotrusion) might be a solution. The aim of our study was to assess the potential of these strategies for resolving an open lock and we hypothesised that both strategies work equally well in resolving open locks. We assessed the interplay of muscle forces, joint reaction forces and their moments during closing of mouth, following maximal mouth opening. We used a 3D biomechanical model of the masticatory system with a joint shape and muscle orientation that predispose for an open lock. In a forward dynamics approach, the effect of relaxation and laterotrusion strategies was assessed. Performing a laterotrusion movement was predicted to release an open lock for a steeper anterior slope of the articular eminence than relaxing the jaw-closing muscles, herewith we rejected our hypothesis. Both strategies could provide a net jaw closing moment, but only the laterotrusion strategy was able to provide a net posterior force for steeper anterior slope angles. For both strategies, the temporalis muscle appeared pivotal to retrieve the mandibular condyles to the glenoid fossa, due to its' more dorsally oriented working lines.

Validity of the Oral Behaviours Checklist: correlations between OBC scores and intensity of facial pain

The first purpose of this study was to translate the Oral Behaviours Checklist (OBC) into Dutch and to examine its psychometric properties. The second purpose was to examine the correlations between scores on the OBC and facial pain, while controlling for the possible confounding effects of psychosocial factors, such as stress, depression, somatisation and anxiety. The OBC was translated, following the international RDC/TMD consortium guidelines. Its psychometric properties were examined by assessing the test-retest reliability and concurrent validity [correlations between the OBC and the previously developed Oral Parafunctions Questionnaire (OPQ)]. Participants were 155 patients with TMD (77% female; mean age and s.d. = 43.6 and 14.4 years). The translation of the OBC into Dutch proceeded satisfactorily. The psychometric properties of the Dutch OBC were good; test-retest reliability was excellent (ICC = 0.86, P < 0.001). Concurrent validity was good: the correlation between the OBC and OPQ was high (r = 0.757, P < 0.001), while the correlations between individual items ranged from 0.389 to 0.892 (P < 0.001). Similar to previous Dutch studies using the OPQ, no significant correlation was found between oral parafunctions and facial pain (r = 0.069, P = 0.892). No significant correlations could be found between oral parafunctional behaviours and facial pain.

Social support in chronic pain: development and preliminary psychometric assessment of a new instrument

Satisfaction with social support (pain-relevant social support) may influence pain experience and behaviour in patients with chronic pain. Prior studies on measurement of social support, however, have been limited by the use of general, rather than of pain-specific assessment instruments. In this study, a new pain-relevant social support instrument, the Social support and Pain Questionnaire (SPQ), is presented together with an evaluation of its psychometric properties. A literature search was performed to establish different aspects of social support. For each of the six aspects found, one item was selected for inclusion in the new questionnaire. The draft version of the questionnaire was field tested. Thereafter, the psychometric properties of the SPQ were assessed in 250 patients with oro-facial pain. Principal component analysis (n=250) showed that the SPQ had a one-factor structure. The test-retest reliability of the SPQ (in a subsample of 54 patients) was fair-to-good (R=0·70; P<0·000). Convergent validity, as compared with a non-specific social support instrument, was good (n=140; R=0·54; P<0·000). The SPQ is a valid and reliable instrument, which offers the possibility to explore the patient's satisfaction with pain-related social support. With the SPQ, a useful tool to assess the influence of social support in patients with various types of pain is provided.

[Synovial chondromatosis of the temporomandibular joint. A systematic review of the literature on its characteristics]

Synovial chondromatosis of the temporomandibular joint is a disease which occurs rarely. A systematic review of the literature was carried out to identify its demographical, etiological, radiological, and clinical characteristics. A total of 191 case presentations were discovered. The mean age of patients was 47. The disease has been identified more frequently in women than in men. A part from pre-auricular swelling, the most frequently reported clinical characteristics resembled those of temporomandibular disorders. Abnormalities on radiographs were often evident. Insufficient evidence was found that trauma or rheumatoid arthritis plays a role in the development of this disease. Given the similarities with temporomandibular disorders, synovial chondromatosis should be considered in the differential diagnosis of patients suffering from complaints of temporomandibular dysfunction.

Developing abbreviated OHIP versions for use with TMD patients

The aim of this study was to evaluate the psychometric characteristics of three versions of the Dutch Oral Health Impact Profile (OHIP-NL), for clinical use with temporomandibular disorder (TMD) patients. To that end, two abbreviated OHIP versions (OHIP-NL14 and OHIP-NL5) were developed by respectively selecting 14 and five items from the officially translated and culturally adapted original 49-item OHIP-NL questionnaire. A total of 245 consecutive patients, referred by their dentist to the TMD clinic of the Academic Centre for Dentistry Amsterdam (77% women; mean age ± s.d. = 41·0 ± 14·9 years), completed the Research Diagnostic Criteria for TMD (RDC/TMD) axis II questionnaire and the OHIP-NL. Reliability and validity of all three OHIP versions were compared, and their associations with four psychological axis II variables, indicating the level of impairment of patients with TMD, were examined. According to guidelines for clinical application, internal consistency scores were sufficient for OHIP-NL and OHIP-NL14, but insufficient for OHIP-NL5. Test-retest reliability (n = 64) was excellent for OHIP-NL and OHIP-NL14 and fair to good for OHIP-NL5. For all three versions, there was evidence for score validity: associations between OHIP summary scores on the one hand and validation variables and other RDC/TMD axis II variables on the other hand met the expectations and were statistically significant (P < 0·001). In conclusion, the OHIP-NL and OHIP-NL14 both performed comparatively well and better than the OHIP-NL5. When the length of the questionnaire (i.e. the time needed for its completion) is an issue, the OHIP-14 would therefore be the preferred version.

[Oral health impact profile. an instrument for measuring the impact of oral health on the quality of life]

A Dutch-language version of the Oral Health Impact Profile, a questionnaire by means of which the impact of oral health on the quality of life of patients can be determined, was developed and subsequently psychometrically tested among a group of patients with complaints concerning missing dentition or their dentures. In addition, a shortened version of this so-called OHIP-NL49, the OHIP-NL14, was psychometrically tested among a group of patients with temporomandibular disorders. The psychometrical characteristics of both the OHIP-NL49 and the OHIP-NL14 were very good: both the reliability and the validity were high. The conclusion was, that the OHIP-NL49 and the OHIP-NL14 are well suited for determining the impact of oral health on the quality of life.

[Oral kinesiology and the quality of life]

In a comparative study, the influence of oral health on the quality of life was investigated for people with temporomandibular pain, people with tooth wear and people with complete dentures. To this end, the study made use of the Oral Health Impact Profile. Both the total score and the scores on 4 of the 7 domains of the Oral Health Impact Profile were significantly higher in the research group with temporomandibular pain than in the research groups with tooth wear and complete dentures. These results suggest that among people with temporomandibular pain the influence of oral health on the quality of life is more negative than among people with tooth wear and among people with complete dentures. This result can probably be linked with the general finding that patients with temporomandibular pain bear a relatively high psycho-social burden.

Some remarks on the RDC/TMD Validation Project: report of an IADR/Toronto-2008 workshop discussion

A large-scale, multi-site study has been performed to examine the reliability and validity of the research diagnostic criteria for temporomandibular disorders (RDC/TMD) and to suggest revisions of the current RDC/TMD. During an International Association for Dental Research (IADR) Workshop in July 2008, preliminary results of this RDC/TMD Validation Project were presented. One of us was invited to be the critical discussant of the Workshop session in which the Study Group's papers were presented. This article is based on that contribution. One of our concerns relates to the possible circularity and bias, introduced by incorporating the RDC/TMD tests under investigation into the criterion examination. This may have had serious consequences for the outcomes of the validity study as well as for the proposed revisions of the diagnostic algorithms. In addition, a more detailed description of the process of replacing the RDC/TMD tests by other tests is needed. Further, to come to a revised RDC/TMD, it is crucial to know not only how the test outcomes are capable of discriminating between patients with TMD pain and pain-free subjects, as studied in this Validation Project, but also, more importantly, how they discriminate between patients with TMD pain and patients with oro-facial pain (OFP) complaints of non-TMD origin. We welcome the suggestion of an international expert panel to consider, deliberate, and reach consensus on a revised version of the RDC/TMD. Finally, we agree that the suggested expansions of the RDC/TMD taxonomy stress the need for the development of an RDC for OFP, which would include, as an integral part, the revised RDC/TMD.

Effects of intense chewing exercises on the masticatory sensory-motor system

Nociceptive substances, injected into the masseter muscle, induce pain and facilitate the jaw-stretch reflex. It is hypothesized that intense chewing would provoke similar effects. Fourteen men performed 20 bouts of 5-minute chewing. After each bout, 20 min and 24 hrs after the exercise, muscle fatigue and pain scores and the normalized reflex amplitude from the left masseter muscle were recorded. Before, 20 min, and 24 hrs after the exercise, signs of temporomandibular disorders and pressure-pain thresholds of the masticatory muscles were also recorded. Fatigue and pain scores had increased during the exercise (P < 0.001), but the reflex amplitude did not (P = 0.123). Twenty minutes after the exercises, 12 participants showed signs of myofascial pain or arthralgia. Pressure-pain thresholds were decreased after 20 min (P = 0.009) and 24 hrs (P = 0.049). Intense chewing can induce fatigue, pain, and decreased pressure-pain thresholds in the masticatory muscles, without concomitant changes in the jaw-stretch reflex amplitude.

[Myogenous temporomandibular pain: treat with care!]

For the treatment of myogenous temporomandibular pain, a clinician can choose from among a wide variety of possibilities. Unfortunately, a paper summarizing the effectiveness of all these forms of treatment does not yet exist. The aim of this paper is to provide specific advice for dentists concerning the treatment of patients with myogenous temporomandibular pain by means of a systematic review of the relevant literature. The results of this review of the literature suggest that all forms of treatment selected, including treatment with placeboes, are equally effective in reducing myogenous temporomandibular pain. In order to avoid liability issues, it is advisable to choose for a restrained, reversible form of treatment. The dentist and the patient must, in this respect, be aware that the pain can continue after treatment (albeit at a reduced level) or can return after a period of time.

Effects of pergolide on severe sleep bruxism in a patient experiencing oral implant failure

In the patient described in this study, oral implants failed as a probable consequence of severe, polysomnographically confirmed sleep bruxism. As this patient had the wish to be re-implanted after this failure, we decided to try diminishing the frequency of bruxism and duration first. To that end, two management strategies were used. Their efficacy was evaluated polysomnographically, yielding a total of six overnight recordings. Of the selected management strategies, the administration of low doses of the dopamine D1/D2 receptor agonist pergolide finally resulted in a substantial and lasting reduction in the bruxism outcome measures under study. This result supports the previous suggestion that central neurochemicals like dopamine may be involved in the modulation of sleep bruxism. The case report also illustrates the importance of an extensive history taking (questionnaires as well as oral) and clinical examination of oral implant patients for the presence of severe bruxism before the implant procedure is started. In case of doubt, polysomnography may be considered to definitively confirm or rule out the presence of severe sleep bruxism.

[Predictive factors for treatment outcome of temporomandibular disorder patients. A retrospective study]

Not all temporomandibular disorder patients respond positively to the treatment given. The aim of this retrospective investigation was to study the possible associations between some clinical and psychological factors, recorded at the patient's first visit, and treatment outcome. Data of 102 patients referred to the department's clinic was collected. In 51 patients the treatment was unsuccessful (no or only partial relief of pain), in 51 patients, matched for age and gender, the treatment was successful (complete relief of pain complaints). Logistic regression modeling (p = 0.008, explained variance = 15%; sensitivity = 59%; specificity = 57%) showed that an unsuccessful treatment was associated with more preceding treatments and more jaw-disability, a successful treatment with higher scores on the graded chronic pain severity scale. In conclusion, the results of this study suggest that some predictive factors may be helpful in identifying patients who are at risk of being resistant to the usual treatment given.

Is condylar position a predictor for functional signs of TMJ hypermobility?

Temporomandibular joint (TMJ) hypermobility is noted only when it interferes with smooth mandibular movements. These interferences (viz. clicking sounds and jerky mandibular movements) result from condylar dislocation in front of the eminence at wide mouth opening, or alternatively in front of the articular disc (posterior disc displacement). The aim of this study was to test the hypothesis that condyles of hypermobile persons are positioned more anterosuperiorly to the crest of the eminence during maximum mouth opening than those of persons without TMJ hypermobility. Possible posterior disc displacement was also evaluated. Nine persons with symptomatic hypermobility and nine control persons free of internal derangements were included, their diagnoses being based upon opto-electronic movement recordings. Condylar positions during maximum mouth opening were analysed on magnetic resonance images with two slightly different methods, showing the degree to which the condyles are displaced around the eminence. No posterior disc displacements were found in any of the magnetic resonance images. After excluding an outlier and using both measurement methods, a small difference in condylar position was found between the two groups of subjects. The condyles of all hypermobile persons travelled beyond the eminence; however, so were the condyles of nearly half of the non-hypermobiles. The large overlap between both groups suggests that condylar position alone is not a good predictor for symptomatic TMJ hypermobility. It is probably the combination of condylar location in front of the eminence with a particular line of action of the masticatory muscles, which gives rise to functional signs of hypermobility.

[Occupational differentiation in dentistry 3. Hypermobility of the temporomandibular joint and condylar position at maximal mouth opening]

Hypermobility of the temporomandibular joint is only noted when it interferes with smooth mandibular movements. These interferences may result from a condylar dislocation beyond the temporal eminence at maximum mouth opening. Aim of this study was to test whether the condyle of a symptomatically hypermobile temporomandibular joint is positioned more anterosuperiorly to the temporal eminence at maximum mouth opening than a condyle without hypermobility. Nine persons with a hypermobile temporomandibular joint and 9 control persons participated. Diagnostics were based upon opto-electronic mandibular movement recordings. Condylar positions at maximum mouth opening were assessed by magnetic resonance imaging. A small significant difference in condylar position was found between groups. Condyles of persons with a hypermobile temporomandibular joint moved beyond the temporal eminence. However, this was also true for nearly half of the control persons. This suggests that condylar position alone is not a sufficient condition for symptomatic hypermobility of the temporomandibular joint. Maybe, symptoms of hypermobility only become apparent in combination with a particular line of action of the masticatory muscles.

[Occupational differentiation in dentistry 2. From Brueghel's syndrome to a radiant smile. An advanced postgraduate programme in oral kinesiology]

Oral movement disorders, jaw pain, and tooth wear are examples of clinical problems that are part of the dental discipline 'oral kinesiology'. About half of the advanced postgraduate programme in oral kinesiology involves the diagnosis, indication, and management of patients with one or more oral kinesiologic problems. The remaining time is available for thematic courses and a research project. The breadth of the programme will hopefully lead to improved care for patients whose treatment until now has been dispersed between various dental specialists. Successful candidates will obtain an advanced postgraduate diploma in Oral Kinesiology, and can also apply to be recognized as a gnathologist.

Bruxism: its multiple causes and its effects on dental implants - an updated review*

There is a growing interest in bruxism, as evidenced by the rapidly increasing number of papers about this subject during the past 5 years. The aim of the present review was to provide an update of two previous reviews from our department (one about the aetiology of bruxism and the other about the possible role of this movement disorder in the failure of dental implants) and to describe the details of the literature search strategies used, thus enabling the readers to judge the completeness of the review. Most studies that were published about the etiology during the past 5 years corroborate the previously drawn conclusions. Similarly, the update of the review about the possible causal relationship between bruxism and implant failure reveals no new points of view. Thus, there is no reason to assume otherwise than that bruxism is mainly regulated centrally, not peripherally, and that there is still insufficient evidence to support or refute a causal relationship between bruxism and implant failure. This illustrates that there is a vast need for well-designed studies to study both the aetiology of bruxism and its purported relationship with implant failure.

Dental implants in patients with bruxing habits

Bruxism (teeth grinding and clenching) is generally considered a contraindication for dental implants, although the evidence for this is usually based on clinical experience only. So far, studies to the possible cause-and-effect relationship between bruxism and implant failure do not yield consistent and specific outcomes. This is partly because of the large variation in the literature in terms of both the technical aspects and the biological aspects of the study material. Although there is still no proof for the suggestion that bruxism causes an overload of dental implants and of their suprastructures, a careful approach is recommended. There are a few practical guidelines as to minimize the chance of implant failure. Besides the recommendation to reduce or eliminate bruxism itself, these guidelines concern the number and dimensions of the implants, the design of the occlusion and articulation patterns, and the protection of the final result with a hard occlusal stabilization splint (night guard).

[Treatment of temporomandibular disorders in general practice. A survey in view of insurance claims]

In the eighth decade of the last century, about 3.5% of Dutch men and about 6% of Dutch women reported temporomandibular disorders. In 5% of the Dutch population temporomandibular disorders were diagnosed. It is unknown how many persons are seeking treatment for temporomandibular complaints. The aim of the present study was determining for how many persons and at which age of these persons treatments of temporomandibular disorders in general practices were reimbursed by an insurance company. On the basis of the yearly number of reimbursements by this insurance company, the yearly number of treatments of the Dutch population as a whole was estimated. The estimation was 0.87 treatments per 1.000 inhabitants, which figure was substantial lower as could be expected on the basis of the outcome of epidemiologic research projects. Within the limitations of this explorative study, a careful conclusion could be that only few treatments for temporomandibular disorders are charged by general practitioners. Probably, they are focussing on consultation and diagnosing, and not on treating the disease themselves.

[Evidence-based management of temporomandibular dysfunction. Think before you begin!]

Nowadays, dentists are expected to base their treatment decisions on the strongest available evidence. This so-called evidence-based approach has four steps: the formulation of a clinical problem, the search for evidence, the evaluation of the evidence, and the treatment of the patient. As part of this approach, the strongest evidence comes from systematic reviews, which are free of any author-related bias. Since working according to the principles of evidence-based dentistry is time consuming, dental schools should assist general practitioners through producing sufficient numbers of high-quality systematic reviews. The ever-increasing emancipation of patients stresses the need of adopting the principles of evidence-based dentistry. 'Think twice' should be the motto.

Short-term effects of a mandibular advancement device on obstructive sleep apnoea: an open-label pilot trial

Obstructive sleep apnoea (OSA) is a common sleep disorder, which is, among others, associated with snoring. OSA has a considerable impact on a patient's general health and daily life. Nasal continuous positive airway pressure (nCPAP) is frequently used as a "gold standard" treatment for OSA. As an alternative, especially for mild/moderate cases, mandibular advancement devices (MADs) are prescribed increasingly. Their efficacy and effectiveness seem to be acceptable. Although some randomized clinical trials (RCTs) have been published recently, most studies so far are case studies. Therefore, our department is planning a controlled RCT, in which MADs are compared with both nCPAP and a control condition in a parallel design. As a first step, an adjustable MAD was developed with a small, more or less constant vertical dimension at different mandibular positions. To test the device and the experimental procedures, a pilot trial was performed with 10 OSA patients (six mild, four moderate; one women, nine men; mean age = 47.9 +/- 9.7 years). They all underwent a polysomnographic recording before as well as 2-14 weeks after insertion of the MAD (adjusted at 50% of the maximal protrusion). The apnoea-hypopnoea index (AHI) was significantly reduced with the MAD in situ (P = 0.017). When analysed as separate groups, the moderate cases showed a significantly larger decrease in AHI than the mild cases (P = 0.012). It was therefore concluded from this pilot study that this MAD might be an effective tool in the treatment of, especially, moderate OSA.

Effects of masticatory muscle fatigue without and with experimental pain on jaw-stretch reflexes in healthy men and women

OBJECTIVE

To examine the effects of experimentally evoked masticatory muscle fatigue, without and with experimental muscle pain, on the short-latency jaw-stretch reflex, using a randomised crossover design.

METHODS

Reflexes were evoked in both the masseter and temporalis muscles in 15 men and 13 women. The study was performed in two blocks, both containing 3 experimental conditions (before, directly after, and 15 min after provocation). Provocation consisted of a fatiguing chewing test, followed by an intramuscular injection of either isotonic saline (IS; non-painful) or hypertonic saline (HS; painful).

RESULTS

No significant effects of the experimental condition 'fatigue+IS' were found for any of the reflex outcome variables. For each muscle, the 'fatigue+HS' condition yielded significantly higher normalized reflex amplitudes than the other conditions. Several muscles displayed gender differences regarding both onset latency and normalized reflex amplitude.

CONCLUSIONS

Experimentally evoked mild-to-moderate muscle fatigue does not modulate the human jaw-stretch reflex. On the other hand, experimental muscle pain, evoked after the performance of a fatiguing chewing test, does yield a facilitation of this reflex. The gender differences found in both onset latency and peak-to-peak amplitude stress the need to take gender into consideration in future jaw reflex studies.

SIGNIFICANCE

The sensitivity of the human jaw-stretch reflex can be modulated by HS-induced muscle pain; not by muscle fatigue that is provoked by intense chewing.

Craniomandibular pain, oral parafunctions, and psychological stress in a longitudinal case study

In a single case study, the most frequently suggested contributing factors to craniomandibular pain, viz., oral parafunctions and psychological stress, were studied in more detail. During a 13-week study period, questionnaires were completed, in which, among others, jaw muscle pain, bruxism behaviour, and experienced/anticipated stress were noted. During about 40% of the nights, nocturnal masticatory muscle activity (NMMA) was recorded, using single-channel electromyography (EMG). The number of NMMA events per recorded hour was scored, using a detection threshold of 10% of the maximum voluntary contraction level. This threshold was established in a separate study, in which EMG was compared with polysomnography. Stepwise regression analyses indicated, that morning jaw muscle pain could be explained by evening jaw muscle pain for 64% and by alcohol intake for another 2%. In turn, evening jaw muscle pain was explained by daytime clenching for 56% and by vacuum sucking of the tongue for an additional 6%. Finally, daytime clenching was significantly explained by experienced stress for 30%. Data of the recorded nights showed, that variations in NMMA did not contribute to variations in morning jaw muscle pain. This case study corroborates the paradigm that experienced stress may be related to daytime clenching and, in turn, to evening and morning jaw muscle pain.

Recognition of internal derangements

One of the most common symptoms of temporomandibular disorders is an internal derangement (ID). The aim of this study was to test the inter-observer reliability of the recognition of IDs by means of auscultation, palpation or both. To that end, 120 women and 100 men were screened by two trained examiners for the presence of IDs. Anterior disc displacement was diagnosed in 14% of the cases and hypermobility in 12%. In 4% of the cases, the ID was classified as 'other'. The inter-rater reliability (Cohen's kappa) was moderate for the presence of an ID for all techniques, while for the classification into type, an almost perfect reliability was found for the combined technique. It was concluded that the type of ID can best be established with the combination of auscultation and palpation; for the establishment of an ID as such, any of the three techniques would suffice.

[Dental implants in tooth grinders]

Bruxism (tooth grinding and clenching) is generally considered a contraindication for dental implants, although the evidence is usually based on clinical experience only. So far, studies to the possible cause-and-effect relationship between bruxism and implant failure do not yield consistent and specific outcomes. This is partly due to the large variation in the technical and the biological aspects of the investigations. Although there is still no proof that bruxism causes overload of dental implants and their suprastructures, a careful approach is recommended. Practical advices as to minimize the chance of implant failure are given. Besides the recommendation to reduce or eliminate bruxism itself, these advices concern the number and dimensions of the implants, the design of the occlusion and articulation patterns, and the use of a hard nightguard.

Oral kinesiology. A new postgraduate programme in the Netherlands

As one of the dental differentiations in The Netherlands, temporomandibular disorders (TMD) focuses on the diagnosis and treatment of pain and dysfunction of the masticatory system. Bruxism (i.e. tooth clenching and/or grinding) is thought to play an important aetiological role in TMD. Among others, bruxism may result in TMD pain and dental attrition. The close relationship between TMD, bruxism, and attrition necessitates an integrated approach to these clinical problems. This could be achieved through the multidisciplinary differentiation 'oral kinesiology', that covers not only the diagnosis and treatment of TMD and bruxism but also the restoration of worn dentitions. This article focuses on the background of oral kinesiology, as well as on the rationale to develop a curriculum for the postgraduate training of dentist-kinesiologists in the Netherlands. Further, the oral kinesiology curriculum of the Academic Centre for Dentistry Amsterdam will be introduced. This curriculum will ensure that specialized professionals, who are able to approach the different aspects of oral kinesiology in an integrated manner, are available not only for general dental practice but also for centres for special dental care and university departments. This will lead to improved care for patients, whose management is until now dispersed between various dental specialists.

Biomechanics of the human temporomandibular joint during chewing

Experimental data on the loading of the human temporomandibular joint during chewing are scarce. Coincidence of the opening and closing chewing strokes of the condyles probably indicates compression in the joint during chewing. Using this indication, we studied the loading of the joint during chewing and chopping of a latex-packed food bolus on the left or right side of the mouth. Mandibular movements of ten healthy subjects were recorded. Distances traveled by the condylar kinematic centers were normalized with respect to the distances traveled during maximum opening. We judged coincidence of the opening and closing condylar movement traces without knowing their origin. When subjects chewed, the ipsilateral condyles traveled shorter distances than did the contralateral condyles. During chewing and chopping, all contralateral condyles showed a coincident movement pattern, while a significantly smaller number of ipsilateral condyles did. These results suggest that the ipsilateral joints were less heavily loaded during chewing and chopping than were the contralateral joints.

Measurement of condylar motion: a plea for the use of the condylar kinematic centre

In this study, a plea is given for the use of the kinematic centre in studies of the kinematics of the human temporomandibular condyle. The concept of the kinematic centre is based upon the assumption that the movements of the condyle-disc complex within the temporomandibular joint can reasonably well be described by those of a ball-shaped condyle-disc complex. The kinematic centre is then the centre of the sphere. Its movement traces have the advantage that they are smooth and have a good reproducibility between consecutive movements. Moreover, the open and close traces are just a few tenths of a millimetre apart and show no crossings. This makes the kinematic centre a suitable choice in order to avoid false-positive diagnoses in the study of internal derangements by means of condylar movement recordings. However, the kinematic centre has the disadvantage that the mandibular movements have to be recorded by rather complicated six degrees of freedom recording equipment and that the exploration algorithm for its location may sometimes have difficulties in finding the right location.

Reports of SSRI-associated bruxism in the family physician's office

AIMS

Recently, the use of selective serotonin reuptake inhibitors (SSRIs) has been associated with the occurrence or worsening of bruxism. The aim of this study was to obtain a first indication of the prevalence of SSRI-associated bruxism reported to family physicians, the main prescribers of SSRIs.

METHODS

A questionnaire, with questions about prescription rate, already registered adverse reactions, and bruxism-related side effects of 4 different types of SSRIs, was sent to all family physicians in greater Amsterdam (n = 391).

RESULTS

With a response rate of 42.5%, frequent observations of already registered side effects were found. In addition, 5 family physicians (3.2%) reported the occurrence of bruxism in relation to the use of SSRIs.

CONCLUSION

The use of SSRIs might be associated with the occurrence of bruxism. A case report is provided that corroborates this suggestion.

Is there a relationship between head posture and craniomandibular pain?

An often-suggested factor in the aetiology of craniomandibular disorders (CMD) is an anteroposition of the head. However, the results of clinical studies to the relationship between CMD and head posture are contradictory. Therefore, the first aim of this study was to determine differences in head posture between well-defined CMD pain patients with or without a painful cervical spine disorder and healthy controls. The second aim was to determine differences in head posture between myogenous and arthrogenous CMD pain patients and controls. Two hundred and fifty persons entered the study. From each person, a standardized oral history was taken and blind physical examinations of the masticatory system and of the neck were performed. The participants were only included into one of the subgroups when the presence or absence of their symptoms was confirmed by the results of the physical examination. Head posture was quantified using lateral photographs and a lateral radiograph of the head and the cervical spine. After correction for age and gender effects, no difference in head posture was found between any of the patient and non-patient groups (P > 0.27). Therefore, this study does not support the suggestion that painful craniomandibular disorders, with or without a painful cervical spine disorder, are related to head posture.

Local kinematic and anthropometric factors related to the maximum mouth opening in healthy individuals

The aim of the present study was to investigate the influence of local anthropometric (mandibular length and width) and kinematic (forward and downward condylar translation and angle of rotation) variables upon the maximum mouth opening (MMO). Thirty-five healthy individuals, 17 men and 18 women, mean age 23 years with a range from 18 to 31 years, performed six to eight maximal, symmetrical and pain-free open-close movements during a 20-s recording. Mandibular movements were recorded by means of the OKAS-3D jaw movement recording system. A stepwise regression analysis showed that differences in MMO are mainly explained by differences in the angle of rotation and in mandibular length (R2adj=91.5%). Including the downward and forward component of condylar translation into the regression model increased the explained variance with only 4.7%. A second stepwise analysis showed that the angle of rotation is positively related to the forward component of the condylar translation and negatively related to its downward component (R2adj=52.7%). In conclusion, differences in MMO between healthy individuals are, to a large extent, explained by differences in the angle of rotation and in mandibular length. In its turn, differences in the angle of rotation are related to differences in condylar translation.

Bruxism is mainly regulated centrally, not peripherally

Bruxism is a controversial phenomenon. Both its definition and the diagnostic procedure contribute to the fact that the literature about the aetiology of this disorder is difficult to interpret. There is, however, consensus about the multifactorial nature of the aetiology. Besides peripheral (morphological) factors, central (pathophysiological and psychological) factors can be distinguished. In the past, morphological factors, like occlusal discrepancies and the anatomy of the bony structures of the orofacial region, have been considered the main causative factors for bruxism. Nowadays, these factors play only a small role, if any. Recent focus is more on the pathophysiological factors. For example, bruxism has been suggested to be part of a sleep arousal response. In addition, bruxism appears to be modulated by various neurotransmitters in the central nervous system. More specifically, disturbances in the central dopaminergic system have been linked to bruxism. Further, factors like smoking, alcohol, drugs, diseases and trauma may be involved in the bruxism aetiology. Psychological factors like stress and personality are frequently mentioned in relation to bruxism as well. However, research to these factors comes to equivocal results and needs further attention. Taken all evidence together, bruxism appears to be mainly regulated centrally, not peripherally.

A reliability study of clinical tooth wear measurements

STATEMENT OF PROBLEM

Most studies examining tooth wear severity have been performed on dental casts. This indirect approach has limited applicability to dental practice because during the assessment of the casts, the identification of dentin exposure is difficult or even impossible.

PURPOSE OF STUDY

The purpose of this study was to assess occlusal and incisal tooth wear clinically to determine the reliability of the assessment procedure and to establish the influence of selected relevant clinical variables (dental quadrant, tooth type, and severity of wear) on the reliability.

MATERIAL AND METHODS

Forty-five volunteers (17 men, 28 women; mean age 33.7 +/- 10.7 years), 32 with temporomandibular disorders and 13 free from signs and symptoms of such disorders, were evaluated on 4 occasions. Two trained observers graded tooth wear at 2 different points in time with a 5-point ordinal scale developed for use in this study. The inter-rater and intra-rater reliability of the scale was expressed as Cohen's kappa. The influence of 2 clinical variables, dental quadrant and tooth type, on the values of kappa was tested with 1-way analysis of variance and post hoc Bonferroni tests. Probability levels of P< .05 were considered statistically significant. The influence of the final clinical variable, severity of wear, was assessed qualitatively.

RESULTS

The overall values of the inter-rater and intra-rater reliability were substantial (kappa = 0.632 to 0.678). The clinical variable dental quadrant did not influence the kappa values, whereas the inter-rater reliability during the first session was better for incisors and canines than for premolars (1-way analysis of variance: F(3,23)=4.577, P=.012; post hoc Bonferroni tests: P=.030 and.036). Qualitative assessment of severity of wear indicated that the more advanced the tooth wear, the more reliably it could be graded.

CONCLUSION

By means of the developed 5-point ordinal scale and within the limitations of this study, it was concluded that tooth wear can be assessed reliably in the clinical dental setting.

The three-dimensional active envelope of jaw border movement and its determinants

The sagittal and frontal active envelope of border movement is applied regularly as a clinical tool in functional examinations of the human masticatory system. In contrast, the three-dimensional movement area has hardly been examined. Furthermore, the determinants of this area are not established unambiguously. In the present study, the three-dimensional envelope of incisor movement was predicted with a three-dimensional mathematical model of the human masticatory system, which included the morphology of the system and the fine architecture of its muscles. With this model, the influence of the temporomandibular ligaments and the passive muscle tensions on the envelope were estimated. The predicted three-dimensional active envelope of border movements was limited in horizontal directions, predominantly by the temporomandibular ligaments. The passive tensions of the masticatory muscles influenced, although marginally, its vertical extension. It appeared unlikely that, in a normal situation, active muscle tensions (casu quo muscle reflexes) contribute to the shape of the envelope.

Prevalence of cervical spinal pain in craniomandibular pain patients

It has often been suggested that patients with a craniomandibular disorder (CMD) more often suffer from a cervical spine disorder (CSD) than persons without a CMD. However, in most studies no controlled, blind design was used, and conclusions were based on differing signs and symptoms. In this study, the recognition of CMD and CSD was based upon the presence of pain. The aim of this study was to determine the prevalence of cervical spinal pain in persons with or without craniomandibular pain, using a controlled, single-blind design. From 250 persons, a standardised oral history was taken, and a physical examination of the masticatory system and the neck was performed. Three classification models were used: one based on symptoms only; a second on signs only; and a third one based on a combination of symptoms and signs. The CMD patients were also subdivided in three subgroups: patients with mainly myogenous pain; mainly arthrogenous pain; and both myogenous and arthrogenous pain. Craniomandibular pain patients more often showed cervical spinal pain than persons without craniomandibular pain, independent of the classification model used. No difference in the prevalence of cervical spinal pain was found between the three subgroups of craniomandibular pain patients.

Psychological distress in chronic craniomandibular and cervical spinal pain patients

Recent studies to chronic pain have shown that the number of painful body areas is related to the level of psychological distress. Therefore, the first aim of this study was to analyse differences in level of psychological distress between craniomandibular pain patients with or without cervical spinal pain. In this analysis, the number of painful body areas below the cervical spine was also taken into account. The second aim was to determine psychological differences between subgroups of craniomandibular pain patients. In this study, 103 out of 250 persons with or without craniomandibular pain were included in the final analyses. Patients who suffered from both craniomandibular and cervical spinal pain showed higher levels of psychological distress, as measured with the Symptom Checklist 90 (SCL-90) than patients with local craniomandibular pain and persons without pain. Further, a positive relationship was found between the number of painful body areas below the cervical spine, as measured on a body drawing, and the SCL-90 scores. No psychological differences were found between myogenous and arthrogenous craniomandibular pain patients. In conclusion, chronic craniomandibular pain patients with a coexistent cervical spinal pain showed more psychological distress compared to patients with only a local craniomandibular pain and asymptomatic persons.

Influence of periodontal receptors on the jaw-jerk reflex amplitude in man

To study the role of periodontal mechanoreceptors in the modulation of the human jaw-jerk reflex, 60 reflexes were elicited in each of six healthy individuals under three different conditions: (a) with unilateral tooth support on the ipsilateral side; (b) with support on the contralateral side; and (c) with support and local anesthesia of the periodontal tissues on the ipsilateral side. During all conditions, background muscle activity and mandibular displacement were kept as constant as possible. Using on-surface EMG and the amplitude of the first peak of the biphasic jaw-jerk potential as the outcome variable, a condition-dependent reflex amplitude was found for the visually controlled right anterior temporalis muscle. Specifically, the 'ipsilateral support plus anesthesia' condition yielded higher amplitudes than the 'ipsilateral support' condition. Highest amplitudes were found for the 'contralateral support' condition. It was concluded that periodontal mechanoreceptors on the ipsilateral side have an inhibitory effect on the jaw-jerk reflex amplitude in the anterior temporalis muscle.

Clinical tests in distinguishing between persons with or without craniomandibular or cervical spinal pain complaints

The recognition of a craniomandibular or cervical spinal pain is usually based upon the pain complaint of the patient, reported during an oral history, and the pain responses provoked in a clinical examination. Often used clinical tests are palpation, and function tests like dynamic/static tests or active movements. The relative importance of these tests for the recognition of the musculoskeletal pain is important. Therefore, it was the aim of the present study to determine which test, or combination of tests, best discriminates between persons with or without craniomandibular and/or cervical spinal pain complaints. Two hundred and fifty persons participated. From each person, a standardized oral history was taken. Then, in a randomized order and using a blind design, physical examinations of the craniomandibular system and of the neck were performed. Forward stepwise logistic regression analyses showed that the dynamic/static tests discriminated better between persons with and without pain complaints than the other tests did. In conclusion, in studies to the coexistence of craniomandibular and cervical spinal pain, it may be a good choice to base the recognition of these disorders on the pain complaints reported in the oral history which are verified by the pain response of the dynamic/static tests.

[Multidisciplinary diagnosis and treatment of craniomandibular disorders]

Treatment of craniomandibular disorders (CMD) requires a multidisciplinary approach. The CMD-team of the Academic Centre for Dentistry Amsterdam (ACTA) therefore consists not only of specialists in CMD and orofacial pain, but also of physiotherapists and a psychologist. Possible CMD-patients are referred to this team by the dentist-general practitioner, either directly or upon request of a family physician or a medical specialist; the many rules of such referrals are outlined in the article. The CMD-team regularly consults other disciplines for diagnosis and/or treatment of their patients. For instance, internal referrals are sometimes made to the departments of Oral radiology, Endontology, Periodontology, Orthodontics, or Oral and maxillofacial surgery. External referrals to, for example, a speech therapist or a medical specialist (e.g., a pain specialist) are arranged by the family physician upon request of the CMD-team.

[Treatment protocol for craniomandibular dysfunction 2. Treatment]

In two essays the treatment strategy of the department of Oral Function of the Academic Center of Dentistry Amsterdam for treating craniomandibular disorder (CMD) patients is described. In this second essay a description is given of several dental, physiotherapeutical and psychological treatment modalities for CMD. Then treatment strategies for the different categories of CMD are described. It is also indicated which aspects of the treatment strategy are based upon 'evidence based care' and which aspects are more based upon principles of 'common sense' and 'clinical prudence'.

Functional subdivision of the human masseter and temporalis muscles as shown by the condylar movement response to electrical muscle stimulation

In previous studies from our laboratory, a functional subdivision of the human temporalis and masseter muscles was demonstrated by means of opto-electronic recordings of the lower incisal point movement responses to electrical muscle stimulation. In the present study, it was examined whether this subdivision was also reflected in different movement responses of the mandibular condyle. To that end, the condylar movement responses to unilateral stimulation of four masseter muscle parts and three temporalis muscle parts were studied in four different jaw positions. The kinematic centre was used for condylar reference point. For both the amplitude and the direction of the movement responses, the effects of stimulation location and jaw position were studied using multivariate ANOVA and contrast analyses. It was found that for both outcome variables, the functional subdivision of the masseter and temporalis muscles was also reflected in some, but not all, of the movement responses of the mandibular condyles. The deep masseter muscle part and the (anterior) temporalis muscle part responded similarly to electrical stimulation.

[Treatment protocol for craniomandibular disorder 1. Diagnosis]

In two essays the treatment strategy of the department of Oral Function of the Academic Center of Dentistry Amsterdam for treating craniomandibular disorder (CMD) patients will be presented. This first essay starts with a short description of the symptomatology, classification and etiology of CMD. Then it is described how to diagnose a CMD with the use of a standardized diagnostic protocol. Some important aspects of the differential diagnosis of CMD are discussed. Furthermore it is discussed when a CMD-patient can be treated by the dentist or when referral to a CMD specialist or oral surgeon is necessary.

[Role of the psychologist in the treatment of bruxism]

Although there is a controversy about the importance of psychological factors in the development, enhancement and perpetuation of bruxism and other parafunctional activities, the contribution of a psychologist in the treatment of the individual patient is recommended. This contribution consists of diagnostic examination and treatment, most often a short cognitive behavior modification therapy. Because bruxism is mostly examined and treated in relation to the complaints it might cause, especially CMD-complaints, diagnosis and treatment are mostly directed at both. For the diagnosis a questionnaire is used, including a psychological test, which is followed by one or more interviews. The treatment is directed at learning to recognize bruxism activities, to practice alternative behavior, and to learn to cope better with situations that may lead to an increase of bruxism.

[Treatment of bruxism: physiotherapeutic approach]

Epidemiological and experimental studies suggest that there is a relationship between bruxism and pain in the orofacial region, and between bruxism and restricted mandibular movements. However, the exact nature of this relationship remains unclear. Therefore, up till now, the following working hypothesis is used: bruxism can lead to (chronic) pain complaints and restricted mandibular movements, when its intensity exceeds the adaptation capacity of the musculoskeletal structures. In that case, the aims of physical therapy treatment are twofold: to decrease symptoms, such as pain ('symptom therapy'), and to teach the patient to recognise and reduce the bruxism ('behavioral therapy'). Techniques used for symptom treatment are massage and stretching exercises. For the behavioral therapy exercises and myofeedback are often used.

[Etiology of bruxism: morphological, pathophysiological and psychological factors]

Bruxism is a controversial phenomenon, but there is consensus about the multifactorial nature of the etiology. Besides peripheral (morphological) factors, central (pathophysiological and psychological) factors can be distinguished. In the past, morphological factors, like occlusal discrepancies and the anatomy of the bony structures of the orofacial region, have been considered the main causative factors for bruxism. Nowadays, these factors play only a minor role, if any. Recent focus is more on the pathophysiological factors. For example, bruxism has been suggested to be part of a sleep arousal response. In addition, bruxism appears to be modulated by various neurotransmitters in the central nervous system. More specifically, disturbances in the central dopaminergic system have been linked to bruxism. Further, factors like smoking, alcohol, drugs, diseases, and trauma may be involved in the bruxism etiology. Psychological factors like stress and personality are frequently mentioned in relation to bruxism as well, but research shows controversial results. Taken all evidence together, bruxism appears to be mainly regulated centrally, not peripherally.