TMD: Psychosocial or not?

Evidence supports the use of psychosocial interventions for chronic orofacial pain.

Themessl-Huber M. Evid Based Dent. 2012.

Oral Health and Health Research Programme, Dental Health Services Research Unit, University of Dundee, Scotland UK.


DATA SOURCES:  Cochrane Oral Health Group’s Trials Register, Central, Medline, Embase, PsycINFO.

STUDY SELECTION:  Randomised controlled trials of psychosocial interventions for chronic orofacial pain were included. Psychosocial interventions targeted towards changing thoughts, behaviors and/or feelings that may exacerbate pain symptoms through a vicious cycle were eligible. Primary outcomes were pain intensity/severity, satisfaction with pain relief and quality of life.

DATA EXTRACTION AND SYNTHESIS:  Two reviewers independently screened studies, extracted data and assessed risk of bias. Dichotomous outcomes, were expressed as risk ratios with 95% confidence intervals, continuous outcomes as mean differences with 95% confidence intervals. Heterogeneity was assessed using the Cochrane test for heterogeneity and the I2 test. Meta-analyses were conducted using the random-effect or the fixed-effect models.

RESULTS:  Fifteen of the 17 eligible studies were on temporomandibular disorders (TMDs), two on burning mouth syndrome. Psychosocial interventions improved long-term pain intensity (standardized mean difference (SMD) -0.34, 95% confidence interval (CI) -0.50 to -0.18) and depression (SMD -0.35, 95% CI -0.54 to -0.16). However, the risk of bias in these studies was high.

CONCLUSIONS:  There is weak evidence to support the use of psychosocial interventions for chronic orofacial pain.


The effect of experimental occlusal interferences on nerve growth factor levels in periodontal tissues

Dong Y, Wang XM, Liu HC, Widmalm SE

Arch Oral Biol. 2010 Sep 22 [Epub ahead of print]

Department of Oral Medicine, College of Medicine, Second Affiliated Hospital, Zhejiang University, 88, Jiefang Road, Hang zhou, China

OBJECTIVE: To test the hypothesis that experimental occlusal interferences increase the nerve growth factor (NGF) levels in periodontal tissues and cause an up-regulation of preprotachykinin-A (PPTA) mRNA. BACKGROUND: NGF is related to hyperalgesia and inflammation. PPTA mRNA, a primer of substance P, is a possible factor in the aetiology of pain. METHODS: Experimental interferences were created by placing inlays in the right maxillary molars of 15 dogs. The right side molars formed the experimental group. The left side molars served as controls. Three dogs with cavities prepared without changing the occlusion formed a sham group. The dogs in the first group were sacrificed, 3 at each time, after 3, 7, 14, 30, and 60 days. The sham group was sacrificed after 14 days. The levels of NGF in periodontal tissues and PPTA mRNA in the trigeminal ganglions were detected by ELISA and TR-PCR. Comparisons were made with paired t-tests and a multivariate MANOVA test. RESULTS: On all measurement days, there were higher levels of NGF mRNA, PPTA mRNA, and NGF on the experimental than on the control side in 14 of 15 comparisons and in the sham group. NGF production in periodontium was time-dependent. No differences in NGF protein levels were observed between the control and the sham groups. CONCLUSION: The results which need confirmation in further tests are of clinical interest.

They indicate that occlusal experimental interferences may be an etiologic factor in oral facial pain by increasing mRNA and NGF protein levels in the periodontal tissues.

Occlusal interferences: how can this concept influence the clinical practice?

Lima AF, Cavalcanti AN, Martins LR, Marchi GM

Eur J Dent. 2010 October; 4(4): 487–491

This brief review discusses the role of occlusal interferences on the development and progression of temporomandibular dysfunction (TMD) and postural disorders. The eligible literature is described and critically presented to demonstrate   that occlusal interferences are an important factor in the risk of TMD.

Several studies have demonstrated through their findings that the use of occlusal adjustments, whether or not associated with restorative procedures, might avoid the development of articular problems in vulnerable patients. The occlusal interferences caused by restorative procedures or orthodontic treatment can cause TMDs  in susceptible patients, and occlusal adjustments can be an alternative in the treatment of these TMDs.

Experimental occlusal interference induces long-term masticatory muscle hyperalgesia in rats

Cao Y, Xie QF, Li K, Light AR, Fu KY

Department of Prosthodontics, Peking University School & Hospital of Stomatology, 22 Zhong Guan Cun South Avenue, Beijing 100081, PR China 2009.

Temporomandibular joint or related masticatory muscle pain represents the most common chronic orofacial pain condition. Patients frequently report this kind of pain after dental alterations in occlusion. However, lack of understanding of the mechanisms of occlusion-related temporomandibular joint and muscle pain prevents treating this problem successfully. To explore the relationship between improper occlusion (occlusal interference) and masticatory muscle pain, we created an occlusal interference animal model by directly bonding a crown to a maxillary molar to raise the masticating surface of the tooth in rats. We raised the occlusal surface to three different heights (0.2, 0.4, and 0.6mm), and for one month we quantitatively measured mechanical nociceptive thresholds of the temporal and masseter muscles on both sides. Results showed a stimulus-response relationship between the height of occlusal interference and muscle hyperalgesia. Removal of the crown 6 days after occlusal interference showed that the removal at this time could not terminate the 1 month duration of mechanical hyperalgesia in the masticatory muscles. Lastly, we systemically administered NMDA antagonist MK801 (0.2, 0.1, and 0.05 mg/kg) to the treated rats and found that MK801 dose dependently attenuated the occlusal interference-induced hyperalgesia.

These findings suggest that occlusal interference is directly related to masticatory muscle pain, and that central sensitization mechanisms are involved in the maintenance of the occlusal interference-induced mechanical hyperalgesia.


Oral Rehabil. 1996 Jun;23(6):401-8.

Open-close movements in the human temporomandibular joint: does a pure rotation around the intercondylar hinge axis exist?

Ferrario VF, Sforza C, Miani A Jr, Serrao G, Tartaglia G.

Laboratorio di Anatomia Funzionale dell’Apparato Stomatognatico, Facoltà di Medicina e Chirurgia, Università degli Studi di Milano, Italy.


Mandibular movements near the maximum intercuspal position were analysed for the location of the mean instantaneous centre of curvature of the interincisal point path. Measurements were performed using a kinesiograph in 28 healthy young adults with sound dentitions and free from temporomandibular joint disorders. The subjects performed habitual open-close cycles at different speeds; opening movements starting from the centric relation occlusion were also analysed. In none of the 28 subjects was the interincisal point path derived from pure rotation movements performed around the intercondylar axis, not even in the first millimetres of motion. Translation and rotation were always combined, and the position of the centre of curvature changed during the motion, showing different characteristics in the open and close movements; these patterns were also dependent upon motion speed. The results show that the hinge axis theory cannot explain the mandibular movements because a pure rotation did not occur around the intercondylar axis.

Centric relation definitions taught in 7 dental schools: results of faculty and student surveys.

Jasinevicius TR Jasinevicius TR, Yellowitz JA Yellowitz JA, Vaughan GG Vaughan GG, Brooks ES Brooks ES, Baughan LW Baughan LW, Cline N Cline N, Theiss LB Theiss LB.

 Restorative Department, Case Western Reserve University-School of Dentistry, 10900 Euclid Avenue, Cleveland, OH 44106-4905, USA.

 Prosthodont. 2000 Jun;9(2):87-94.

 PURPOSE: The purpose of this investigation was to assess the level of consensus regarding the definition of centric relation and its clinical use in 7 US dental schools. MATERIALS AND METHODS: The preclinical and clinical faculty in the departments of prosthodontics, operative, and general dentistry (n = 137) at 7 dental schools and a convenience sample of fourth year students (n = 150) at the same schools were invited to complete 2-page surveys regarding the definitions and use of centric relation at their institutions.

The faculty and student survey included 6 commonly used centric relation definitions from the 1994 Glossary of Prosthodontic Terms, and provided space for writing in definitions not listed on the form. The participants were asked to identify which definition was used at their school. RESULTS: Return rate was 85% for faculty and 75% for students. Both faculty and students identified a low level of consensus regarding the definition and clinical use of centric relation at their dental school. Numerous definitions are in use at each institution. Extramural practice participation and the number of years since dental school graduation were variables associated with the faculty’s choice of definition. The faculty who did not participate in an extramural practice chose older definitions. Dental educators graduating before 1975 selected either the oldest or the most recent centric relation definition, whereas the more recent graduates frequently selected the newer definitions. There were no statistical differences between prosthodontic specialists and nonspecialists in choice of definitions. Three courses identified by the students as having the most influence on their understanding of centric relation were preclinical removable prosthodontics, preclinical occlusion, and clinical removable prosthodontics. CONCLUSION: The results of this survey suggest that the controversy will continue, because to date there is no consensus regarding the definition of centric relation within the 7 dental schools surveyed.

 Cranio. 1993 Jul;11(3):178-83.

A comparison of electromyographic activity between anterior repositioning splint therapy and a centric relation splint.

 Williamson EH””Williamson EH, Navarro EZ””Navarro EZ, Zwemer JD””Zwemer JD.

 Medical College of Georgia in Augusta.


The purpose of this study was to compare the electromyographic activity of masticatory muscles (temporal and masseter) with the use of an anterior repositioning splint and a centric relation superior repositioning splint. Twenty-six consecutive patients, who referred with the chief complaint of temporomandibular pain and/or headache were selected from one of the author’s practices. All these subjects were diagnosed as having internal derangement of the temporomandibular joint. Ten normal subjects were used as controls. Surface electromyographic recordings were taken of each subject prior to the beginning of clinical therapy for the patients. The results show significantly less masseter and temporal muscle activity with anterior repositioning splint therapy compared to the centric relation superior repositioning splint therapy.


 Int J Comput Dent. 2008;11(2):81-106. Links

 Surface electromyography of the masticatory muscles for application in dental practice. Current evidence and future developments.

Hugger AHugger A, Hugger SHugger S, Schindler HJSchindler HJ.

Poliklinik für Zahnärztliche Prothetik, Westdeutsche Kieferklinik, Heinrich-Heine-Universität Düsseldorf.

On the basis of well-founded clinical evaluations and taking into account special methodological recommendations, surface electromyography (EMG) enables the acquisition of valid and reliable quantitative data on the functional condition of the masticatory muscles as a “neuromuscular functional analysis”. On the basis of a current review of the literature, surface EMG appears to be able to deliver additional diagnostic and therapy-relevant information. Meaningful EMG data can be gained regarding resting activity, maximum muscle activation, frequency spectrum under various loading conditions, as well as bilateral symmetry of the contraction behavior of the jaw muscles. With these parameters–completed by kinematic information on movements of the mandible–it appears to be possible under clinical conditions to assess (a) the neuromuscular chewing performance after prosthetic reconstructions, (b) to record the influence of pain on the neuromuscular system, and (c) to document the individual efffect of therapeutic interventions on temporomandibular disorders

Surface EMG of the masticatory muscles. (Part 4): Effects of occlusal splints and other treatment modalities.

Hugger S, et al. Int J Comput Dent. 2013.

literature review on the clinical relevance of surface electromyography (EMG) of the masticatory muscles summarizes the results of clinical studies in patients with temporomandibular disorders (TMD), preferably randomized controlled trials, examining the impact of changes to the dynamic occlusion or the effects of occlusal splints and other treatment measures on electromyographic activity. Surface electromyography is a useful tool for neuromuscular functional analysis in the field of dentistry. In combination with a thorough history and detailed clinical examination, it is able to provide objective, documentable, valid and reproducible information about the individual functional status of the masticatory muscles if the user strictly adheres to the specific guidelines.

Med Sci Monit. 2013 May 31;19:416-23.

Surface electromyography in orthodontics – a literature review.

Woźniak K, Piątkowska D, Lipski M, Mehr K.

Source: Department of Orthodontics, Pomeranian Medical University of Szczecin, Szczecin, Poland.
Electromyography is the most objective and reliable technique for evaluating muscle function and efficiency by detecting their electrical potentials. It makes it possible to assess the extent and duration of muscle activity. The main aim of surface electromyography is to detect signals from many muscle fibers in the area of the detecting surface electrodes. These signals consist of a weighted summation of the spatial and temporal activity of many motor units. Hence, the analysis of the recordings is restricted to an assessment of general muscle activity, the cooperation of different muscles, and the variability of their activity over time. This study presents the main assumptions in the assessment of electrical muscle activity through the use of surface electromyography, along with its limitations and possibilities for further use in many areas of orthodontics. The main clinical uses of sEMG include the diagnostics and therapy of temporomandibular joint disorders, an assessment of the extent of stomatognathic system dysfunctions in subjects with malocclusion, and the monitoring of orthodontic therapies

The electromyographic activity of masseter and anteriortemporalis during orofacial symptoms induced by experimental occlusal highspot


 *Department of Prosthodontics, Peking University School of Stomatology, Beijing, China, †Orofacial Pain Laboratory, Center for Sensory-Motor Interaction,

 Aalborg University, Denmark and ‡Laboratory of Brain Research, Oral Health Science Centre, Tokyo Dental college, Chiba, Japan


The aim of the present study was to investigate the short-term impact of an occlusal highspot on the occurrence of orofacial symptoms by collecting self-evaluation and using electromyography (EMG) evaluation. A rigid unilateral intercuspal occlusal highspot (A cast onlay of 0Æ5 mm) was placed on the right lower first molar of six adult volunteers (three males, three females), and remained for 6 days. Continuously all the induced orofacial symptoms were collected and the subjects scored the orofacial pain on a 10-cm visual analogue scale (VAS) during the placement of onlay. The surface EMG was recorded before the placement of onlay, during (on the 3rd and 6th day) and after the onlay was removed. Then the contractile symmetry of bilateral masseter (MAL, MAR) and anterior temporalis (TAL, TAR) was measured by using an asymmetry index. On the 3rd day of the placement of the occlusal highspot, all subjects complained of headache in right temporal region .

 The activity of TAR at rest position of mandible increased significantly (P = 0Æ027). In addition, on the 3rd and 6th day with the highspot the EMG activity of the tested muscles during maximal voluntary contraction (MVC) was significantly reduced; the asymmetry index of bilateral anterior temporalis during MVC was increased significantly (P3rd = 0Æ028; P6th = 0Æ046). A unilateral occlusal highspot may make the ipsilateral anterior temporalis become tenser at rest position. Furthermore, the activity of bilateral anterior temporalis becomes more unsymmetrical during MVC although there are inter-individual differences between subjects. The changes in muscular activity may have some relationship with the occurrence of tensiontype headache in temporal region. 


[Muscle relaxation by transcutaneous electric nerve stimulation (TENS) in bruxism. An electromyographic study].

Frucht S1, Jonas I, Kappert HF.

Fortschr Kieferorthop. 1995 Sep;56(5):245-53.


In recent years transcutaneous electrical neuromuscular stimulation (TENS) has become increasingly more common in the treatment of functional diseases of the masticatory muscles and currently the practitioner can choose among a variety of stimulators. In an electromyographic study of 17 adults suffering from nocturnal bruxism and of a control group consisting of 18 adults without any functional disturbances of the masticatory muscles, the effect of this kind of neuromuscular stimulation on the temporal and masseter muscle was examined. The myoelectric signals were registered before and after TENS treatment in 3 different positions of the mandible. Each person was treated 3 times with both the Myo-Monitor (Myo-Tronics, Seattle) and the TNS SM2 MF stimulator (schwa-medico, Giessen). The different effects of continuous low frequency and intermittent high frequency muscular stimulation were studied simultaneously. Muscular activity was determined by computer aided integration of the electromyographically measured raw signals. A fourier analysis of the power spectrum yielded information on the frequency behavior of the studied muscles resulting from the TENS treatment. A statistical analysis of the results led to the following significant conclusions: 1. TENS treatment decreased the values of the registered integrated signals on all test persons, however, the treatment increased the median frequency and the mean power frequency (MPF). Since this effect is contrary to muscle fatigue, these electromyographic results can be interpreted as providing objective proof of a relaxation in the treated muscles. 2. The electromyographic changes after TENS treatment were similar when using either the Myo-Monitor or the TNS SM2 MF stimulator. In addition, the 2 different types of stimulation (high or low frequency) showed the same effects. 3. Compared to the persons in the control group, there was no significant increased muscular activity in patients with nocturnal bruxism. Following TENS treatment both groups showed the same alterations in the electromyograms. The results of the study provide further evidence that TENS treatment is an adequate supportive procedure in the treatment of nocturnal bruxism.

 J Orofac Orthop. 2000;61(2):100-11

Transcutaneous electrical nerve stimulation (TENS): its short-term and long-term effects on the masticatory muscles.

 Eble OS1, Jonas IE, Kappert HF.


In an electromyographic study on subjects with no functional disturbances of the masticatory muscles, the duration of the post-therapeutic effects of transcutaneous electrical nerve stimulation (= TENS) on the superficial masseter and anterior temporal muscle was analyzed. The myoelectric signals were registered from 20 healthy volunteers in 3 different mandibular positions. The recordings were performed before a 20-minute TENS application with the J-4 Myomonitor and continued with a sequence of follow-up registrations with increasing interval to the initial stimulation. The EMG signals underwent computer-aided analysis and were evaluated by determining the integrated values as a parameter of muscle activity, and after Fourier transformation by 7 describing parameters of the power spectrum (e.g. mean power frequency = MPF). A detailed analysis of variance of all data was used to investigate significant changes of the parameters during the observation period. Muscular response to TENS includes a decrease in muscular activity (= reduction in integrated EMG signals) and a shift in the power spectrum to higher frequencies (increase in MPF). These changes were statistically highly significant for both analyzed muscles and for all different mandibular exercises. As these reactions to TENS are contrary to muscle fatigue, the results can be interpreted as indicating that this type of therapy stimulates a change in the biochemical and physiological muscular conditions, which leads to muscle relaxation. Electromyographically, the post-therapeutic effect lasted for 2 hours in case of normal masticatory muscle activity but for more than 7 hours in case of low muscular loading. The alterations of the integrated EMG values were more persistent than those of the parameters of the power spectrum.

Blood flow changes in the trapezius muscle and overlying skin following transcutaneous electrical nerve stimulation.

Randomized controlled trial

Sandberg ML, et al. Phys Ther. 2007.

Department of Rehabilitation Medicine, Faculty of Health Sciences, and Pain and Rehabilitation Centre, University Hospital, S-581 85 Linköping, Sweden.


BACKGROUND AND PURPOSE: Various researchers have studied the effects of transcutaneous electrical nerve stimulation (TENS) on hemodynamics. The purpose of this study was to examine the effects of TENS on local blood flow in the trapezius muscle and overlying skin.

SUBJECTS: Thirty-three women who were healthy, aged 25 to 55 years, were randomly assigned to receive 1 of 3 different modes of TENS.

METHODS: Skin and muscle blood flow were monitored noninvasively using a new application of photoplethysmography for 15 minutes of TENS applied at high frequency (80 Hz) and sensory-level intensity and at low frequency (2 Hz) and motor-level intensity and for 15 minutes after stimulation. Subliminal 80-Hz TENS was used as a control. Blood flow was monitored simultaneously on stimulated and nonstimulated shoulders.

RESULTS: Blood flow in the trapezius muscle, but not skin blood flow, increased significantly with motor-level 2-Hz TENS, whereas no increase occurred with sensory-level 80-Hz TENS or subliminal 80-Hz TENS.

DISCUSSION AND CONCLUSION: Muscle contractions induced by motor-level 2-Hz TENS appear to be a prerequisite for increasing blood flow in the trapezius muscle. However, high stimulation intensity may prevent increased blood flow.

NM vs CR

Arch Oral Biol. 1993 Mar;38(3):261-4.

The effect of four jaw relations on electromyographic activity in human masticatory muscles.

Hickman DM1, Cramer R, Stauber WT.


Significant differences were found in the electromyographic (EMG) activation between the masseter and temporalis muscles for the leaf gauge (LG), manually manipulated (CR) and neuromuscular (NM) bite positions during maximal static clench. The LG position consistently demonstrated the lowest EMG activity, while the NM position displayed the highest degree of muscle activity. Similarly, the ratio of the masseter/temporalis EMG activity during maximal clench was lower for the LG and CR positions and highest for the NM position. These data indicate that the NM position produced the greatest total muscle recruitment, with more masseter involvement during maximal clench, and enabled the subjects to generate greater clenching forces in the NM position as compared to the LG and CR positions.

Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1998 Jan;85(1):18-23.

The effect of different condylar positions on masticatory muscle electromyographic activity in humans.

Hickman DM1, Cramer R.


OBJECTIVES: The purpose of this study was to determine a condylar position that permitted the greatest total temporalis and masseter muscle activity in maximum static clench.

 STUDY DESIGN: Twenty normal adults, 9 women and 11 men, were evaluated to determine masseter and temporalis activity in maximum static clench with mandibular condyles in different therapeutic positions. Bimanually manipulated, leaf gauge, centric occlusion, and neuromuscular condylar positions were studied.

RESULTS: When mandibular condyles were placed anteroinferiorly in a neuromuscular position, total masticatory muscle recruitment was the greatest. In a bimanually manipulated or a leaf gauge position, mandibular condyles were positioned superoposteriorly, producing the least amount of muscle recruitment.

 CONCLUSIONS: The result of any therapeutic position should be an improvement in muscle function. With respect to balance and activation, a neuromuscular condylar position proved to be the position capable of recruiting the greatest motor unit activity when compared with a bimanually manipulated position, a leaf gauge position, and a neuromuscular position.

Effects of myocentric vs. manual methods of jaw position recording in occlusal splint therapy – ( randomized clinical trial)

J CranioMand Func 3 (2011), No. 3  (26.09.2011)Page 177-203
Weggen, Tjerk / Schindler, Hans-Jürgen / Hugger, Alfons

Univ. of Dusseldorf

Occlusal splint therapy is a central element of the treatment of temporomandibular disorders (TMD). However, little has been reported about the effect of transcutaneous electrical nerve stimulation (TENS)-based methods of myocentric jaw position recording on the effect of splint therapy. In this randomized clinical trial, 40 patients with myofascial pain of the jaw muscles were treated with occlusal splints fabricated using bimanual manipulation (Michigan group, n = 20) or myocentric jaw position recording (myocentric group, n = 20) for determination of centric vs. myocentric relation. Therapeutic effects were evaluated based on the change in pain symptoms and the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) procedure after 4 and 12 weeks of treatment. The extent of change in mandibular position was determined by condymeter measurements and magnetic kinesiography as well as by comparison with a healthy control group. Twelve weeks of wearing the respective splints at night resulted in the significant relief of symptoms in both groups, as determined based on subjective pain reports and visual analog scale (VAS) scores. Group comparison revealed that the VAS scores were significantly lower in the myocentric group. Myocentric positioning of the mandible led to mandibular position changes of similar extent in TMD patients and healthy controls. The use of TENS to establish myocentric relation for splint therapy is therapeutically effective and achieves a greater reduction in pain. Furthermore, TENS treatment alone also has a significant pain-relieving effect.