Oral behaviours and wake-time masseter activity in patients with masticatory muscle pain.

BACKGROUND: Little is known about wake-time masseter activity of patients with masticatory muscle pain in real-life settings. OBJECTIVES: The aims of this study were (1) to assess wake-time masseter activity of women with masticatory muscle pain (MMP) and compare it with that of pain-free women; and (2) to investigate the association between objectively measured masseter contractions and self-reported oral behaviours. METHODS: Adult women (N = 27) diagnosed with MMP were age-matched with pain-free women (N = 26). The electromyographic (EMG) activity of the masseter muscle when awake was recorded unilaterally for two consecutive days. The number of contraction episodes and relative contraction time (%) were calculated using cut-off thresholds of 3%, 5% and 10% of maximum voluntary contraction (MVC). Self-reported daytime oral activity was assessed using the Oral Behaviours Checklist (OBC, items 3-21). Data were analysed using univariate tests and mixed-model analyses. RESULTS: The number of contraction episodes was similar between groups for all detection thresholds, but the relative contraction time at the lower detection thresholds (i.e. 3% MVC and 5% MVC) was significantly longer (1.5-fold) in the MMP than in the pain-free group. The OBC scores were significantly higher in the women with MMP than in controls, but no positive association could be found between EMG variables and OBC scores. CONCLUSION: Women with MMP engage in low-level masseter muscle contractions, which last longer than those of pain-free controls. There was no relationship between self-reported oral behaviours and masseter activity when awake. These findings support the notion that prolonged low-level clenching when awake may play a role in the pathophysiology of MMP.

Open-label randomized clinical trial of standard neoadjuvant chemotherapy with paclitaxel followed by FEC versus the combination of paclitaxel and everolimus followed by FEC in women with triple receptor-negative breast cancer†.

BACKGROUND: Everolimus synergistically enhances taxane-induced cytotoxicity in breast cancer cells in vitro and in vivo in addition to demonstrating a direct antiproliferative activity. We aim to determine pharmacodynamics changes and response of adding everolimus to standard neoadjuvant chemotherapy in triple-negative breast cancer (TNBC). PATIENTS AND METHODS: Phase II study in patients with primary TNBC randomized to T-FEC (paclitaxel 80 mg/m(2) i.v. weekly for 12 weeks, followed by 5-fluorouracil 500 mg/m(2), epirubicin 100 mg/m(2), and cyclophosphamide 500 mg/m(2) every 3 weeks for four cycles) versus TR-FEC (paclitaxel 80 mg/m(2) i.v. and everolimus 30 mg PO weekly for 12 weeks, followed by FEC). Tumor samples were collected to assess molecular changes in the PI3K/AKT/mTOR pathway, at baseline, 48 h, 12 weeks, and at surgery by reverse phase protein arrays (RPPA). Clinical end points included 12-week clinical response rate (12-week RR), pathological complete response (pCR), and toxicity. RESULTS: Sixty-two patients were registered, and 50 were randomized, 27 received T-FEC, and 23 received TR-FEC. Median age was 48 (range 31-75). There was downregulation of the mTOR pathway at 48 h in the TR-FEC arm. Twelve-week RR by ultrasound were 29.6% versus 47.8%, (P = 0.075), and pCR were 25.9% versus 30.4% (P = 0.76) for T-FEC and TR-FEC, respectively. mTOR downregulation at 48 h did not correlate with 12-week RR in the TR-FEC group (P = 0.58). Main NCI grade 3/4 toxicities included anemia, neutropenia, rash/desquamation, and vomiting in both arms. There was one case of grade 3 pneumonitis in the TR-FEC arm. No grade 3/4 stomatitis occurred. CONCLUSION: The addition of everolimus to paclitaxel was well tolerated. Everolimus downregulated mTOR signaling but downregulation of mTOR at 48 h did not correlate with 12-week RR in the TR-FEC group. CLINICAL TRIAL NUMBER: NCT00499603.

Interindividual differences in the perception of dental stimulation and related brain activity.

For identical diagnoses in the trigeminal innervation territory, individual differences have been clinically observed among the symptoms reported, such as dysesthesia and pain. Different subjective perceptions of unpleasantness and pain intensity may have different cortical substrates. The aim of this study was to identify brain areas in which activation depends on the subjective perception (intensity and unpleasantness) of electric dental stimulation. Electrical stimuli of increasing intensity were applied to maxillary canines in 14 healthy volunteers. Ratings for stimulus intensity and unpleasantness perceived across the stimulation session were reported postscan on 11-point numerical scales. The rating values were then included as covariates in the functional magnetic resonance imaging (fMRI) group analysis. Interindividual differences of intensity ratings were reflected in differential activity of the following brain areas: superior parietal lobule, superior temporal gyrus/anterior insula, inferior and middle temporal gyrus, lingual gyrus, anterior cingulate, and caudate nucleus. Differences related to unpleasantness ratings were reflected in the lingual gyrus. In conclusion, differences of perceived intensity between individuals are reflected in the differential activity of a set of brain areas distinct from those regions, reflecting rating differences of unpleasantness.

Relationship between kinematic center and TMJ anatomy and function.

The kinematic center (KC)-defined by coinciding jaw-opening/-closing and protrusion-retrusion trajectories-has been proposed in the literature as a reference point to represent TMJ movements. In this study, we tested whether the KC lies in a peculiar anatomical point and whether its trajectory reflects intra-articular distance. In 11 asymptomatic individuals (seven females, four males, aged 24-37 yrs), 4 openings/closings and 4 protrusions/retrusions were tracked with dynamic stereometry. In a 3D lattice (0.5 mm grid) constructed solidly around each condyle, the KC was the point with maximal cross-correlation between opening-closing and protrusion-retrusion paths. KC trajectories were more cranial on closing than on opening, consistent with intra-articular distances being smaller on closing than on opening. However, KCs were never located on condylar main axes (distance, 4.5 +/- 2.9 mm), nor did they coincide with points best approximating fossa shapes (distance, 12.5 +/- 6.4 mm). The kinematic center's anatomical and functional significance therefore appears to be questionable.

Stereometric assessment of TMJ space variation by occlusal splints.

Occlusal splints are used for the management of temporomandibular disorders, although their mechanism of action remains controversial. This study investigated whether insertion of an occlusal splint leads to condyle-fossa distance changes, and to mandibular rotation and/or translation. By combining magnetic resonance images with jaw tracking (dynamic stereometry), we analyzed the intra-articular distances of 20 human temporomandibular joints (TMJs) before and after insertion of occlusal splints of 3 mm thickness in the first molar region. For habitual closure, protrusion, and laterotrusion in the contralateral joint, occlusal splints led to minor--yet statistically significant--increases of global TMJ space and to larger increases at defined condylar areas. Condylar end rotation and translation in habitual closure were reduced. Hence, the insertion of a 3-mm-thick occlusal splint led to a change in the topographical condyle-fossa relationship, and therefore to a new distribution of contact areas between joint surfaces.

Masticatory muscle activity during deliberately performed oral tasks.

The aim of this study was to investigate masticatory muscle activity during deliberately performed functional and non-functional oral tasks. Electromyographic (EMG) surface activity was recorded unilaterally from the masseter, anterior temporalis and suprahyoid muscles in 11 subjects (5 men, 6 women; age = 34.6 +/- 10.8 years), who were accurately instructed to perform 30 different oral tasks under computer guidance using task markers. Data were analyzed by descriptive statistics, repeated measurements analysis of variance (ANOVA) and hierarchical cluster analysis. The maximum EMG amplitude of the masseter and anterior temporalis muscles was more often found during hard chewing tasks than during maximum clenching tasks. The relative contribution of masseter and anterior temporalis changed across the tasks examined (F 5.2; p < or = 0.001). The masseter muscle was significantly (p < or = 0.05) more active than the anterior temporalis muscle during tasks involving incisal biting, jaw protrusion, laterotrusion and jaw cupping, the difference being statistically significant (p < or = 0.05). The anterior temporalis muscle was significantly (p < or = 0.01) more active than the masseter muscle during tasks performed in intercuspal position, during tooth grinding, and during hard chewing on the working side. Based upon the relative contribution of the masseter, anterior temporalis, and suprahyoid muscles, the investigated oral tasks could be grouped into six separate clusters. The findings provided further insight into muscle- and task-specific EMG patterns during functional and non-functional oral behaviors.

Mechanical work during stress-field translation in the human TMJ.

The pathomechanics of degenerative joint disease of the temporomandibular joint (TMJ) may involve fatigue produced by mechanical work on the articulating tissues. This study tested the hypotheses that mechanical work in the TMJ (i) varies with the type of mandibular activity, and (ii) is evenly distributed over TMJ surfaces. Ten healthy human participants were recorded with Magnetic Resonance Imaging (MRI) and jaw tracking. The data were used to reconstruct and animate TMJ activity. Aspect ratios, instantaneous velocities, and distances of stress-fields translation were used to calculate work (mJ). The results were analyzed by least-squares polynomial regression and ANOVA. Work magnitudes were related to peak velocity (R(2) = 0.92) and distance of stress-field translation (R(2) = 0.83), and were distributed over the joint surfaces (p < 0.03). During mandibular laterotrusion, average mechanical work was 1.5 times greater in the contralateral joint. Peak magnitudes of work (> 3000 mJ) were 4 times that previously reported.

Cross-sectional association between markers of inflammation and serum sex steroid levels in the postmenopausal estrogen/progestin interventions trial.

BACKGROUND: Standard risk factors do not adequately capture cardiovascular risk in postmenopausal women. We sought to determine the associations between levels of sex steroids and levels of inflammatory markers in postmenopausal women. METHODS: We analyzed baseline data from a subset of postmenopausal women aged 45-64 years who had stored samples during a randomized controlled trial. We measured levels of C-reactive protein (CRP), interleukin-6 (IL-6), matrix metalloproteinase-9 (MMP-9), soluble intercellular adhesion molecule (sICAM), and circulating sex steroids. Multiple linear regression models were created with each of the following hormone levels as the primary exposure variable: estrone, total estradiol, bioavailable estradiol, total testosterone, bioavailable testosterone, progesterone, and sex hormone-binding globulin (SHBG). Sociodemographic and lifestyle covariates were derived from standardized self-report questionnaires and direct measurement (weight, height). RESULTS: Mean age of the 623 women was 56 years. After adjustment for age, body mass index (BMI), physical activity, alcohol consumption, and smoking, the bioavailable testosterone level (p = 0.03) was positively and the SHBG level (p < 0.001) was negatively associated with the logCRP level. The increment in CRP level between the highest and lowest quartile of bioavailable testosterone was 1.28 microg/mL. The increment in CRP level between the lowest and highest quartile of SHBG was 2.62 microg/mL. Compared with SHBG or bioavailable testosterone as predictors of logCRP in separate regression models, when both SHBG and bioavailable testosterone were included in the same multivariate linear regression model, only SHBG remained a statistically significant predictor of logCRP. Progesterone level was positively associated with the logMMP-9 level (p < 0.001); no other sex steroid level was associated with the logMMP-9 level. In multiply adjusted models, no association was found between levels of any sex steroid and IL-6 or sICAM level.

Relevance of mandibular helical axis analysis in functional and dysfunctional TMJs.

The helical axis (HA), or motion screw, yields a comprehensive description of joint motion. The perspective representation of this axis clearly visualizes the regularity of mandibular functional movements (Yatabe et al. 1997. Journal of Dentist Research 76, 714-719 and Gallo et al. 2000. Journal of Dental Research 79, 1566-1572). In this study, the sensitivity of the HA representation was investigated relative to (a) irregularities in pathologic motion of clicking temporomandibular joints (TMJs) for jaw opening/closing and (b) differences in food bolus size and consistency for unilateral mastication in subjects with normal TMJs. Mandibular motion relative to the head was acquired using a jaw tracker with six degrees-of-freedom with a sampling frequency of 70 Hz. The HA was calculated according to an eigenvalue method (Spoor and Veldpaus 1980. Journal of Biomechanics 13, 391-393) and parameters were defined describing its position and orientation relative to the anatomy. We analyzed 39 subjects with unilateral or bilateral reciprocal TMJ clicking during jaw opening/closing and seven asymptomatic subjects during unilateral mastication of five different types of soft and hard food in two different bolus sizes. The results showed a greater variability of the HA parameters in the group of clicking joints than in the asymptomatic group: in particular, the area in which the HA moved was wider in clicking joints than in normal ones and the HA in clicking TMJs had a much greater fluctuation than in normal ones. During unilateral mastication, for more consistent food or a bigger bolus the HA showed a significantly greater excursion of the orientation parameters. Furthermore a significantly greater excursion of the dorsoventral and of the craniocaudal component of the distance vector from the HA to the condyle were found. The helical axis analysis of mandibular movements was sensitive to kinematic irregularities of the mandible due to an internal joint derangement as well as to differences in food bolus size and consistency.

Effect of occlusal interference on habitual activity of human masseter.

It has been suggested that occlusal interference may increase habitual activity in the jaw muscles and may lead to temporomandibular disorders (TMD). We tested these hypotheses by means of a double-blind randomized crossover experiment carried out on 11 young healthy females. Strips of gold foil were glued either on a selected occlusal contact area (active interference) or on the vestibular surface of the same tooth (dummy interference) and left for 8 days each. Electromyographic masseter activity was recorded in the natural environment by portable recorders under interference-free, dummy-interference, and active-interference conditions. The active occlusal interference caused a significant reduction in the number of activity periods per hour and in their mean amplitude. The EMG activity did not change significantly during the dummy-interference condition. None of the subjects developed signs and/or symptoms of TMD throughout the whole study, and most of them adapted fairly well to the occlusal disturbance.

Automatic on-line one-channel recognition of masseter activity.

The etiology of myoarthropathies of the masticatory system (MAP) is not fully understood. For the hypothetical association between the myogenous pain of MAP patients and masticatory muscle overuse to be proved, functional and parafunctional behavior of the masticatory muscles should be analyzed in normal and diseased subjects. The aim of this study was to test on-line the validity and reliability of an algorithm, applied to the electromyographic signal, to recognize various oral activities. The surface electromyogram of the masseter muscle was recorded in 12 subjects (seven females and five males, from 18 to 32 years old) who performed a series of functional and parafunctional activities (chewing soft food, chewing hard food, swallowing, laughing, speaking, and tooth grinding and clenching), as well as no activity. During the computer training phase, intra-individual classification functions of a multivariate discriminant analysis were calculated while each subject performed the described activities. During the test phase, each subject repeated the same activities, and the computer continuously classified them on-line. The percentage of correctly recognized activities was calculated for each activity and for each subject. No activity, chewing hard food, swallowing, laughing, grinding, and clenching were recognized correctly > 99% of the time. Chewing soft food was recognized correctly 97% and speaking 86% of the time. The sensitivity values for the recognition rates of the complete oral activities were, with one exception, > 0.82; the specificity values were > 0.95, and the kappa-values > 0.80. These results show that the algorithm had high sensitivity, specificity, and reliability in the classification of different oral activities under laboratory conditions.

Nocturnal masseter EMG activity of healthy subjects in a natural environment.

Facial pain of patients with craniomandibular disorders might be caused by muscle overload. However, the activity of masticatory muscles of healthy individuals is still unknown. The aim of this study was therefore a first attempt to clarify this question by recording the masseter muscle activity of healthy subjects during sleep by means of portable recorders. The study was performed on 21 healthy subjects selected after telephone and questionnaire screenings and clinical examination from among randomly selected inhabitants of Zürich. The masseter EMG was recorded during seven nights in each subject's natural environment with the electrodes in reproducible position. The signal was analyzed for number, amplitude, and duration of contraction periods defined as signal portions above a threshold which could contain sub-threshold signal portions shorter than the standby time of 5 sec. The signal amplitude was expressed in percent of the amplitude recorded during maximum voluntary clenches (%MVC). An average of 71.9 +/- 28.7 contraction episodes per night (men, 74.7 +/- 30.1; women, 65.0 +/- 23.8; p = 0.043), i.e., of 10.5 +/- 3.8 per hour (men, 11.0 +/- 4.0; women, 9.3 +/- 3.0; p = 0.005), was found. The average mean amplitude was 26.2 +/- 6.4% MVC (men, 27.0 +/- 6.8; women, 24.4 +/- 4.5; p = 0.009). The duration of the episodes had a mode of 0.5 sec, and the group mean of the integral of the amplitude over time was 123.7 +/- 157.9% MVC (men, 138.9 +/- 184.0; women, 85.9 +/- 28.2; p = 0.005). Healthy subjects showed intermittent periods of masseter activity during sleep which, on average, were of rather low intensity and short duration.

Mandibular helical axis pathways during mastication.

Condylar and incisor trajectories are often used for the study of mandibular movements. Condylar trajectories, however, depend on the location of the reference point and can be interpreted erroneously. In contrast, the helical axis analysis yields an unequivocal description of rigid body kinematics. The aim of this study was to analyze the mandibular helical axis during mastication. Seven subjects without signs and symptoms of craniomandibular disorders and with class I occlusion were recorded by means of the opto-electronic system Jaws-3D during unilateral mastication of bread cubes (2-cm side). The helical axis was computed every 14 ms with a rotation threshold of 1 . Parameters describing its spatial orientation and position relative to the condyles were calculated. The helical axis changed orientation and position more pronouncedly during the closing than during the opening phases of mastication. The orientation varied significantly from beginning to end of closing but not of opening, indicating less fluctuation of the helical axis on opening than on closing. Also, the distance dCP between helical axis and reference condylar point varied more significantly (p < 0.05) on the working than on the balancing side: On the working side, dCP decreased during both opening and closing, whereas on the balancing side, dCP increased only for closing. Furthermore, the helical axis pathway often showed a bowing ventrally to the balancing condyle, indicating that, during closing, the balancing condyle still translated backward while essentially only rotation occurred around the working condyle. Thus, the helical axis changed its position and orientation continuously during mastication.

Description of mandibular finite helical axis pathways in asymptomatic subjects.

Despite wide use of systems to record jaw motion with six degrees of freedom, most studies have analyzed only the movement of a single mandibular point. The finite helical axis (FHA) is a mathematical model which can be used to describe comprehensively the movements of a rigid body. The aim of this investigation was to describe the FHA of the mandible during habitual jaw movements. Thirty subjects (13 females, 17 males; mean age, 26 years; range, 18 to 34 years) without myoarthropathies of the masticatory system participated in the study. Opening and closing movements, performed at 1-Hz frequency, were recorded with the optoelectronic system Jaws-3D. Three opening and closing movements were recorded from the right side and three from the left side of the jaw. The movement data were low-pass-filtered for noise reduction prior to the computation of the finite helical axis by means of a software program developed in our laboratory. The following parameters were calculated: the rotation of the FHA, its spatial orientation, and the translation along it, as well as its position and distance relative to an intracondylar point. In addition, methodological errors of the model were calculated. During opening and closing, the group mean FHA rotation was 24.3 degrees +/- 4.2 degrees. The group mean of the maximum total translation along the FHA was 0.9 +/- 0.7 mm. The group mean distance between the FHA and the intracondylar point was 48.9 +/- 9.9 mm. The FHA pathways were smooth and varied between individuals. Furthermore, the finite helical axes were never localized within the condyle, and often were located outside of the mandible. The analysis of the FHA pathways yields more information on whole mandibular movements than simply the movements of a single condylar point.

Dynamic intra-articular space variation in clicking TMJs.

During mandibular movement, the geometric relationships of the articular surfaces in the temporomandibular joint (TMJ) change, so that the disc undergoes different stress concentrations with respect to time and position. In this study, we compared the intra-articular space variations of 13 clicking and 15 asymptomatic TMJs for jaw opening/closing. Magnetic resonance imaging and jaw tracking were combined to display the motion of the whole condyle within the fossa. In clicking TMJs, the mediolateral spread s of the stress-field trajectories was 2.4 +/- 1.0 mm (s(max) = 4.9 +/- 2.1 mm) with an aspect ratio a/h of 2.5 +/- 1.6, both significantly greater than in controls (p < 0.05). The stress-field trajectories of the controls coincided during opening/closing (s = 0.9 +/- 0.2 mm, s(max) = 1.8 +/- 0.8 mm, a/h = 1.6 +/- 0.3). Clicking TMJs showed much less coincident stress-field paths and much "flatter" stress-fields than controls during jaw opening/closing.

Stress-field translation in the healthy human temporomandibular joint.

Movement over the surface of the temporomandibular joint (TMJ) disc produces tractional forces. These forces potentially increase the magnitude of shear stresses and contribute to wear and fatigue of the disc. Theoretically, tractional forces in all synovial joints are the result of frictional forces, due to rubbing of the cartilage surfaces, and plowing forces, due to translation of the stress-field through the cartilage matrix as the joint surface congruency changes during motion. For plowing forces to occur in the TMJ, there must be mediolateral translation of the stress-field as the condyle moves dorsoventrally during jaw function. To test whether mediolateral stress-field translation occurs in the intact TMJ, we measured stress-field position and translation velocities in ten normal individuals during rhythmic jaw opening and closing. Magnetic resonance imaging and jaw tracking were combined to animate the three-dimensional position of the stress-field between the articulating surfaces. This allowed for mediolateral translation velocity measurements of the centroid of the stress-field. The results showed that during jaw opening and closing at 0.5 Hz, the average peak mediolateral translation velocity was 35 +/- 17 mm/sec. When opening and closing increased to 1.0 Hz, the average peak velocity was 40 +/- 19 mm/sec. Theoretical model estimates of the work done during such translation ranged from 6 to 709 mJ between the individual joints studied. The potential clinical importance of this measure is that long-term exposure of the TMJ disc to high work may result in fatigue failure of the TMJ disc.

Power spectral analysis of temporomandibular joint sounds in asymptomatic subjects.

Very little has been done to quantify temporomandibular joint (TMJ) sound amplitudes and background noise and to determine the spectrum from healthy TMJs. Thus, the aim of this study was to record acoustically the sounds emitted by healthy TMJs with and without mandibular movements, for determination of baseline spectra. TMJ sounds were recorded bilaterally from 40 subjects with healthy joints by means of a self-developed recording system using miniature capacitor microphones inserted into the earpieces of a medical stethoscope placed in the meatus of the auditory canal. The recordings were performed without mandibular movements and during three consecutive opening and closing movements. The signals were high-pass-filtered at 50 Hz, low-pass-filtered at 2 kHz, and analyzed by fast Fourier transform computation on a 1024-point window (fs = 5 kHz). The linearly weighted average baseline spectrum recorded without motion showed maximum values of 31 dBSPL (sound pressure level) with a standard error of +2 to -3 dB. The linearly weighted average movement spectrum had a peak of 66 dBSPL at 156 Hz and decreased almost linearly by about 40 dB/decade to 25 dBSPL at 2000 Hz with a standard error of +/- 2 dB. Thus, the TMJ sound spectrum of mandibular movements in asymptomatic subjects differed at low frequencies by up to 35 dB from the baseline spectrum in absence of motion.

Cortical activation resulting from painless vibrotactile dental stimulation measured by functional magnetic resonance imaging (FMRI).

There have been few investigations on hemodynamic responses in the human cortex resulting from dental stimulation. Identification of cortical areas involved in stimulus perception may offer new targets for pain treatment. This initial study aimed at establishing a cortical map of dental representation, based on non-invasive fMRI measurements. Five right-handed subjects were studied. Eight maxillary and 8 mandibular teeth were stimulated after the vibratory perception threshold was determined for each tooth. Suprathreshold stimulation was repeated thrice per session, in a total of three sessions performed on three consecutive days. Statistical inference on cluster level identified increased blood-oxygen-level-dependent signal during vibratory dental stimulation, primarily in the insular cortex bilaterally and in the supplementary motor cortex. No significant brain activation was observed in the somatosensory cortex with this stimulation protocol. These results agree with previous findings obtained from invasive direct electrical cortical stimulation of the human insula.

Analysis of human mandibular mechanics based on screw theory and in vivo data.

In this paper the mechanics of human mandibular function is described in terms of the associated screws. The two distinct, yet related features of jaw mechanics, involving the motion itself as well as the forces, are both functions of the anatomical constraints, namely the contact areas that exist within the temporomandibular joint, and the forces of the muscles and tendons that allow motion to occur. The relationships that exist between these two aspects of jaw-motion are identified in this paper showing that muscle forces can be uniquely represented in terms of the action screw. This new approach to analyzing the mechanics of jaw-motion also incorporates the previously studied motion screw or helical axis. A consistent dynamic model is formulated where the action screw is used to represent the action of the closing muscle forces while the moment arms of the muscle forces are determined about the motion screw representing mandibular kinematics. The action screw formulation is verified using in vivo motion data and MR image information for a single asymptomatic subject. The results confirm the feasibility of the method and its application in dental research. A general increase in the mechanical advantage of most muscles, in the distance between action and motion screws as well as in the expended energy towards the end of the jaw-closing phase was observed. Asymmetries in the distribution of muscle force magnitudes appeared to influence the resultant force and moment of the action screw but had little effect on its spatial location. The method presented is intended to facilitate understanding of mandibular function and dysfunction.

Reproducibility of temporomandibular joint clicking.

AIMS: To investigate the stability of temporomandibular joint (TMJ) clicking over a 10-day period and the effect of different open/close velocities on sound amplitude and power spectra in a group of subjects with subjectively stable unilateral clicking during the 3 months preceding the recordings. METHODS: Ten volunteers were recorded with a self-developed microcomputer-based system used in a previous study on asymptomatic subjects. The recordings were performed during 4 different sessions at 3 different open/close rates in each session. The subjective sound intensity was measured with a 100-mm visual analog scale (VAS). The VAS scores, the maximum amplitudes, and the power spectra of the signals were tested for statistical differences among the different open/close rates and over the sessions. The reliability of measurements was also calculated. RESULTS: The maximum amplitude and the power spectra of the TMJ clicking varied between subjects in a broad range that differed from those reported for asymptomatic subjects. No statistically significant differences were found within subjects for the subjective VAS scores for the maximum signal amplitudes or for the power spectrum parameters among the open/close rates and over the 4 sessions. For all 3 open/close rates and for the 4 sessions, a good to excellent reliability of measurements was determined, the values of r being mostly over 0.75. CONCLUSION: Within the limits of the experiment, TMJ clicking was subjectively and objectively stable over a period of 10 days. Therefore, the constant subjective perception of sound intensity was supported by the objective measurements.