Diagnostic group differences in temporomandibular joint energy densities

Temporomandibular disorder: A previously unreported complication of chronic suppurative otitis media

OBJECTIVE

The aim of the current clinical study was to test the hypothesis that chronic suppurative otitis media (CSOM) might be significantly associated with signs of temporomandibular joint (TMJ) internal derangement.

METHODS

The study involved 79 patients with CSOM and 79 control subjects. The TMJ was clinically examined in both groups.

RESULTS

Signs of internal derangement of the TMJ(s) were found in 67.1% of CSOM patients versus 26.6% of control subjects (p = .001).

CONCLUSION

CSOM may be associated with the extension of the inflammatory process into the TMJ, thereby predisposing to internal derangement of the joint.

A clinical study on the incidence of internal derangement of the temporomandibular joint following harvesting of temporalis fascia

OBJECTIVE

The aim of the current clinical study was to reveal whether harvesting of a temporalis fascia graft would be associated with a higher incidence of temporomandibular joint (TMJ) internal derangement.

METHODS

The study group involved 104 patients who had middle-ear operations, 67 of which involved harvesting of temporalis fascia and 37 that did not. The TMJs were clinically examined in each group.

RESULTS

The total incidence of internal derangement of the TMJ was significantly higher in the group that had temporalis fascia harvesting (79.1%), compared to the group that did not have temporalis fascia harvesting (29.7%), (p= 0.001).

CONCLUSION

Harvesting of temporalis fascia probably alters mandibular kinematics and predisposes to internal derangement of the TMJs.

Effects of condylar neck inclination and counterclockwise rotation on the stress distribution of the temporomandibular joint

Three different kinds of condylar inclination were manually modelled anteriorly inclined condylar neck, vertical condylar neck, and posteriorly inclined condylar neck. Three different maxillary impactions were simulated to evaluate the effect of counterclockwise rotation. The von Misses stresses of the disc, compressive stresses of the glenoid fossa, and compressive stresses of the condyle were the highest in the models with posteriorly inclined neck and lowest in the models with vertical condylar neck design. Stresses of the temporomandibular joint increase with the counterclockwise rotation of the maxilla-mandibular complex. The posteriorly inclined neck should be considered a risk factor for condylar resorption with increased counterclockwise rotation.

Mechanics- and Behavior-Related Temporomandibular Joint Differences

Fatigue of temporomandibular joint (TMJ) tissues reflects the effects of magnitude (energy density; ED) and frequency of loading (jaw muscle duty factor; DF). This observational study measured these variables and tested for differences in mechanobehavior scores (MBS = ED2 × DF) and component variables in subjects with and without TMJ disc displacement (±D). In accordance with Institutional Review Board and STROBE guidelines, written informed consent was obtained, and examination and imaging protocols identified eligible adult subjects. Specifically, magnetic resonance imaging was used to assign subjects' TMJs to ±D groups. Subjects were trained to record in-field jaw muscle activities, from which DFs (percentage of recording time) were determined. EDs (mJ/mm3) were estimated using modeled TMJ loads and in vivo dynamic stereometry. Multivariate analysis of variance, post hoc independent t tests, and K-means cluster analysis identified significant group differences (P < 0.05). Of 242 individuals screened, 65 females (TMJs: 78 +D, 52 -D) and 53 males (TMJs: 39 +D, 67 -D) participated. Subjects produced 312 daytime and 319 nighttime recordings of average duration 6.0 ± 0.2 h and 7.6 ± 0.1 h, respectively, and 219 (114 right, 105 left) intact dynamic stereometry recordings. Average EDs were 2-fold and significantly larger in +D than -D TMJs (P < 0.0001). DFs were on average 3-fold larger during the daytime versus nighttime for both masseter and temporalis muscles and 1.8- and 3.0-fold larger for the masseter versus temporalis muscle during the daytime and nighttime, respectively. Daytime masseter MBSs for +D TMJs in females were the largest overall at 621 ± 212 (mJ/mm3)2% and 2- to 43-fold larger versus -D TMJs in both sexes during daytime and nighttime. Cluster analysis (P < 0.0001) identified groups 2 and 3, which comprised 87% +D TMJs and had average MBSs 21-fold larger than group 1. The results show MBS as a potential biomarker to predict homeostasis versus progression or reversal of degenerative TMJ structural changes.

Mechanisms Underlying Sex Differences in Temporomandibular Disorders and Their Comorbidity with Migraine

Sexual dimorphism in temporomandibular disorders (TMDs) and their comorbidity with migraine are important phenomena observed in clinics. TMDs are the most prevalent orofacial pain conditions with jaw joint and masseter muscle dysfunction. Migraine is the predominant headache commonly associated with TMDs. Women much more often suffer from this orofacial pain than men. However, currently, there is no gender-specific therapy for such pain conditions. Understanding the pathophysiological mechanisms behind sex differences in TMDs as well as their comorbidity with migraines is essential for developing novel approaches for gender-specific treatment of TMDs and related orofacial pain comorbidity. In this review, we summarize recent research progress regarding sex differences in TMDs, focusing on the underlying mechanisms including craniofacial anatomy, hormonal regulation, and roles of opioids, transient receptor potential channels, and endocannabinoid systems. We also discuss the mechanisms of comorbid TMDs and migraine. The information covered in this review will provide mechanistic insights into sex differences in TMDs and their comorbidity with migraine, which could aid in developing effective treatment strategies for the overlapping orofacial pain condition.

Changes in strain energy density in the temporomandibular joint disk after sagittal split ramus osteotomy using a computed tomography-based finite element model

PURPOSE

We evaluated the changes in the strain energy density (SED) in the temporomandibular joint (TMJ) disk after sagittal split ramus osteotomy (SSRO) at three time points. A finite element model (FEM) based on real patient-based computed tomography (CT) data was used to examine the effect of SSRO on the TMJ.

METHODS

Measurements of the condylar position and angulation in CT images and FEM analyses were performed for 17 patients scheduled to undergo SSROs at the following time points: before surgery, immediately after surgery, and 1 year after surgery. SED on the entire disk was calculated at each of the three time points using FEM. Furthermore, the relationship between individual SED values and the corresponding condylar position was also evaluated.

RESULTS

No significant change was observed in the condylar position at the three time points. The FEM analysis showed that SED was the highest and lowest immediately after and 1 year after surgery, respectively. A possible SED distribution imbalance between the left and right joints was improved 1 year after SSRO. Concerning the effect of fossa morphometry and condylar position, wide and deep glenoid fossae and a more posterior condylar position tended to show lower SED.

CONCLUSION

SED in the articular disk temporarily increased after surgery and significantly decreased 1 year after surgery compared with that before surgery. SSRO generally improved the imbalance between the left and right joints. Thus, SSRO, which improves maxillofacial morphology, may also improve components of temporomandibular disorders.

Temporomandibular disorders in migraine and tension-type headache patients: a systematic review with meta-analysis

The simultaneous occurrence of primary headaches and temporomandibular disorders can pose a challenge in determining the best clinical management of patients. Therefore, we aimed to summarize evidence regarding the risk and prevalence of temporomandibular disorders (TMDs) in migraine and tension-type headaches (TTH) patients. Cross-sectional studies published in English comparing the presence of TMDs in adults with TTH or migraine to subjects without headaches were included, International Classification of Orofacial Pain, Diagnostic Criteria for Temporomandibular Disorders or Research Diagnostic Criteria for Temporomandibular Disorders, and large epidemiological studies (sensitive diagnostic criteria (SDC)). The methodological quality was assessed by Modified Newcastle-Ottawa Quality Assessment Scale. Odds ratio (OR) and random effects were calculated. 1405 articles were identified in PubMed, Embase and Central databases, and 13 cross-sectional studies were finally included. Overall Risk of TMDs was statistically significantly higher than control groups in both Migraine (SDC: 11 studies; OR: 3.79 (2.43, 5.90); I2 = 99%), with higher values in chronic migraine (OR: 24.27; (95% Confidence interval (CI): 5.84, 100.82); I2 = 0%) and TTH populations (SDC: 8 studies; OR: 4.45 (2.63, 7.53); I2 = 86%). Headache subjects presented a higher risk of muscular TMDs (5 studies; OR: 2.01 (1.62, 2.50); I2 = 0%), Combined TMDs (5 studies; OR: 2.74 (1.40, 5.36); I2 = 63%), or Painful TMDs (8 studies; OR: 5.31 (2.96, 9.54); I2 = 96%). Headache patients didn't show the risk of arthrogenous TMDs (4 studies; OR: 0.96 (0.54, 1.71); I2 = 33%) or nonpainful TMDs (2 studies; OR: 1.10 (0.28, 4.26); I2 = 84%). The high heterogeneity in the results was reduced following subgroup analysis. Migraine and TTH appear to increase the risk of painful, myogenous or combined arthrogenous and myogenous TMDs.

Otological symptoms in patients with rheumatoid arthritis of the temporomandibular joint

OBJECTIVE

The aim of the current study was to describe the pattern of otological symptoms in patients with rheumatoid arthritis (RA), having clinical temporomandibular joint (TMJ) involvement. This issue had not been previously addressed.

METHODS

A questionnaire and examination findings protocol was applied for 141 patients with RA and 141 control subjects.

RESULTS

Otological symptoms (otalgia, hearing loss, tinnitus, and vertigo), all had a significantly higher incidence in RA patients, compared to control subjects (P = .001).

CONCLUSION

The onset and maintenance of otological symptoms in patients with TMJ involvement by RA probably result from peripheral, as well as central nervous system alterations in sensory stimuli programming.

A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth

OBJECTIVES

To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, °) and ramus length (Condylion-Gonion (Co-Go), mm).

MATERIALS AND METHODS

Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go.

RESULTS

Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n = 36) compared to meso-brachyfacial (FHMPA< 27°, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49).

CONCLUSIONS

Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.

Influence of bolus size and chewing side on temporomandibular joint intra-articular space during mastication

Previous studies suggested that, during mastication, magnitude and location of mechanical load in the temporomandibular joint (TMJ) might depend on chewing side and bolus size. Aim of this study was to dynamically measure the TMJ space while chewing on standardized boluses to assess the relationship among minimum intra-articular distances (MID), their location on the condylar surface, bolus size, and chewing side. Mandibular movements of 12 participants (6f, 24±1y.o.; 6 m, 28±6y.o.) were tracked optoelectronically while chewing unilaterally on rubber boluses of 15 × 15 × 5, 15 × 15 × 10, and 15 × 15 × 15 mm³ size. MID and their location along the main condylar axis were determined with dynamic stereometry. MID were normalized on the intra-articular distance in centric occlusion. Repeated measures ANOVA (α = 0.05) showed that MID were smaller on the balancing (0.74±0.19) than on the working condyle (0.89±0.16) independently of bolus size (p < 0.0001). MIDs did not differ between 5 and 10 mm bolus thicknesses (0.80±0.17) but increased for 15 mm (0.85±0.22, p = 0.024) and were located mostly laterally, close to the condylar center. This study confirmed higher reduction of TMJ space on the balancing than on the working condyle during mastication. Intra-articular distances increased significantly for the greatest bolus thickness. Loaded areas were located laterally, for both working and balancing joint.

Mechanobehavior and mandibular ramus length in different facial phenotypes

OBJECTIVES

To test the hypotheses that mechanobehavior scores (MBS) were correlated with mandibular ramus lengths (Co-Go) and differed between facial phenotypes.

MATERIALS AND METHODS

Subjects gave informed consent to participate. Co-Go (mm), mandibular plane angles (SN-GoGn, °), and three-dimensional anatomy were derived from cephalometric radiography or cone beam computed tomography. Temporomandibular joint (TMJ) energy densities (ED) (mJ/mm3) were measured using dynamic stereometry and duty factors (DF) (%) were measured from electromyography, to calculate MBS (= ED2 × DF,) for each TMJ. Polynomial regressions, K-means cluster analysis, and analysis of variance (ANOVA) with Tukey post-hoc tests were employed.

RESULTS

Fifty females and 23 males produced replete data. Polynomial regressions showed MBS were correlated with Co-Go (females, R2 = 0.57; males, R2 = 0.81). Cluster analysis identified three groups (P < .001). Dolichofacial subjects, with shorter normalized Co-Go, clustered into two subgroups with low and high MBS compared to brachyfacial subjects with longer Co-Go. SN-GoGn was significantly larger (P < .03) in the dolichofacial subgroups combined (33.0 ± 5.9°) compared to the brachyfacial group (29.8 ± 5.5°).

CONCLUSIONS

MBS correlated with Co-Go within sexes and differed significantly between brachyfacial and dolichofacial subjects.

MRI characteristics of the asymptomatic temporomandibular joint in patients with unilateral temporomandibular joint disorder

OBJECTIVE

To determine the association between unilateral temporomandibular joint disorder (TMD) and the presence of imaging abnormalities in the contralateral, asymptomatic joint.

METHODS

MRI studies of 219 subjects with symptoms of unilateral TMD were examined for signs of disc displacement, osteoarthritis, disc deformation, and effusion in both temporomandibular joints (TMJ). The Chi-Square test and stepwise logistic regression analysis were performed.

RESULTS

Disc displacement, osteoarthritis, disc deformation, and effusion were more common on the symptomatic side. However, in the category of disc displacement with a reduction in open mouth position (DDWR), the difference was not significant between the symptomatic and the asymptomatic TMJs. Stepwise logistic regression showed that the presence of any imaging abnormality other than DDWR was related to osteoarthritis and disc deformity on the symptomatic side. On the other hand, the presence of any MRI abnormality (including DDWR) on the asymptomatic side was related only to the presence of osteoarthritis on the symptomatic side.

CONCLUSIONS

Unilateral symptomatic TMD is related to the presence of imaging abnormalities on the contralateral, asymptomatic side, suggesting that the development and progression of joint changes in symptomatic and contralateral asymptomatic TMJs are interrelated.

Three-dimensional temporomandibular joint muscle attachment morphometry and its impacts on musculoskeletal modeling

In musculoskeletal models of the human temporomandibular joint (TMJ), muscles are typically represented by force vectors that connect approximate muscle origin and insertion centroids (centroid-to-centroid force vectors). This simplification assumes equivalent moment arms and muscle lengths for all fibers within a muscle even with complex geometry and may result in inaccurate estimations of muscle force and joint loading. The objectives of this study were to quantify the three-dimensional (3D) human TMJ muscle attachment morphometry and examine its impact on TMJ mechanics. 3D muscle attachment surfaces of temporalis, masseter, lateral pterygoid, and medial pterygoid muscles of human cadaveric heads were generated by co-registering measured attachment boundaries with underlying skull models created from cone-beam computerized tomography (CBCT) images. A bounding box technique was used to quantify 3D muscle attachment size, shape, location, and orientation. Musculoskeletal models of the mandible were then developed and validated to assess the impact of 3D muscle attachment morphometry on joint loading during jaw maximal open-close. The 3D morphometry revealed that muscle lengths and moment arms of temporalis and masseter muscles varied substantially among muscle fibers. The values calculated from the centroid-to-centroid model were significantly different from those calculated using the 'Distributed model', which considered crucial 3D muscle attachment morphometry. Consequently, joint loading was underestimated by more than 50% in the centroid-to-centroid model. Therefore, it is necessary to consider 3D muscle attachment morphometry, especially for muscles with broad attachments, in TMJ musculoskeletal models to precisely quantify the joint mechanical environment critical for understanding TMJ function and mechanobiology.

Jaw closing movement and sex differences in temporomandibular joint energy densities

Energy densities (ED, mJ/mm3 ) quantify mechanical work imposed on articular cartilages during function. This cross-sectional study examined differences in temporomandibular joint (TMJ) ED during asymmetric versus symmetric jaw closing in healthy females versus males. ED component variables were tested for differences between and within sexes for two types of jaw closing. Seventeen female and 17 male subjects gave informed consent to participate. Diagnostic criteria for temporomandibular disorders and images (magnetic resonance (MR), computed tomography) were used to confirm healthy TMJ status. Numerical modelling predicted TMJ loads (Fnormal ) consequent to unilateral canine biting. Dynamic stereometry combined MR imaging and jaw-tracking data to measure ED component variables during 10 trials of each type of jaw closing in each subject's TMJs. These data were then used to calculate TMJ ED during jaw closing asymmetrically and symmetrically. Paired and Student's t tests assessed ED between jaw closing movements and sexes, respectively. Multivariate data analyses assessed ED component variable differences between jaw closing movements and sexes (α = 0.05). Contralateral TMJ ED were 3.6-fold and significantly larger (P < .0001) during asymmetric versus symmetric jaw closing, due to significantly larger (P ≤ .001) distances of TMJ stress-field translation in asymmetric versus symmetric movement. During asymmetric jaw closing, contralateral TMJ ED were twofold and significantly larger (P = .036) in females versus males, due to 1.5-fold and significantly smaller (P ≤ .010) TMJ disc cartilage volumes under stress fields in females versus males. These results suggest that in healthy individuals, asymmetric compared to symmetric jaw closure in females compared to males has higher TMJ mechanical fatigue liabilities.

Mechanobehavioral Scores in Women with and without TMJ Disc Displacement

Cartilage fatigue may be a factor in the precocious development of degenerative changes in the temporomandibular joint (TMJ). This cross-sectional study estimated potential for cartilage fatigue via TMJ energy densities (ED) and jaw muscle duty factors (DF), which were combined to calculate mechanobehavioral scores (MBS) in women with (+) and without (-) bilateral TMJ disc displacement (DD). All subjects gave informed consent to participate and were examined using Diagnostic Criteria (DC) for Temporomandibular Disorders (TMD) and magnetic resonance (MR) and computed tomography (CT) images. Forty-seven subjects were categorized into +DD ( n = 29) and -DD ( n = 18) groups. Dynamic stereometry (MR images combined with jaw-tracking data) characterized individual-specific data of TMJ stress-field mechanics to determine ED (ED = W/ Q mJ/mm3, where W = work done, Q = volume of cartilage) during 10 symmetrical jaw-closing cycles with a 20-N mandibular right canine load. Subjects were trained to record masseter and temporalis electromyography over 3 days and 3 nights. Root mean square electromyography/bite-force calibrations determined subject-specific masseter and temporalis muscle activities per 20-N bite-force (T20 N, µV), which defined thresholds. Muscle DF (DF = % duration of muscle activity/total recording time) were determined for a range of thresholds, and MBS (ED2 × DF) were calculated. Intergroup differences in ED, DF, and MBS were assessed via analyses of variance with Bonferroni and Tukey honest significant difference post hoc tests. Average ED for contralateral TMJs was significantly larger ( P = 0.012) by 1.4-fold in +DD compared to -DD subjects. Average DF were significantly larger (all P < 0.01) for +DD compared to -DD subjects by 1.7-, 2.5-, and 1.9-fold for day, night, and overall, respectively. Daytime MBS were significantly larger (all P < 0.04) by up to 8.5-fold in +DD compared to -DD subjects. Significantly larger ED, DF, and MBS were shown in women with compared to women without bilateral TMJ DD.

TMJ energy densities in healthy men and women

OBJECTIVE

Cartilage fatigue, due to mechanical work, may account for the early development of degenerative joint disease (DJD) in the temporomandibular joint (TMJ), and why women are three times more likely to be afflicted. This study tested for gender differences in mechanical energy densities in women and men with healthy TMJs.

DESIGN

Eighteen women and eighteen men gave informed consent. Research diagnostic criteria including imaging were used to ensure that subjects' TMJs were normal, without disc displacement or signs of DJD. Numerical modeling determined TMJ loads (F_normal). Jaw tracking and three-dimensional dynamic stereometry characterized individual-specific data of stress-field dynamic mechanics during 10 symmetrical jaw closing cycles. These data were used to estimate tractional forces (F_traction). Energy densities were then calculated, where: Energy Density = W/Q (W = work done or mechanical energy input = F_traction*distance of stress-field translation, Q = volume of cartilage). Two-way analysis of variance (ANOVA) and follow-up two-group comparisons tested mean energy densities for ipsilateral and contralateral TMJs in women vs men.

RESULTS

Mean energy densities ± standard deviations in ipsilateral and contralateral TMJs in women were 9.0 ± 9.7 and 8.4 ± 5.5 mJ/mm³, respectively, and were significantly larger (P = 0.004 and 0.001, respectively) compared to ipsilateral and contralateral TMJs in men, which were 5.6 ± 4.2 and 6.3 ± 4.2 mJ/mm³, respectively.

CONCLUSIONS

Energy densities were significantly larger in healthy TMJs of women than men. Larger TMJ energy densities during normal jaw functions could predispose earlier mechanical fatigue of the TMJ disc.

Is There an Association Between Temporomandibular Joint Effusion and Arthralgia?

PURPOSE

The literature on joint effusion (JE) and its association with clinical and radiologic variables in patients with temporomandibular disorders (TMDs) is inconsistent and is characterized by multiple methodologic limitations. The primary aim of this investigation was to evaluate the association between magnetic resonance imaging (MRI) identified JE and temporomandibular joint (TMJ) arthralgia. The secondary aim of this investigation was to determine the association between JE and other clinical and MRI-identified soft tissue characteristics.

MATERIALS AND METHODS

A retrospective cohort study was conducted. Clinical and soft tissue imaging assessments were carried out according to the Diagnostic Criteria for Temporomandibular Disorders guidelines. The dependent variable was JE and the primary independent variable was arthralgia. The secondary independent variables were TMJ pain-associated characteristics and MRI-identified variables. When applicable, Pearson χ² or t test was used to determine the statistical associations between JE and clinical characteristics and between JE and MRI-identified variables. Furthermore, generalized estimating equation (GEE) modeling was conducted to determine which of the independent clinical and MRI-identified variables were associated with JE.

RESULTS

Data for 158 participants, representing 312 joints, were extracted. The mean age of the female sample (59.4%) was 31 ± 11.1 years and that of the male sample (40.6%) was 29.8 ± 9.7 years. No association was found between JE and arthralgia. However, statistically significant associations were found between JE and lateral disc rotation (P = .001) and between JE and disc position in the coronal and sagittal planes (P = .001). The GEE model suggested that disc displacement with reduction (odds ratio = 2.5) was a statistically relevant contributing factor for JE in the absence of degenerative joint disease.

CONCLUSION

Results associated JE with the position of the disc in the sagittal plane. No association was found between JE and arthralgia or TMJ pain-associated clinical characteristics in patients with TMDs.

Properties and Mechanobiological Behavior of Bovine Nasal Septum Cartilage

Bovine nasal septum (BNS) is a source of non-load bearing hyaline cartilage. Little information is available on its mechanical and biological properties. The aim of this work was to assess the characteristics of BNS cartilage and investigate its behavior in in vitro mechanobiological experiments. Mechanical tests, biochemical assays, and microscopic assessment were performed for tissue characterization. Compressions tests showed that the tissue is viscoelastic, although values of elastic moduli differ from the ones of other cartilaginous tissues. Water content was 78 ± 1.4%; glycosaminoglycans and collagen contents-measured by spectrophotometric assay and hydroxyproline assay-were 39 ± 5% and 25 ± 2.5% of dry weight, respectively. Goldner's Trichrome staining and transmission electron microscopy proved isotropic cells distribution and results of earlier cell division. Furthermore, gene expression was measured after uniaxial compression, showing variations depending on compression time as well as trends depending on equilibration time. In conclusion, BNS has been characterized at several levels, revealing that bovine nasal tissue is regionally homogeneous. Results suggest that, under certain conditions, BNS could be used to perform in vitro cartilage loading experiments.

A pilot study of ambulatory masticatory muscle activities in temporomandibular joint disorders diagnostic groups

OBJECTIVE

To determine differences in masticatory muscle usage between temporomandibular joint disorders diagnostic groups.

SETTING AND SAMPLE POPULATION

Seventy-one informed and consented subjects (27 men; 44 women) participated at the University at Buffalo.

MATERIAL AND METHODS

Research diagnostic criteria and imaging data were used to categorize subjects according to the presence/absence +/- of TMJ disc placement (DD) and chronic pain (P) (+DD+P, n=18; +DD-P, n=14; -DD-P, n=39). Electromyographic (EMG)/bite-force calibrations determined subject-specific masseter and temporalis muscle activities per 20 N bite-force (T20N , μV). Over 3 days and nights, subjects collected EMG recordings. Duty factors (DFs, % of recording time) were determined based on threshold intervals (5-9, 10-24, 25-49, 50-79, ≥80% T20N ). anova and Tukey-Kramer post hoc tests identified 1) diagnostic group differences in T20N and 2) the effects of diagnostic group, gender, time and interval on muscle DFs.

RESULTS

Mean (±SE) temporalis T20N in +DD+P subjects was significantly higher (71.4±8.8 μV) than masseter T20N in these subjects (19.6±8.8 μV; p=0.001) and in -DD-P subjects (25.3±6.0 μV, p=0.0007). Masseter DFs at 5-9% T20N were significantly higher in +DD-P women (3.48%) than +DD-P men (0.85%) and women and men in both other diagnostic groups (all p<0.03), and in +DD+P women (2.00%) compared to -DD-P men (0.83%; p=0.029). Night-time DFs at 5-9% T20N in +DD-P women (1.97%) were significantly higher than in -DD-P men (0.47%) and women (0.24%; all p<0.01).

CONCLUSIONS

Between-group differences were found in masticatory muscle activities in both laboratory and natural environmental settings.