The challenge of ecological validity in temporomandibular disorders research.

OBJECTIVE: To review the ecological validity of outcomes from current research involving temporomandibular disorders (TMDs), with an emphasis on chronic myofascial pain and the precocious development of degenerative disease of the temporomandibular joint (TMJ). MATERIALS AND METHODS: Current approaches used to study TMDs in terms of neuromechanics, masticatory muscle behaviours, and the dynamics of the autonomic nervous system (ANS) were assessed for ecological validity in this review. In particular, the available literature was scrutinized regarding the effects of sampling, environmental and psychophysiological constraints and averaging data across biological rhythms. RESULTS: Validated computer-assisted numerical modelling of the neuromechanics used biological objective functions to accurately predict muscle activation patterns for jaw-loading tasks that were individual-specific. With respect to masticatory muscle behaviour, current findings refute the premise that sustained bruxing and clenching at high jaw-loading magnitudes were associated with painful TMDs such as myofascial pain. Concerning the role of the ANS in TMDs, there remains the need for personalized assessments based on biorhythms, and where the detection of dysregulated physiologic oscillators may inform interventions to relieve pain and restore normal function. CONCLUSIONS: Future human research which focuses on TMD myofascial pain or the precocious development and progression of TMJ degenerative joint disease requires experimental designs with ecological validity that capture objectively measured data which meaningfully reflect circadian and ultradian states.

Standardised Tool for the Assessment of Bruxism.

OBJECTIVE: This paper aims to present and describe the Standardised Tool for the Assessment of Bruxism (STAB), an instrument that was developed to provide a multidimensional evaluation of bruxism status, comorbid conditions, aetiology and consequences. METHODS: The rationale for creating the tool and the road map that led to the selection of items included in the STAB has been discussed in previous publications. RESULTS: The tool consists of two axes, specifically dedicated to the evaluation of bruxism status and consequences (Axis A) and of bruxism risk and etiological factors and comorbid conditions (Axis B). The tool includes 14 domains, accounting for a total of 66 items. Axis A includes the self-reported information on bruxism status and possible consequences (subject-based report) together with the clinical (examiner report) and instrumental (technology report) assessment. The Subject-Based Assessment (SBA) includes domains on Sleep Bruxism (A1), Awake Bruxism (A2) and Patient's Complaints (A3), with information based on patients' self-report. The Clinically Based Assessment (CBA) includes domains on Joints and Muscles (A4), Intra- and Extra-Oral Tissues (A5) and Teeth and Restorations (A6), based on information collected by an examiner. The Instrumentally Based Assessment (IBA) includes domains on Sleep Bruxism (A7), Awake Bruxism (A8) and the use of Additional Instruments (A9), based on the information gathered with the use of technological devices. Axis B includes the self-reported information (subject-based report) on factors and conditions that may have an etiological or comorbid association with bruxism. It includes domains on Psychosocial Assessment (B1), Concurrent Sleep-related Conditions Assessment (B2), Concurrent Non-Sleep Conditions Assessment (B3), Prescribed Medications and Use of Substances Assessment (B4) and Additional Factors Assessment (B5). As a rule, whenever possible, existing instruments, either in full or partial form (i.e. specific subscales), are included. A user's guide for scoring the different items is also provided to ease administration. CONCLUSIONS: The instrument is now ready for on-field testing and further refinement. It can be anticipated that it will help in collecting data on bruxism in such a comprehensive way to have an impact on several clinical and research fields.

The development of the Standardised Tool for the Assessment of Bruxism (STAB): An international road map.

This paper summarises the background reasoning and work that led to the selection of the items included in the Standardised Tool for the Assessment of Bruxism (STAB), also introducing the list of items. The instrument is currently being tested for face validity and on-field comprehension. The underlying premise is that the different motor activities included in the bruxism spectrum (e.g. clenching vs. grinding, with or without teeth contact) potentially need to be discriminated from each other, based on their purportedly different aetiology, comorbidities and potential consequences. Focus should be on a valid impression of the activities' frequency, intensity and duration. The methods that can be used for the above purposes can be grouped into strategies that collect information from the patient's history (subject-based), from the clinical assessment performed by an examiner (clinically based) or from the use of instruments to measure certain outcomes (instrumentally based). The three strategies can apply to all aspects of bruxism (i.e. status, comorbid conditions, aetiology and consequences). The STAB will help gathering information on many aspects, factors and conditions that are currently poorly investigated in the field of bruxism. To this purpose, it is divided into two axes. Axis A includes the self-reported information on bruxism status and potential consequences (subject-based report) together with the clinical (examiner report) and instrumental assessment (technology report). Axis B includes the self-reported information (subject-based report) on factors and conditions that may have an etiological or comorbid role for bruxism. This comprehensive multidimensional assessment system will allow building predictive model for clinical and research purposes.

Signal acquisition and analysis of ambulatory electromyographic recordings for the assessment of sleep bruxism: A scoping review.

BACKGROUND: Ambulatory electromyographic (EMG) devices are increasingly being used in sleep bruxism studies. EMG signal acquisition, analysis and scoring methods vary between studies. This may impact comparability of studies and the assessment of sleep bruxism in patients. OBJECTIVES: (a) To provide an overview of EMG signal acquisition and analysis methods of recordings from limited-channel ambulatory EMG devices for the assessment of sleep bruxism; and (b) to provide an overview of outcome measures used in sleep bruxism literature utilising such devices. METHOD: A scoping review of the literature was performed. Online databases PubMed and Semantics Scholar were searched for studies published in English until 7 October 2020. Data on five categories were extracted: recording hardware, recording logistics, signal acquisition, signal analysis and sleep bruxism outcomes. RESULTS: Seventy-eight studies were included, published between 1977 and 2020. Recording hardware was generally well described. Reports of participant instructions in device handling and of dealing with failed recordings were often lacking. Basic elements of signal acquisition, for example amplifications factors, impedance and bandpass settings, and signal analysis, for example rectification, signal processing and additional filtering, were underreported. Extensive variability was found for thresholds used to characterise sleep bruxism events. Sleep bruxism outcomes varied, but typically represented frequency, duration and/or intensity of masticatory muscle activity (MMA). CONCLUSION: Adequate and standardised reporting of recording procedures is highly recommended. In future studies utilising ambulatory EMG devices, the focus may need to shift from the concept of scoring sleep bruxism events to that of scoring the whole spectrum of MMA.

Temporomandibular Joint Bioengineering Conference: Working Together Toward Improving Clinical Outcomes.

The sixth temporomandibular joint (TMJ) Bioengineering Conference (TMJBC) was held on June 14-15 2018, in Redondo Beach, California, 12 years after the first TMJBC. Speakers gave 30 presentations and came from the United States, Europe, Asia, and Australia. The goal of the conference has remained to foster a continuing forum for bioengineers, scientists, and surgeons and veterinarians to advance technology related to TMJ disorders. These collective multidisciplinary interactions over the past decade have made large strides in moving the field of TMJ research forward. Over the past 12 years, in vivo approaches for tissue engineering have emerged, along with a wide variety of degeneration models, as well as with models occurring in nature. Furthermore, biomechanical tools have become more sensitive and new biologic interventions for disease are being developed. Clinical directives have evolved for specific diagnoses, along with patient-specific biological and immunological responses to TMJ replacement devices alloplastic and/or bioengineered devices. The sixth TMJBC heralded many opportunities for funding agencies to advance the field: (1) initiatives on TMJ that go beyond pain research, (2) more training grants focused on graduate students and fellows, (3) partnership funding with government agencies to translate TMJ solutions, and (4) the recruitment of a critical mass of TMJ experts to participate on grant review panels. The TMJ research community continues to grow and has become a pillar of dental and craniofacial research, and together we share the unified vision to ultimately improve diagnoses and treatment outcomes in patients affected by TMJ disorders.

Towards a Standardized Tool for the Assessment of Bruxism (STAB)-Overview and general remarks of a multidimensional bruxism evaluation system.

The aim of the present paper was to give an overview of the general project and to present the macrostructure of a comprehensive multidimensional toolkit for the assessment of bruxism, viz. a bruxism evaluation system. This is a necessary intermediate step that will be detailed in a successive extended publication and will ultimately lead to the definition of a Standardized Tool for the Assessment of Bruxism (STAB) as the final product. Two invitation-only workshops were held during the 2018 and 2019 General Session & Exhibition of the International Association for Dental Research (IADR) meetings. Participants of the IADR closed meetings were split into two groups, to put the basis for a multidimensional evaluation system composed of two main axes: an evaluation Axis A with three assessment domains (ie subject-based, clinically based and instrumentally based assessment) and an aetiological/risk factors Axis B assessing different groups of factors and conditions (ie psychosocial assessment; concurrent sleep and non-sleep conditions; drug and substance use or abuse; and additional factors). The work of the two groups that led to the identification of different domains for assessment is summarised in this manuscript, along with a road map for future researches. Such an approach will allow clinicians and researchers to modulate evaluation of bruxism patients with a comprehensive look at the clinical impact of the different bruxism activities and aetiologies. The ultimate goal of this multidimensional system is to facilitate the refinement of decision-making algorithms in the clinical setting.

Night-time autonomic nervous system ultradian cycling and masticatory muscle activity.

OBJECTIVES: To test if there was a correlation between night-time masticatory muscle activity, as measured by duty factors, and ultradian cycling of autonomic nervous system (ANS) spectral powers in subjects without temporomandibular disorder (TMD)-related pain. SETTING AND SAMPLE POPULATION: The University of Missouri-Kansas City School of Dentistry. Three women and four men of average ages 38 ±8 and 56 ± 17 years, respectively, gave informed consent to participate. MATERIAL AND METHODS: Investigators taught subjects to record heart (electrocardiography, ECG) and masticatory muscle activities (electromyography, EMG). ECG recordings were analysed for ANS ultradian cycling by a polynomial fit to the ratio of sympathetic and parasympathetic spectral powers (ms2 ). Masseter and temporalis EMG recordings were analysed over 20-minute epochs around peaks and valleys in the ANS ultradian cycles. Duty factors (% time of masticatory muscle activity/20-minute epoch) were determined relative to average threshold EMG (TEMG ) required to produce a given bite force (N). Regression analyses quantified relationships between normalized muscle duty factors and ANS spectral powers. RESULTS: Subjects made a total of 27 sets of night-time ECG and EMG recordings that averaged 6.6 ± 1.1 hours per recording. Highest average duty factors were associated with TEMG of 1-2 N and showed cumulative masseter and temporalis activities of 9.2 and 8.8 seconds/20-minute epoch, respectively. Normalized masticatory muscle duty factors showed non-linear relationships with normalized sympathetic (R2  = +0.82), parasympathetic (R2  = -0.70) and sympathetic/parasympathetic spectral powers (R2  = +0.75). CONCLUSIONS: Night-time ANS spectral powers showed ultradian cycling and were correlated with masseter and temporalis muscle activities in adult subjects without TMD.

A model system of the dynamic loading occurring in synovial joints: the biological effect of plowing on pristine cartilage.

Mechanical stress is listed as a main risk factor for cartilage degradation. The aim of this study was to investigate the biological response of cartilage to dynamic loading such as plowing. Cartilage strips harvested from bovine nasal septum were submitted to plowing using a cylindrical indenter, applying a constant normal force in the vertical axis and moving at constant speed in the horizontal axis. After plowing, cell viability, gene expression and glycosaminoglycan (GAG) release were measured with conventional assays. The cell-viability assay and qRT-PCR showed that plowing induces cell death and matrix metalloproteinase 3 (MMP-3) upregulation. The addition of actinomycin D, before or after plowing, confirmed that plowing was responsible for the observed MMP-3 upregulation. Even if the transcriptions of the tissue inhibitor of metalloproteinase (TIMP-1), aggrecan (Agg), collagen type I (Coll1), collagen type II (Coll2) and fibronectin (Fn) were not significantly affected by plowing, actinomycin D treatment revealed that plowing induces a strong increase in TIMP-1 and Coll1 messenger RNA content and influences the gene regulation of Agg, Coll2 and Fn. Furthermore, plowed cartilage explants exhibited enhanced GAG release. Application of hydroxamate MMP inhibitor after loading showed that plowing induces GAG release via the activation of catabolic enzymes. Plowing causes cell death of the chondrocytes closer to the surface as well as matrix damage, observed as GAG loss. Moreover, in healthy chondrocytes, plowing promotes the production and activation of catabolic enzymes like MMP-3.

Masticatory Muscles Activation and TMJ Space During Asymmetrically Loaded Jaw Closing.

Masticatory muscle activation and temporomandibular joint (TMJ) load generated during asymmetrically loaded jaw closing are largely unknown. Two different strategies were developed to explain how the central nervous system (CNS) generates muscle activation patterns during motion: minimization of joint load (MJL) vs. minimization of muscle effort (MME). The aim of the present study was to investigate, experimentally, the neuromuscular strategy selected by the CNS to coordinate jaw closing in reaction to the application of an external asymmetric load. Masticatory muscle activation was measured with electromyography (EMG) and the minimum intra-articular distance (MID) was assessed by dynamic stereometry to infer joint loading. Ten healthy subjects performed jaw-closing movements against an asymmetric mandibular load set from 0.0 to 2.0 kg in 0.5-kg steps. Recordings were analyzed by exploratory and graphical statistical tools. Moreover, the observed differences in MID and EMG among the various mandibular loads were tested using non-parametric tests for repeated measures data. The ipsilateral-contralateral differences in MID and EMG of the anterior temporalis showed a significant increase (p < 0.001, p = 0.01) with increasing asymmetrical load with both joints being most heavily loaded at 1 kg. EMG signals of the masseter did not change significantly with increasing load. This study is the first to have analyzed the changes in the TMJ intra-articular space during asymmetrically loaded jaw-closing movements, not only three dimensionally and dynamically, but also combined with EMG. Asymmetrical load affected the TMJ space and masticatory muscle activation patterns, primarily resulting in an increased activation of the anterior temporalis muscle. This might suggest the involvement of a control mechanism to protect the joints from overloading. However, the results do not fully support the hypothesis of MJL nor the MME strategy.

Comparison between the rhythmic jaw contractions occurring during sleep and while chewing.

The masticatory central pattern generator (CPG) may be implicated in the pathophysiology of sleep bruxism (SB). The aim of this study was to compare rhythmic masticatory muscle activity (RMMA) occurring during sleep related to SB with that of natural voluntary chewing in a sample of sleep bruxers. It was hypothesized that the pace of RMMA during sleep is correlated with the chewing pace. Electromyographic (EMG) surface activity was recorded unilaterally from the masseter muscle of 13 participants diagnosed with SB (mean age ± standard deviation =26.1 ± 9.0 years) by means of portable recorders. For each participant, recordings were carried out in the natural environment setting, always including the dinner time and the entire sleeping period. The time-frequency features of RMMA episodes were extracted automatically offline using a previously validated algorithm. Comparisons between chewing and SB activity indicated that chewing RMMA episodes almost doubled sleep RMMA in duration and power. The mean frequency of SB episodes was 1.0 ± 0.3 Hz, whereas the mean frequency of chewing episodes was 1.5 ± 0.4 Hz. The pace of SB and that of chewing were not correlated significantly (R = -0.13; P = 0.96). We conclude that sleep RMMA is not related to that of chewing. Despite both activities being accompanied by rhythmic jaw contractions, the pace-generating mechanism of SB may be independent from that of chewing.

Prevalence of Temporomandibular Disorders Based on a Shortened Symptom Questionnaire of the Diagnostic Criteria for Temporomandibular Disorders and Its Screening Reliability for Children and Adolescents Aged 7-14 Years.

The prevalence and adequacy of diagnostic approaches for temporomandibular disorders (TMD) in children and adolescents are still matters of debate. This study aimed to determine the prevalence of TMD and oral habits in children and adolescents aged 7-14 years and evaluate the consistency between self-reported TMD symptoms and clinical findings using a shortened Axis I of Diagnostic Criteria for TMD (DC/TMD). Children (aged 7-10) and adolescents (aged 11-14) of both sexes were invited to participate in this study (n = 1468). Descriptive statistics for all observed variables and Mann-Whitney U-Tests for the clinical examination were performed. A total of 239 subjects participated in the study (response rate 16.3%). The self-reported prevalence of TMD was found to be 18.8%. The most frequently reported oral habit was nail biting (37.7%), followed by clenching (32.2%) and grinding (25.5%). Self-reported headache increased with age, while clenching and grinding decreased. Based on the answers to the DC/TMD Symptom Questionnaire, subgroups of asymptomatic and symptomatic participants (n = 59; 24.7%) were established and randomly selected for the clinical examination (f = 30). The shortened Symptom Questionnaire showed a sensitivity of 0.556 and a specificity of 0.719 for pain during the clinical examination. Although the Symptom Questionnaire exhibited high specificity (0.933), its sensitivity (0.286) for temporomandibular joint sounds was low. Disc displacement with reduction (10.2%) and myalgia (6.8%) were the most common diagnoses. In conclusion, the self-reported prevalence of TMD in children and adolescents in this study was comparable to that reported in the literature for adults. However, the accuracy of the shortened Symptom Questionnaire as a screening tool for TMD-related pain and jaw sounds in children and adolescents was found to be low.

Implant-supported mandibular splinting affects temporomandibular joint biomechanics.

OBJECTIVES: Mandibular functional movements lead to complex deformations of bony structures. The aim of this study was to test whether mandibular splinting influences condylar kinematics and temporomandibular joint (TMJ) loading patterns. MATERIALS AND METHODS: Six subjects were analyzed by means of dynamic stereometry during jaw opening-closing with mandibles unconstrained as well as splinted transversally by a cast metal bar fixed bilaterally to two implant pairs in the (pre)molar region. Statistical analysis was performed by means of ANOVAs for repeated measurements (significance level α=0.05). RESULTS: Transversal splinting reduced mandibular deformation during jaw opening-closing as measured between two implants in the (pre)molar region on each side of the mandible significantly by 54%. Furthermore, splinting significantly reduced the distance between lateral condylar poles (average displacement vector magnitude of each pole: 0.84±0.36 mm; average mediolateral displacement component: 45±28% of the magnitude) and led to a medial displacement of their trajectories as well as a mediolateral displacement of stress-field paths. CONCLUSIONS: During jaw opening-closing, splinting of the mandible leads to a significant reduction of mandibular deformation and intercondylar distance and to altered stress-field paths, resulting in changed loading patterns of the TMJ structures.

Nocturnal masseter electromyographic activity of complete denture wearers.

OBJECTIVE: Collection of normative data on activity patterns of the masseter during sleep in elderly denture wearers by portable electromyography (EMG) recorders. BACKGROUND: Complete denture wearers might suffer from orofacial pain caused by myoarthropathies of the masticatory system. Indeed, denture instability may precipitate parafunctional habits and consequently muscle soreness and/or temporomandibular pain. MATERIALS AND METHODS: We collected normative masseter EMG data during sleep in 15 complete denture wearers (five women, 10 men, 56-88 years) by portable recorders in their natural environment. Activity periods (AP) were signal portions including subthreshold intervals ≤5 s. Signal amplitude was expressed in per cent of maximum voluntary contraction (%MVC). For this reason, maximum bite force was assessed. Twenty age-matched dentate controls were also recorded for the maximum bite force. RESULTS: We found 157.2 ± 86.5 AP per night, i.e. 24.0 ± 12.2 AP/h. Mean amplitude was 15.1 ± 4.3%MVC. AP lasted 6.8 ± 4.1 s, and their time integral was 126.3 ± 112.5%MVC•s. Maximum bite force was 116.8 ± 69.6 N in the edentulous, significantly lower than in controls (344.8 ± 150.4 N). CONCLUSIONS: Healthy complete denture wearers showed intermittent periods of nocturnal masseter activity of very low intensity and short duration.

Bone mineral density in young women on methadone substitution.

Little is known about bone mineral density (BMD) in patients with heroin addiction and subsequent methadone substitution. The goal of this study was to compare bone mass density of young HIV-negative women on long-term methadone treatment to a local group of young healthy women. Eleven women (aged 20-29) with previous heroin dependence and current methadone substitution (20-140 mg, median 60, daily) for 1.5-9 (median 3) years were compared to 30 healthy women (aged 20-28). Participants were examined with dual-energy X-ray absorptiometry of the lumbar spine (L2-L4), of the total proximal hip area, and of the femoral neck. Patients and controls had neither current nor lifetime underweight condition, had comparable ages at menarche, and did not differ significantly in current body mass index (21.9 ± 4.0, respectively, 20.5 ± 1.5 kg/m(2)) in spite of a largely unhealthy lifestyle (cigarette, alcohol, and cocaine consumption in patients). Patients' total-hip parameters were marginally lower than those of controls (BMD P = 0.054, T score P = 0.049), whereas the femoral neck and lumbar spine parameters did not differ significantly between the two groups. Long-term methadone substitution in HIV-negative women seems to slightly affect bone mass density.

Short-term effects of NTI-tss and Michigan splint on nocturnal jaw muscle activity: A pilot study.

OBJECTIVES: Sleep bruxism is mostly assessed by reporting of tooth-grinding or clenching during sleep and by clinical signs (tooth wear, cracks, or fractures). Parafunctional tooth damage is usually prevented by employing occlusal appliances mainly of the full arch covering type (Michigan splint) and of the partial type covering only central incisors (NTI-tss). To date, the effects of occlusal appliances on sleep bruxism or jaw muscle activity during sleep are still controversial. The present study is a randomized controlled clinical trial that evaluated the effects of two different splint designs on jaw muscle activity in sleep bruxers otherwise healthy. MATERIAL AND METHODS: Ten patients from a private dental practice were treated by a single operator. A Michigan splint and an NTI-tss device were manufactured individually and used at random order. Electromyographic jaw muscle activity was recorded for four consecutive nights in the first, fourth, and seventh week with and without splint. Participants reported on splint comfort and side effects. RESULTS: Muscle activity decreased only while wearing the NTI-tss device. Most patients preferred though the Michigan splint due to its greater wearing comfort. CONCLUSIONS: NTI-tss devices proved more effective for the reduction of jaw muscle activity during sleep. The main advantage of the prefabricated NTI-tss is its prompt availability in an acute phase of temporomandibular disorders associated with sleep bruxism. In long-term therapies, patients should be informed of the possible risk of irreversible occlusal changes. Subjective preferences, wearing comfort, and costs should also be considered.

In-vivo kinematic assessment of alloplastic temporomandibular joint replacements by means of helical axis: A cohort study with historical control.

Alloplastic total temporomandibular joint replacement (TJR) is a surgical procedure used to restore normal mandibular function when conservative therapies fail. The instantaneous helical axis (HA), is a mathematical model used to visualize globally rigid body kinematics. It can be applied to mandibular motion for quantification of movement patterns and irregularities. Aim of this study was to analyze HA pathways in subjects with unilateral and bilateral TJR and compare them to a control group. An optoelectronic system was employed to track mouth opening/closing cycles (n = 3) of 15 patients (7 operated unilaterally, 8 bilaterally, 11 F, aged 24-72) and 12 controls (6 F, aged 23-40). HA position in space was determined for 30 equally-distributed steps of the observed movement. Total mandibular rotation around HA (Φtot) and total translation along HA (Ttot) were determined. Angles between HA and the anatomical coordinate system of the head (θx, θy, θz); global fluctuation of HA spatial orientation (θe), distance between condylar center (CP) and HA (dCP) and its projections on the axes (xdCP, ydCP, zdCP) were calculated. Overall, Φtot was larger in controls than in bilaterally operated subjects (p = 0.002, p = 0.003) and θz was larger in unilaterally operated subjects than in controls (p = 0.004) and bilaterally operated subjects (p = 0.002, p = 0.024). During opening, θe¯ was smaller in controls than in unilaterally operated subjects (p = 0.01). The distance dCP was smaller for alloplastic joints than for controls (p < 0.01 overall). In conclusion, mandibular HA pathways in patients with TJR differ significantly from controls in terms of spatial location and variability.

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.

Temporomandibular joint loading patterns related to joint morphology: a theoretical study.

It is unclear which aspects of the temporomandibular joint (TMJ) anatomy and/or kinematics determine shape and location of disk-compressive areas (stress field). The aim of this study was a quantitative analysis of TMJ anatomy to predict stress field path direction. Twenty-five asymptomatic TMJs (12 females and 13 males, aged 20-38 years) were tracked during unloaded opening/closing cycles. All TMJs were magnetic resonance (MR) imaged, reconstructed and animated with the recorded kinematics. Quantitative morphological parameters were calculated and entered into cross-validated multivariate discriminant analysis. Stress field paths during jaw opening were classified as mediolateral (ML) in 14 (9 females and 5 males) and lateromedial (LM) in 11 joints (3 females and 8 males). Curvature and incongruence as well as the dorsoventral position of the condyle in the fossa showed statistically significant differences (Mann-Whitney U test, p < 0.05). A combination of the lateral incongruence, the distance from the posterior slope of the eminence as well as the maximum posterior sagittal curvature enabled to correctly predict the direction of stress field paths in 92% of cases. In particular, ML type joints had laterally more congruent condyles/fossae and condyles more distant from the posterior slope of the eminence than LM type joints. Within the limits of this study, TMJ morphology seems to determine stress field path patterns.

Articular cartilage response to a sliding load using two different-sized spherical indenters1.

BACKGROUND: Cartilage surface contact geometry influences the deformational behavior and stress distribution throughout the extracellular matrix (ECM) under load. OBJECTIVE: To test the correlation between the mechanical and cellular response of articular cartilage when loaded with two different-sized spherical indenters under dynamic reciprocating sliding motion. METHODS: Articular cartilage explants were subjected to a reciprocating sliding load using a 17.6 mm or 30.2 mm spherical ball for 2000 cycles at 10 mm/s and 4 kg axial load. Deformation of the cartilage was recorded and contact parameters were calculated according to Hertzian theory. After mechanical loading cartilage samples were collected and analyzed for ECM collagen damage, gene regulation and proteoglycan (PG) loss. RESULTS: Significantly higher ECM deformation and strain and lower dynamic effective modulus were found for explants loaded with the smaller diameter indenter whereas contact radius and stress remained unaffected. Also, the 17.6 mm indenter increased PG loss and significantly upregulated genes for ECM proteins and enzymes as compared to the 30.2 mm indenter. CONCLUSION: Sliding loads that increase ECM deformation/strain were found to induce enzyme-mediated catabolic processes in articular cartilage explants. These observations provide further understanding of how changes in cartilage contact mechanics under dynamic conditions can affect the cellular response.