Clinical/occlusal scores and jaw-muscle EMGs were recorded in 24 TMD symptomatic (group S) and 20 normal (group N) subjects to evaluate the significance of EMG parameters and their clinical associations. Results indicated: (1) integrated EMG activity (IEMG) was larger at the rest position (RP) in anterior temporalis (Ta) but smaller at maximal voluntary clenching (MVC) in masseter (Ma) and Ta, and the ratios of IEMG at 70%MVC to the corresponding bite force (70%BF) were greater in group S; (2) mean power frequency (MPF) were almost the same in both groups but its shift was more rapid in group S; (3) silent period duration (SPD) was longer in group S; (4) asymmetry indices for SPD and silent period latency (SPL) were larger in group S; (5) muscle pain was associated negatively with IEMG at MVC and 70%BF but positively with IEMGs at RP and 70%MVC, and impaired jaw movements were associated negatively with the above EMG values; (6) muscle pain was positively associated with SPD in Ma, while joint pain and sound showed positive and negative associations with SPD, respectively; (7) associations between occlusion and EMG parameters were found more in group N. These findings verify: (1) jaw elevators in TMD may have hyper-tonic activities and a weak functional efficiency; (2) jaw muscles in TMD may become easily fatigued following a functional effort, and less relaxed following a muscle twitch; (3) the severity of pain could not be reflected in EMG activities, but impaired jaw movement may increase tonic activity and decrease functional effort; (4) TMD symptoms may alter the functional adaptation of jaw-muscle activities and occlusion.

Disc displacement is accepted as one of major findings in temporomandibular disorders (TMD). However, the associations of disc positions with morphological and positional changes of temporomandibular joint (TMJ) components and lateral pterygoid (LP), TMD clinical symptoms, and occlusion have rarely been discussed quantitatively. In this study, the morphological and positional changes of TMJ components and LP were assessed by means of magnetic resonance imaging (MRI) and tomography of the TMJ in 41 TMD and nine control (CN) subjects. Disc positions in TMD subjects were divided into normal position (NP) and anterior displacement with and without reduction (ADR+ and ADR-, respectively). From MRI scans and tomograms, the morphological and positional changes of TMJ components and LP were measured and compared among CN, NP, ADR+ and ADR- groups. Correlations between these measurements and the scored clinical symptoms and occlusal factors were analysed in TMD subjects. The results indicated that: (1) TMJ osseous structures and LP showed no significant difference among CN and the three TMD groups, except for a posterior seat of condyle and shorter/steeper condylar movement during jaw opening; (2) disc length and inclination were significantly shorter and steeper, respectively, in ADR+ and ADR-; (3) disc positions were not specified by clinical symptoms and occlusal factors, except for the dominant TMJ sounds in ADR+; (4) an uncoordinated movement of the condyle/disc complex was found in ADR+ and/or ADR-; (5) TMJ osseous structures and the disc were weakly associated with clinical symptoms and occlusal factors. However, the LP showed negative associations with palpable pain for both the TMJ and jaw muscles and the static occlusal factors. These findings suggest that TMJ internal derangements are more related to the positional changes or spatial relationships of TMJ components but less to the individual morphologies of TMJ osseous structures, disc and LP, as well as specific clinical symptoms and occlusal factors, which might be in disagreement with a large body of previous statements.

summary  Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross‐correlation functions. Jaw‐adductor muscle activity of MA and ZM was found to be highly cross‐correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non‐homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement.

Objectives-Tongue volume reduction is an adjunct treatment with several orofacial orthopedic procedures for various craniofacial deformities; it may affect structural reconstitution and functional recovery as a result of the repair process. The aim of this study was to investigate the myogenic regeneration and structural alteration of the tongue following surgical tongue volume reduction.Materials and Methods-Five 12-week-old sibling pairs of Yucatan minipigs (3 males and 2 females) were used. Midline uniform glossectomy was performed on one of each pairs (reduction); the other had the same incisions without tissue removal (sham). All pigs were raised for 4 weeks, and received 5-bromo-2-deoxyuridine (BrdU) injection intravenously one day before euthanasia. Tissue sections of tongues were stained with anti-BrdU antibody to evaluate the number of replicating cells. H&E and Trichrome stains were applied to assess muscular structure.Results-Reduction tongues contained significantly more BrdU+ cells as compared to sham tongues (p < 0.01). However, these BrdU+ cells were mostly identified in the reparative connective tissues (fibroblasts) rather than the regenerated muscle tissues (myoblasts). Trichrome stained sections showed disorganized collagen fibers linking with a few intermittent muscle fibers in the reduction tongues. These myofibers presented the signs of atrophy with reduced perimysium and endomysium. The matrix between these reduced perimysium and endomysium was fully filled with fibrous tissue.Conclusions-Fibrosis without predominant myogenic regeneration is the major histologic consequence after surgical tongue volume reduction.