Thresholds, Firing Rates, and Order of Recruitment of Anterior Temporalis Muscle Single-Motor Units During Experimental Masseter Muscle Pain.

AIMS: To test the hypothesis that, in comparison with control, experimental noxious stimulation of the right masseter muscle would result in significant changes in the firing rates, thresholds, and recruitment orders of single-motor units (SMUs) of the nonpainful, synergistic right anterior temporalis muscle during goal-directed isometric biting task performance. METHODS: Twenty healthy volunteers received an infusion of hypertonic saline (HS; 5% sodium chloride) into the right masseter to produce pain intensity of 40 to 60 on a 100-mm visual analog scale (VAS). Isotonic saline (IS) infusion was a control. Standardized biting tasks were performed with an intraoral force transducer, and intramuscular electromyographic activity was recorded from the right anterior temporalis muscle. Tasks (slow and fast ramp biting tasks, two-step biting task) were performed in 3 blocks: baseline, HS infusion, and IS infusion. Across blocks, SMU thresholds and firing rates were statistically compared, and SMU recruitment sequences were qualitatively compared. Statistical significance was set at P < .05. RESULTS: No significant differences (P > .05) were noted between HS and IS infusion blocks in thresholds or firing rates of anterior temporalis SMUs. Individual SMUs showed increases or decreases in thresholds or firing rates or changes in recruitment sequences mostly during HS compared to IS infusion. CONCLUSION: The reorganization of SMU activity that has been suggested to occur in both painful and nonpainful agonist jaw muscles may involve not only recruitments and de-recruitments of SMUs, but may also extend to more subtle increases and/or decreases in firing rates, thresholds, and recruitment sequences of individual SMUs in the nonpainful synergistic muscles.

Injectable porcine bone demineralized and digested extracellular matrix-PEGDA hydrogel blend for bone regeneration.

Extracellular matrix (ECM) has a major role in the structural support and cellular processes of organs and tissues. Proteins extracted from the ECM have been used to fabricate different scaffolds for tissue engineering applications. The aims of the present study were to extract, characterize and fabricate a new class of hydrogel with proteins isolated from pig bone ECM and combine them with a synthetic polymer so it could be used to promote bone regeneration. Porcine bone demineralized and digested extracellular matrix (pddECM) containing collagen type I was produced, optimized and sterilized with high pressurized CO2 method. The pddECM was further blended with 20% w/v polyethylene glycol diacrylate (PEGDA) to create an injectable semi interpenetrating polymer network (SIPN) scaffold with enhanced physicochemical properties. The blend tackled the shortfall of natural polymers, such as lack of structural stability and fast degradation, preserving its structure in more than 90% after 30 days of incubation; thus, increasing the material endurance in a simulated physiological environment. The manufactured injectable hydrogel showed high cytocompatibility with hOb and SaOs-2 cells, promoting osteogenic proliferation within 21 days of culture. The hydrogel had a high compression modulus of 520 kPa, low swelling (5.3 mg/mg) and millimetric volume expansion (19.5%), all of which are favorable characteristics for bone regeneration applications.

Reorganization of Masseter and Temporalis Muscle Single Motor Unit Activity During Experimental Masseter Muscle Pain.

AIMS: To test the hypothesis that experimental noxious stimulation of the right masseter muscle results in a reorganization of motor unit activity within the right temporalis and right masseter muscles during jaw closing tasks. METHODS: A total of 20 healthy participants received hypertonic saline (5% sodium chloride) infusion into the right masseter muscle, and pain intensity was maintained at 40-60/100 mm on a visual analog scale. Standardized isometric biting tasks were performed with an intraoral force transducer while single motor units (SMUs) were recorded from the right masseter and temporalis muscles. Tasks were repeated in four blocks: block 1 (baseline 1), block 2 (hypertonic saline [HS] infusion or isotonic saline [IS] infusion), block 3 (infusion of the other solution), and block 4 (baseline 2). The occurrences of SMUs were tabulated across blocks. Statistical significance was considered to be P < .05. RESULTS: There were no significant effects of block on the tasks. A total of 83 SMUs were discriminated in the temporalis and 58 in the masseter. For the comparison between HS and IS across tasks, the occurrences of 74.6% to 82.8% of SMUs were unchanged (70.2% to 94.3% for masseter), while during HS, 10.3% to 17.1% of SMUs were recruited (0% to 12.8%, masseter) and 6.9% to 12.7% were de-recruited (5.7% to 17%, masseter). CONCLUSION: The present findings suggest that most biting-task-related jaw muscle SMUs remain active during experimental muscle noxious stimulation. There was some evidence in both the anterior temporalis and masseter muscles for motor unit recruitment and de-recruitment consistent with a motor unit reorganization during experimental pain.

Experimental noxious stimulation of the right masseter muscle does not affect bilateral masseter and temporalis muscle activity and force parameters during standardised isometric biting tasks.

AIM: To determine if the electromyographic (EMG) activity of the left and right masseter and anterior temporalis muscles is altered by experimental right masseter muscle noxious stimulation during goal-directed isometric biting tasks in asymptomatic humans. METHODS: Isometric biting tasks (slow and fast ramp biting tasks, 2-step biting task) were performed on an intraoral force transducer in 18 participants during the following blocks: baseline block, hypertonic saline infusion into the right masseter muscle (painful block) and isotonic saline infusion into the right masseter (control block). Bipolar surface electrodes recorded EMG activity from the bilateral masseter and anterior temporalis muscles. A 100-mm visual analogue scale (VAS) quantified pain intensity, and the McGill Pain Questionnaire (MPQ), the Depression, Anxiety and Stress Scales-21 (DASS-21) and the Pain Catastrophizing Scale (PCS) were completed. Repeated measures ANOVA assessed the effects of pain on the force rates (N/s), force amplitudes (N) and the root mean square (RMS) jaw muscle EMG activity across blocks. Statistical significance accepted at P < 0.05. RESULTS: VAS scores were significantly (P < 0.001) higher during hypertonic than isotonic saline infusion blocks. There was no significant effect of pain on the force rates, or force levels or the RMS EMG activity of each masseter and anterior temporalis muscle. CONCLUSION: The findings suggest that experimentally induced right masseter muscle pain does not modify force or surface jaw muscle EMG activity during isometric biting tasks.

Prevalencia de Trastornos Temporomandibulares según los CDI/TTM, en un Grupo de Adultos Mayores de Santiago, Chile / Prevalence of Temporomandibular Disorders According to RDC/TMD in Older People of Santiago, Chile

En la población chilena, los adultos mayores representan un 13% de la población total del país (2,2 millones), proyectándose para el 2020 un aumento del grupo de 60 años o más en un 45%. Todos los seres humanos sufren un proceso de envejecimiento y, los tejidos orales y periorales no escapan de este proceso. Las repercusiones sobre el sistema estomatognático, podrían manifestarse a través de sintomatología en alguno de sus componentes, compatible con un trastorno temporomandibular (TTM). El objetivo de este trabajo, fue determinar la prevalencia de TTM según los Criterios de Investigación Diagnóstica ó CDI/TTM (Eje I), en adultos mayores examinados en la Clínica Odontológica de la Facultad de Odontología de la Universidad de Chile (FOUCh), durante el año 2012 y establecer la relación entre ambos sexos. Este estudio determinó, que existe una alta prevalencia de TTM en la muestra de adultos mayores chilenos estudiados (47%), principalmente diagnósticos de tipo articular y sin una relación significativa entre ambos sexos.

In Chilean population, elders represent a 13% of the overall population (2.2 million), projected for 2020 an increase of 45%, from the group of 60 and over. All humans undergo a process of aging. Oral and perioral tissues do not escape from this process, whose impact on the condyle and articular disc could be observed, in the presence of symptoms consistent with temporomandibular disorders (TMD). The aim of this study was to determine the prevalence of TMD according to the Research Diagnostic Criteria or RDC/TMD (Axis I), in older adults examined at the Dental Clinic of the Faculty of Dentistry, University of Chile during 2012, and establish the relationship between the sexes. In conclusion, this study found that there is a high prevalence of TMD in Chilean elderly sample studied (47%), mainly articular diagnoses without a statistically significant relationship between the sexes.