Influence of restricted mastication on swallowing function.

BACKGROUND: Oral food processing is an important part of daily food intake. A major part of this process is mastication, which prepares a bolus of food for swallowing by mechanically crushing and grinding ingested food between the teeth using rhythmic movements. Masticatory dysfunction is common in the elderly and in some neurological disorders and can have serious negative health consequences. OBJECTIVE: This study investigated the effect of restricted mastication, achieved by experimentally reducing the duration of mastication, on masticatory patterns and subsequent swallowing function. METHODS: Thirty healthy men (25 ± 3 years old) were instructed to chew gum jelly with a free mastication duration (G100), a half and a quarter duration of G100. Masseter and digastric electromyographic (EMG) activity was recorded to assess mastication and swallowing activity, respectively. In addition, the acceleration of the thyroid cartilage ridge was measured with an accelerometer. The root mean square (RMS) of muscle EMG activity in the masseter and digastric muscles, the number of masseter EMG bursts, time to peak and total duration of each masseter EMG burst, swallowing duration and laryngeal elevation latency were analysed. RESULTS: Restricting masticatory duration reduced the number of mastication cycles (p < .001), prolonged the time to peak (p < .001) and total duration of masseter EMG bursts (p < .001) and resulted in an overall increased RMS score of masseter muscle activity (p = .017). Furthermore, restricted masticatory duration led to a decrease in both swallowing duration (p = .001) and laryngeal elevation latency (p = .012), with a significant increase in the RMS score of digastric muscle activity (p < .001). CONCLUSIONS: Under the experimental conditions of restricted mastication, several adaptation features were observed, including changes in masticatory cycle characteristics and swallowing duration. Thus, although the overall masticatory efficiency was reduced, these adaptations allowed healthy individuals to still swallow safely.

Effect of clinical experience and training with visual feedback on standardized palpation outcomes-Potential implications for assessment of jaw muscle sensitivity.

BACKGROUND: The evaluation of muscle pain and sensitivity by manual palpation is an important part of the clinical examination in patients with myalgia. However, the effects of clinical experience and visual feedback on palpation of the masticatory muscles with or without a palpometer are not known. OBJECTIVE: To estimate the effects of clinical experience and visual feedback on the accuracy of palpation in standardized settings. METHODS: Thirty-two dentists (age 35 ± 11 years) classified as either specialists (n = 16) or generalists (n = 16) participated in this experiment. All dentists were instructed to target force levels of 500- or 1000-gf, as determined on an electronic scale using either standardized palpometers or manual palpation (MP). All dentists participated in four different tests: MP, MP with visual feedback (MPVF), palpometer (PAL) and PAL with visual feedback (PALVF). Actual force values for each type of palpation from 0 to 2, 2 to 5 and 0 to 5 s were analysed by calculating target force level. RESULTS: The relative differences during 2-5 and 0-5 s with 1000 gf were significantly lower for generalists than for specialists (p < .05). In generalists and specialists, the coefficients of variation and the relative differences during 2-5 s were significantly lower for PAL and PALVF than for MP (p < .05). CONCLUSIONS: These findings suggest that the use of a palpometer, but not clinical experience with palpation of masticatory muscles, increases the accuracy of palpation, and ≥2 s of palpation with a palpometer is optimal for masticatory muscles.

Comparison of 0.5% chlorhexidine gluconate alcohol with 10% povidone-iodine for skin disinfection in children to prevent blood culture contamination.

INTRODUCTION: Various disinfectants, such as povidone iodine (PVI)1, alcohol preparations, and chlorhexidine gluconate ethanol (CHG-ALC), are used for disinfection prior to blood sampling for culture. METHODS: This retrospective cohort study compared the usefulness and effectiveness of CHG-ALC and PVI in pediatric venipuncture. We applied 0.5% w/v CHG-ALC or 10% PVI as an antiseptic for phlebotomies on pediatric outpatients and inpatients with suspected bacterial infection between November 2017 and April 2019. We conducted logistic regression analysis to define the differences associated with the choice of disinfectant, collection site, and the staff member collecting the blood sample (explanatory variables) and the presence of contamination (objective variable). Based on these results, we performed propensity score matching. RESULTS: The total number of specimens was 1460. The propensity score matching indicated that CHG-ALC reduced the incidence of blood culture contamination more effectively than PVI (0.4%, 2/479 cultures versus 2.5%, 12/479 cultures; relative risk, 0.163 [95% confidence interval, 0.036 to 0.733]; P = 0.012). There were no differences in the contamination rates between cultures of blood drawn from a vascular catheter and those of blood obtained percutaneously. Higher contamination rates were found when junior residents performed the venipuncture. CONCLUSIONS: Compared with PVI, CHG-ALC dries rapidly with no pigmentation and has a long-lasting antiseptic effect. Overall, CHG-ALC skin preparations were more efficacious than the PVI preparations for blood sampling in children.

Diagnostic criteria for temporomandibular disorders (DC/TMD) for children and adolescents: An international Delphi study-Part 1-Development of Axis I.

BACKGROUND: Since in children and adolescence prevalence is assessed mainly on self-reported or proxy-reported signs and symptoms; there is a need to develop a more comprehensive standardised process for the collection of clinical information and the diagnosis of TMD in these populations. OBJECTIVE: To develop new instruments and to adapt the diagnostic criteria for temporomandibular disorders (DC/TMD) for the evaluation of TMD in children and adolescents. METHOD: A modified Delphi method was used to seek international consensus among TMD experts. Fourteen clinicians and researchers in the field of oro-facial pain and TMD worldwide were invited to participate in a workshop initiated by the International Network for Orofacial Pain and Related Disorders Methodology (INfORM scientific network) at the General Session of the International Association for Dental Research (IADR, London 2018), as the first step in the Delphi process. Participants discussed the protocols required to make physical diagnoses included in the Axis I of the DC/TMD. Thereafter, nine experts in the field were added, and the first Delphi round was created. This survey included 60 statements for Axis I, and the experts were asked to respond to each statement on a five-item Likert scale ranging from 'Strongly disagree' to 'Strongly agree'. Consensus level was set at 80% agreement for the first round, and at 70% for the next. RESULTS: After three rounds of the Delphi process, a consensus among TMD experts was achieved and two adapted DC/TMD protocols for Axis I physical diagnoses for children and adolescents were developed. CONCLUSION: Through international consensus among TMD experts, this study adapted the Axis I of the DC/TMD for use in evaluating TMD in children and adolescents.

Combination of jaw and tongue movement training influences neuroplasticity of corticomotor pathways in humans.

Since humans in daily life perform multiple motor behaviors that often involve the simultaneous activation of both jaw and tongue muscles, it is essential to understand the effects of combined orofacial sensorimotor tasks on plasticity in corticomotor pathways. Moreover, to establish novel rehabilitation programs for patients, it is important to clarify the possible interrelationships in corticomotor excitability between jaw and tongue motor control. The aim of this study was to examine the effect of a combination of a repetitive tooth bite task (TBT) and a repetitive tongue lift task (TLT) on corticomotor excitability of the tongue and jaw muscles as assessed by transcranial magnetic stimulation (TMS). Sixteen healthy individuals participated in three kinds of training tasks consisting of 41-min TBT, 41-min TLT, and 82-min TBT + TLT. Motor-evoked potentials (MEPs) from the tongue muscle, masseter muscle, and first dorsal interosseous muscle were measured before and after the training tasks. The amplitude of tongue MEPs after training with TLT and TLT + TBT, and masseter MEPs after training with TBT and TLT + TBT, were significantly higher than before training (P < 0.05). Tongue MEPs and masseter MEPs were significantly higher after TLT + TBT than after TBT or TLT (P < 0.05). The present results suggest that a task combining both jaw and tongue movement training is associated with a greater degree of neuroplasticity in the corticomotor control of jaw and tongue muscles than either task alone.

Mechanical sensitivity and psychological factors in patients with burning mouth syndrome.

OBJECTIVES: The aim of this study was to compare mechanical sensitivity on the tongue using quantitative sensory testing (QST) and psychological factors using the General Health Questionnaire (GHQ) between burning mouth syndrome (BMS) patients and healthy participants. MATERIALS AND METHODS: Participants comprised 20 female BMS patients (68.1 ± 7.4 years) and 20 healthy females (65.4 ± 4.6 years). Psychological factors were evaluated with GHQ. Tactile detection thresholds (TDT) and filament-prick pain detection thresholds (FPT) were used to evaluate mechanical sensitivity on the tongue in all participants. TDT and FPT were measured on the tongue within both the painful area and the non-painful area in BMS patients, and on the tongue on both sides in healthy participants. As controls, TDT and FPT were measured with Semmes-Weinstein monofilaments on the skin of the mentum and palm in all participants. RESULTS: GHQ scores were significantly higher in BMS patients than in healthy participants (P = 0.024). No significant differences in TDT or FPT on the tongue, mentum, or palm were seen between BMS patients and healthy participants (P > 0.05). BMS patients showed no significant differences in TDT or FPT between the painful and non-painful areas on the tongue (P > 0.05). There were no significant correlations among TDT/FPT and GHQ score in BMS patients (P > 0.05). CONCLUSIONS: These findings could indicate a more important role for psychological factors than mechanical sensitivity in BMS pathophysiology. CLINICAL RELEVANCE: Pain on the tongue in elderly female patients with BMS may be more related to psychological factors.

Effects of exercise therapy on painful temporomandibular disorders.

Temporomandibular disorders (TMD) are common chronic musculoskeletal pain conditions among orofacial pain. Painful TMD condition such as myalgia and arthralgia can be managed by exercise therapy. However, as it is hard to access actual effect of each modality that is included in an exercise therapy programme due to multiple choice of the management modality, their efficacy remains controversial. Therefore, this review focused on the effects of exercise therapy for the management of painful TMD. The aims of this review were to summarise the effects of exercise therapy for major symptoms of painful TMD and to establish a guideline for the management of painful TMD, resulting in higher quality and reliability of dental treatment. In this review, exercise modalities are clearly defined as follows: mobilisation exercise, muscle strengthening exercise (resistance training), coordination exercise and postural exercise. Furthermore, pain intensity and range of movements were focused as outcome parameters in this review. Mobilisation exercise including manual therapy, passive jaw mobilisation with oral appliances and voluntary jaw exercise appeared to be a promising option for painful TMD conditions such as myalgia and arthralgia. This review addressed not only the effects of exercise therapy on various clinical conditions of painful TMD shown in the past, but also an urgent need for consensus among dentists and clinicians in terms of the management of each condition, as well as terminology.

Perceptual distortion of the tongue by lingual nerve block and topical application of capsaicin in healthy women.

OBJECTIVES: The aim of this study was to examine reports of perceptual distortion evoked by transient deafferentation and burning pain as models of aspects of burning mouth syndrome (BMS). MATERIALS AND METHODS: Sixteen healthy women took part in three experimental sessions that included exposure to lingual nerve block, capsaicin, and control substance. In each session, reported perceptual distortion and mechanical detection threshold (MDT) were assessed at four areas (the tongue, lower front teeth, lower lip, and right thumb) before and at 5, 15, 30 min and 1 and 3 h after the injection or application. A numerical rating scale (NRS) and a template matching procedure were used to quantify the perceptual distortions. RESULTS: There was a significantly higher MDT on the tongue during the lingual nerve block session at 5 min up until 1 h, with the perceived tongue size significantly increased at 5, 15, and 30 min and at 1 h compared to baseline (P < 0.05). Although the perceived size determined by the NRS scores during the capsaicin session was significantly larger for the lower lip at 5 min compared to baseline (P < 0.001), there were no significant effects on the MDT or the perceived sizes for the tongue, lower front teeth, or right thumb at any of the time points. CONCLUSIONS: Perceptual distortions of the tongue may be influenced by non-nociceptive somatosensory changes rather than nociceptive activity. CLINICAL RELEVANCE: The perceptual distortion of the tongue was investigated with models of aspects of BMS and may have implications for future studies in clinical populations.

Repeated clenching causes plasticity in corticomotor control of jaw muscles.

This study tested the effect of short-term tooth-clenching on corticomotor excitability of the masseter muscle using transcranial magnetic stimulation (TMS). Fifteen subjects with normal stomatognathic function participated. All subjects performed a tooth-clenching task (TCT) on five consecutive days. The TCT consisted of 10, 20, and 40% of maximum voluntary contraction in a randomized order within 1 h. All subjects underwent TMS in four sessions: pretask day 1 (baseline), post-task day 1, pretask day 5, and post-task day 5. Motor-evoked potentials (MEPs) from the masseter and the first dorsal interosseous (FDI) muscles were obtained using TMS in four sessions. Motor thresholds decreased, after the TCT, for the masseter muscle MEPs. Masseter muscle MEPs were dependent on stimulus intensity and on session, whereas FDI muscle MEPs were only dependent on stimulus intensity. Post-hoc Tukey tests demonstrated significantly higher masseter muscle MEPs post-task on day 5 with 80 and 90% stimulus intensity and above when compared with pre- and post-task day 1 values. Our results suggest that the performance of repeated TCTs can trigger neuroplastic changes in the corticomotor control of the jaw-closing muscles and that such neuroplastic changes may contribute to the mechanism underlying the clinical manifestations of tooth clenching.

Analysis of definite awake bruxism using a portable electromyography device.

PURPOSE: This study aimed to compare awake bruxism events between subjective and objective evaluations using a questionnaire survey and a modified portable electromyography (EMG) device, and to examine correlations between sleep quality and awake bruxism. METHODS: The Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), and awareness of awake bruxism as clarified via interviews were conducted on 34 participants as subjective evaluations. The EMG device was used to record left temporal muscle activity for 6.5 h (from 09:00 to 15:30) and the number of awake bruxism episodes per hour. The participants were then classified into "bruxer" and "non-bruxer" groups based on the number of awake bruxism episodes. RESULTS: The mean number of awake bruxism episodes per hour was 33.6 ± 21.4, and 23% of the participants who reported having no awareness of awake bruxism in the interviews were defined as "bruxers" in the objective evaluations. In the bruxer group, positive correlations were found between the number of awake bruxism episodes and both ESS and PSQI scores. CONCLUSION: These findings suggest that objective measurements using a portable EMG device can increase the diagnostic accuracy for awake bruxism, and that sleep quality is a major risk factor for awake bruxism.

Comparison of masticatory muscle activity between young adults and elderly participants using a novel standardized bite device.

OBJECTIVES: Standardized bite training is required to prevent oral hypofunction in elderly individuals. We aimed to compare masticatory muscle activity between 24 young adults and 16 pre-elderly individuals during a biting task using a novel standardized bite device (BD). METHODS: The BD was made of silicone rubber and included a high-force or low-force plate spring or no plate spring (dummy). The compressive stiffness of the material in each BD was measured using a texture analyzer. All participants performed a biting task 50-times at a rate of 1/s each using the three types of BDs on the right first molar. Electromyographic (EMG) activity was recorded bilaterally from the masseter and temporalis muscles. The variability of each biting training session was calculated as the coefficient of variance (CV) from the EMG activity during each biting task for each muscle. Masticatory muscle fatigue was assessed using a numerical rating scale (NRS). RESULTS: Compressive stiffness was significantly different between each BD (P < 0.001). The CV and NRS scores were not significantly different between the groups. The EMG activities during each bite task in all muscles were not significantly different for any measurement item between the age groups. The EMG activities of high- and low-force BDs in the right temporalis (ipsilateral) muscle were significantly higher than those of the dummy BD (P < 0.001). CONCLUSIONS: Compressive stiffness of the BD affected EMG activity only in the ipsilateral temporalis muscle, but not in the masseter or contralateral temporalis muscles, without any age effect.

Shock absorption and dispersion capability of a novel five-layer mouthguard sheet material.

There is a growing need for a mouthguard sheet material with higher shock absorption and dispersion capacity than those obtained by conventional materials. A five-layer mouthguard sheet material was previously developed using laminated ethylene vinyl acetate and polyolefin copolymer resin. In this study, the shock absorption capacity and dispersion capability of the new sheet material were investigated and compared with those of other materials. Impact testing for the new sheet material showed that the force required to displace the sheet by 1 mm was significantly higher at all thicknesses (p<0.001), whereas the puncture energy and displacement were significantly lower than those for ethylene vinyl acetate (p<0.05). The five-layer mouthguard sheet material successfully absorbed and resisted shock. Therefore, the sheet material potentially increases resistance to applied deformation in teeth and alveolar bone and maintains structure. The five-layer sheet material could expand the range of mouthguard products and help prevent oral trauma.

Changes in expression of growth-associated protein-43 in trigeminal ganglion neurons and of the jaw opening reflex following inferior alveolar nerve transection in rats.

The aim of the present study was to clarify an involvement of growth-associated protein-43 (GAP-43) in the regeneration of primary afferent trigeminal ganglion (TG) neurons following inferior alveolar nerve transection (IANX). A larger number of GAP-43 immunoreactive (GAP-43 IR) TG neurons was observed in rats 3 d after IANX compared with sham rats. Growth-associated protein-43 IR TG neurons were also detected for 30 d after IANX, and the number of GAP-43 IR TG neurons was significantly higher in the IANX model until day 30. The relative number of large (>600 µm2) GAP-43 IR TG neurons was significantly lower, whereas the relative number of small (<400 µm2) GAP-43 IR TG neurons was significantly higher than that at day 0 until 30 d after IANX. To evaluate the functional recovery of damaged IAN, the jaw opening reflex (JOR), elicited by the electrical stimulation of the IAN, was measured before and after IANX. Jaw opening reflex occurrence was gradually increased and the relative threshold of electrical stimulation eliciting JOR was gradually decreased over the 30-d duration of the study. On day 30 after IANX, the JOR occurrence and relative JOR threshold were similar to those in sham rats. The present findings suggest that changes in the expression of GAP-43 in TG neurons after IANX are involved in regeneration and functional recovery of the transected IAN.

Influence of periodontal afferent inputs for human cerebral blood oxygenation during jaw movements.

Using functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS), we examined the role of periodontal afferent inputs on cerebral activation pattern evoked by masticatory muscle activity in twenty-two subjects. Statistical comparisons were used to identify brain regions with significant activation after subtraction of baseline activity from sham teeth-tapping (no periodontal input) and teeth-tapping (periodontal input) activity in an fMRI (N = 14) and NIRS study (N = 8). Both sham teeth-tapping and teeth-tapping significantly activated bilateral sensorimotor cortex and supplementary motor area in the fMRI study. NIRS revealed that oxygenated hemoglobin concentrations increased in sensorimotor cortex; however, there was no significant difference in degree of oxygenated hemoglobin changes between sham teeth-tapping and teeth-tapping. A control study (N = 8) characterized the jaw muscle activity and amplitude of the two motor tasks and demonstrated significantly higher electromyogram (EMG) activity in the jaw closing muscles during teeth contact in the teeth-tapping session. Since the cerebral activation during sham teeth-tapping and teeth-tapping was similar, we suggest that the influence of periodontal afferent inputs and associated jaw muscle activity is relatively minor compared to the rhythmic jaw movements. Although the clinical significance of the present findings remains unknown, they may have implications for the understanding of awake or sleep-related bruxism characterized by subconscious and rhythmic teeth-grinding or teeth-clenching.

Mandibular Advancement Device Therapy in Japanese Rugby Athletes with Poor Sleep Quality and Obstructive Sleep Apnea.

Obstructive sleep apnea (OSA) may contribute to poor sleep quality. This study assessed subjective sleep quality, the Respiratory Event Index (REI), reaction times, and the therapeutic effects of a custom-made mandibular advancement device (MAD) in male Japanese elite rugby athletes. The Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and level III sleep test (REI and minimum oxygen saturation [SpO2 min]) were used to evaluate sleep quality. MAD therapy was used daily for 3 weeks. A telephone-based reaction time test of kinetic vision (the ability to identify moving objects) was recorded within 15 min of waking and over 5 days of pre- and post-MAD therapy. Differences in variables were evaluated using paired t-tests. Of the 42 players (mean age, 26.3 ± 3.7 years; mean body mass index, 28.7 ± 3.2 kg/m2) included in this study, 29 (69.0%) had poor sleep quality (PSQI > 5.5), and 27 were diagnosed with OSA (64.3%) (mild = 16/moderate = 9/severe = 2). Six were treated with MAD therapy, which significantly improved the REI (p < 0.01), SpO2 min (p < 0.001), ESS score (p < 0.001), reaction times (p < 0.01), and sleep quality. A significant reduction in reaction times suggests that OSA treatment can improve kinetic vision. Future studies should systematically evaluate the impact of sleep-disordered breathing on kinetic vision in athletes.

Effect of the amount of light energy transmitted through CAD/CAM resin block on bonding performance of four types of resin cement adhesive systems.

Resin-ceramic hybrid materials for computer-aided design/computer-aided manufacturing (CAD/CAM resins) have been developed. In this study, the effects of the amount of light energy transmitted through the four types of 1.5-mm-thick CAD/CAM resin blocks on the bond performance of corresponding resin cement adhesive systems consisting of an adhesive and a dual-curable resin cement were examined. The bond strengths of the four types of resin cement adhesive systems decreased with decreasing the amount of light energy transmitted through CAD/CAM resin block, due to a decrease in the light-curable ability of dual-curable resin cements. However, the degradation behavior of the bond strengths was strongly affected by the types of adhesives and initiator systems utilized. The adhesive consisting of a dimethacrylate monomer and redox-initiators enhanced the bonding performance of the dual-curable resin cement more effectively than the adhesive, which consists of a dimethacrylate monomer and photo-initiators or a γ-me thacryloxypropyltrimethoxysilane and a 10-methacryloyloxydecyl dihydrogen phosphate.

Plasticity in corticomotor pathways linked to a jaw protrusion training task: Potential implications for management of patients with obstructive sleep apnea.

This study investigated the effect of a repeated and standardized jaw protrusion training (JPT) task on corticomotor excitability as assessed by motor evoked potentials (MEPs) in masseter and tongue muscle with the use of transcranial magnetic stimulation (TMS). Sixteen healthy participants performed three series of a standardized JPT task on three consecutive days. Each day participants performed 41-min of JPT consisting of three series. In all series, participants were instructed to target 50% and 100% of the maximum jaw protrusion positions. In the first and third series without any feedback but during the second series, participants were provided a custom-made mandibular advancement device to help achieve the correct protruded position. Single pulse TMS was applied to elicit MEPs from right masseter, right tongue and right first dorsal interosseous muscles (FDI) (as control), pre and post-task on Day-1 and -3. Masseter MEPs and tongue MEPs were significantly dependent on stimulus intensity (P < 0.001) and on task session (P < 0.001). Amplitude of masseter and tongue MEPs at post-task Day-3 were significantly higher compared to baseline values (pre-task Day-1) (P < 0.005). FDI MEPs were dependent on stimulus intensity only (P < 0.001) but not on task session (P = 0.677). Our novel findings suggest that participants performing an active and repeated JPT task demonstrate neuroplasticity in terms of increased corticomotor excitability not only in masseter muscles but also in tongue muscles. This finding may have implications for patients with obstructive sleep apnea treated by a mandibular advancement device where the lower jaw is passively held in a protruded position.

Assessment of Screening for Nasal Obstruction among Sleep Dentistry Outpatients with Obstructive Sleep Apnea.

Oral appliances (OA), a common treatment modality for obstructive sleep apnea (OSA), are not suitable for patients with nasal obstruction. Rhinomanometry, the gold standard technique to assess nasal airway resistance, is not readily available in sleep dentistry clinics. We demonstrate the use of a portable lightweight peak nasal inspiratory flow (PNIF) rate meter to objectively assess nasal airflow and utilized the Nasal Obstruction Symptom Evaluation (NOSE) scale to subjectively assess nasal obstruction in 97 patients with OSA and 105 healthy controls. We examined the correlations between the following variables between the groups: demographics, body mass index, PNIF, NOSE scale scores, apnea-hypopnea index (AHI), minimum SpO2 (SpO2min), Mallampati classification, and Epworth Sleepiness Scale (ESS) scores. Patients with OSA had significantly lower PNIF values and higher NOSE scores than controls. In the patient group, PNIF was not significantly correlated with AHI, SpO2min, Mallampati classification, or NOSE or ESS scores. Lower PNIF values and higher NOSE scores suggested impaired nasal airflow in the OSA group. As daytime PNIF measurement bears no relationship to AHI, this cannot be used alone in predicting the suitability of treatment for OSA with OA but can be used as an adjunct for making clinical decisions.

Mandibular Jaw Movement and Masticatory Muscle Activity during Dynamic Trunk Exercise.

The examination of jaw movement during exercise is essential for an improved understanding of jaw function. Currently, there is no unified view of the mechanism by which the mandible is fixed during physical exercise. We hypothesized that during strong skeletal muscle force exertion in dynamic exercises, the mandible is displaced to a position other than the maximal intercuspal position and that mouth-opening and mouth-closing muscles simultaneously contract to fix the displaced mandible. Therefore, we simultaneously recorded mandibular jaw movements and masticatory muscle activities during dynamic trunk muscle force exertion (deadlift exercise) in 24 healthy adult males (age, 27.3 ± 2.58 years). The deadlift was divided into three steps: Ready (reference), Pull, and Down. During Pull, the mandibular incisal point moved significantly posteriorly (-0.24 mm, p = 0.023) and inferiorly (-0.55 mm, p = 0.019) from the maximal intercuspal position. Additionally, temporal, masseter, and digastric muscles were activated simultaneously and significantly during Pull (18.63 ± 17.13%, 21.21 ± 18.73%, 21.82 ± 19.97% of the maximum voluntary contraction, respectively), with maintained activities during Down (p < 0.001). Thus, during dynamic trunk muscle force exertion, the mandibular incisal point moved to a posteroinferior position without tooth-touch (an open-mouth position). Simultaneously, the activities of the mouth-opening digastric muscles and the mouth-closing temporal and masseter muscles led to mandibular fixation, which is a type of mandible fixing called bracing.

Impact of sleep bruxism on training-induced cortical plasticity.

PURPOSE: To investigate if sleep bruxism (SB) influences training-induced cortical plasticity and performance in terms of accuracy and precision of a tooth-clenching task (TCT). METHODS: Thirty-eight participants were allocated into SB group (N=19) and control group (N=19) according to presence of SB based on a 2-week screening. The participants were instructed to perform a standardized TCT for 58min at three different force levels (10%, 20% and 40% of maximum voluntary contraction; MVC) in three series (first and third without visual-feedback and second with visual-feedback). Accuracy and precision of the TCT were calculated from actual bite force values. Transcranial magnetic stimulation was applied to elicit motor evoked potentials (MEPs) from the masseter and first dorsal interosseous muscle (FDI) before the TCT (pre-TCT-session) and 5-min after the TCT (post-TCT-session). RESULTS: Accuracy was significantly dependent on the series and target force level (P<0.001), however, there was a significant decrease only in the control group at 10% MVC from first to third session (P<0.001). No significant differences between groups were observed for the precision of the TCT. Masseter MEPs in the SB group in the pre-TCT-session at 120% and 160% motor threshold were significantly lower than in the control group (P<0.05). Masseter MEPs of the control group in the post-TCT-session were significantly higher than the pre-TCT-session (P<0.05) but not SB. FDI MEPs were only dependent on stimulus intensity (P<0.001). CONCLUSIONS: SB is associated with significant changes not only in excitability of corticomotor control but also motor learning of jaw movements and force control.