Kazuo Okura

Sleep bruxism is associated to micro-arousals and an increase in cardiac sympathetic activity

Sleep bruxism (SB) subjects show a higher incidence of rhythmic masticatory muscle activity (RMMA) than control subjects. RMMA is associated with sleep micro‐arousals. This study aims to: (i) assess RMMA/SB episodes in relation to sleep cycles; (ii) establish if RMMA/SB and micro‐arousals occur in relation to the slow wave activity (SWA) dynamics; (iii) analyze the association between RMMA/SB and autonomic cardiac activity across sleep cycles. Two nights of polygraphic recordings were made in three study groups (20 subjects each): moderate to high SB, low SB and control. RMMA episodes were considered to occur in clusters when several groups of RMMA or non‐specific oromotor episodes were separated by less than 100 s. Correlations between sleep, RMMA/SB index and heart rate variability variables were assessed for the first four sleep cycles of each study group. Statistical analyses were done with SYSTAT and SPSS. It was observed that 75.8% of all RMMA/SB episodes occurred in clusters. Micro‐arousal and SB indexes were highest during sleep cycles 2 and 3 (P < 0.001). Within each cycle, micro‐arousal and RMMA/SB indexes showed an increase before each REM sleep (P ≤ 0.02). The cross‐correlation plot for micro‐arousal index showed positive association from 4 min preceding SB onset in the moderate to high SB subjects (P ≤ 0.06). The cross‐correlation plot revealed that SWA decreases following SB onset (P ≤ 0.05). Further cross‐correlation analysis revealed that a shift in sympatho‐vagal balance towards increased sympathetic activity started 8 min preceding SB onset (P ≤ 0.03). In moderate to severe SB subjects, a clear increase in sympathetic activity precedes SB onset.

Quantitative analysis of surface EMG activity of cranial and leg muscles across sleep stages in human.

OBJECTIVE The aim of this study was to make a quantitative analysis of the changes in cranial and limb muscle activity from wakefulness to light and deep sleep stages and during rapid eye movement (REM) sleep of normal subjects. METHODS Polysomnographic recordings were made of the sleep of 9 healthy human subjects, including electromyograms of the suprahyoid, temporalis and masseter cranial muscles and the anterior tibialis limb muscle. Quantitative assessments of EMG activity were carried out with root mean square (RMS) and frequency-spectral analysis (FSA) methods. RESULTS From wakefulness to sleep, a significant reduction (-25.2 to -71.2%; P < 0.01) was observed in EMG activity (for both RMS and FSA) of the 3 cranial muscles using both methods of analysis. The EMG activity of suprahyoid muscle further decreased from non-REM to REM sleep (-17.8 to -43.0%; P < 0.01). In contrast, the EMG activity of the anterior tibialis muscle was only slightly reduced across sleep stages and did not further reduce during REM sleep. During REM sleep, all the 4 muscles maintained minimal activity. CONCLUSIONS The maintenance of muscle activity during REM sleep suggests that a minimal level of activity is required to preserve physiological functions (e.g. airway patency, posture) related to homeostasis and bodily protection. SIGNIFICANCE This study suggests that quantitative sleep EMG analysis is important for understanding the mechanisms of sleep-related movement disorders or when objective assessment of changes in EMG activity are needed for diagnostic purposes or for the assessment of drug efficiency.

A longitudinal retrospective study of the analysis of the risk factors of implant failure by the application of generalized estimating equations

PURPOSE Many studies have identified risk factors for dental implant failure, although few have investigated the correlation among implant fixtures within single patients. A better analytical method may include repeated measures analysis including generalized estimating equations (GEE). This retrospective cohort study aimed to (1) identify the risk factors for failure of dental implantation and (2) evaluate an analytical method using GEE analysis. METHODS We analyzed data on early and late implant failures in 296 patients providing 721 rough surface dental implants (2.44 implants per patient). Potential predictors of implant failure included age, gender, smoking, location of implant, use of bone augmentation, number of remaining teeth, opposing tooth condition, fixture length, fixture diameter and type of suprastructure (fixed or removable partial denture). The likelihood of early and late implant failure was estimated by GEE. RESULTS The early failure rate was 1.5% (11/721 implants, 7/296 patients) and the 10-year cumulative survival rate was 94.0% (7/710 implants, 5/293 patients). The GEE analysis revealed that a significant risk factor for early implant failure was smoking (p<0.01), whereas significant risk factors for late failure were maxillary implant (p=0.02), posterior implant (p<0.01), number of remaining teeth (≥20) (p<0.01), opposing unit being a removable partial denture or nothing (p=0.04) and having a removable type suprastructure (p<0.01). CONCLUSIONS GEE analysis showed that smoking was a risk factor for early implant failure, and several risk factors were identified for late implant failure.

Gender specificity of the slow wave sleep lost in chronic widespread musculoskeletal pain

OBJECTIVES The majority of patients suffering from musculoskeletal chronic widespread pain (CWP) are females, and they tend to report poor sleep. We tested the hypothesis that the poor sleep of female patients reporting CWP is gender specific for changes in (1) electroencephalograph (EEG) features and (2) heart rate variability (HRV). METHODS Twenty-four normal sleepers were compared to 24 patients with CWP who complained of poor sleep. Patients were referred from general practice and were matched for age (41-47 years) and gender (25 W, 23 M). Sleep variables and spectral EEG activity analyses were performed during 1 night of sleep recording. Time-domain cardiac RR interval and spectral autoregressive analyses were also performed from the same data set. RESULTS Compared to normal females, female patients with CWP had significantly shorter sleep duration (-68 min), lower sleep efficiency (-9.9%), twice the awakenings and a trend for more periodic limb movements per hour of sleep. Daytime napping was reported by 78% of CWPs. Compared to all controls, females with CWP had significantly less power in the EEG delta band in the first and second non-REM sleep cycle. Although RR interval analysis revealed that CWP patients had a faster heart rate, neither the sympathetic nor sympathovagal analysis reached statistical significance for gender or pain status comparisons. CONCLUSIONS Female CWP patients have shorter sleep duration with many awakenings and lower sleep EEG delta activity without gender difference in HRV.

Comparison between flipped classroom and team-based learning in fixed prosthodontic education

PURPOSE We previously investigated the effects of team-based learning (TBL) on fixed prosthodontic education and reported that TBL could have higher efficiency with high student satisfaction than traditional lecture. In the current report, we introduced flipped classroom to the fixed prosthodontic education and compared their effectiveness based on the final examination score in addition to TBL. METHODS Participants were 41 students from Tokushima University School of Dentistry who attended a fixed prosthodontics course. The first six classes adopted the flipped classroom style while the latter eight classes adopted TBL. To evaluate the relationship between learning styles and their effectiveness, we compared results from the term-end examination between the curriculum covered by flipped classroom and TBL-style classes. To draw comparisons, a referential examination with the same questions was conducted to eight faculty members who had not attended any of these classes. RESULTS Term-end examination results showed that TBL classes had slightly higher scores than flipped classroom classes. Referential examination results also showed higher scores for the same curriculum and no significant interaction was found between class formats and the term-end and referential examination scores. Analysis revealed no noticeable difference in the effectiveness of the class formats. CONCLUSION Our previous study reported that TBL had higher efficiency than traditional style lecture. In the current study, there was no statistical difference in the examination score between flipped classroom and TBL. Therefore, we conclude that both styles are highly effective than traditional style lecture and constitute valid formats for clinical dental education.

Mandibular movement during sleep bruxism associated with current tooth attrition

PATIENT Observation of attrition patterns suggests that mandibular movement in sleep bruxism (SB) may be associated with current tooth attrition. The aim of this study was to confirm this phenomenon by investigating mandibular movement and masseter muscle activity. The subject was a healthy 21-year-old Japanese male. We recorded biological signals including mandibular movement and masseter electromyograms (EMGs) with a polysomnograph. Based on the EMG using Okuras criteria, SB events were classified into clenching, grinding and mixed types according to mandibular movement criteria. The close-open mandibular movement cycles (CO-cycles) during grinding and mixed type events were selected based on mandibular movement trajectories. DISCUSSION Fifty-eight CO-cycles were selected in seven grinding and three mixed types. We found that SB mandibular movements associated with current tooth attrition. Excessive lateral movements (ELM) beyond the canine edge-to-edge position were observed in the closing (10.3%) and opening (13.8%) phases of the CO-cycle. Total masseter muscle activity was significantly higher during voluntary grinding (VGR) than during CO-cycle including ELM (working side: P=0.036, balancing side: P=0.025). However, in the middle and late parts of the opening phase, working side masseter muscle activity was significantly higher during CO-cycle including ELM than during VGR (P=0.012). In the early part of the closing phase, balancing side masseter muscle activity was significantly higher during CO-cycle including ELM than during VGR (P=0.017). CONCLUSION These findings suggest that excessive forceful grinding during ongoing SB events may have caused canine attrition in this patient.

Chapter 55 – Sleep bruxism

Sleep bruxism is a sleep-related movement disorder with repetitive jaw muscle contraction. It is occasionally associated with tooth-grinding noises. Patients may experience jaw muscle and joint pain, headaches, and sensitivity to teeth due to forceful jaw muscle contractions. It is important to distinguish clenching while awake from sleep bruxism during sleep, because of different etiology and pathophysiology. In the absence of any medical or sleep disorders, use of medication or recreational drugs, sleep bruxism is classified as primary. Age seems to be an important variable, as the condition is reported in 14% in children, compared with 3% in older people. Furthermore, the prevalence of sleep bruxism–tooth grinding stands at 8% in adults. The pathophysiology of sleep bruxism remains unclear, but may be associated with: some neurological and psychiatric disorders; influence of sensory factors on motor control; interaction with neurotransmitters; and some mechanisms related to sleep arousal. A diagnosis of sleep bruxism is reached following patient interview, clinical examination, and sleep recordings. The most appropriate strategy to manage patients with sleep bruxism is to reassess the main motive for the consultation, such as tooth-grinding noises or morning pain. A dental device, adapted to either the maxillary or the mandibular arches, is the recognized procedure used to prevent the grinding sounds in absence of sleep apnea. If sleep-disordered breathing is suspected, the mandibular advancement appliance may be used. In mild cases, the first line of approach might be short-term use of a muscle relaxant.

A preliminary investigation of reproducibility of EMG signals during daytime masticatory muscle activity using a portable EMG logging device

Continuous parafunctional masseter muscle activities (MMA) that are associated with daytime bruxism have been suspected to be one of the main pathoetiology for orofacial pain. The purpose of this study was to examine the long-term stability and reliability of daytime EMG measurement of MMA using a portable device (Actiwave; CamNtech Ltd). Daytime masseter muscle EMG of five subjects were recorded for four days in their normal living environment. There was no significant time dependent effect on EMG amplitude during recording period. A total of 4923 MMA events were detected in all analysis periods (129.4h) and classified into phasic type (1209 events, 24.6%), tonic type (1759 events, 37.0%), and mixed type (1377 events, 28.0%). There was no significant difference in the number of occurrence among three MMA types. With respect to the duration and peak MMA, there were significant differences among three MMA types. The result of this study indicated that Actiwave can be used to measure MMA events during daytime with high stability and reliability under the normal living environment and it was suspected that parafunctional habits may be associated with the occurrence patterns of MMA during daytime.

Effect of an exclusion range of jaw movement data from the intercuspal positionon the estimation of the kinematic axis point

In patients who have lost natural occlusal contacts, the centric relation is usually estimated based on several anatomical factors such as the temporomandibular joint and masticatory muscles except dental arch. The clinical procedure to record the centric relation often depends on the clinicians expertise and technique; an objective method to determine proper occlusal position is desirable. The kinematic axis point (KAP) is kinematically estimated from sagittal movements and is an ideal posterior reference point that is used in dental articulators for reproducing jaw movement. Occlusal registration using the KAP may serve as a definite objective technique. The aim of this study is to investigate the effect of the exclusion range of sagittal jaw movement data from the intercuspal position (ICP) on the estimation of the KAP. The complete and incomplete sagittal border movement data of dentate subjects were used to estimate the KAPs. The locations of the estimated KAPs were compared. The results indicate that the incomplete sagittal border jaw movement data set does not include data points inside a 7 mm distance from the ICP can be used for estimation of the KAP. In conclusion, the sagittal border jaw movement data around the ICP is not indispensable in the valid identification of the KAP.

Pain Perception - Nociception during Sleep

During sleep, a state in which the brain is partially disconnected from external influences, subjects can be awakened by an episode of sudden pain. Approximately 2/3 of subjects who experience pain episodes report poor sleep quality, often accompanied by sequelae ranging from feeling unrefreshed to cognitive impairments such as memory and attention problems. Animal studies demonstrate that brief nociceptive stimulation tends to be processed similarly to sound, with dominant physiologic and behavioral responses during light sleep (stages 1 and 2) and attenuated responses during deep (stages 3 and 4) and rapid eye movement (REM) sleep. However, recent studies suggest that during sleep most somatosensory inputs are filtered below the thalamocortical pathway. At the behavioral level, if nociceptive stimulus is of a sufficient duration, a sleep arousal or sleep awakening response can be observed and, if perceived consciously, it can cause insomnia. Moreover, recent evidence suggests a circular influence between pain and sleep: a day of intense pain is followed by a night of poor sleep and a night with more sleep disruption is followed by an increase in pain the following day. The long-term health consequences of the exacerbation in pain and disruption in sleep homeostasis are unknown. It is critical that further investigation be made of the effects of pain medication (particularly opioids and other sedating agents) on sleep and daytime alertness, since sleep disturbance may interact with medication side-effects to magnify daytime sleepiness and cause a decrease in work productivity and safety and in driving performance, etc.