Takeshi Suganuma

Association of genetic, psychological and behavioral factors with sleep bruxism in a Japanese population.

Sleep bruxism is a sleep‐related movement disorder that can be responsible for various pains and dysfunctions in the orofacial region. The aim of the current case–control association study was to investigate the association of genetic, psychological and behavioral factors with sleep bruxism in a Japanese population. Non‐related participants were recruited and divided into either a sleep bruxism group (n = 66) or control group (n = 48) by clinical diagnoses and 3‐night masseter electromyographic recordings by means of a portable miniature device. The Epworth Sleepiness Scale, Temperament and Character Inventory, NEO‐Five Factor Inventory and custom‐made questionnaires that asked about familial aggregation, alcohol intake, caffeine intake, cigarette smoking, past stressful life events, daytime tooth‐contacting habit, temporomandibular disorder, daily headache, snoring, apnea/hypopnea symptoms, leg‐restlessness symptoms and nocturnal‐myoclonus symptoms were administered. In addition, 13 polymorphisms in four genes related to serotonergic neurotransmission (SLC6A4, HTR1A, HTR2A and HTR2C) were genotyped. These factors were compared between case (sleep bruxism) and control groups in order to select potential predictors of sleep‐bruxism status. The statistical procedure selected five predictors: Epworth Sleepiness Scale, leg‐restlessness symptoms, rs6313 genotypes, rs2770304 genotypes and rs4941573 genotypes. A multivariate stepwise logistic regression analysis between the selected predictors and sleep‐bruxism status was then conducted. This analysis revealed that only the C allele carrier of HTR2A single nucleotide polymorphism rs6313 (102C>T) was associated significantly with an increased risk of sleep bruxism (odds ratio = 4.250, 95% confidence interval: 1.599–11.297, P = 0.004).This finding suggests a possible genetic contribution to the etiology of sleep bruxism.

Involvement of reticular neurons located dorsal to the facial nucleus in activation of the jaw-closing muscle in rats

The location of excitatory premotor neurons for jaw-closing motoneurons was examined by the use of electrical and chemical stimulation and extracellular single-unit recording techniques in the anesthetized rat. Single-pulse electrical stimulation of the supratrigeminal region (SupV) and the reticular formation dorsal to the facial nucleus (RdVII) elicited masseter EMG response at mean (+/-SD) latencies of 2.22 +/- 0.59 ms and 3.10 +/- 1.14 ms, respectively. Microinjection (0.1-0.3 microl) of glutamate (50 mM) or kainate (0.5-100 microM) into RdVII increased masseter nerve activity in artificially ventilated and immobilized rats by 30.2 +/- 40.5% and 50.7 +/- 46.8% compared to baseline values, respectively. Forty reticular neurons were antidromically activated by stimulation of the ipsilateral trigeminal motor nucleus (MoV). Twenty neurons were found in RdVII, and the remaining 20 neurons were located in SupV, or areas adjacent to SupV or RdVII. Eleven neurons in RdVII responded to at least either passive jaw opening or light pressure applied to the teeth or tongue. Nine neurons responded to passive jaw opening. Five of the nine neurons responded to multiple stimulus categories. A monosynaptic excitatory projection from one neuron in RdVII was detected by spike-triggered averaging of the rectified masseter nerve activity. We suggest that reticular neurons in RdVII are involved in increasing masseter muscle activity and that excitatory premotor neurons for masseter motoneurons are likely located in this area. RdVII could be an important candidate for controlling activity of jaw-closing muscles via peripheral inputs.

The effect of bruxism on periodontal sensation in the molar region: A pilot study

STATEMENT OF PROBLEM Periodontal sensation in individuals with bruxism may differ from that in nonbruxers, as excessive amounts of occlusal force may be applied to the teeth during the night. However, this concept is not adequately addressed in the literature. PURPOSE The purpose of this study was to investigate the effects of bruxism on periodontal sensation in the molar region. MATERIAL AND METHODS Fourteen dental school faculty and students lacking objective or subjective abnormalities of stomatognathic function were divided into 2 groups representing nonbruxers (n=7) and bruxers (n=7). Bruxism was confirmed based on the nocturnal electromyography activities of the masseter muscle. Periodontal sensation was assessed based on interocclusal tactile threshold, which refers to the minimal thickness that can be detected between the occlusal surfaces of the teeth. Interocclusal tactile threshold was measured in the first molar region each for the left and right sides by placing variable thicknesses of metal foil and recording the threshold twice daily (morning and afternoon) on 3 separate days. Multivariate ANOVA was performed for bruxism (with or without) as a between-subjects effect, and time of day (morning and afternoon) and side (left and right) as within-subjects effects (alpha=.05) RESULTS Multivariate ANOVA revealed no significant differences in interocclusal tactile threshold between morning and afternoon or between the left and right sides in either group. The mean (SD) interocclusal tactile threshold for the bruxers was 17.1 (3.9) microm, while that for the nonbruxers was significantly greater at 29.9(5.6) microm (P<.001). CONCLUSIONS The periodontal sensation in bruxers was increased compared to nonbruxers.

Effect of clonazepam and clonidine on primary sleep bruxism: a double-blind, crossover, placebo-controlled trial

The aim of this study was to assess the acute effects of clonazepam and clonidine on rhythmic masticatory muscle activity in young adults with primary sleep bruxism, as well as accompanying effects on sleep architecture and cardiac activity. This study used a double‐blind, crossover, placebo‐controlled design. Polysomnography was performed on 19 subjects [nine men and 10 women; mean age (±SE): 25.4 ± 2.7 years] for 5 nights. The first 2 nights were used for the habituation and diagnosis of sleep bruxism. The other 3 nights were randomly assigned for clonazepam (1.0 mg), clonidine (0.15 mg) or placebo (all administered 30 min before bedtime). Sleep, oromotor activity and cardiac activity variables were assessed and compared among the three drug conditions. Clonidine significantly reduced the median percentage of time spent in the rapid eye movement sleep stage compared with placebo and clonazepam. The number of rhythmic masticatory muscle activity episodes was reduced with clonidine by >30% compared with placebo and clonazepam. The reduction of rhythmic masticatory muscle activity index by clonidine was associated with an increase of mean RR intervals (slower heart rate) during quiet sleep periods and during a 70‐s period before the onset of rhythmic masticatory muscle activity episodes. However, no changes in cardiac activity variables were observed for clonazepam. In young adults with primary sleep bruxism, clonidine was significantly more effective in suppressing sleep bruxism than clonazepam. The acute effects of clonidine on rhythmic masticatory muscle activity episodes may be mediated by suppression of autonomic nervous system activity and non‐rapid eye movement–rapid eye movement sleep processes.

Effects of sleep bruxism on periodontal sensation and tooth displacement in the molar region.

Abstract The purpose of this study was to investigate the effects of sleep bruxism on periodontal sensation and tooth displacement in the molar region. Twenty-eight (28) subjects lacking objective or subjective abnormalities in stomatognathic function were divided into two groups representing bruxers (n=14) and controls (n=14). Sleep bruxism was confirmed based on the nocturnal electromyography activity of the masseter muscle. Periodontal sensation was assessed based on interocclusal tactile threshold (ITT), which refers to the minimal thickness that can be detected between the occlusal surfaces of the teeth. ITT was measured in the first molar region. Displacement of teeth during clenching was measured using a two-dimensional tooth displacement transducer. Statistical analysis of the differences in ITT and tooth displacement between the bruxers and controls was performed by Mann Whitney U-test (p<0.05). Mean ITT for bruxers was significantly lower than that for controls (p<0.01). The mean displacement of both the maxillary and mandibular first molar for the bruxers was significantly larger than that for the controls (p<0.05). The results of this study suggest that sleep bruxism affects both periodontal sensation and tooth displacement.

Association between patterns of jaw motor activity during sleep and clinical signs and symptoms of sleep bruxism.

The aim of this study was to investigate the association between patterns of jaw motor activity during sleep and clinical signs and symptoms of sleep bruxism. A total of 35 university students and staff members participated in this study after providing informed consent. All participants were divided into either a sleep bruxism group (n = 21) or a control group (n = 14), based on the following clinical diagnostic criteria: (1) reports of tooth‐grinding sounds for at least two nights a week during the preceding 6 months by their sleep partner; (2) presence of tooth attrition with exposed dentin; (3) reports of morning masticatory muscle fatigue or tenderness; and (4) presence of masseter muscle hypertrophy. Video‐polysomnography was performed in the sleep laboratory for two nights. Sleep bruxism episodes were measured using masseter electromyography, visually inspected and then categorized into phasic or tonic episodes. Phasic episodes were categorized further into episodes with or without grinding sounds as evaluated by audio signals. Sleep bruxism subjects with reported grinding sounds had a significantly higher total number of phasic episodes with grinding sounds than subjects without reported grinding sounds or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). Similarly, sleep bruxism subjects with tooth attrition exhibited significantly longer phasic burst durations than those without or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). Furthermore, sleep bruxism subjects with morning masticatory muscle fatigue or tenderness exhibited significantly longer tonic burst durations than those without or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). These results suggest that each clinical sign and symptom of sleep bruxism represents different aspects of jaw motor activity during sleep.

Effect of stabilization splint on occlusal force distribution during voluntary submaximal tooth clenching: a preliminary sleep simulation study.

Abstract The purpose of the study was to clarify the effect of a stabilization splint (SS) on the distribution of occlusal force around the dental arch during voluntary submaximal tooth clenching. Ten healthy volunteers participated in this study. For each subject, the maxillary SS was made of heat-cured hard acrylic resin with approximately one mm thickness at the molar regions. The subjects were asked to perform static clenching at either 40% or 80% maximum voluntary contraction (MVC) levels, with and without the SS in place, using visual feedback. The occlusal contact area and occlusal force were analyzed. When the SS was inserted, the mean tooth contact area and occlusal force significantly decreased at both 40% and 80% MVC levels (p<0.01). The location of the occlusal balancing point changed towards the anterior after insertion of the SS. The results suggest that the SS has potential to reduce individual tooth-loading forces by evenly distributing the forces generated during sleep bruxism.

The Effect of Bite Force on Occlusal Contact and Masticatory Functions

目的: 咬頭嵌合位付近の側方咬合位において, 咬合力による咬合接触面積の変化と咀嚼機能との関係について検討する.方法: 正常有歯顎者12名について, 咬頭嵌合位および顎位規定装置で規定した1, 2mmの左右側方咬合位の咬合接触を, 軽い咬合時と強い咬合時において, 咬合印象法によって記録した. 咬合接触領域は50μm以下の近接領域とした. また, ガム咀嚼時の咬筋, 側頭筋の筋活動と咀嚼運動を同時に測定し, 咬合接触面積と咀嚼筋の筋活動比の関係を検討した.結果: 1. 咬頭嵌合位から側方咬合位に移動することで, 咬合接触面積は有意に減少し, それぞれの側方咬合位において咬合力を大きくすることにより, 増加した咬合接触面積も有意に減少した. 2. 平衡側2mmの咬合接触面積の増加量と咬筋の筋活動比は, 有意な負の相関関係が認められたが, 側頭筋の筋活動比との相関関係は認められなかった.結論: 咬頭嵌合位および側方咬合位の作業側と平衡側の咬合接触面積は, 強く咬合することで増加した. また, 側方咬合位の作業側では, 軽い咬合時の咬合接触面積が大きいほど, 咬合力負荷に伴う咬合接触面積の増加量も大きいという関係が認められ, 平衡側では, 咬合力が加わった場合の咬合接触面積の増加量が大きいと, 作業側と平衡側の筋活動比に影響があることが示された.

Influence of alterd anterior guidance on the activity of the masticatory muscles.

補綴物に適切なガイドを付与することは顎口腔機能に対して重要である.しかし, 与えられたガイドと咀嚼機能との関係については不明な点も多く存在する.本研究では, ガイドを変化させた場合の咬筋および側頭筋後部筋活動に与える影響について検討した.被験者は, 顎口腔系に異常を認めない成人3名を用いた.各被験者は, 咬合関係が切端咬合や前歯部開咬で, いずれか一方の側方滑走運動時に平衡側大臼歯に咬合接触が認められた.実験は, G0: ガイドなし, G1: 切歯路の角度が同一のガイド, G2: +約10°のガイド, G3: +約200のガイドを両側の上顎犬歯に装着し, 筋電図および下顎運動を記録した.G2およびG3のガイドは, 側方滑走運動時に平衡側の接触が離開するように調整した側方滑走運動時にG1のガイドを装着した場合の筋活動は様々な変化を示した.G2のガイドを装着した場合, GO, G1と比較すると, 往路では筋活動が減少する傾向にあり, 復路では筋活動が増加する場合があった.G3は, G2と比較すると筋活動が減少する傾向にあった.ガイドの変化による筋活動への影響は, 咀嚼運動時より側方滑走運動時の方が大きかった.ガイドの変化による咀嚼リズムの変化には一定の傾向がなかった.平衡側の咬合接触は, 咀嚼リズムの安定性や咀嚼経路に影響している可能性があった.

Measurement Accuracy of Condylar Position on Corrected Lateral Tomography of Temporomandibular Joint with Scanora Multimodal Radiography.

Accurate measurement of the condylar position is important for diagnosis and treatment of temporomandibular joint (TMJ) dysfunction. Radiography has been used for this purpose and recently, Scanora® multimodal radiography was introduced to Showa University. The projection capacity of the Scanora® in TMJ is still unclear. The purpose of this study was to estimate the accuracy of the measurement of the condylar position on sagittal tomography with Scanora® and to compare Scanora® images with LGM-1 images. Six TMJs obtained from dried skulls were used. Impressions of the joint space were obtained in order to estimate the actual dimensions. The Scanora® images, LGM-1 images, and impressions were measured with a profile projector. The results were as follows: 1) The measurement error of condylar position on Scanora® with a mean value of 0.29mm was similar to that on LGM-1 (0.25mm). 2) The measurement errors on both images in 1 of 6 TMJs were especially great (Scanora: 0.72mm, LGM-1: 0.87mm) while the measurement of the other 5 TMJs on both images showed smaller mean errors (Scanora: 0.2mm, LGM-1: 0.12mm). Therefore, there may be a considerable value of errors in the measurement on both images in the case of particular morphological types of joints. 3) It showed that the measurement errors of Y coordinates were larger than those of X coordinates. 4) The projection grade of both images were similar. These results suggested that sagittal tomography on Scanora® is useful for clinical estimate of the condylar position.