Akiyuki Shinya

Stimulation of the locus coeruleus suppresses trigeminal sensorimotor function in the rat

The nucleus locus coeruleus (LC) has been implicated in the modulation of the spinal sensorimotor function. The aim of the present study was to examine the effect of electrical stimulation of the LC on sensorimotor function in the trigeminal system. The following two cases of sensorimotor behaviors mediated by the trigeminal brainstem sensory nuclear complex were examined: (1) the activity of the masseter muscle evoked by pressure on the region of the temporomandibular joint (TMJ); and (2) the activity of the digastric muscle evoked by electrical stimulation of the tooth pulp, resulting in the jaw-opening reflex. In the first case, LC stimulation at 10, 30 and 50 microA resulted in a 70%, 68% and 55% reduction in the magnitude of electromyogram (EMG) activity of the masseter muscle compared with the control (without LC stimulation), respectively. The threshold intensity for the onset of masseter EMG activity increaced to 106%, 111% and 121% of the control with 10, 30 and 50 microA LC stimulation, respectively. In the second case, EMG magnitude in response to the digastric muscle decreased to 42% of the control when 30 microA of LC stimulation was delivered. These results suggest that descending influences from the LC can act in suppression of the trigeminal sensorimotor function.

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs from the temporomandibular joint (TMJ) and/or the masseter muscle (Mm) were examined in rats. Of 230 neurons tested, 24 could be antidromically stimulated from the contralateral ventral posteromedial thalamic nucleus (VPM), and 27 of 91 neurons tested were stimulated from the ipsilateral posteromedial part of crus II of the cerebellar cortex. None had dual projections. The thalamic-projecting neurons were recorded in the dorsomedial region of the interpolaris; most cerebellar-projecting neurons were at the medial border of the interpolaris. Ten of 24 thalamic- and 17 of 27 cerebellar-projecting neurons received nociceptive information. Afferent inputs from the TMJ and the Mm converged on 6 of 24 thalamic-projecting neurons and on 16 of 27 cerebellar-projecting neurons. In both the thalamic- and cerebellar-projecting neurons, there was no difference between the non-nociceptive and nociceptive neurons in mean antidromic latency. The results suggest that the interpolaris integrates and relays afferent inputs from deep oral structures.

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.

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.

Coeruleotrigeminal suppression of nociceptive sensorimotor function during inflammation in the craniofacial region of the rat

Descending action from the locus coeruleus (LC) on the trigeminal sensorimotor function was evaluated in a rat model of oral-facial inflammation. For the induction of oral-facial inflammation, mustard oil (20% solution in 20microl mineral oil) was injected into the region of the temporomandibular joint (TMJ). One week before testing, rats received bilateral lesions of the LC using a cathodal current. The electromyogram (EMG) threshold, which is the threshold intensity for the onset of EMG activity of the masseter muscle evoked by pressure on the TMJ region, was used in the present study as an indicator of the trigeminal sensorimotor function. Following mustard oil injection, in the LC-lesioned rats, EMG thresholds significantly decreased at 30min, which lasted up to 240min. In contrast, EMG thresholds in the LC-intact rats returned to the level before injection after 180min. Systemic naloxone (1.3mg/kg, i.v.) produced a further decrease of EMG thresholds in both the LC-intact and LC-lesioned rats. Under the existence of naloxone, EMG thresholds in the LC-lesioned rats were significantly lower than those of the LC-intact rats. These results suggest that oral-facial inflammation activates the coeruleotrigeminal modulating system and that an action of this system is independent of the opioid depressive mechanism.

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.

In vivo Study on the Adaptation of Full Cast Crowns.

The adaptation of crowns and bridges is a significant factor in relation to secondary caries or periodontal disease. In this study, eight premolars which would be extracted for orthodontictreatment were used to investigate in vivo adaptation of full cast crowns. The results wereas follows:1. The mean cement thickness was similar to the results of an in vitro study previouslyreported.2. All the impression methods investigated in this study were considered to be clinicallyacceptable. The individual tooth tray method was the most exact and stable of the three methods.3. In two combined impression methods, the marginal cement was thicker than that of theaxial surfaces. This tendency was more remarkable in the mesial and distal surfaces compared tothe buccal and lingual surfaces.4. Marginal cement layers of the buccal and distal surfaces were thicker than those of thelingual and mesial surfaces.