Shuichiro Yamashita

Tokyo Dental College, Edo, Tōkyō, Japan

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Publications (15)12.45 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: To elucidate the mechanisms of individual differences in pain and analgesic sensitivity, we analyzed the variable number of tandem repeat polymorphism in the third exon of the dopamine D4 receptor gene. Alleles that were less than four repeats long and four or more repeats long were considered Short and Long, respectively. We found that the Short/Short genotype group was significantly more sensitive to pain and less sensitive to analgesics than the Short/Long+Long/Long genotype group. Our data suggest that this polymorphism may predict individual differences in pain and analgesic sensitivity and help achieve adequate pain control in the future.
    Neuroscience Letters 02/2013; · 2.03 Impact Factor
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    ABSTRACT: We aimed to characterize the association between jaw muscle contractions and respiratory events in patients with obstructive sleep apnea syndrome (OSAS) and to investigate the responsiveness of the contractions to respiratory events in comparison with that of leg muscles in terms of arousal types and sleep states. Polysomnographic (PSG) recordings were performed in 19 OSAS patients (F/M: 2/17; 53.1 ± 13.7 years; AHI: 31.8 ± 19.9/h) with no concomitant sleep bruxism or other sleep-related movement disorders. Muscle contractions of unilateral masseter (MAS) and anterior tibialis (AT) muscles were scored during sleep in association with graded arousals (microarousals and awakenings) related or unrelated to apneahypopnea events. Arousals were scored for 68.2% and 52.3% of respiratory events during light NREM and REM sleep, respectively. Respiratory events with arousals were associated with longer event duration and/or larger transient oxygen desaturation than those without (ANOVAs: p < 0.05). Median response rates of MAS events to respiratory events were 32.1% and 18.9% during NREM and REM sleep. During two sleep states, MAS muscle was rarely activated after respiratory events without arousals, while its response rate increased significantly in association with the duration of arousals (Friedman tests: p < 0.001). A similar response pattern was found for AT muscle. Motor responsiveness of the two muscles to arousals after respiratory events did not differ from responsiveness to spontaneous arousals in two sleep stages. In patients with OSAS, the contractions of MAS and AT muscles after respiratory events can be nonspecific motor phenomena, dependent on the duration of arousals rather than the occurrence of respiratory events. Kato T; Katase T; Yamashita S; Sugita H; Muraki H; Mikami A; Okura M; Ohi M; Masuda Y; Taniguchi M. Responsiveness of jaw motor activation to arousals during sleep in patients with obstructive sleep apnea syndrome. J Clin Sleep Med 2013;9(8):759-765.
    Journal of clinical sleep medicine: JCSM: official publication of the American Academy of Sleep Medicine 01/2013; 9(8):759-65. · 2.93 Impact Factor
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    ABSTRACT: Sleep-related movement disorders are characterized by the specific phenotypes of muscle activities and movements during sleep. However, the state-specific characteristics of muscle bursts and movement during sleep are poorly understood. In this study, jaw-closing and -opening muscle electromyographic (EMG) activities and jaw movements were quantified to characterize phenotypes of motor patterns during sleep in freely-moving and head-restrained guinea pigs. During non-REM (NREM) sleep, both muscles were irregularly activated in terms of duration, activity and intervals. During REM sleep, clusters of phasic bursts occurred in the two muscles. Compared to NREM sleep, burst duration, activity and intervals were less variable during REM sleep for both muscles than during NREM sleep. Although burst activity was lower during the two sleep states than during mastication, burst duration and intervals during REM sleep were distributed within a similar range to those during mastication. A trigger-averaged analysis of muscle bursts revealed that the temporal association between the bursts of the jaw-closing and -opening muscles during REM sleep was analogous to the temporal association during natural chewing. The burst characteristics of the two muscles reflected irregular patterns of jaw movements during NREM sleep and repetitive alternating bilateral movements during REM sleep. The distinct patterns of jaw muscle bursts and movements reflect state-specific regulations of the jaw motor system during sleep states. Phasic activations in the antagonistic jaw muscles during REM sleep are regulated, at least in part, by the neural networks involving masticatory pattern generation, demonstrating that waking jaw motor patterns are replayed during sleep periods.
    Journal of Applied Physiology 11/2012; · 3.48 Impact Factor
  • Hiromi Hotta, Yuki Kanai, Shuichiro Yamashita
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    ABSTRACT: When multiple tooth loss causes loss of occlusal-masticatory function, functional recovery is normally obtained with the help of removable dentures. After resection of the jawbone or tongue because of tumors, the movement of the tongue and its surrounding tissues is limited, and patients exhibit a more pronounced loss of chewing and swallowing than that observed in other cases of multiple tooth loss. In such cases, it is necessary to take extra care in determining the position of the mandible, arrangement of artificial teeth, and morphology of the palate. In the present case, the left lower jawbone was resected because of a gingival tumor, and when the new denture was manufactured, the intercuspal position was based on the resting position of the mandible. The stability of the lower complete denture was a priority and the artificial teeth were partially arranged on the lingual side. The new denture, however, caused insufficient closing of the mouth aperture and insufficient impact between tongue and palate, resulting in dysphagia. Therefore, the vertical dimension of occlusion was reduced multiple times to improve chewing and swallowing function.
    The Bulletin of Tokyo Dental College 01/2012; 53(4):173-80.
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    ABSTRACT: The purpose of this study was to examine the usefulness of a new gustatory test based on the progress of mastication by counting the number of chewing strokes required for recognizing tastes. Thirty-nine subjects (20 males and 19 females, 25.3±6.4 years old) without missing teeth were selected. Four types of newly designed test materials made from 15% gelatine were prepared, containing sucrose, sodium chloride, tartaric acid, or quinine hydrochloride. Five or six concentrations, representing weak to strong tastes, were prepared for each tastant. Subjects were instructed to chew the food, and the number of chewing strokes necessary to recognize the taste was counted. Female subjects recognized the sweet taste more accurately than male subjects (Friedman test: p<0.05). For each tastant of the test materials, the average number of chewing strokes (recognition threshold) was approximately 10. The frequency of correct responses and the average number of chewing strokes tended to be higher and lower, respectively, as the concentration of the taste in the test material increased (Kruskal-Wallis test: sweet p<0.01, salty p<0.01, sour p<0.01 and bitter p<0.01). Using the newly designed test materials, counting the number of chewing strokes necessary for recognizing the taste would be a useful index of a new gustatory test to investigate taste sensation.
    Journal of prosthodontic research. 11/2011; 56(3):210-5.
  • Annals of Japan Prosthodontic Society 01/2009; 1(4):378-385.
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    ABSTRACT: The relationship between the steepness of the articular eminence and the condylar positioning during clenching was investigated in 19 volunteers with natural dentitions. The condylar positioning during maximal voluntary contraction was measured using a mandibular movement analysis system with six degrees of freedom. The sagittal condylar guide inclination was also measured using the same apparatus. A significant negative correlation was observed between the sagittal condylar guide inclination and the distance of ipsilateral condylar positioning. This result suggests that the steepness of the articular eminence is an important factor in condylar positioning during clenching.
    The European journal of prosthodontics and restorative dentistry 01/2008; 15(4):159-64.
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    ABSTRACT: This study aimed to investigate the relationship between missing occlusal units and oral health-related quality of life (OHRQoL) in subjects with shortened dental arches (SDAs). Subjects with SDAs (N = 115) were recruited consecutively from 6 university-based prosthodontic clinics. OHRQoL was measured using the Japanese version of the Oral Health Impact Profile (OHIP-J). An increase of 1 missing occlusal unit was associated with an increase of 2.1 OHIP-J units (95% CI: 0.6-3.5, P = .02) in a linear regression analysis. Missing occlusal units are related to OHRQoL impairment in subjects with SDAs.
    The International journal of prosthodontics 01/2008; 21(1):72-4. · 1.63 Impact Factor
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    ABSTRACT: In the last two decades, the Shortened Dental Arch (SDA) concept has been introduced as a treatment strategy for posterior edentulous patients. This study investigated whether the SDA concept applies to all posterior edentulous patients. In the first study, objective evaluations for the temporomandibular joint (radiographic evaluation and measurement of condylar positioning during maximal voluntary contraction) were performed in patients with unilaterally posterior missing teeth. Abnormal condylar appearances were observed in 73% of subjects by radiographic evaluation and these phenomena coincided with edentulous-side in 55% of them. Condylar positioning during clenching was significantly larger on the edentulous-side compared to that in the dentulous-side. In the second study, we investigated the mandibular positioning during maximal voluntary contraction related to simulated loss of posterior occlusal supports in volunteers with natural dentitions. A greater bilateral loss of posterior occlusal support was associated with increased distances of positioning of both condyles. Moreover, subjects could be divided into two groups depending on the condylar mobility following reduced occlusal support. In the first group, the distance of condylar positioning significantly increased by cutting the splint sequentially from the posterior toward the anterior side. On the other hand, in the second group, no significant difference was observed between the distances measured under all the experimental occlusal conditions. In the supplemental study, a significant negative correlation was observed between the sagittal condylar guide inclination and the distance of ipsilateral condylar positioning. This result suggests that the steepness of the articular eminence is an important factor in condylar positioning during clenching. We propose that clinical guidelines should be developed for determining whether to adopt a "Wait and See" approach for SDA patients without any proactive treatment, or to start prosthetic intervention immediately.
    Nihon Hotetsu Shika Gakkai Zasshi 11/2007; 51(4):699-709.
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    ABSTRACT: Many studies have reported the relationship between facial morphology and stomatognathic functions. The steepness of the articular eminence is an important morphological factor to determine the mandibular movement or mandibular positioning. The present study analyzed the relationship between the condylar displacement during clenching and the condylar guide inclination related to simulated loss of posterior occlusal support. Nineteen clinical residents (4 females and 15 males, 24-31 years old) with healthy natural dentitions were recruited as subjects. To change the posterior occlusal support, occlusal splints fitted to maxillary dental arches were cut in sequence from the posterior toward the anterior side. The condylar displacements during maximum voluntary clenching under every occlusal condition were measured using a mandibular movement analyzing system with six-degrees of freedom. The sagittal condylar guide inclination was also measured using the same apparatus. 1. A greater loss of posterior occlusal support was associated with increased displacement distance of both condyles, however these values varied with the subject. 2. A significant positive correlation was observed between the displacement distance without splint and the relative displacement distance with splint (difference between before and after loss of occlusal supports). 3. A significant negative correlation was observed between the displacement distance without splint and the sagittal condylar guide inclination, and was also observed between the relative displacement distance with splint (above-mentioned) and the sagittal condylar guide inclination. These results suggest that the sagittal condylar guide inclination is an important factor in condylar displacement during clenching.
    Nihon Hotetsu Shika Gakkai Zasshi 08/2007; 51(3):546-55.
  • Hideyuki Koike, Yumiko Kato, Shuichiro Yamashita, Ken Kumita
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    ABSTRACT: PATIENT: The patient was a 27-year-old male with a chief complaint of pain in the upper-left incisors. These teeth were diagnosed as chronic apical periodontitis and the cemented post-cores of these teeth had to be removed for the following infected root canal treatment. The volume of metal core of the upper left central incisor had already been greatly reduced to an unfavorable size, and we failed to remove the cemented post-core using the Little Giant Post Puller. A supplementary device that fitted to the core was cast to aid the Little Giant Post Puller to work properly. By using this device, the jaws of the Post Puller gripped the core securely so that the instrument did not slip as the post was being unseated. Finally, the post-core was successfully removed without any troubles such as root fracture or postoperative pain. DISCUSSION: In the case reported here, the volume of metal core had already been greatly reduced by the previous doctor, and there was a risk of metal fracture of the core if additional trimming of the core had been performed to accommodate the size of the Post Puller. The success in removing the post-core by the aid of the supplementary device might have been due to the skill of the operator, who was experienced in using the Post Puller and also well versed in both the advantages and disadvantages of the instrument. CONCLUSIONS: Great satisfaction of both the patient and the operator were obtained, since the fabricated supplementary device worked well under the operator's proper judgment for solving this difficult case.
    Nihon Hotetsu Shika Gakkai Zasshi 11/2006; 50(4):527-33.
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    ABSTRACT: To assess the occurrence and the modality of spontaneous orofacial behaviors of awake healthy subjects without pain who were unaware of bruxism during wakefulness. Sixteen asymptomatic subjects read silently for 30 minutes while polygraphic recordings, including electromyographic (EMG) activity from masticatory and leg muscles, chest respiratory movements, and the movements and sounds of larynx, were made with simultaneous audio-video monitoring. Orofacial behaviors were scored based on the polygraphic and audio-video records. The activity and duration of masseter EMG bursts were calculated for the types of orofacial behaviors. The number of orofacial behaviors varied between subjects; swallowing was most frequently observed. Approximately half of the orofacial behaviors occurred closely with body movements. Of all masseter EMG bursts detected, 55% were associated with functional orofacial behaviors, while 45% were regarded as nonfunctional. More than 80% of these masseter bursts lasted for less than 2 seconds, with an activity less than 20% of maximal voluntary clenching. These values did not differ between the types of associated orofacial behaviors. Although the occurrence of spontaneous orofacial motor activity is variable, asymptomatic subjects can exhibit substantial masseter bursts during wakefulness that are not associated with functional orofacial behaviors. The use of physiological and audio-video records permits spontaneous orofacial behaviors to be specifically identified, thereby allowing nonfunctional masseter EMG activity to be differentiated from functional masseter EMG activity.
    Journal of orofacial pain 02/2006; 20(4):317-24. · 2.39 Impact Factor
  • Takanao Kirihara, Shuichiro Yamashita, Yoshimasa Igarashi
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    ABSTRACT: Mandibular displacement related to simulated loss of posterior occlusal support was investigated. Twenty-four volunteers with natural dentitions were selected. To change the posterior occlusal support, occlusal splints fitted to maxillary dental arches were cut in sequence from the most posterior to anterior. The more the absence of posterior occlusal support increased, the more both condylar displacements were increased (R: 0.97mm, L: 0.94mm). Moreover, subjects could be divided into two groups depending upon their condylar mobility following with reduced occlusal support. These results suggest that individual adaptability to the imbalanced occlusal condition should be always considered.
    The European journal of prosthodontics and restorative dentistry 01/2006; 13(4):170-6.
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    ABSTRACT: This study investigated both the setting expansion and compressive strength of dental gypsum mixed with slightly acidic hypochlorous acid water for the prevention of hospital infection. Slightly acidic hypochlorous acid water (PURESTER Mp-240B, Morinaga Milk Industry) was used to mix each of three types of gypsum (model plaster, dental stone and high strength dental stone), and both the setting expansion and compressive strength of these gypsum products were analyzed in comparison with those mixed with tap water. 1. With regard to the setting expansion, a significant difference was not observed between gypsum products mixed with the two types of water, except for both the model plaster and dental stone 30 minutes after the start of mixing. 2. Regarding the compressive strength, a significant difference was not observed between gypsum products mixed with the two types of water, except for the model plaster 90 minutes after the start of mixing. From the results of the study, it was revealed that both the setting expansion and compressive strength of gypsum products using the slightly acidic hypochlorous acid water showed almost the same characteristics as those using tap water.
    Nihon Hotetsu Shika Gakkai Zasshi 11/2005; 49(5):716-25.
  • Takeshi Kozawa, Yoshimasa Igarashi, Shuichiro Yamashita
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    ABSTRACT: Three-dimensional mandibular displacement related to loss of posterior occlusal support was investigated. Five subjects, whose mandibular premolars and molars needed to be restored, were selected. Their experimental prostheses were removed in sequence from the most posterior to anterior. The more the absence of posterior occlusal support increased, the more condylar displacements were increased. On the other hand, maximum bite forces were decreased, by removing each prosthesis in sequence from posterior to anterior. These results suggest that condylar position would be easily displaced with low level bite force following loss of posterior occlusal support.
    The European journal of prosthodontics and restorative dentistry 04/2003; 11(1):33-40.

Publication Stats

21 Citations
6 Downloads
759 Views
12.45 Total Impact Points

Institutions

  • 2011–2012
    • Tokyo Dental College
      Edo, Tōkyō, Japan
  • 2003–2011
    • Matsumoto Dental University
      • • Division of Oral and Maxillofacial Biology
      • • Department of Removable Prosthodontics
      Shiojiri, Nagano-ken, Japan
  • 2008
    • Showa University
      • Department of Prosthodontics
      Shinagawa, Tōkyō, Japan