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BACKGROUND Masticatory movement occurs complicatedly and bilaterally. Although the tongue plays an important role in mastication, bilateral tongue function during mastication has not been clarified yet. OBJECTIVE To investigate the effect of food properties on posterior tongue activity and coordination of muscles bilaterally by electromyography (EMG). METHODS Twenty healthy adults (10 males and 10 females; mean age 28 years; range: 22-33 years) participated in this study. Three test foods, gummy jelly (hard food), sponge cake (soft food requiring crushing), and mashed potatoes (soft food not requiring crushing), were used. Bilateral masseter N-EMG (surface electromyography for measuring the muscle activity of posterior tongue) and submental EMG were carried out while the participants chewed three test foods. The participants were instructed to masticate three test foods only on the right side and only on the left side unilaterally. RESULTS In the case of gummy jelly, N-EMG activity on the mastication side was significantly larger than that on the non-mastication side (P

Purpose This study aimed to investigate the effect of removable denture prostheses on the comminution progress in elderly people. Methods Twenty-two denture wearers of Eichner’s classification B and C (75.1 ± 5.3 years old) and 20 young fully dentate subjects (27.6 ± 1.9 years old) participated in the masticatory examination, which used a combined test food from 5 daily food materials. Full masticatory cycles lasting until subjects needed to swallow and the half number of the cycles were adopted as masticatory conditions. Digital images of food particles under wet conditions were obtained for each bolus, and particles were analyzed by calculating the homogeneity and particle size indices. Results The characteristic properties of the food particles were observed using a homogeneity index in the elderly denture group for half masticatory strokes. Their homogeneity index was significantly higher than that of the young dentate group. By contrast, no significant difference was observed in the indices for particles immediately before swallowing between two groups. Conclusions The comminuted particle size before swallowing in healthy denture wearers was not significantly different from that in the natural dentate group. The comminution of the first-half process in denture wearers was typical and could be one possible focus for meal property specifications in future studies.

PURPOSE To examine how particle loss affects the evaluation of masticatory ability using the image analysis method. METHODS The subjects were divided into two groups:Y-group (healthy young adults: 10 male, 10 female; mean age 27.6 ± 1.9 years), and D-group (denture wearing older adults: 13 male, 9 female; mean age, 75.1 ± 5.3 years). Raw carrots, peanuts, and a combined test food from 5 daily food materials (mixed foods) were selected as test foods. Images of the boluses were captured and processed after the subjects freely masticated the test foods until the point of swallowing or completed half strokes of total chewing cycles. The median particle size (X50) was calculated from the data for each particle. We compared X50 calculated from all particles obtained from the masticatory bolus (as X50N) with the X50 of only selectively larger particles (as X50R). RESULTS Significant correlations were observed between X50N and X50R (p 0.75). CONCLUSION The method of analyzing only larger particles makes it possible to evaluate masticatory ability without losing the characteristics of the original particle size distribution of the entire bolus. This finding can be applied for the evaluation of masticatory ability, especially among older adults who have difficulty retrieving the total amount of test food due to decreased activities of daily living.

Purpose Animal experiments have shown that the loss of occlusal support causes impairments in spatial cognition. Many reports have focused on the memory encoding process, and only few studies have investigated the effect on memory retrieval. This study aimed to examine the effects of both the loss and reconstruction of occlusal support on the memory retrieval process and on the number of hippocampal pyramidal cells. Methods The experimental animals were divided into a molarless group, in which molars were extracted, a denture-wearing molarless group with experimental dentures inserted after molar extraction, and a control group. Radial maze trials were performed for 20 consecutive days (acquisition phase). The rats were tested on long-term memory retention following the acquisition phase in eight trials every five days, and in an additional trial 20 days later (probe phase). Results The denture-wearing molarless group showed higher levels of spatial learning and memory than the molarless group. There were no significant differences in memory retrieval during the probe phase between the denture-wearing molarless and the control group. The molarless group showed significantly worse spatial learning and memory and had fewer neurons in the hippocampus than the control group. Conclusions Our results suggest that the loss of occlusal support decreases the number of pyramidal cells in the hippocampus and impairs memory decoding and retrieval. However, this effect is suppressed by the reconstruction of occlusal support.

Purpose The lack of occlusal support is an epidemiological risk factor linked to Alzheimer's disease. This study sought to assess the relationship between amyloid β (Aβ) deposition and the lack of occlusal support in amyloid precursor protein (APP) knock-in mice. Methods Sixteen experimental animals were divided into two groups. The upper molars were extracted in the extraction group (group E), and a sham operation was performed in the control group (group C). The Morris water maze test was performed 4 months after the tooth extraction. Aβ immunohistochemical staining and Nissl staining of the hippocampus were performed. Hippocampal plasma corticosterone and Aβ protein levels were measured. Results In the maze task, the escape latency was significantly longer in group E than in group C. In the probe trials, the time elapsed in the target quadrant was significantly shorter in group E than in group C. The number of hippocampal neurons decreased in group E. There was no significant difference in the plasma corticosterone levels between the two groups, indicating that there was no effect of chronic stress on the behavioral results. Hippocampal Aβ40 and Aβ42 protein levels and Aβ deposition areas by immunohistochemical staining were not significantly different between the two groups. Conclusions Aβ deposition was not increased in the hippocampus of molarless APP knock-in mice. As such, it appears that cognitive impairment due to a lack of occlusal support was not related to Aβ deposition.

BACKGROUND Fatigue is an important factor for muscle strengthening in rehabilitation medicine. Frequency analysis has been regarded as the gold standard for muscle fatigue assessment in surface electromyography (EMG). However, there are no experiments quantifying fatigue with grouped discharge (GD), which is one of the historical phenomena observed in patients having fatigue, by using high sampling rate recording of EMG. OBJECTIVE To investigate the effect of fatigue, which is induced by repeated posterior tongue lift movement (TLM), on the occurrence of GD peaks, thus, to provide possible basis as a parameter for future fatigue evaluation. METHODS Nineteen healthy adults (9 men and 10 women) participated in this study. The muscle fatigue protocol consisted of repetitive posterior TLM and maximum voluntary contractions (MVC). Bilateral N-EMG (Neck surface EMG for measuring the muscle activity of the posterior tongue) was recorded. RESULTS Subjective tongue fatigue at the end of the protocol was significantly higher than at beginning throughout the muscle fatigue protocol (p

Purpose To design an efficient tongue prosthesis with reproducibility and to objectively evaluate improvement in speech function. Methods A silicon anatomical artificial tongue (AT) and a flat surface artificial tongue system (FTS) were used in our study. Twenty healthy participants (10 males and 10 females, 26.3 ± 1.8 years) were fitted with a tongue movement suppression appliance (TSA) that fit the dental arch to simulate the glossectomy condition. TSA, TSA + FTS, and TSA + AT simulated the state of glossectomy patients without artificial tongue, with normal artificial tongue, and newly designed artificial tongue, respectively. Three speech intelligibility tests were performed for each of the following conditions: pronouncing 100 Japanese monosyllables, 40 Japanese words, and reading a short story. One-way ANOVA, Wilcoxon signed-rank test, and Tukey-Kramer post-hoc test were used for statistical analyses. Results Significant differences were observed for 100 Japanese monosylla bles and 40 Japanese words between the TSA + FTS, TSA, and TSA + AT conditions (p ‹ 0.05). Regarding the speech intelligibility test for reading a short story, the TSA + FTS condition resulted in a significantly higher speech intelligibility than the TSA and TSA + AT conditions (p ‹ 0.05). Conclusions A flat surface artificial tongue system contributed to the improvement in speech function. This structure can be easily used in cases where conventional artificial tongue are applicable, regardless of variation in the oral condition; thus, making it a widely applicable treatment option for glossectomy patients.

Background and Objective: The relationship between periodontal sensation and Myofascial Pain (MP) is not yet fully clarified. The aim of this study was to test the null hypothesis that there is no difference in the periodontal sensation threshold between subjects with MP and subjects with no Temporomandibular Disorders (TMD). Methods: Participants have clinically assessed in accordance with the Research Diagnostic Criteria for Temporomandibular Disorders version 1.0 guidelines and assigned to the MP group (mean age 54.8 ± 14.8 years; 1 male and 11 females) or the control group (mean age: 63.9 ± 13.2 years; 1 male and 15 females). The Passive Periodontal Sensation Threshold (PPST) was evaluated using impulsive mechanical stimulation on the occlusal surface parallel to the tooth axis of the maxillary first molar, if present. The difference in the mean PPST between the MP group and the control group was evaluated using the Student t-test after checking for homoscedasticity. Results: The mean PPST value was 1050.1 ± 480.3 mN in the MP group and 712.3 ± 288.5 mN in the control group. A significant difference was observed between these mean PPST values (p = 0.045). Conclusion: There was a significant difference in PPST between the MP group and the control group. Although the etiology of the change of PPST is still unknown, the higher PPST value observed in MP patients suggests that future study on occlusal dysesthesia or occlusal sensation-related pathosis is warranted.

To provide a scientific data related to the tonic activity of masseter muscle in subjects with and without history of orofacial pain during their normal daily life.Thirty-three subjects were divided into two groups, a pain history group (PHG) and a non-pain history group (non-PHG), based on their responses to the Research Diagnostic Criteria for Temporomandibular Disorders questionnaire. After excluding four subjects with incomplete recordings, full-day masseter muscle surface EMGs of 29 subjects (10 men, 19 women; mean age 24.1 years) were analyzed. Tonic episode (TE) was defined as continuous EMG activity with a duration at least 2s with intensities above twice the baseline noise level. TEs were classified into 6 strength categories (7.5%, 7.5-10%, 10-15%, 15-25%, 25-40% and40% of the maximum voluntary clenching (MVC)). The mean duration of activity observed in the non-PHG+2 SD was adopted as a cutoff for identifying sustained TE.During waking hours, the incidence of sustained TEs was significantly higher in the PHG than in the non-PHG (p0.05). The incidence and total duration of sustained TEs were significantly higher in the PHG than in the non-PHG at intensities of 7.5-10% MVC, 10-15% MVC, and 15-25% MVC (p0.05). No significant difference was observed during sleep.Within the limitations of this study, it would be concluded that sustained TEs may have a correlation with orofacial pain and the intensity range of 7.5-25% MVC would be an important range for future clenching studies.

Background: Mastication has been regarded to play an important role in achieving quality daily life for the elderly. On the occlusal surface of posterior artificial teeth, parallel grooves of 1 mm depth and 1 mm width with an inter-groove distance of 2 mm have been found to significantly improve masticatory efficiency on a mechanical simulator. Materials and Methods: In the present study, the effect of the grooved design on masticatory efficiency in edentulous subjects using a short-term crossover trial was evaluated. Six edentulous participants, 1 male and 5 females, were assigned into two groups. One received duplicated complete dentures with grooved molars first, and the other received duplicated complete dentures with conventional molars first. The design of the teeth was crossover after evaluating masticatory efficiency. Raw carrot, raw lettuce and mixed foodstuffs were used to evaluate masticatory efficiency. Subjects were instructed to masticate 20 strokes and arbitrary strokes until they felt like swallowing. Results: The number of masticatory strokes taken was significantly smaller using the grooved design (pp Conclusion: Results show that compared with conventional lingualized occlusion, the grooved design accomplishes higher masticatory efficiency in vivo. Considering the distinction of this design that it can be applied to any existing denture occlusion, the design might help improve the dietary life of the elderly.

During mastication, some portion of the food bolus is gradually transported to the oropharynx before deglutition, which is known as stage II transport (STII). Although the importance of STII in mastication and deglutition has been widely acknowledged, food particle properties that are transported into the oropharynx by STII have not yet been fully specified. To reveal the food particle properties that are transported into the oropharynx by STII and to assess the usefulness of new food bolus sampling methods for the evaluation of masticatory efficiency. Twenty-two healthy volunteers participated in this study. Four different bolus sampling conditions were adopted: (a) the whole food particles were expectorated when the subject was aware of the first deglutition, (b) the last bolus to be swallowed at the end of unrestrained food intake was expectorated (aftermost bolus sample), (3) the whole food particles were expectorated when the subject felt ready to swallow after swallow-inhibited mastication (swallow-inhibited sample), (4) the particles were regurgitated from the oropharynx after the first STII (stage II-transported sample). Food particles were analysed using the homogeneity index and particle size index. There was no significant difference between food particles in the aftermost bolus sample and swallow-inhibited sample. The particles in the stage II-transported sample showed significantly more homogeneous and smaller sizes than other sampling conditions (P < .05). The food particles transferred to the oropharynx in the stage II-transported sample were smaller than those broken down by natural mastication.

Background Retraction of the posterior tongue facilitates bolus formation, food transfer and Stage II transport in chewing and swallowing. Surface electromyography of the neck region (N-EMG) enabled the evaluation of muscle function at the posterior tongue. Although previous studies showed that food hardness increased masticatory muscles EMG activity and volitional chewing altered swallowing, the effect of food properties and chewing condition on N-EMG activity has not yet been elucidated. Objective To investigate the effect of food properties and chewing conditions on N-EMG. Methods Twelve healthy adults (six men and six women, mean age 28.1 ± 2.7) participated in this study. Three test foods were used: a cookie (solid food), crushed cookies adjusted using agar and water (semisolid food) and crushed cookies adjusted using thickening agent and water (soft food). Masseter and submental muscle EMG and N-EMG activity were recorded while chewing the three test foods. Participants were instructed to masticate the three test foods in three chewing conditions: (a) chewing freely, (b) chewing test foods with the same number of chewing cycles as when chewing solid food and (c) chewing with a maximum effort. Results Total N-EMG activity when chewing solid food was higher than that in the other two test foods regardless of the chewing condition. In soft food and semisolid food, the total N-EMG activity was increased by increasing the number of chewing cycles. Conclusion The total N-EMG activity was increased while chewing hard food, which indicates the positive effect of chewing hard food on rehabilitation at the posterior tongue.

Elevation of the posterior part of the tongue is important for normal deglutition and speech. The purpose of this study was to develop a new surface electromyography (EMG) method to non-invasively and objectively evaluate activity in the muscles that control lifting movement in the posterior tongue. Neck surface EMG (N-EMG) was recorded using differential surface electrodes placed on the neck, 1 cm posterior to the posterior border of the mylohyoid muscle on a line orthogonal to the lower border of the mandible. Experiment 1: Three healthy volunteers (three men, mean age 37·7 years) participated in an evaluation of detection method of the posterior tongue lifting up movement. EMG recordings from the masseter, temporalis and submental muscles and N-EMG revealed that i) N-EMG was not affected by masseter muscle EMG and ii) N-EMG activity was not observed during simple jaw opening and tongue protrusion, revealing the functional difference between submental surface EMG and N-EMG. Experiment 2: Seven healthy volunteers (six men and one woman, mean age 27·9 years) participated in a quantitative evaluation of muscle activity. Tongue-lifting tasks were perfor-med, exerting a prescribed force of 20, 50, 100 and 150 gf with visual feedback. For all subjects, a significant linear relationship was observed bet-ween the tongue-lifting force and N-EMG activity (P < 0·01). These findings indicate that N-EMG can be used to quantify the force of posterior tongue lifting and could be useful to evaluate the effect of tongue rehabilitation in future studies.

The wave analysis of swallowing sounds has been receiving attention because the recording process is easy and non-invasive. However, up until now, an expert has been needed to visually examine the entire recorded wave to distinguish swallowing from other sounds. The purpose of this study was to establish a methodology to automatically distinguish the sound of swallowing from sound data recorded during a meal in the presence of everyday ambient sound. Seven healthy participants (mean age: 26·7 ± 1·3 years) participated in this study. A laryngeal microphone and a condenser microphone attached to the nostril were used for simultaneous recording. Recoding took place while participants were taking a meal and talking with a conversational partner. Participants were instructed to step on a foot pedal trigger switch when they swallowed, representing self-enumeration of swallowing, and also to achieve six additional noise-making tasks during the meal in a randomised manner. The automated analysis system correctly detected 342 out of the 352 self-enumerated swallowing events (sensitivity: 97·2%) and 479 out of the 503 semblable wave periods of swallowing (specificity: 95·2%). In this study, the automated detection system for swallowing sounds using a nostril microphone was able to detect the swallowing event with high sensitivity and specificity even under the conditions of daily life, thus showing potential utility in the diagnosis or screening of dysphagic patients in future studies.

Experimental loss of occlusal support caused by the extraction or grinding of molar teeth has been reported to foment the impairment of learning and memory in laboratory animals. The purpose of this study was to examine the effect of occlusal reconstruction after long-term loss of molars on spatial memory by using 8-arm radial maze and by assessing histopathological changes of neuron density in the hippocampus. Experimental dentures were inserted into the oral cavities of molarless rats to recover the occlusal support. Age-matched groups of control, molarless and denture-wearing rats were trained to perform the maze tasks. The difference of the error incidence in the maze task was evaluated between three groups. The difference of neuron density between three groups was also evaluated at the end of the maze task. Serum corticosterone levels were also measured to estimate the chronic stress, which could be caused by extraction, insertion of the experimental denture or any experimental procedure. The error incidence in the denture-wearing group was significantly higher than that of the control group, but significantly lower than that of the molarless group. Significant differences of neuron density were observed between three groups in each of the hippocampal CA1, CA3 and DG subfields. No significant difference of the serum corticosterone levels between three groups could be observed. From the results of this study, it was suggested that the recovery of occlusal support would bring amelioration of cognitive impairment concomitant with long period loss of molars in rats.

Summary Recently, the swallowing sound has been used to detect swallowing events non-invasively. A previous study, using an accelerometer, showed that the site over the lateral border of the trachea immediately inferior to the cricoid cartilage was the optimal site for detecting swallowing sounds. However, the optimal site for detection of the swallowing sound using a microphone remains undetermined. To validate the optimal site in the neck region for detecting swallowing sounds. Fourteen healthy subjects (mean age, 27·6 ± 2·2 years; seven male and seven female) participated in this study. Twenty condenser microphones were attached to 20 sites on the left neck surface to detect swallowing sounds. Participants were instructed to swallow five different stimuli three times as follows: Resting saliva, 1 and 5 mL of Japanese tea, and 1 and 5 mL of yoghurt. Mean relative peak intensity was used to indicate the magnitude of the swallowing sound. Sound spectrograms were used to illustrate differences in the properties of swallowing sounds. Mean relative peak intensity number was highest in sites at the inferior border of the mandible just above the sternocleidomastoid muscle (site 11) and sites over the lateral border of the trachea immediately inferior to the cricoid cartilage (site 8). Comparison of spectrograms showed a greater density distribution of higher frequency components at site 11 compared with site 8. These results indicate that the inferior border of the mandible just above the sternocleidomastoid muscle is the optimal site for the detection of swallowing sounds.

Aims: To assess the influence of clenching side and location (ie, tooth) on the bite force necessary to induce pain or discomfort in patients with unilateral anterior disc displacement (ADD) of the temporomandibular joint (TMJ). Methods: A total of 17 patients with unilateral ADD diagnosed clinically and with magnetic resonance imaging were included. A bite force meter was positioned at each of four experimental positions: the mandibular first premolars and first molars, bilaterally. Subjects were instructed to clench on the bite force meter until they felt pain or discomfort in the orofacial area and to report the location of the pain. Differences in pain location (ADD side versus contralateral side) and in the bite force thresholds for eliciting pain or discomfort were assessed by means of the paired t test and Wilcoxon signed-rank test. Results: Only 18% of subjects (3 out of 17) reported pain in the TMJ with ADD during clenching at the ipsilateral molar, whereas 65% (11 out of 17) reported joint pain during clenching on the contralateral molar (P = .005). At the molars, the mean ± standard deviation bite force necessary to induce pain was 241.2 ± 135.5 N on the side with ADD and 160.9 ± 78.0 N on the contralateral side. The mean molar bite force necessary to induce pain on the side with ADD was significantly higher than that on the contralateral side (P = .002). Conclusion: Patients with unilateral ADD had fewer reports of TMJ pain and discomfort when they were molar clenching on the ipsilateral side compared to molar clenching on the contralateral side.

Summary The lifting-up movement of the posterior part of the tongue to touch the palate, which is a requirement for performing physiological functions such as deglutition and speech, is an important phenomenon that is difficult to objectively evaluate. The purpose of this study was to develop a new modality to evaluate the tongue-lifting function, especially in the posterior part of the tongue, and to elucidate the dynamic properties of the tongue in normal subjects. Twenty-three healthy volunteers (9 men and 14 women; mean age, 27·6 years) participated in this study. A new device was developed that could evaluate the up-down movement of the posterior part of the tongue in a non-invasive manner. The experimental tasks were as follows: (i) /a/ pronunciation for 1 s followed by /ka/ pronunciation (a-ka task), (ii) /a/ pronunciation for 1 s followed by /ga/ pronunciation (a-ga task) and (iii) /a/ pronunciation for 1 s followed by a voluntary push-up movement of the posterior part of the tongue (a-lift task). Maximum upward velocity in the a-ga task was larger than that in the a-ka task (P

The activity of the lateral pterygoid muscle has been regarded to be related to the pathological condition of the temporomandibular joint (TMJ) in the craniomandibular disorders. Because the lateral pterygoid muscle is a deep muscle, a needle electrode is necessary for EMG recordings. The purpose of this study was to establish a non-invasive method for the evaluation of muscle activity of the lateral pterygoid muscle using mechanomyogram (MMG). In three male subjects, surface electromyogram (EMG) in the left masseter muscle, left anterior and posterior belly of the temporal muscle, left anterior belly of the digastric muscle and needle EMG of the inferior head of the lateral pterygoid were recorded during mandibular movement tasks simultaneously with the MMG derived from a condenser microphone in the external ear canal. There were significant positive correlations between the needle EMG signal of the lateral pterygoid muscle and the MMG signal for the tasks of static jaw opened position of 30 mm of interincisal distance (p = 0.000, R(2)=0.725), static jaw opened position of 40 mm of interincisal distance (p = 0.000, R(2) = 0.753), 5 mm protruded mandibular position (p = 0.000, R(2) = 0.653), the most protruded mandibular position (p = 0.000, R(2) = 0803). On the contrary, for the task of maximal clenching, there was no significant correlation between the EMG signal of the lateral pterygoid muscle and the MMG signal. These results suggest that the activity of the lateral pterygoid muscle could be evaluated by the MMG signals recorded in the external ear canal, unless jaw closing major muscles show active contraction.

*Occlusion and Removable Prosthodontics, Okayama Univ. Hosp., 2-5-1 Shikata-cho, Okayama 700-8525, Japan E-mail: ykmar@md.okayama-u.ac.jp **Dept. of Biomaterials, Okayama Univ.Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8525, Japan ***Dept. of Occlusal and Oral Functional Rehabilitation, Okayama Univ.Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8525, Japan **** Leuven BIOMAT Research Cluster, Dept of Conservative Dentistry, Catholic Univ. of Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium

The purpose of this study was to reveal the relationship between chewing-side preference and anterior disc displacement (ADD) of the TMJ. Thirty-two healthy subjects with ages ranging from 26 to 34 years were selected from volunteer students at the Okayama University Dental School. Subjects were asked to chew freely with two kinds of test foods, beef jerky (hard food) and chiffon cake (soft food), thus expecting different amounts of mechanical loading on the TMJ. One, 4, and 7 s after starting the mastication, subjects were asked to open their mouth momentarily to have a digital image of their mouth taken. The bolus placement area was measured by processing the digital images, calculated as the number of pixel of bolus area. Area asymmetry index was used for the determination of preferred chewing side (PCS). Oblique sagittal MRI scanning in the closed mouth position was taken to evaluate the articular disc position. In asymptomatic subjects with ADD, a significant predominance of the PCS on the ipsilateral side of ADD was observed during the mastication of hard food. On the contrary, no correlation was found between unilateral ADD and PCS for the soft food. From the results of this study, it is suggested that ADD is the associating factor of PCS for hard food. Therefore, it would be necessary to break down the concept of PCS into at least two categories, one for hard food and one for soft food, considering the mechanical loading on the TMJ.

Although decayed/fractured teeth can be reconstructed minimally invasively and nearly invisibly using adhesive technology, the clinical longevity of dental composite restorations is still too short. Water sorption is thought to be the principal cause of destabilization of the biomaterial–tooth bond. However, the actual mechanisms of interfacial degradation are far from understood. Here we report how nano-controlled molecular interaction at the biomaterial–hard tissue interface can improve bond durability. The use of functional monomers with a strong chemical affinity for the calcium in hydroxyapatite is essential for long-term durability. Correlative X-ray diffraction and solid-state nuclear magnetic resonance disclosed a time-dependent molecular interaction at the interface with stable ionic bond formation of the monomer to hydroxyapatite competing in time with the deposition of less stable calcium phosphate salts. The advanced tooth–biomaterial interaction model gives not only an insight into the mechanisms of bond degradation, but also provides a basis to develop functional monomers for more durable tooth reconstruction.

目的：阪神・淡路大震災において被災者の一部は，地震による家屋の倒壊により避難時に義歯を放置・紛失するという状態に陥った．復興のさなか，簡便で効率的な義歯製作法が求められたので，われわれが阪神・淡路大震災において実施した大規模災害時における有床義歯製作の考え方とその製作方法について報告する．材料と方法：通法に従い口腔内のアルジネート印象を採得し，印象用石膏により製作した作業用模型上にて基礎床を作る．上顎 6前歯・下顎 6前歯が一塊となった人工歯と 4臼歯が一塊となったシェル臼歯を口腔内で基礎床と常温重合レジンにより位置決めし，両者の間隙に粉液比を低く低粘稠度に混和した常温重合レジンを流し込み研磨面形態を製作する．最後に粘膜面に暫間軟質裏装材を適応する．考察：本義歯製作方法は，審美性にやや劣り永続的使用に適さないという欠点を有する．しかし，通法と比較して大幅に作業時間が短縮し，復興後のかかりつけ歯科医のコンセプトに従った補綴装置の設計・製作を阻害しないという点を有しており，災害時の歯科救援活動に貢献するものと考える．結論：本義歯製作方法は，大規模災害時において簡便かつ効率的な義歯製作を可能とするものであり，半年程度で現地歯科医療機関の一次的な復興が望める被災地においては特に有効であると考えられる．

Experimental equipment for recording mandibular excursive position during nocturnal bruxism has been devised. The equipment consists of chromium-cobalt alloy cast frameworks for each upper and lower dental arch and two pairs of tiny magnetic sensors and magnets, capable of electromyographic (EMG) recordings of the bilateral masseter muscles and simultaneously recording mandibular position. The two subjects tested were confirmed to be bruxing during sleeping. Although EMG records for the two subjects showed a common EMG pattern as a bruxer, the sensor records revealed that one subject was a bilateral bruxer and the other bruxed almost unilaterally. The present study demonstrated that this newly devised equipment is practical for studying mandibular position during nocturnal bruxism.

Velopharyngeal incompetence (VPI) is a contributing factor to speech disorders, frequently accompanying disorders, such as cleft palate, congenital paralysis of the soft palate, and cerebrovascular disease. For the treatment of these types of dysarthria, a Nasal Speaking Valve (NSV), which regulates nasal emission utilizing one-way valve, has been reported to be effective. As the unpleasantness while wearing the NSV was less than that with the conventional Palatal Lift Prosthesis, the NSV could be worn for a longer period of time. As NSV is inserted into the nostrils, this device could easily be provided for edentulous patients. This study aimed to evaluate the effect of NSV on experimentally induced VPI condition. Intelligibility of monosyllabic speech, intelligibility of conversational speech, nasalance score and acoustic analysis were used to evaluate the effect of NSV. Local infiltration anaesthesia was achieved to the area of levator veli palatini muscle and tensor veli palatine muscle of seven adult male subjects. In all subjects, remarkable suppression of the soft palate movement could be observed after the local infiltration anesthesia. Although the utterance supported by NSV under the experimentally induced VPI condition was less natural than the normal utterance, the intelligibility was markedly improved by the device. From the results of this study, the acoustic properties of NSV on the pure VPI condition, which was enabled by the newly established experimental induction, were revealed. This experimental model was also proved to provide a basis for the improvement in the treatment modalities for VPI.

Summary Velopharyngeal incompetence is a contributing factor for speech disorders, and other frequently accompanying disorders, such as cleft palate, congenital paralysis of the soft palate and cerebrovascular disease. A palatal lift prosthesis (PLP) has been fabricated for managing velopharyngeal incompetence to improve speech. Because of discomfort, such as difficulty in swallowing or vomiting reflex, while wearing the PLP, rigorous adjustment is required. Patients may have difficulty becoming accustomed to using the prosthesis. This article reports on a newly developed device, the nasal speaking valve, for improving hypernasal speech caused by velopharyngeal incompetence.

Purpose The low masticatory efficiency of denture prostheses impairs the ability of wearers to consume high-fiber foods. Hence, artificial teeth with high masticatory efficiency are required. This study aimed to establish an occlusal surface design for posterior artificial teeth in denture prostheses that is compatible with the existing artificial teeth arrangement and that has high masticatory efficiency for the comminution of raw vegetables. Methods A masticatory simulator for occluding complete dentures was used to evaluate the masticatory efficiency of four occlusal surface designs, i.e., with parallel grooves occluding at right angles to the opposing teeth, groove depths of 1 and 0.5mm, and inter-groove distances of 1, 2, and 3mm. Raw carrots, rice, raw lettuce, chicken breasts, and peanuts were used as test foods to evaluate food comminution. Results Grooved occlusal surface designs with a 1-mm groove depth and a 2- or 3-mm inter-groove distance demonstrated significantly greater masticatory efficiency than the conventional occlusal form ( p Conclusions The superiority of grooved designs over the conventional design was particularly evident for lettuce and raw carrots in this study, both of which are considered difficult foods to chew with complete dentures.

This paper describes a closed, hollow obturator with a nondetachable screw cap to seal the access hole that also allows cleaning of the inside of the bulb. A small screw cap was fabricated from a cobalt-chromium alloy. This screw was screwed to the access hole prepared at the top of the hollow obturator and when removed allows the inside of the obturator to be cleaned through the access hole. At the end of the screw, a preformed cobalt-chromium wire was attached that works as the safety retention mechanism of the screw. This ensures the screw in not aspirated or swallowed if it becomes unscrewed and falls from the prosthesis during wear in the patient's mouth. This device enables the patient to clean the inside of the closed obturator at home.

This study aimed to reveal whether masseter muscle activity during sleep is affected by the difference in design of non-occlusal intraoral appliances on hard palate. Eight healthy Japanese participants were selected and wore each of the four types of appliances (horse shoe, thin, thick and medium thick) during sleep for one week with a one week interval without appliance during sleep. A masseter muscle electromyograph (EMG) was recorded during sleep. The EMG activities were analyzed by calculating the number of bursts per hour, episodes per hour, and bursts per episode. The EMG parameters with the thick type appliance were significantly lower than the baseline condition without appliance. In this study, it is suggested that a thick type appliance has an active effect on suppression of masseter muscle activity.

Despite progress in the development of denture base resin and artificial tooth materials, dental clinics are still plagued with artificial teeth falling off the denture base--due to poor bond strength--after denture delivery. Against this background, this study sought to examine the effect and durability of an adhesive primer developed exclusively for heat-curing resin on the adhesive strength of heat-curing denture base acrylic resin to plastic artificial tooth. Test specimens were divided into four groups according to the treatment method of the artificial tooth's test bonding surface: air abrasion, adhesive primer application, adhesive primer application after air abrasion, and pretreatment only (control). After heat curing of acrylic resin onto the bonding surface, shear test was performed for two storage periods: 24-hour versus 100-day water storage. From the results obtained, it was revealed that the evaluated adhesive primer was significantly effective in increasing adhesive strength between artificial tooth and acrylic resin, although specimens were stored in water for 100 days.

Objectives: This study aimed to establish a reliable method for detecting the threshold for perception of force applied to tooth and to report the basic properties of force threshold in the normal dentition subjects. Background: The perception of mechanical stimulation exerted to tooth is formed by input from periodontal ligament mechanoreceptors and intradental mechanoreceptors. Periodontal ligament mechanoreceptors respond to a wide range speed of stimulus, whereas intradental mechanoreceptors are activated only by a rapid stimulation. Reliable properties of perception have not been reported because of the difficulties to regulate velocity and degree of the stimulus. Methods: Eighteen healthy subjects were observed in this study (mean age: 27.2 ± 5.7 years). A loading device to generate slow speed loading was fabricated and measured as follows: (i) the fluctuation of the force threshold within a day, (ii) day-to-day fluctuation, (iii) changes in the force threshold by a transient mechanical loading. Results: In the normal dentition, it was observed that the fluctuation within a day and day to day of the pressure sense showed no significant differences; however, a transient mechanical loading caused the sensitivity of the periodontal ligament to decrease significantly. Conclusions: The device examining the force threshold resulted from periodontal ligament mechanoreceptors was useful in evaluating the sensitivity of the periodontal ligament.

summary To improve the quality of the complete denture prosthesis, the bucco-lingual position of the artificial posterior teeth must be determined with consideration of the shape of the maxillary and mandibular residual ridge and the relationship between them. The arrangement of posterior artificial teeth should be considered not only for the denture stability but also for the avoidance of high pressure on the supporting structures. A two-dimensional finite element method program to investigate the statics for the contour of the complete denture and the residual ridge was developed. With this program, the effect of the bucco-lingual position of the artificial posterior teeth under occlusal force on the denture supporting bone could be investigated.

OBJECTIVES: To investigate the correlations among various temporomandibular joint (TMJ) findings on MRI and the relationships between MRI findings and symptoms. METHODS: 425 patients (850 TMJs) with temporomandibular joint disorders (TMDs) who underwent MRI were enrolled. Oblique sagittal proton density-weighted and T (2) weighted images in open- and closed-mouth positions were evaluated. MRI findings included disc configuration, disc position, condylar morphology, bone marrow pattern, and joint effusion. Symptoms included TMJ pain, TMJ noise, and limitation of mouth opening. For statistical analyses, Spearman's rank correlation coefficient and logistic regression analysis were applied. RESULTS: Folded disc, disc displacement without reduction (DDWOR), and osteophytes had significant negative correlations with other normal MRI findings (p < 0.01). DDWOR and marrow edema were associated with TMJ pain. Conversely, osteophytes [odds ratio (OR): 0.52; 95% CI (0.30–0.90)] and combination-type condylar degeneration [OR: 0.45; 95% CI (0.24–0.83)] were associated with decreased risk of TMJ pain. Condylar flattening was positively associated with TMJ noise [OR: 5.25; 95% CI (1.44–19.07)] and negatively associated with limitation of mouth opening [OR: 0.34; 95% CI (0.11–0.99)]. High-grade joint effusion was significantly associated with TMJ pain and noise. CONCLUSIONS: DDWOR and high-grade joint effusion (an indicator of inflammation in the articular cavity) were associated with TMD symptoms. This finding suggests that treatment strategy for DDWOR and decreasing inflammation might lessen clinical TMD symptoms. Condylar degeneration was not associated with indicators of inflammation or TMJ symptoms. These results suggest that patients with TMD symptoms should undergo initial MRI to allow rapid selection of appropriate therapies.

summary The purpose of this study was to evaluate the relationship between balancing-side occlusal contact patterns and the prevalence of the internal derangement of the temporomandibular joint (TMJ). Forty-one patients were used for the magnetic resonance image (MRI) analysis of TMJ and occlusal examination. Balancing-side occlusal contact patterns observed during mandibular lateral excursive movements were classified into the three following categories: group A, simultaneous balancing-side contact, group B, balancing-side contact (with clenching only) and Group C, no balancing-side contact (with or without clenching). By the occlusal examination of 57 sides, 31·6% showed group A, 8·8% showed group B and 59·6% showed group C contact. Group A could not be observed in the patient group with normal disc position. In the disc displacement group, the prevalence of group A, group B and group C were 40·9, 6·8 and 52·3%, respectively. The higher prevalence of simultaneous balancing-side contact was revealed to be associated with articular disc dislocation.

In this study, the experimental denture base on the hard palate of the molar region of osteoporotic rats was designed to cover without any mechanical pressure or to load continuous pressure (0.5, 1.5 or 3.4 kPa). Experimental osteoporosis was induced by ovariectomy and feeding on a low calcium diet. Histopathological changes induced by non-pressure covering or continuous pressure in the tissues under the experimental denture bases were examined. Regarding the histological changes induced by continuous pressure, this was evaluated in relation to the time course of the intensity of the continuous pressure. In the tissues under the denture base in osteoporotic condition with non-pressure covering, no histopathological changes caused by non-pressure covering were observed except for a transient slight proliferative reaction in the epithelial ridge. The following histopathological changes were observed in the tissues under the denture base in the osteoporotic condition bearing continuous pressure; (i) bone resorption was induced on the periosteal surface (Ps) in the osteoporotic-3.4 kPa group, and on the pressure side of the endocortical surface (p-Ec) in the osteoporotic-1.5 and -3.4 kPa group, (ii) the appearance of osteoclasts on the p-Ec in the osteoporotic-3.4 kPa group was earlier than that on the Ps in a same group, (iii) bone resorption on the pressure side of the Ec in the osteoporotic-3.4 kPa group manifested at the earlier stage than that in the osteoporotic-1.5 kPa group, (iv) bone formation following bone resorption on the p-Ec was observed more markedly than that on the Ps and (v) histopathological changes in the tissues under the denture base in experimental osteoporosis bearing continuous pressure had an intimate relationship with the initial intensity and the time course of continuous pressure.

Summary Aim of this study was to quantitatively evaluate the adaptation of the denture base to the mucosa using a non-setting pressure-indicating paste and to examine the relationship between quality of fit and the need for denture relining. A total of 123 dentures from 70 partially edentulous patients were studied. Examination paste extruded from the tip of the 18-G needle was applied to those denture surfaces contacting the alveolar crest. The denture was manually positioned with all clasps engaged on abutment teeth, and adaptation was assessed through paste distribution. Multiple logistic regression was used to analyse variables associated with diagnosing the need for a denture reline, producing odds ratios and 95% confidence intervals. The spread width was inversely proportional to the gap between the denture and mucosa. Regression analysis revealed statistically significant associations between the need for a denture reline and both the paste spread width and the duration of denture use. According to ROC curve analysis of the ‘reline’ and ‘non-reline’ groups, the need for a denture reline was indicated at a paste spread width of 2·0 mm or less. At this 2·0-mm threshold, the sensitivity was 85·1% and the specificity was 75·0%. The fit of removable denture bases was quantitatively evaluated by measuring the spread width of non-setting pressure-indicating paste extruded onto denture fit surfaces. The results suggest that the paste spread width is a useful parameter for discriminating the need for a denture reline.

Summary One obstacle to placing artificial posterior teeth in manufacturing complete dentures is a reduction of the space between the maxilla and the mandible. Occasionally, second molar placement is not performed, as it does not affect aesthetics, phonetics or comfort. The aim of this study was to compare the masticatory efficiency between patients wearing maxillary and mandibular complete dentures with reduced dental arches (without second molars) (WSM) and with full dental arches (FDA). Twenty subjects were divided into two groups and randomly received new complete dentures. Patients in Group 1 were given dentures WSM, and those in Group 2 were given dentures with FDA. After the post-placement visits, an initial masticatory efficiency test was performed with Optocal, an artificial test food. Fifteen days later, second molars were placed in Group 1 and removed from Group 2, and a new test was performed. Comminuted material was treated and sieved under vibration. The mean and standard deviation of masticatory efficiency with FDA were 10·4 and 8·1, respectively. In the tests WSM, the mean and standard deviation were 8·4 and 3·3, respectively. After removing the second molars in Group 2 and adding them in Group 1, the mean and standard deviation were 15·7 and 14·7 for Group 1 and 12·5 and 10·4 for Group 2, respectively. Within the limitations of this study, placing artificial teeth up to the first molars can be performed when needed without compromising masticatory efficiency.

Several treatment modalities for myofascial pain dysfunction syndrome (MPD) are being used at present. However, from the standpoint of patients' quality of life, it would be reasonable to seek a more effective treatment modality. This study aimed to show clinical data of a preliminary study regarding the effect of a thick palatal appliance, designed to fill the palatal concavity with a thick resin base, on muscular symptoms in eighteen MPD patients. Shown here are the clinical results of two volunteer patients using palatal appliances of two different thicknesses. In this study, MPD patients were divided into the three following groups: 1. no-treatment group; 2. thick palatal appliance group; and 3. medication group. Based on the results of this study, it was suggested that the thick palatal appliance could bring about early improvement of MPD syndrome. It is suggested that the thickness of the palatal plate was an important factor in obtaining the clinical effect.

The purpose of this study was to evaluate changes in the argyrophilic nucleolar organizer region (AgNOR) counts in mucosal epithelium induced by continuous or intermittent compressive pressure exerted through experimental denture bases and to examine the relationships between the AgNOR count, histopathological changes and the intensity of the pressure under denture bases. Continuous or intermittent compressive pressure exerted through the denture bases was applied to the hard palate of the molar region in rats. A morphometric analysis of AgNORs was performed in denture-supporting tissue 3 days and 1, 2, 4, 8, 12 and 20 weeks after the denture insertion. From the results of this study, it was found that non-pressure contact of the denture bases with palatal tissues did not change the AgNOR count. The AgNOR count was decreased by continuous or intermittent compressive pressure, and then recovered to almost the same level as with the non-pressure contact at 20 weeks following a decrease of the pressure. The AgNOR counts in the epithelium under the denture bases were revealed to be related to the histopathological changes in the denture-supporting tissues and the intensity of the pressure under the denture bases.

Statement of problem. Special technical skills and experiences are required to fabricate a telescopic crown to provide adequate retention with precise frictional retention ("conus friction force") between coping and telescope. It is also difficult to control clinically alterations of retentive forces after prolonged usage. Purpose. This study examined an innovative telescopic crown system for removable partial dentures that can be fabricated without special technical skill or experience and readily adjusted retentive forces. The retention of telescopic crowns was investigated after repeated insertion/separation tests. Material and methods. Ten telescopic crowns were constructed to evaluate retentive forces. Each telescopic crown was adjusted to provide a retentive force of approximately 9.8 N. Each telescopic crown was then subjected to 10,000 insertion/separation cycles, and retentive force of each telescopic crown was recorded initially and after every 1,000 cycles. The retentive force of each telescopic crown was re-adjusted after these measurements to provide a retentive force of approximately 9.8 N. The retentive force was recorded a second time after each 1,000 insertion/separation cycles up to 10,000 cycles. Results. Retention of the telescopic crowns gradually diminished, depending on the number of insertion/separation cycles. The mean retentive force after 10,000 insertion/separation cycles was over 2 N. All 10 telescopic crowns were re-adjusted to exert a retentive force of 9.8 N after the initial 10,000 cycles, and the retentive force also diminished on the second 10,000 cycles. Conclusions. Reduction of retention was dependent on insertion/separation cycles. This new telescopic crown with reduced retention could be easily readjusted. Readjusted retentive forces were at least equivalent to the initial retention. (J Prosthet Dent 1999;81:684-8.)

The purpose of this study was to investigate whether the area and weight of removable dentures could influence patients' satisfaction with their dentures. The weight and area (projected area on occlusal plane) of 37 maxillary removable resin-based dentures fabricated in Okayama University Hospital were measured. Full consent from all of the denture users examined in this study was obtained prior to the test. Examination of the visual analogue scale (VAS) for denture satisfaction (0-100%) was performed for 13 users of these dentures. Statistical correlation between the denture areas and the number of missing teeth, and between denture weights and the number of missing teeth was examined. Statistical correlation between the VAS satisfaction level for dentures and the area⁄number of missing teeth, and between the VAS satisfaction level for dentures and the weight⁄number of missing teeth was also examined. A positive correlation was observed between the area of the denture base and the number of missing teeth (r = 0.854, p

One of the prominent roles of the occlusion would be to support the force balance wobbling in stomatognathic system, thus pacing and minimizing the change of force distribution with age. Patient's demands on the prosthetic treatment have been becoming higher and more complicated during the past several decades. These demands include not only the precise restoration of the decayed tooth but also the treatment to provide stable and comfortable state of the stomatognathic system in the longer term. These demands would deeply be related to ; 1) How to finalize the information on temporary or treatment prosthesis, which has the resulted shape of the precise functional adjustment, on the final prosthesis, and 2) How to cope with the persistent complaints regarding tooth, tongue and other related sensations. In these aspects, patient's subjectivity and/or esthesis might need to be satisfied with the form and/or function of the resulted prosthesis. The clinical difficulties might be related to the following two points, which are 1) the accuracy of the reproduction procedure from the treatment prosthesis to the final one and 2) stability of the mandibular position or the condylar position which support the functional basis for the prosthesis. In order to cope with the complicated requirements, we have been using double-casting method for providing cast restorations. This is a method to produce a cast restoration in two functional parts. The first casting step consists of a base-crown which covers the abutment tooth and adjacent proximal contact point(s). The second step is the molding of the functionally required occlusal form onto the base-crown. The third step is the metal casting onto the base-crown replacing the molded portion. This method could be applied in various situations where we are forced to match the function and the form. The purpose of this paper is to provide a good orientation to the double-casting method and also to discuss the concept that might pace and minimize the change of force distribution in stomatognathic system.