Katsushi Tamaki

Clinical application of removable partial dentures using thermoplastic resin. Part II: Material properties and clinical features of non-metal clasp dentures

This position paper reviews physical and mechanical properties of thermoplastic resin used for non-metal clasp dentures, and describes feature of each thermoplastic resin in clinical application of non-metal clasp dentures and complications based on clinical experience of expert panels. Since products of thermoplastic resin have great variability in physical and mechanical properties, clinicians should utilize them with careful consideration of the specific properties of each product. In general, thermoplastic resin has lower color-stability and higher risk for fracture than polymethyl methacrylate. Additionally, the surface of thermoplastic resin becomes roughened more easily than polymethyl methacrylate. Studies related to material properties of thermoplastic resin, treatment efficacy and follow-up are insufficient to provide definitive conclusions at this time. Therefore, this position paper should be revised based on future studies and a clinical guideline should be provided.

Identification of the occurrence and pattern of masseter muscle activities during sleep using EMG and accelerometer systems

BackgroundSleep bruxism has been described as a combination of different orofacial motor activities that include grinding, clenching and tapping, although accurate distribution of the activities still remains to be clarified.MethodsWe developed a new system for analyzing sleep bruxism to examine the muscle activities and mandibular movement patterns during sleep bruxism. The system consisted of a 2-axis accelerometer, electroencephalography and electromyography. Nineteen healthy volunteers were recruited and screened to evaluate sleep bruxism in the sleep laboratory.ResultsThe new system could easily distinguish the different patterns of bruxism movement of the mandible and the body movement. Results showed that grinding (59.5%) was most common, followed by clenching (35.6%) based on relative activity to maximum voluntary contraction (%MVC), whereas tapping was only (4.9%).ConclusionIt was concluded that the tapping, clenching, and grinding movement of the mandible could be effectively differentiated by the new system and sleep bruxism was predominantly perceived as clenching and grinding, which varied between individuals.

Detecting mental disorders in dental patients with occlusion-related problems

Abstract  Dentists often treat patients who may be suffering from comorbid mental disorders without paying attention to their symptoms. This leads to a delay in starting the treatment of mental disorders and to inappropriate dental treatments for physical symptoms originating from mental disorders. In the present study, the ways in which dentists can easily detect mental disorders in dental patients with occlusion‐related problems were examined. Fifty‐three patients who visited the Occlusion Clinic of Kanagawa Dental College were interviewed by a psychiatrist and a dentist specialized in psychosomatic medicine. Thirty‐five patients (66.0%) were diagnosed as having DSM‐IV Axis I disorders. The demographic and psychological factors that correlate with the presence of mental disorders are duration of chief complaint, number of clinics and hospitals visited for the current symptom, total score of the General Health Questionnaire (GHQ), the scores of the anxiety and insomnia and social dysfunction subscales in the GHQ and the scores of the confusion–bewilderment and fatigue–inertia subscales in the Profile of Mood States (POMS). A logistic regression analysis indicated that number of clinics and hospitals visited markedly correlated with cormobidity of a mental disorder. This information may be useful for screening mental disorder patients. Dental patients having comorbid mental disorders should be treated both odontologically and psychologically.

Asymmetry of masticatory muscle activity during the closing phase of mastication.

ABSTRACT The purpose of this study was to investigate the asymmetry of masticatory muscle activity between working and nonworking sides in the closing phase during mastication. Fifty adult subjects displaying normal oral function and occlusion participated in this study. Electromyographic (EMG) activity of the anterior temporalis and the superficial masseter muscle were recorded during mastication, simultaneously with motion data of the mandible. EMG activities of elevator muscles and their Asymmetry Index (AI) were analyzed depending on the vertical deviation of the lower incisal point with a two mm gap from the intercuspal position (ICP). EMG activities of both the anterior temporalis and the masseter on the working side were significantly greater than those on the nonworking side. Masseter muscles tended to show greater AI than the anterior temporalis muscles. Thus, asymmetry of the elevator muscles during mastication was a common finding in normal subjects. The normal range of variability of EMG activity and AI was confirmed in each section.

Diagnosis of occlusal dysesthesia utilizing prefrontal hemodynamic activity with slight occlusal interference

Clinical diagnosis of occlusal dysesthesia (OD), also referred to as phantom bite syndrome, is currently based on the absence of objective occlusal discrepancy despite the persistent complaint of uncomfortable bite sensation. We previously demonstrated that the subjective feeling of occlusal discomfort generated by artificial occlusal interference can be objectively evaluated using prefrontal hemodynamic activity in young healthy individuals. The aim of this study was to investigate whether dental patients with and without OD show distinct prefrontal activity during grinding behavior with an occlusal interference. Six dental patients with OD (OD group) and eight patients without OD (control group) grinded piled occlusal strips placed between their first molars and reported their perception and discomfort thresholds during continuous monitoring of prefrontal hemodynamic activity with a portable functional near‐infrared spectroscopy. Although patients without OD showed the typical hemodynamic pattern of increased oxyhemoglobin and reduced deoxyhemoglobin (HHb) concentration, those with OD showed persistent incremental increases of HHb concentration that began at the loading of occlusal strips on their molars before they executed grinding. The intensities of the task‐related HHb activities showed statistically significant differences between OD and control groups, particularly at channel 3, arranged over the left frontal pole cortex. When the discrimination criterion was set using the intensity values of channel 3 from both groups, the overall accuracy of the OD discrimination was 92.9%. Although physiological interpretation has yet to be elucidated, the task‐related response of an increase in HHb may be a useful neuronal signature to characterize dental patients with OD.

Prefrontal Hemodynamic Changes Associated with Subjective Sense of Occlusal Discomfort

We used functional near-infrared spectroscopy to measure prefrontal brain activity accompanying the physical sensation of oral discomfort that arose when healthy young-adult volunteers performed a grinding motion with mild occlusal elevation (96 μm). We simultaneously evaluated various forms of occlusal discomfort using the visual analogue scale (VAS) and hemodynamic responses to identify the specific prefrontal activity that occurs with increased occlusal discomfort. The Oxy-Hb responses of selected channels in the bilateral frontopolar and dorsolateral prefrontal cortices increased in participants who reported increased severity of occlusal discomfort, while they decreased in those who reported no change or decreased occlusal discomfort during grinding. Moreover, the cumulative values of Oxy-Hb response in some of these channels were statistically significant predictive factors for the VAS scores. A generalized linear model analysis of Oxy-Hb signals in a group of participants who reported increased discomfort further indicated significant cerebral activation in the right frontopolar and dorsolateral prefrontal cortices that overlapped with the results of correlation analyses. Our results suggest that the increased hemodynamic responses in the prefrontal area reflect the top-down control of attention and/or self-regulation against the uncomfortable somatosensory input, which could be a possible marker to detect the subjective sense of occlusal discomfort.

Development of chair-side evaluation system of swallowing discomfort of denture wearers

We investigated the appropriate hemodynamic parameters of functional near-infrared spectroscopy (fNIRS) to best differentiate the discomfort intensity related to swallowing in healthy subjects wearing different types of simulated dentures. Thirty-one subjects performed 4 sessions of water-swallowing task in a sitting position without or with wearing any one of the 3 simulated dentures under continuous fNIRS monitoring of the prefrontal cortex. The simulated dentures were consisted of a flat maxillary palatal bar and bilateral support attachment to the teeth and gum. The palatal bar positions were arranged along with the anterior, middle, or posterior areas of the upper jaw. The cumulative values of oxyhemoglobin and deoxyhemoglobin concentration changes were calculated for periods of 5 - 10 s from completion of swallowing. Subjective rating of swallowing-discomfort was the lowest without wearing denture and increased along with the palatal bar position placed from anterior to posterior. Cumulated deoxyhemoglobin signals calculated for 10 s post-swallowing event in the left frontopolar prefrontal cortex showed the best correlation with the subjective rating of discomfort in swallowing with dentures. These neurological signatures would be beneficial to detect swallowing discomfort in elderly denture wearers who have difficulty in communicating with dentists.

Occlusal Dysesthesia: A Clinical Report on the Psychosomatic Management of a Japanese Patient Cohort.

PURPOSE A cohort of Japanese patients diagnosed with occlusal dysesthesia (OD) was clinically analyzed for psychosomatic background, management, and treatment outcome. MATERIALS AND METHODS The study group comprised 61 patients (17 men and 44 women) who met the OD criteria. Treatment outcomes were categorized as improvement, interruption, and transfer to another department. RESULTS The diagnosed OD was resolved in 25 patients (41%), 20 patients (33%) discontinued treatment, 13 (21%) were referred or transferred to other specialties such as psychiatry, and 3 (5%) continued to receive treatment following an engagement period of 3 months, 2 years, and 5 years, respectively. Among the 20 patients who discontinued treatment, complaints persisted for 10 and they did not comply with treatment, 1 had immodithymia characterized by adherence to symptoms, 3 had depressive states, 2 were suspected to have schizophrenia, and 2 were suspected to have so-called phantom bite syndrome. CONCLUSION This study suggests that OD treatment should take into account the underlying psychiatric disorder manifesting as physical complaints.