The greatest known risk factor for Alzheimer's disease (AD) is aging. Since AD is a progressive neurodegenerative brain disease, the altered cognitive symptoms in the very early stage of AD involve mild learning, memory or planning problems. Eventually, AD patients will lose their ability to carry out the simplest tasks of daily living when in the later severe stage. Currently, no medical tests are available to diagnose AD conclusively pre-mortem. A large number of studies convincingly demonstrate that the cognitive deficits of AD are possible to detect during a preclinical period spanning several years. In this review, we focus on the early detection of AD with combined psychological and neuropsychological approaches such as functional magnetic resonance imaging (fMRI) and Electroencephalogram (EEG).

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Although mastication has long been studied in the field of dentistry, it was reported that only few dentists play a part of decision making in food preparation level for elderly people in nursing home. Needless to say, serving denture prosthesis to a patient might not result in the improvement of his/her food intake level. For this purpose, the masticatory efficiency would be needed to be evaluated using daily consumption natural food to provide a medical background to decide the food preparation level. This review highlights issues identified in the literature to date that influence the property of the evaluation methods for masticatory efficiency. Knowledge gaps and considerations that need to be taken into account when conducting research are discussed.

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The purpose of this study was to investigate the usefulness of a newly developed small and lightweight mandibular movement recording device by two experiments. Experiment I: Triangles consisting of 3 LEDs (Light-emitting diode) were attached to the upper and lower frames of the articulator in parallel with the frontal plane. Subsequently, the upper frame was rotated on the sagittal plane and the position coordinates of each LED were recorded by a newly developed mandibular movement recording device (Device A). Then, the movement of the center of gravity of the triangle was observed. Experiment II: Ten healthy subjects in their 20s were asked to chew gum on their habitual chewing side and the mandibular movements were recorded simultaneously using Device A and TRIMET^® (Tokyo Shizaisha, Device B). The path of each of 10 cycles beginning from the 5th cycle, their superposition, and the average path were displayed and observed. Subsequently, the amount of vertical movement and masticatory width were calculated from the average path and compared between the two devices. It was confirmed that the center of gravity of the triangle attached to the upper frame of the articulator describes a true arc around the intercondylar axis. In addition, it was also confirmed that the masticatory path recorded by Device A was similar to that recorded by Device B in all subjects. Furthermore, the amount of vertical movement and masticatory width calculated using Device A were similar to those calculated using Device B, with no significant differences in the results between the two devices. These findings confirmed that the newly developed three-dimensional mandibular movement recording device can record and analyze masticatory movements as efficiently as the TRIMET^®, a highly accurate mandibular movement recording device, and suggested that it is also clinically applicable.

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To clarify the accuracy of a portable electromyogram (EMG) device, simultaneous recordings of the EMG during sleep detected via polysomnography (PSG) with sampling rate of 1000 Hz and the portable EMG device with 16 Hz were determined in three male subjects (22.7 ± 0.6 years old) having sleep bruxism referral.
 Under the event of EMG recorded from the PSG was set as a gold standard, the detected rate from the portable EMG device for a tonic, a phasic and a mixed type were 94.1, 80.0 and 83.3 %, respectively. From the results above, it is fair to say that 16 Hz sampling rate showed good enough for the tonic event detection, however it would be better for the phasic and mixed events to increase higher rate of data sampling.

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