We succeeded in making comparatively simple and cheap masticatory movement observation equipment of connecting a small 2 axis acceleration sensor to a personal computer through a general-purpose interface, without special equipment.
Since only one sensor is attached to the chin and X-Y 2 axis data is obtained simultaneously, this device can record masticatory movement by detecting changes in 2-dimensional acceleration.
Using this equipment two subjects with natural dentition and two subjects with full dentures were examined. Chewing gum mastication was recorded for about 10 seconds, and observation of the 2 dimension-original wave form of the mastication movement locus, frequency component analysis by FFT, and chaos analysis were tried. We had a purpose of examining the possibility of clinical application by this system.
Consequently, according to the acceleration movement graph, natural dentition subjects had a small amplitude, whereas complete denture wearers had a wide amplitude. Moreover, when the FFT frequency analyses were compared, the complete denture wearers had movement with a regular frequency component, and had a steady wave form. The natural dentition subjects did not have a regular frequency component, and did not show any special tendency.
Also in chaos analysis, the complete denture wearers were unstable and there was little complexity. Especially, on the vertical axis of complete denture wearers, although the jaw was moved greatly, when seen from the viewpoint of complexity, the movement was simple. Conversely, the natural dentition subjects moved their teeth horizontally during masticatory movement, and had gentle motion and with free complexity in the after bite.
As mentioned above, this equipment allowed us to observe mastication movement clinical by in spite its comparative simplicity.

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The effect of impression taking on the respiratory function and hemodynamics of the bed-bound elderly was investigated by using two types of impression materials.
The subjects were 20 patients at the Tanpopo Dental Clinic in Katsushika-ward, Tokyo who required edentulous jaw impression taking. These patients were randomly divided into two groups as follows based on the types of impression material used:
Group 1: used alginate impression material
Group 2: used silicone rubber impression material
The measurement parameters were ETCO₂, RR, SpO₂, HR and BP.
We measured at different times during resting, impression taking of upper jaw, impression taking of lower jaw, and after the impression taking.
The results were as follows. There was a difference in impression taking time between the two groups. We found a significant increase of ETCO₂ in Group 2 during upper jaw impression taking (41.9±2.1mmHg) compared with 35.4±3.7mmHg during resting. Six cases in Group 1 and nine cases in Group 2 showed more than 10% fluctuation, while all of these cases were observed during upper jaw impression taking. We found that RR in Group 2 significantly decreased during upper jaw impres-sion taking (16.7±3.2times/minute) compared with 21.8±1.7times/minute during resting. Nine cases in Group 1 and all the cases in Group 2 showed more than 10% fluctuation, while all of these cases were observed during upper jaw impression taking. SpO₂ in Group 2 decreased significantly during upper jaw impression taking (95.6±2.0%) as well as lower jaw (97.0±1.3%) rather than while resting (99.0±0.9%). No particular change was found with regard to HR or BP.
Considering these results, we assume that when impression taking of the upper jaw rather than the lower jaw is performed, and if the duration of impression taking is long, it will induce a decrease in RR, and an increase in ETCO₂ due to suspension of respiration, which might result in decrease of SpO₂.
Therefore, we conclude from this study that when performing impression taking for bed-bound elderly, it is advisable to reduce the duration of impression taking especially on the upper jaw and to monitoring the patient's whole bodily system including the respiration status.

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Purpose: Recently, there has been a resurgence of interest in the interactions between oral conditions and a number of prevalent systemic diseases The purpose of this study was to assess the existence of oral infectious pathogens potentially causing respiratory disease, endocarditis and opportunistic infectious disease in the dependent elderly, with specific attention to plaque present on denture and pharyngeal mucosal surfaces. The additional purpose was to investigate the relationship between the colonies on dentures and on pharyngeal mucosa.
Materials and methods: Both the denture and the pharyngeal bacterial flora of 20 dependent elderly were examined to identify microorganisms by the culture method.
Results: A variety of pathogens potetially causing respiratory, endocardiac and opportunistic infections colonized the oral cavities both on the denture and pharyngeal mucosa of dependent elderly. The ratio of colonies on dentures and on the pharyngeal mucosa was 70.6%.
Discussion: The results of the present study revealed that bacteria that commonly cause respiratory, endocardiac and opportunistic infection colonized on the dentures as well as on the pharyngeal mucosa of dependent elderly, suggesting that denture plaque may function as a reservoir of these organisms to facilitate colonization on the oropharynx.

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In order to elucidate the influence of tooth loss and concomitant masticatory alterations on learning memory in rats, male Wistar rats (25 weeks old) were divided into three groups: a control group (fed with a solid diet); a soft diet group (fed with a powder diet containing the same components as the solid one) and a molar crown-less group (all molars were removed at 25 weeks and then the rats were fed with a powder diet). At 40-weeks, the passive avoidance test using a one-way step through type of apparatus divided into light and dark chambers, the determination of dopamine (DA) concentration of the cerebral cortex, and the measurement of the number of DA-positive neurons in the nucleus of the ventral tegmental area (VTA) were performed. The results obtained were as follows.
1) At day 4 and 7 after the acquisition trials, the response latency of the molar crown-less group was significantly shorter than that in the control group (p<0.05).
2) The DA levels of the molar crown-less group and soft diet group in the cerebral cortex was significantly lower than those of the control group (p<0.05).
3) The number of DA-positive neurons in the nucleus of the VTA of the molar crown-less group was significantly smaller than those of the control group (p<0.05).
These results suggest that a decrease of oral sensory information or concomitant masticatory alterations caused a reduction in the number of DA-positive neurons in the nucleus of the VTA, which in turn caused a transient decline of DA concentrations in the cerebral cortex, resulting in a learning memory disorder in rats.

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In order to evaluate the appropriate management of patients whose treatment with complete upper and lower dentures had been completed, the Department of Prosthodontics of Tokyo Dental College, Chiba Hospital, designed a survey to evaluate all the patients who received complete denture treatment between 1990-1997, but were absent from examination for more than two years, in order to establish their actual condition. The samples of patients chosen for this study consisted of 136 complete edentulous persons (56 males and 80 females, from 50 to 92 years of age, mean age: 75 years). All these patients were contacted by phone to ask them to attend the dental clinic and also to answer the questionnaire. In those patients who were able to attend the dental clinic, not only an intraoral exami-nation, but also an evaluation of their dentures were performed.
We successfully contacted 76 out of 136 patients (55.8%), 60 out of 76 patients answered the questionnaire (78.9%), and 15 out of 136 patients attended the clinical examination (11.0%).
From the 57 patients who satisfactorily answered the questionnaire, 49 patients were actually wearing dentures made by dentists from this department (85.9%), and of these 49, 6 were using some kind of denture adhesive. From the group of patients who were not using any denture adhesive (43 patients) 22 were conscious of the need to attend the recall dental exemination (51.2%).
In the 15 patients who attend the clinical examination, evaluation of the complete dentures was performed by the operator and the results were compared to patients' evaluation of their own dentures in order to establish a possible correlation. As a result, except for denture's retention, there were no correlations between the two sets of evaluation results (the one made by the dentist and the one made by the patient). Thus, we concluded that regarding denture retention, the patients' subjective evaluation is not precise enough to be reliable.
On the basis of these results we concluded that the patients' evaluation of their own dentures was not precise. Moreover some physical impediments, as well as difficult transportation to the hospital were mentioned as the reason for the absence from clinical examination. In order to properly deal with patients who have received complete dentures as prosthodontics treatment, we suggest the importance not only of an adequate patient education but also of the cooperation between hospitals and private dental offices and finally of dental treatment at home when necessary.

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Purpose: Recently, it has become clear that loss of teeth is one of the causes of learning and memory ability impairment. On the other hand, learning and memory ability impairment occurs spontaneously with aging. However, little consideration has so far been given to the impairment of learning and memory ability due to the effect of loss of teeth, aging, or both of them in human beings. In this study, we consider the effect of age-related changes in learning and memory ability, the effect of molar teeth loss and longitudinal molarless condition on learning and memory ability using SAMP 8//Ymi (Senescence-Accelerated Mouse P 8//Ymi).
Methods: SAMP 8//Ymi shows that the age-accelerated characteristic in a short life span and median survival time is 12 months. In addition, age-related deterioration of learning and memory has been demonstrated. 60 Male SAMP 8//Ymi aged 2 months were divided into 6 groups. Each of the three control groups of 10 mice was kept until 3 (young adult), 5 (middle age), 8 (old age) months of age (normal condition). The remaining three groups of 10 mice each had their maxillary molar teeth extracted and were kept until 3, 5, 8 months of age (molarless condition). For the behavioral study, a passive avoidance test of the step-through type was adopted. The two-compartment stepthrough passive avoidance apparatus consisted of an illuminated chamber and a dark chamber. The two chambers were separated by a guillotine door and the dark chamber had a grid floor. In an acquisition trial, the mouse was placed in the illuminated chamber and the time before it entered the dark chamber was recorded. As soon as the mouse entered the dark chamber, the door was closed and an AC 0.3mA scrambled footshock was applied to the floor grid for 3 seconds. A Retention test was carried out by replacing the mouse in the illuminated chamber 24 hours after the acquisition trial, and the latency to enter the dark chamber was measured. The learning and memory ability were evaluated on the basis of the latency time.
The degree of senescence was evaluated using the grading score system for SAM. The Grading score was recorded at intervals of one month.
Statistical analyses of data were performed by the Kruskal-Wallis test and the Mann-Whitney U-test.
Result: In SAMP 8//Ymi with molar teeth, 8-month-old mice showed significantly shorter latency time than 3 and 5-month-old mice (p<0.05). In SAMP 8//Ymi without maxillary molar teeth, 5 and 8- month-old mice showed significantly shorter latency time than 3-month-old mice (p<0.05). As a result, in 5-month-old mice, the ones without molar teeth showed significant shorter latency time than the mice with molar teeth (p<0.05). In the degree of senescence, the grading score increased significantly in mice with and without molar teeth associated with aging (p<0.05). The mice without molar teeth showed a significantly higher grading score than the mice with molar teeth at 5-months-old (p<0.05). However, there were no significant differences between 3-month-old mice and 8-month-old mice.
Conclusions: SAMP 8 with molar teeth showed age-related changes in impairment of learning and memory ability. SAMP 8 without molar teeth showed earlier impairment of learning and memory abil-ity than SAMP 8 with molar teeth. In addition to this, accelerated senescence was observed in SAMP 8 without molar teeth. Accordingly, we suggest that the earlier aging phenomenon and the impairment of learning and memory ability are due to the loss of molar teeth occur at the same time.

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Although masticatory ability depends on the number of permanent teeth in elderly persons, artificial prostheses such as dentures are used for restoring lost masticatory function in their daily life. In this study, the relationships between masticatory ability and the number of functional teeth (both natural and artificial teeth) were evaluated by means of a functional tooth triangle map.
We analyzed the results of a longitudinal nationwide investigation of Nihon University Center for Information Networking research project by questionnaires performed on 4, 049 persons, who were classified into groups based on their gender and masticatory ability. Each person was plotted on a functional tooth triangle map, and the distribution was investigated.
As a result, in the masticatory ability 5 group with high masticatory ability, 41.2% males and 33.2% females had more than 20 permanent teeth. Furthermore, 53.3% males and 62. 2% females had more than 25 functional teeth including full dentures, showing high rates, and prostheses such as full dentures were useful for improving masticatory ability.
The rate of persons with a large number of permanent teeth decreased with the masticatory ability. In the masticatory ability 1 group (insufficient masticatory ability), in which the number of per-sons was less than 10% of all the subjects, although the number of functional teeth was almost restored by wearing dentures, no sufficient functional recovery was obtained. As the rate of persons with low masticatory ability was higher in females than in males, which may be due to the differences in masticatory muscular force, recovery of masticatory ability in more elderly persons can be expected by improving the quality of the dentures that they are wearing.

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The purpose of this clinical study was to estimate the usefulness of an air abrasive technique for removal of proximal root surface caries observed frequently in aged patients.
Fifteen healthy aged patients over 60 years old were selected from the outpatients who visited the Hyogo College of Medicine Hospital for the purpose of dental treatment. Eighteen proximal root surface caries lesions were used for this study. The air abrasive unit, Air Flow S1^® (EMS/Shofu Co.), which jets abrasive powder of sodium bicarbonate with water under pressure, was applied to remove the root surface caries lesions. The air abrasive procedures were carried out at 3.0kgf/cm² air pressure and the jet nozzle was moved continuously over the carious lesion. At l5 second intervals during theair abrasion, CARIES DETECTOR^® (KURARAY Co.) was applied to the remaining dentin for a check of caries removal.
The results were as follows: the air abrasive technique with sodium bicarbonate powder and water removed proximal root surface caries without abrading sound dentin. However it was difficult to undermine the carious dentin by this air abrasive technique, therefore it was neccesary to enlarge an orifice of the cavity by other instruments.
In conclusion, these results suggested that the air abrasive technique with sodium bicarbonate powder could be useful for the removal of proximal root surface caries in aged patients.

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