The last frontier of science is to understand the biological basis of consciousness and the mental processes by which we perceive, act, learn, and remember. The brain science has recently been promoted to remarkable development by virtue of a rapid advance in the methodology in such scientific fields as the science of information, molecular biology, health sciences, and so on. The purpose of the present review is to explain roughly“What the brain science is, ”giving a couple of examples from synaptic plasticity, motor learning in the cerebellum, with special reference to our recent experiments on masticatory motor learning in young rats. Finally, working memory in the prefrontal cortex will briefly be introduced as an up-to-date topic.
1. Synaptic plasticity
Synapses denote the functional juxtaposition of one neuron to another. Three kinds of synapse were recognized-chemical, electrical, and mixed. In the general sense, synaptic transmission exhibits synaptic plasticity. In the brain, synapses occur not so much on the dendritic shafts as on spines that project from the dendrites. According to F. Crick's hypothesis (1982), spines could increase in girth when their synaptic contacts are activated. This would lead to a decrease in electrical resistance between spines and its parent dendrite with a consequent potentiation of subsequent synaptic bombardment. On the other hand, Dr. N. Tsukahara (1976) succeeded in an experiment of synaptic spontaneous turnover that occurred in the absence of tissue damage between efferent fibers from the cerebral cortex pyramidal cells and the red nucleus cells in cats.
2. Motor learning in the cerebellum-with special reference to masticatory motor learning in young rats
David Marr (1965) suggested that the cerebellum is capable of storing and executing specific sequences of actions, by means of a gradual process in which the sequences are first generated consciously while the subject is attempting to master the task, but as the result of repetition are gradually taken over by the cerebellum itself. The Purkinje cells are powerfully and specifically excited by their climbing fibers, and one important source of these fibers, via the inferior olive, is the cerebral cortex. During the initial learning phase, the Purkinje cells are driven by these climbing fibers -activated by some kind of volitional process. Every time we carry out a motor act, it necessarily results in a kind of echo that comes back to us through our sense. Each motor act generates a particular pattern of sensory feedback that will be quite specific to that particular action and to no other.This pattern will be reflected in the pattern of activity of the parallel fibers, which convey information of the most diverse kinds to the dendrites of the Purkinje cells. If we suppose that the condition for the synapses between parallel fibers and Purkinje cell (these synapses are plastic) getting stronger is that the parallel fiber should often fire at the same time as the Purkinje cell, then we have a system that will learn to recognize the context associated with a particular action, and eventually respond to it automatically by generating the action itself.
Mastication can be considered to be a learned skill (Welford, 1979) . If the Purkinje cells are interrupted their volitional inputs via the climbing fibers, what kinds of disorder would be caused in chewing movements of young rats during motor learning of mastication. In our experiments using young rats, specific chemical lesion of the inferior olive by i. p. administration of 3-acetylpyridine resulted in an increased number of chewing strokes required for breaking down a certain quantity of chow until swallowing.
3. Working memory in the prefrontal cortex
The article“Working memory and the mind, ”written by P. S. Goldman-Rakic, appeared in the Scientific American, Vol. 267, September 1992, was summarized along with several slides.

View full abstract

Health problems that are specific to modern times may be divided into the following three types: diseases derived from bad habits practiced by some people including the aged, loss of physical strength, visual acuity and reproductive power observed in young people, and an increased number of allergic diseases.
Many of these problems have emerged in the context of westernization of Japanese life-styles including diet. At the time of the civilization and enlightenment, Japanese people had a reputation for having exceptionally strong bodies, being greatly healthy and being clean although they were generally smaller than Westerners. This indicates that Japanese people's diet used to be quite good.
However, “the campaign to improve nutrition” aiming only at westernization increased intake of fat and animal proteins and decreased intake of carbohydrates such as starch, resulting in the destruction of not only the system of dietary habits, but also the health of Japanese people.
Humans are the animals that have specific food habit. However, as food culture became quite influential and dietary habits became diverse since their residence is surrounded by different kinds of natural environment, human food habit became obscure.
The author studied human food habit based on the common principle of the animal kingdom. “What can not be procured by men's own ability should be excluded from the food list.” High activities of amylase in humans indicated that humans are the animals that require a large amount of starch. However, as people except Westerners stop secreting the enzyme required to utilize dairy products after weaning, intake of dairy products becomes meaningless to these people. This study revealed that humans are the plant-eating animals, which require a great deal of starch and lack the ability to synthesize Vitamin C. These results indicated that humans require fruit and green vegetables other than carbohydrates.
To recover human health and life force, human biological yardstick as well as human food habit should be esteemed, the system of dietary habits should be restructured in harmony with modern lifestyles, and grains and soybeans should regain a pivotal role in diet.

View full abstract

Long term clinical results with distal extension saddle cone-crown-retained-dentures (CCRD's) were discussed. Distal extension type of tooth loss may contribute to one of the etiologic factors of TMD's. The concept of shortened dental arch (SDA) advocated by Käyser et al was seem to be still controversial from the researches by the present author. Some of the clinical implications are stressed in this article when one treats the distal extension case using the cone-crown-telescope as direct retainers giving the design of RPD as the rigid supported concept. In conclusion, CCRD's are one of the standard methods in treating the distal extension cases with good and long term clinical results over 20 years.

View full abstract

R. H. Roth and others have incorporated mandibular function analysis using C.P.I. (Condylar Position Indicator) and Axi-Path Recorder as part of orthodontic diagnosis to achieve the treatment goal of establishing centric occlusion with the condyles seated in centric relation. Their approach is to stabilize the mandibular position with a splint prior to orthodontic treatment in patients with unstable mandibular positions due to Temporo-Mandibular Disorder, major CO-CR discrepancy based on C.P.I. data, or facial asymmetry. The treatment procedures are simplified by utilizing the Straight Wire Appliance or SWA with necessary anatomical information built into the brackets, which are directly bonded to tooth surfaces. This comprehensive system integrating all the steps from diagnosis to treatment has improved the accuracy, reliability and simplicity of orthodontic treatment, contributing greatly to the advancement of modern orthodontics.
However, the loss of mandibular stability during orthodontic treatment is unavoidable due to difficulty of wearing a splint with an orthodontic appliance. This paper introduces the mini occlusal splint developed by the authors to compensate for this shortcoming.
The patient had no midline deviation initially. The C. P. I. data showed no discrepancy. There was no difference in the amount of cuspid overjet between the right and left sides. Space closure was accomplished equally on both sides. However, the midline deviation was noticed with a difference in the amount of cuspid overjet between the two sides at the time of space closure or 6 months after the beginning of orthodontic treatment. The midline deviation increased further 9 months into treatment. The most probable cause was “mandibular displacement.” However, the patient was in the midst of maxillary anterior retraction, making it difficult to wear a regular splint. The mini occlusal splints were bonded onto the occlusal surfaces with an adhesive resin so that a maximum number of teeth could come into equal occlusal contact in CR. The mandibular position was stabilized and the midline deviation was eliminated approximately 3 months after the placement of the occlusal splints.
1. GC pattern resin is mixed. Pour in a small amount of water and mix to the consistency of a dough.
2. Take an anterior bite with the resin. Trim the resin to leave shallow indentations of incisal edges of the lower anterior teeth. Replace it in the mouth to check its reproducibility.
3. Take posterior bites with a quick-cure resin. Mark an outline of each splint and the tooth number on the upper side of the posterior bite and lower cusp tips on the bottom side with an indelible pen. Trim the resin to leave only cusp tip indentations. Grind each splint along the recorded outline.
4. Bond the splints to the occlusal surfaces of the upper molars.
1) It is very important to make a differential diagnosis to determine if the problem is skeletal or not. For this purpose, it is necessary to achieve a stable mandibular position prior to orthodontic treatment with a centric splint.
2) This case effectively demonstrates the effectiveness of the mini occlusal splints when midline deviation is caused by mandibular displacement.
3) In our practice, 30 patients have developed TMD symptoms during orthodontic treatment. The symptoms were eliminated in 28 patients of these patients.

View full abstract

Diagnosis and treatment of occlusion is said to be best performed on the basis of the most appropriate mandibular position. Although there are differing views concerning“appropriate mandibular position, ”we support the idea that the appropriate mandibular position is the mandibular position where the masticatory muscles maintain a certain physiological tension without being influenced by external forces.
There are various methods of jaw registration available to reproduce the mandibular position. In this study, we examined the reproducibility of the mandibular position in each method, and the difference between various methods when used in the same patient.
Six patients exhibiting symptoms of arthrosis of the TMJ were chosen as subjects. Five different methods of jaw registration were each performed twice in each patient, and the casts were studied using the split cast method and Bury check instruments.
The results showed that different methods of jaw registration had different degrees of reproducibility, and the induction method which applies no force to the TMJ had the highest reproducibility.

View full abstract

when residual roots are used as anchors to facilitate retention of dentures using clasps and other appliances, post cores often fail to provide sufficient resistance to horizontal movement in simple rooted teeth, especially teeth with short roots which are normally a contraindication. However, magnetic attachments that have been widely used in recent years, and when used as retainers for residual roots, can reduce the lateral force applied to the abutment tooth, thus preventing tooth deciduation. In this study, we applied magnetic attachments and autogenous tooth graft to teeth with short residual roots. Although these teeth could not otherwise be used as abutments, they were used to bear the load, thus correcting imbalance between compression and support. The results were evaluated during and after the procedure using the diagnostic table of mastication form advocated by Miyako, and it was confirmed that satisfactory mastication was gained.

View full abstract

The purpose of this study was to investigate the influence of TMJ clicking on pressure perceptive of tympanic membrane. Eight asymptomatic volunteers (healthy subjects: HE) and eight volunteers with unilateral TMJ clicking were subjected to measure pressure perceptive threshold of tympanic membrane using tubo-tympanic meter.
No right-left ear differences were observed in HE, thus, data from left and right were pooled as the control. While, data obtained from unilateral TMJ clicking were divided clicking side and nonclicking side (CS and NS, respectively) . Pressure perceptive threshold of tympanic membrane was compared among three groups using Scheffe's F-test.
The following results were obtained:
1. The pressure perceptive threshold of tympanic membrane to positive pressure load was 56±17 mmH₂O in HE, 75±18 mmH₂O in NS, and 72+16 mmH₂O in CS. There were no statistically significant differences between HE and NS, HE and CS respectively (p<0.05) .
2. The pressure perceptive threshold of tympanic membrane to negative pressure load was -66±20 mmH₂O in HE, -102±41mmH₂O in NS, and -119±61 mmH₂O in CS. There were no statistically significant differences between HE and NS (p<0.05), HE and CS (p<0.01) respectively.
From these results, it is suggested that pressure perceptive threshold of tympanic membrane are influenced by TMJ clicking.

View full abstract

For more than 30 years since Brånemark and others invented the osseointegrated implant system, its safety as well as high clinical usefulness has been well documented in many reports.
As demonstrated in these reports, the predictability of this system should be evaluated from various perspectives by accumulating a number of cases to follow over a long period, and should be analyzed in a variety of ways.
However, in Japan, there are not as yet many reports in which more than 5 years of follow-up was performed for osseointegrated implant.
At our implant center, 1, 380 osseointegrated implants were placed in 364 cases consisting of 276 patients between the opening of our center and February 1998. The first case treated at our center has been followed up more than 8 years.
In this study, a preliminary survey was conducted to investigate the long-term clinical progress of our early cases which received implants between March 1991 and August 1991 in comparison with the results of our previous preliminary survey conducted in 1995. These preliminary surveys are part of the analysis involving all of our cases to assess clinical usefulness of the osseointegrated implant system.

View full abstract

Static load tests and impact fracture tests were carried out on edentulous mandibles to evaluate the effect of drill hole preparations made in the bone for implant fixtures. Deformation was measured in the mandibles with strain gauges before the drill holes were made, after monocortical preparation of the bone, after bicortical preparation, and after the Brånemark implant fixtures were tightened into the preparations.
Compared with the monocortical implant preparation, the bicortical preparation produced greater deterioration in the resistance of the mandible to external forces, and greater loss in impact fracture strength. However, there was a slight improvement in the strength of the mandibles after acquisition of osseointegration.

View full abstract

Occlusal reconstruction in the case of wearing poorly fitting prosthesis or keeping not seated prosthesis over the long term has many problem since mandibular position is changed followed occlusal disharmony.
The aim of this paper is to describe the good result treated in such case using treatment denture correcting mandibular position.

View full abstract

Regaining appropriate vertical dimension and clearance is necessary to reconstruct occlusion with acute occlusal plane when treating dental compression syndrome. Thus, patients with decreased vertical dimension should be treated by elevating the occlusion to restore the vertical dimension.
However, since occlusal elevation inevitably causes open bite in the anterior region, we have to face an important question of how to restore anterior guidance when correcting disocclusion in the posterior region.
In patients with edge-to-edge occlusion who have no diastema in the anterior region in the upper and lower arch, which makes it hard to insert orthodontic appliances, occlusion may be elevated first to move the mandible backward so as to allow space for elongation of the anterior teeth.
We have attempted various methods including the conventional methods. We herein report a case treated by a simple method.
A comparative study of panoramic radiographs taken before and after treatment by doubling them revealed a 7.5 mm increase of the vertical dimension between the alveolar bones in the third molar region on the right side. However, there was no depression in the molar region, indicating that the anterior overbite was restored by elongation of the anterior teeth.
It was suggested from our study that infraocclusion can be treated not only by the conventional methods using a multibracket technique, but also by some simple methods. by employing these simple methods, we can elevate occlusion before regaining anterior guidance while meeting patients' demands. The prognosis was also found to be stable.

View full abstract

In patients with non stopping occlusion or edentulous jaws whose motor function was impaired, the motor function improved as a result of oral rehabilitation using treatment dentures.

View full abstract

Watanabe and others reported the efficacy of the application of the Electromyogram biofeedback method for occlusal diagnosis and treatment in patients with arthrosis of the TMJ. They also found the mandibular position induced by this method quite stable physiologically, and they named this position PCP or Physiological Centric Position.
We report a case of infraocclusion and problems in horizontal mandibular relationship in which a simple method of EMG biofeedback was used, depending only on the fingertip palpation to improve mandibular relationship as part of oral rehabilitation.

View full abstract