Various kinds of desensitizing method have been tried in case of the operation of the dentine which is highly sensitive. Recently the author devised a new and simple desensitizing method of dentine, “ELECTRO-ANESTHESIA”, only by means of weak direct current, and not by any anesthetica.
PRINCIPLE
It has been well known that the direct current does not cause an irritation to the nerves, but causes the change in excitability while turning on a direct current, except when breaking or making the current, excitability increasing at the negative pole and its surrounding area while decreasing at the positive pole and its surrounding area (Electrotonus by Pflüger, 1859) . Application of this phenomena has been tried in anesthesia during minor operations at the end of the nineteenth century: A positive pole is fixed near to the operating field, while a negative pole is connected to the area far from the positive pole. Then a direct current is sent to both poles in order to decrease excitability of the operating field and to perform an electro-anesthesia and surgical operation.
As the human body, however, is not so simple as a specimen of nerve and muscle, it is impossible to cause sufficient electrotonus jast at the operating field. Consequently this method could not be beyond the confines of theory and it has never been succeeded.
Now the author devised a new method using a metallic surgical instrument as an electrode in order to obtain a successful electric potential in an operating field.
TECHNIC
A positive pole from an electric source of D. C. is connected with an end of a handpiece and bur is used partly as an operating instrument during cavity preparation and partly as an electrode, while a negative pole, i.e., an indifferent electrode is connected, with the hand of a patient, (Fig. 3, 4.) . Then the routine operation is performed by a weak direct current such as about 4μA to 20μA being supplied from a D. C. source. (Fig. 5, 6.) .
NOTICE
The following notices should be taken of:
1. Decreasing an electric current, as we approach the, pulp chamber.
2. Covering or painting a hand-piece and contra-angle with some isolating substances in order to keep from a leakage of the electric current.
3. Keeping a good electric' connection between bur and hand-piece or contra-angle, using some kind of well-conducting lubricant, sich as potassium soap solution (10%) .
4. Keeping a good electric connection between bur and tooth, using some harmless electrolytic solutions, such as procaine hydro-chloride etc..
RESULT
1) Effect
On 294 teeth of the 126 patients ( _??_59, _??_67, ) from 7 to 67 years, the author tried to make the cavity preparation by this method and obtained the following results: effective in 186 cases (91%) and ineffective in 18 cases (9%) .
No case showed that the pain increased when the current had been on.
2) Strength of the current which is effective to sud cient anesthesia
Each frequency curve expressing an effective strength of the current for anterior teeth, premolars, and molars (Figs, 8, 9, 10, ) did not show a normal form in distribution state. The curve for anterior teeth and premolars showed the maximum value at the point of 4μA., and that for molars showed two maximum values at the point of 4μA. and 10μA. It seemed that the curves of anterior teeth and premolars had possibility to show another maximum value at about 10μA.
This technic can be applied not only to the dentin-desensitizing but also to anesthesia in case of incision of absesses, removal of serumal calculi, painful injections, and others.

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With regard to the etiology of the so-called cuneiform defect of the human tooth, there have been many researches so far, but we are unable to find out any reliable theory about this disorder in them.
Then the author tried to make some fundamental experiments on the cause of this defect. At first the author tried to classify the cervical defects which were found on the extracted teeth and the enamel defects which occured on the vital teeth of many patients, in order to investigate their whole picture. Next the author turned this study towards the observation of frequency of these defects.

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The author devised a new apparatus measuring the degree of percussion-pain of the tooth scientifically. It consists of a handle, a prop, a hammer fixed to the handle, and a graduated gauze marking 1 to 10 in the number. Strength of the impulse causing pain can be measured by this meter.
This percussion-meter is characterizcd with the following points:
1. The degree of percussion-pain can scientifically be determined by this apparatus, as it can produce any implae at will, and more accurately than any other method.
2. A constant force can be given without variation by any operator, when we are to determine the degree of pecussion-paix in case of rootcanal treatment.

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Dental Ni-Cr alloy plates are divided into three cans : (A) as received, (B) bending working, and (C) heated at 800°C for 3 minutes.
The authors observed loss in weight, the degree of changed color and the condition of surface when immersed in following stagnant liquids at 37°C for 3 days.
Consequently, could be obtained the same results in these three series of experiment and the data are shown as follows.
liquid loss in weight color
(mg/cm²/3 days)
1) 0.1% Na₂S 0 constant
2) 0.05% HCl 1.2-2.7 white silvery
3) 1.0% NaCl 0 constant
4) 1.0% lactic acid 2.0-3.0 dark brown
5) service water 0 constant
6) a mixture of the liquids above mentioned, 2.0-3.0 dark brown

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A 62-year-old male with edentulous upper jaw had never been given any restorative treatment for these seven years. He has abnormal feeling around the left jaw-joint and fulll denture plates was newly given.
In this case, however, the pain occurred in the left jaw-joint as the result of higher vertical dimension of the bite. It was considered that this condition may be removed by making the biting height low. Replacing the denture plates with the lower vertical dimension the symptom of the jaw-joint became quite well wjth favourable results.

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A 38-year-old man showed a cyst in the area of upper anterior teeth. The cyst was diagnosed as a traumatic bone-cyst at first, as he had a past history of trauma, but post-operative biopsy revealed it was a fissural cyst.

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A girl, 15 years and 5 months old, who had Class II, Division I malocclusion by Angle's classification, was treated successfully in a comparative short period, by means of an orthodontic active plate with inclined plane.

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