The basic problems, that are derived from the measurelnent of electrical impedance of gingiva, were systematically investigated in various experimental conditions. Especially, the A. C. characteristics of metal(Ag-AgCl), conductive rubber and cotton-wick electrodes(φ=5.0㎜)were examined over the frequency range of 3 Hz to 30 KHz. After determination of the intrinsic impedance and reactance ratio of the electrodes, analyses of the pressure effects and time courses of variation in impedance value were carried out in an equivalent model circuit and in animal gingiva. The results obtained in this paper indicated that the value of total impedance gradually decayed wlth increase in pressure applied to the electrode and the metal and conductive rubber electrodes were very unstable and showed poor reproducibility. These decreasing ratio in impedance were more than 20% in those electrodes and less than 5 to 8% in the cotton-wick electrode. With all our data, the latter electrode was one of the most suitable for the measurement of impedance in mucous membrane such as gingiva. A preliminary experiment indicated that the total impedance value was about 5.5 to 6 KΩ in human gingiva.

A 23-year-old male was referred to our clinic due to trismus. He was tried to have an extraction of the right lower third molar 35 days ago at a local dentist, but it resulted in the impaction of the tooth into the mouth floor. Since a week after the operation the patient has had increasing trismus, and he could not open the mouth more than 20 mm when he came to our clinic.

Mucous membrane from the gingiva around the third molar to the pharynx seemed to be inflamed. Therefore, the patient was treated with cephalexin orally for 10 days. Then the impacted tooth was removed under local anesthesia. The tooth was located between the masticatory muscles. The patient was discharged on the 10th postoperative day. At that time he could open his mouth up to 30 mm, and recovered completely in two weeks after discharge.

To many other methods of treatment for zygomatico-maxillary fractures, the antral balloon method seems to be superior in our hands.

A 23 year old man recieved a collision on the left side of the face while he was engaged in a base ball. Physical examination showed moderate swelling over the left side of face, ecchymosis of the left orbital tissues, subconjunctival hemorrhage of the eye and trismus. Multiple roentgenograms of the skull and facial bones revealed a fracture of the zygomatic bone from the anterior border into the maxillary sinus.

Two weeks later, under endotracheal anesthesia, fractures were reduced by the pressure with blunt instruments. The Foley catheter inserted into the sinus by way of a modified Caldwell-Luc approach. The balloon pressure for fixation was maintained for three weeks. The patient was discharged from the hospital 30 days later with no complaints.

The simplicity of reduction and excellent results obtained wilh the balloon technic warrant its use in the selectcd cases.

Four cases of the double.rooted mandibular canine were experienced. Measurements of canine were as follows.

The labial and lingual roots contained root canal shown on dental radiographs.

Bilateral dentes invaginati of the upper central incisors from 11-year-old boy were examined histologically. In addition, X-ray examination revealed four invaginated teeth in the same patient; they were the right lower canine and first premolar, the right upper lateral incisor and left lower first premolar.

Microscopical examination of the both upper central incisors showed that immature enamel matrix has remained in the invaginated cavity which is separated from the pulp by a wall of the dentin. The dentin attached to the base of the cavity was also partially immatured showing an irregular arrangement of the dentinal tubules. In many reports on dens invaginatus the tissues in the cavity were said to be necrotic or disappeared. In the present case the invaginated cavity of the each upper central incisor contained ameloblast-like epithelium probably derived from enamel organ, its metaplastic squamous epithelium, fibrous connective tissues which may be derived from the dental sac and other odontogenic epithelium. Cement-like substance was observed to be directly in contact with the dentin in the deep part of the cavity. Cholesterin crystal was also found in the cavity.

The etiology of the dens invaginatus is still obscure. Based on our findings and literatures, we would agree with the etiological hypothesis that a dens invaginatus may develop by relative retardation in growth(hypoplasia)of the inner enamel epithelium and the dental papilla.