Experimental subluxation was conducted on the bilateral upper lateral incisors with incomplete root in 39 young dogs (3 in control group) and pathohistologic and neuropathohistologic investigations were made. The results were as follows : 1. In the subluxated teeth with incomplete root, the periodontal fibers were restored to the former state on 20th day. 2. None of the cases showed ankylosis between the alveolar bone and subluxated teeth. 3. Revascularization was found in the dental pulp of the subluxated teeth with incomplete root. It was confirmed that a large number of new blood vessel extended from the periodontium to the root pulp from 7th day and reached the coronal pulp on and after 20th day. 4. The dental pulp showed edema immediately after the experimental subluxation and necrosed in places. However organization of the pulp progressed and fibrosis extended to the whole pulp on 30th day. 5. Odontoblasts disappeared in places after the experimental subluxation of the teeth but were recovered on 30th day. Predentin was formed and the pulp was strictured by the deposited dentin. 6. The existence of the epithelial sheath of Hertwig was greatly related to growth of the root. Dentin-like hard tissues began to extend along the epithelial sheath of Hertwig in the root apex on 7th day and apparent growth of the root was noted thereafter with time. 7. In the subluxated teeth with incomplete root, neurotomesis and Wallerian degeneration occurred concurrently in the intraperiodontal nerve tissues. Immediately after experimental subluxation of the teeth, the intraperiodontal nerve fibers and nerve fascicle were severed at the ruptures of the periodontium and degeneration of nerve fibers proceeded with time centering on the ruptures of the periodotium, and ranged over the whole periodontium. These findings were noted until 10th day. 8. In the subluxated teeth with incomplete root, only Wallerian degeneration occurred in the intrapulpal nerve tissues. The nerve tissues invading into the pulp were severed at the ruptures of the periodontium in the apex regions immediately after experimental subluxation of the tooth. The nerve fibers remaining in the pulp decreased with time and the nerve fibers exhibiting degenerative findings disappeared on 15th day. 9. As to regeneration of nerve in the periodontium of the subluxated teeth with incomplete root, marked proliferation of Schwann cells occurred on 7th day from the tip of nerve fascicles on the gingival side and in vasoneural space of the alveolar bone, and fine nerve fibers appeared along that arrangement. On 10th day, the nerve fascicle consisting of fine nerve fibers extended on the side of the alveolar bone up to the midlevel of the root and reached the periodontium in the alveolar crest regions on 20th day. On 30th day, the nerve distribution was approximately completed in the periodontium. 10. As to regeneration of nerve in the pulp of the subluxated teeth with incomplete root, a large number of fine nerve fibers and nerve fascicle invaded through the opened apical foramen on 10th day. The nerve distribution appeared to be restored with the peak on 20th day. However the nerve tissues in the pulp decreased slightly after 30th day. On the basis of the foregoing, the subluxated teeth with incomplete root keep the normal positions in the alveolar bone and mature as complete teeth supported by the periodontium which recovered morphologically and functionally. But the pulp is strictured and fibrosed and the sense response of the pulp is thought to be lowered slightly.

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This study was performed to obtain the response of the Golden Syrian hamster tongue to different concentrations (1.0%, 2.0%) of 9, 10-dimethyl -1, 2-benzanthracene (DMBA). Changes with time in nuclear DNA content during the formation of the hamster lingual tumor, histologic type of the lesions induced in this carcinogenic experiment, and relations between carcinoma and nuclear DNA content were investigated. The results were as follows : 1. Small (papillary) tumor appeared earlier in 2.0% group as compared to 1.0% group. Macroscopically, the infiltrative type tended to appear more in 2.0% group as compared to 1.0% group. 2. Histologically, carcinoma advanced type was observed more in 2.0% group as compared to 1.0% group, but there was no difference in carcinogenicity rate between 1.0% group and 2.0% group. 3. In both 1.0% and 2.0% group, the carcinogenicity rate was higher in 15 week experimental group as compared to 12 week experimental group. There was no difference in carcinogenicity rate by the duration after carcinogenic treatment. 4. The longer carcinogenic treatment period was, the higher were the mean, mode and over 4C of nuclear DNA content. 5. The mean and variation of nuclear DNA content were significantly higher in carcinoma advanced type as compared with carcinoma early type and carcinoma advanced type did not show clearly the mode of nuclear DNA content histogram. The mean, variation and mode of nuclear DNA content were higher in papilloma and dysplasia induced this experiment as compared to those lesions in human. 6. On the basis of macroscopic findings, carcinoma were divided into five types : Exophytic type (Ex type), Ulcerating type (U type), mixed U and Ex type (UEx type), Invasive and Exophytic type (IEx type) and Leukoplakia type (L type). Ex type and L type tended to be well-differentiated squamous cell carcinoma (SSC) and slightly celluar atypia. U type tended to be moderately-differentiated SCC and severely cellular atypia. UEx type and IEx type tended to be mixed Ex, L and U type. 7. In Ex type and L type, the mean of nuclear DNA content was comparably lower, and the mode of nuclear DNA content was 3C area. In U type, the mean of nuclear DNA content was higher and the mode of nuclear DNA content was 5C area. In UEx type and IEx type, the mean and distribution of nuclear DNA content were medium type of Ex, L type and U type.

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Fainting encountered as an episodic occurrence during ambulant dental treatment is an extremely unpleasant symptom for the patient. At the time of this attack, in general, along with a sensation of a falling elevator, the patient suddenly becomes pale, complaining of nausea, cold sweat, generalized muscle relaxation, fall of blood pressure and bradycardia. Consciousness is lost instantaneously, sitting position becomes unstable and the supine position is usually assumed. These general symptoms usually recover after about 20 minutes. During dental treatment, clinical observation was carried out from a psychosomatic viewpoint, both on fainters with past history of fainting and on fainters based on the method of classification of fainters and non-fainters by the Fainting-Questionnaire, which allowed pattern recognition of patients, employing two kinds of criteria for fainters. The following conclusions were drawn based on these results and discussions. Risk factors for fainting of fainters with history of fainting and fainters based on pattern recognition were greater than those of non-fainters without history of fainting and non-fainters based on pattern recognition. In the circumstances of the treatment room prior to the dental treatment, sympathicotonic state was seen in two kinds of male fainters, and parasympathicotonic state was seen in two kinds of female fainters. Two kinds of male and female fainters showed higher rise of catecholamines than two kinds of male and female non-fainters. Such sympathicotonic state appears to represent a risk factor for the fainting attack prior to dental treatment. Based on these results of observation, psychosomatic handling of the patient before dental treatment in the dental treatment room appears to be important as a preventive measure for the fainting attack.

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Morphological changes of nerve cells with advancing age, especially accumulation of lipofuscin granules, were investigated by histochemical and autofluorescent methods with the use of trigeminal ganglion of rats, ranging in age from one week to 18 months. The results were as follows : 1. At one week of age there were some immature cells of large nucleocytoplasmic ratio. The immature cells decreased at four weeks of age and the average size of nerve cells remained fairly constant during later life. 2. The degenerative change of nerve cells such as atrophy and residual nodules were sometimes found in the old age group. But marked decrease and unusual distribution of Nissl bodies was not found and the number of nerve cells did not change significantly with age. 3. PAS positive granules were found at four weeks of age and Sudan Black B positive granules were found at eight weeks of age. The percentage of nerve cells containing PAS positive and Sudan Black B positive granules increased progressively with age and a progressive increase in the percentage of cytoplasmic areas occupied by PAS positive and Sudan Black B positive granules was also observed with age. 4. The distributions in the cytoplasm of PAS positive and Sudan Black B positive granules were shown variously. In the young age group PAS positive and Sudan Black B positive granules were distributed diffusely in the cytoplasm in fine granules. As the aging process advanced, the coarse granules of PAS positive and Sudan Black B positive were accumulated more and more at the perinuclear position. 5. The autofluorescent granules were first seen at the age of six months. The granules exhibited light yellow fluorescence and intense bright yellow granules increased with advancing age. 6. By PAS reaction, Sudan Black B reaction and autofluorescent methods, the location of lipofuscin granules almost corresponded, though the time when they first appeared was different. 7. In the trigeminal ganglion an increase of lipofuscin granules accumulation was revealed. The presence of lipofuscin granules accumulation was revealed. The presence of lipofuscion granules occupying most of the cytoplasmic area in nerve cells may probably affect physiological and metabolic functions of nerve cells.

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Sixty young male Wistar rats, weighing 40g were used. Twenty animals were fed on a standard diet, 40 on a calcium-deficient diet. Latter group resumed a standard diet after three weeks. The effects of dietary content on the growing alveolar bone and tibia were investigated for weight, radiologically, optically, photo-densitically, histopathologically, and hematologically. The results were as follows : 1. The rats in the experimental group showed considerable increase in weight four weeks after the experiment (one week after resumed a standard diet). Thereafter they showed a significant tendency for increase with time although there was some difference as compared with controls. 2. Radiologically, trabeculae increased in the alveolar bone of the rats of the experimental group, and marked increase in thickness and density of the alveolar bone was seen six weeks after the experiment. In the tibia, interosseous cortex and medial cortex thickened and trabeculae increased in number and became dense. 3. Optically, the inferior portion showed higher densitic curves than the superior portion and this tendency continued until the sixth week although the difference became smaller gradually. Unevenness of the densitic curves for trabeculae in the alveolar bone became less with time. In the tibia unevenness of the densitic curves for trabeculae in the tibia became more pronounced with time and densitic curves for bone rose on the whole. The densitic curves for interosseous cortex and medial cortex in the tibia changed from unevenness to smoothness and approximated the pattern of controls. 4. Photo-densitically, density of alveolar bones of rats in the experimental group increased with time although difference was seen between the superior and inferior portions of the alveolar bone. Six weeks after the experiment, bone density for the superior portion for the experimental group increased to 0.78 and for the inferior portion to 0.83 with the value for controls as 1. In the tibia, interosseous cortex and medial cortex increased to 0.92 and 0.83, respectively, of controls four weeks after the experiment. Thereafter, increase in the value was seen, but the ratios decreased. 5. Histopathologically, thickening of bone layer was seen in the superior portion of the alveolar bone of the rats in the experimental group. In the inferior portion of alveolar bone, narrowing of the bone marrow due to thickening of bone layer and thickening of bone layer toward the periodontal membrane were seen. At the same time, Sharpey's fiber bundles also appeared. In the tibia, bone proliferation was seen from internal and external periosteum in interosseous cortex and medial cortex. However, fatty marrow did not improve until six weeks after the experiment. 6. Hematologically, ratios of electrolytic serum Ca to IP, and values of serum Na and Cl were very close to those of controls. However, values of serum IP and K were low. Biochemical CPK values, AL-P values and GOT values decreased to normal values, but GPT values varied up and down. On the basis of the foregoing findings, fragility of the alveolar bone and tibia due to osteoporosis at growing stage could be ameliorated considerably by dietary therapy. However difference remained in comparison with controls. As a means to overcome such difference, administration in combination with diet of calcitonin and activated vitamin D is recommended.

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Effect of deciduous root canal filling materials, Calvital, Vitapex, Kri I, Neodyne and FR, on the periodontal membrane and succeeding permanent tooth buds was investigated histopathologically with use of young dogs about three months old. The results were as follows : 1. The subjects treated with Calvital showed almost no inflammatory changes in the apical periodontal membrane of deciduous teeth. However, Vitapex, Kri I, Neodyne and FR caused inflammatory changes. 2. Resorption of deciduous root was delayed in all the subjects treated by root canal filling, in comparison with controls. In the subjects treated with Vitapex or Neodyne, bony ankylosis of the deciduous root and alveolar bone was observed. 3. With regard to changes in succeeding permanent tooth buds, no changes in the cells of enamel organ were observed in the subjects treated with Calvital. With Vitapex and FR, changes such as flattening, fusion, lytic changes, irregular arrangement, and atrophy were observed in the cells of enamel organ when the filling materials extravasated. With Kri I, the cells of enamel organ showed flattening and atrophy. With Neodyne irregular arrangement and atrophy of the cells of enamel organ were observed. 4. In comparison with controls, eruption of permanent teeth was delayed owing to inflammatory chages caused in the periodontal membrane, delayed resorption of deciduous roots, and changes in the cells of enamel organ. 5. With Vitapex and Neodyne, bony ankylosis in particular was seen and disturbance in eruption of permanent teeth was observed. 6. Calvital, FR, Vitapex, Kri I, and Neodyne, in the descending order, affected the periodontal membrane and the cells of enamel organ of succeeding permanent teeth buds. 7. Use of deciduous root canal filling materials in treatment of non-infected root canals greatly affect the periodontal membrane and succeeding permanent tooth buds when they are applied to immature teeth or when they extravaste beyond the apical foramen.

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Many investigators indicated that there are differences of race and area on human traits. For the present paper, comparative and morphological investigation of the deciduous dentition were made on the plastercasts from 143 Okinawa children (82 boys and 61 girls) ranging in age from 3-5 years Kitakyushu children in same age group. The results were as follows : 1. Percentage of normal occlusion of deciduous dentition in Okinawa children was showed 65% or more in both boys and girls, and it tended higher with an increase in age. In malocclusion, percentage of overbite totaly boys and girls was highest (11.9%), and percentage of edge to edge bite was higher but cross bite was lower in the girls than in the boys. 2. About type of interdental spaces, percentage of mixed type of primate space and developmental space was distinctly higher in the upper dental arch in both boys and girls. But, percentage of closed type as same level as mixed type of primate space and developmental space was higher in the lower dental arch, especially in the girls. 3. About type of terminal plane, percentage of bilateral vertical (straight) type was highest, 56.1% in the boys and 60.6% in the girls, then it was higher in order bilateral mesial step type, bilateral distal step type, vertical-mesial step type. No cases of vertical-distal step type and mesial-distal step type was observed. 4. Upper and lower dental arch lengths were not significantly different between boys and girls in OKinawa. It was recognized that lower anterior dental arch lengths were shorter, but upper anterior, upper posterior and lower posterior dental arch lengths were longer in the Okinawa than in the Kitakyushu children in both boys and girls. 5. Upper and lower dental arch breadths were significantly wider in the boys than in the girls. It was recognized that all the items, except lower posterior dental arch breadth in the girls, of Okinawa children showed wider levels than Kitakyushu children, especially upper and lower anterior dental arch breadths in the boys and upper anterior dental arch breadth in the girls. 6. All the dental arch indices were not significant difference between boys and girls in Okinawa. It was recognized that upper and lower anterior-posterior dental arch breadth indices were significantly higher in the Okinawa than in the Kitakyushu children in both boys and girls, but in the boys, lower anterior-posterior dental arch length index and lower anterior arch index were significantly lower in the Okinawa than in the Kitakyushu children.

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Disturbance of the sense of taste is known to be caused by radiation therapy for tumors in the head and neck region. For the purpose of investigation of changes of the lingual papillae pathohistologically, X-ray irradiation to the lingual dorsal membrane of the tongue was experimented and light microscopic and scanning electron microscopic observations were made. Nineteen young dogs, 3∿5 months old, were used for this experiment. Single dose of 1, 000_R was given in three irradiations at intervals of three days. Observations were made on the 1st, 3rd, 5th, 9th, 15th, 35th, and 60th days. The main findings were as follows. 1. The dogs became slow in motion, lost appetite, and left a third of their feed beginning on the 5th day after irradiation. From the 8th to 9th days, eye mucus and secretion from the eyes increased and appearance of weakness increased. Beginning on the 15th day, signs of recovery were observed. 2. The cases on the 5th day showed marked degeneration of yellowish-brown color of the lingual mucous membrane in the region closest to the irradiation tube. 3. Microscopically, the degenerated region was coincident with the region of erosion formation in which neither the lingual papillae nor epithelial layers were observed. Lamina propria of the mucous membrane where infiltration of inflammatory cells was marked was exposed directly. 4. Scanning electron microscopic observation of this erosion region showed a mixed finding of innumerable inflammatory cell group that migrated to the surface of the lamina propria and debris of the epithelial layer. 5. In the lamina propria of the mucous membrane of this region, connective tissue fibers were disorderly arranged and most blood vessels were congested and expanded. Muscular fiber groups extending to this layer were atrophied and striated structures were unclear. 6. The filiform and fungiform papillae in the ordinary mucous membrane neighboring to the degenerated one maintained their forms. However, erosion in part of the epithelial layer and edema in places including the lamina propria were seen. Scanning electron microscopically, both papillae changed some in morphology and their surfaces were rough, and countless microorganism and parasite-like structures aggregated together densely. The taste buds of fungiform papillae decreased in number, and showed atrophy, decrease, and vacuolar degeneration of their cells (light or sustentacular cells). 7. In the cases on the 5th day and those on the 15th day, the discolored region of mucous membrane was considerably limited beginning with the cases on the 9th day. In the cases on the 15th day, limitation was brought about by restoration of epithelium. Inflammation of adjacent healthy colored region was slight. 8. The shorter the interval after irradiation, the lighter was disturbanced. In the cases of one day after irradiation, especially, any region appeared about the same as that of controls. 9. As epithelium of the mucous membrane recovered and prolifered in the cases on the 15th day and thereafter, the number of taste buds and of taste bud cells was restored. However, atrophy of cells still continued and cell arrangements were irregular. Even in the cases on the 35th day after irradiation infiltration of inflammatory cells was seen in some taste buds and complete restoration to the normal image was seen only after 60 days.

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A morphological study of the maxillary sinus using the computerized three-dimensional reconstruction of the tomographic images was made. Materials of this study were 86 adult dry skulls of the Second Department of Oral Anatomy of Fukuoka Dental College. The results were as follows : 1. A tomographic apparatus which could select varius X-ray tube shifts was used. The hypocycloidal shift was the best for the tomography of the maxillary sinus. 2. In the tomographs of the maxillary sinus, the images of some sections in the maximum cross-section area presented real shapes. However, the images of other sections were indistinct and influenced by the shape of the maximum cross-section. 3. Reconstruction of the tomographic images of the maxillary sinus by computer made it easy and precise to recognize the three-dimensional image. 4. The dimensions in the maximum cross-section of the maxillary sinus of the 86 adult dry skulls obtained from the reconstructed three-dimensional images were 4.59±1.26cm^2 in frontal, 5.21±1.36cm^2 in transversal and 8.09±1.82cm^2 in sagittal tomographs. The majority of the skulls were symmetry, and a few were asymmetry in correlation between the right and left side sinuses. 5. According to the reconstructed three-dimensional images the shapes of the maxillary sinus of the 86 adult dry skulls were classified into 10 types in frontal, 4 types in transversal and 8 types in sagittal tomographs. The most familiar shape was triangular in frontal, trapezoidal in sagittal and triangular in transversal tomographs. 6. The dimension and shape of the maxillary sinus had no correlation with the frontal width of the nasal cavity.

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This study was aimed to investigate histo-pathological changes in the pulp of the dog incisors (240 teeth) after full crown preparation by light, transmission and scanning electron microscopy. The results obtained were summarized as follows : 1. Scanning electron microscopy revealed that dentinal tubules visualized by full crown preparation always contained torn dentinal fibers in the cutting surface of the dentin. This finding suggested that the initial changes of the pulp were caused by the direct damage to odontoblasts. 2. Changes caused by the preparation occurred widely in the coronal pulp, particularly in the pulp horn regions. These changes were dependent on the thickness of remaining dentin. 3. The recovery of odontoblast layer was observed at 3 days after preparation : Undifferentiated pulp cells were seen increasing their number at the site just beneath the odontoblast layer. Undifferentiated pulp cells located just beneath the odontoblast layer were observed to make contact with each other by gap junctions. These peculiar contacts were also observed frequently between this type of cells and odontoblasts. Further, similar cells were also found among injured odontoblast. It was suggested from the present morphological view points that these undifferentiated cells were precursor cells of odontoblasts and migrated into the odontoblast layer. 4. The reparative dentin began to form 7 days after preparation and increased its thickness gradually. The thickness of the reparative dentin was estimated to be about 40μm at the lingual or buccal side of pulp at 28 days after operation. 5. Matrix vesicle-like structures were seen in the predentin where newly formed odontoblasts aggregated. 6. The pathological changes in the pulp almost disappeared by 21 days after preparation. 7. Exposed dentinal fibers were still observed on the cutting surface even 28 days after preparation by scanning electron microscopy. Possibility raised from the present study that the pulp was still influenced by the oral environment through dentinal fibers even long period after preparation. For getting a good prognosis, the adequate post-treatments, that is, use of temporary crowns and suitable cements, seemed to be necessary.

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The periodontal innervation of primary teeth in Macaca irus was examined by light-microscopy. The results were as follows : 1. The nerve fibers distributed in the periodontium of primary teeth in Macaca irus were derived from two directions. The first group of nerve fibers entered the periodontium by passing through the angioneurotic canal of the bottom of the bony socket, and the second group of them entered it passing through some bony canaliculus at the lateral wall of the bony socket in the various height of the periodontium. 2. Nerve supply was the richest in the apical one-third of the tooth root, rich in the middle third, and very poor in the cervical portion. 3. Most of the nerve fibers distributing the periodontium of primary teeth were accompanied by blood vessels. Many myelinated nerve fibers in the periodontium branched and ramified repeatedly, and gradually became unmyelinated nerve fibers. 4. Nerve endings in the periodontium of primary teeth could be classified into the two types by their structure. One type was pointed free nerve endings, and the other type was thick knob-like endings closely resembling Meissner's tactile corpuscles. Both of two types were concentrated near the apical one-third of the tooth root. 5. Pointed free nerve endings terminated in the periodontal ligament, fibrocyte and some of them reached cementoblast and under the cementoblastic layer, but none of them entered the cementum. Most of the thick knob-like endings terminated under the cementoblastic layer. 6. In the vascular connective tissue which filled physiologic absorption area of primary teeth, regressive changed nerve fibers were often found, while just normal nerve fibers were also found.

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In induced peritoneal macrophages, the quantity of Ia antigen was measured by monitoring absorbance using enzyme-linked immunosorbent assay (ELISA). The number of Ia positive cells were counted simultaneously under microscope. Results obtained were as follows : 1. An optimum time for enzyme reaction in ELISA was 40 min using 4×10^4 cells as a sample. 2. Absorbance in ELISA correlated closely with the number of Ia positive cells. 3. It was shown that an increase in absorbance was brought about by an increase in the number of Ia positive cells and not by an increase in Ia quantity in the surface each cell. These results showed that ELISA was a useful method for the study of quantifying cell surface antigens like Ia antigen.

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Formalincresol (FC), a mixture of the same quantity each of formalin and cresol, was tested for its cytotoxic effect on HeLa cell tissue culture system in comparison with formalin and cresol. In the first study, the cells which had grown to monolayers were exposed to FC and observed through the phase contrast microscope for 24 hours. The degree of morphological degeneration was estimated on a scale ranging 0 (no change) through 4 (granulation and rounding up of cells). In the second study, FC, formalin or cresol was added to the suspended cells. At the end of 48-hour cultivation, the degree of inhibitory effect of the drug on cell-growth was estimated on a scale ranging 0 (no inhibition) through 4 (no growth), and then cells were stained with heamatoxylin and eosin for the examination. In the third study, the viable cells were counted up after being treated in the same way as in the second study. The results were as follows : 1. No significance of toxicity was perceived at 5 μg/ml and a slight reversible shrinkage of cells of established monolayer occurred at 10 μg/ml of FC. 2. The cells of established monolayer were brought to the most conspicuous and irreversible change in morphology when exposed to FC in the concentration of 50 to 100μg/ml, and nearly fixed at and over 500 μg/ml. 3. Concentration of drug causing 50% inhibition of adhering of suspended cells was 12.5 μg/ml for FC, 9.0 μg/ml for formalin and 60 μg/ml for cresol. 4. There was more similarity in the morphological changes caused by FC and cresol than by FC and formalin.

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A contrivance, named modified panel method, had been developed for a screening tool for the purpose of the bioassay of carcinogens and anticarcinogens. In this study the growth inhibition and morphological changes which were brought to HeLa cells by three compounds of known mechanism of action, hydroxyurea, proflavin hemisulfate and cycloheximide, were observed with the above method. Then it was tried to measure areas of cytoplasm, nucleus and nucleolus of tested cells with digitizing system of personal computer, and to represent morphological changes by quantitative difference found in the measurement. The results show that these trials are useful for examination of the correlation between changes in morphology and in metabolism of cells affected by bioactive substances and for classification of those changes.

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In a male patient aged 3 years and 6 months we encountered a supernumerary tooth in the median maxillary region of the deciduous dentition. This tooth had erupted behind the left central deciduous incisor dislocated labially. The crown form of the supernumerary tooth was conically shaped, and the partially completed single root had a wide pulp cavity and a large opening at the apical end. Two types have been advanced as the possible origins of the supernumerary tooth in the deciduous dentition ; 1) the genuine supernumerary deciduous tooth and 2) the supernumerary permanent tooth prematurely erupted. In view of our findings on the position of the erupted tooth and the shape and size of the tooth itself, we are of the opinion that in this case it was the supernumerary permanent tooth.

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The frequency of congenitally missing anterior teeth was studied by panoramic radiographic examination, inspection and question. One group of subjects consisted of 1, 433 students trained in radiology (1, 272 males and 161 females) at Fukuoka Dental College whose average age was 24.3 years. The other group of subjects consisted of 1, 209 patients (544 males and 665 females) from a dental office practice in Saseho city. Their ages ranged from 7-30 years. Since some cental incisors were difficult to discriminate from the lateral ones in the lower jaw, both of them were counted as incisors. 1. Two students (0.1%) had three anterior teeth missing : the maxillary bilateral incisors and one mandibular incisor (one student), and one maxillary lateral incisor and the mandibular bilateral incisors (one). 2. Seven students (0.5%) had two anterior teeth missing : the maxillary bilateral incisors (one student), one maxillary lateral incisor and one mandibular incisor (one), the mandibular bilateral incisors (four), and the mandibular ipsilateral incisor and canine (one). Twenty patients (1.7%) had the following two missing : the maxillary bilateral incisors (four patients), the mandibular bilateral incisors (nine), the maxillary contralateral incisor and canine (one), the mandibular ipsilateral incisor and canine (two), the maxillary bilateral canines (three), and the mandibular bilateral canines (one). 3. Twenty-four students (1.7%) had one anterior tooth missing : the maxillary lateral incisor (five students), the mandibular incisor (fifteen), and the maxillary canine (four). Thirty-four patients (2.8%) had a tooth missing : the maxillary lateral incisor (seven patients), the maxillary canine (seven), and the mandibular canine (twenty). 4. No missing central incisor was observed in either the students or the patients. 5. The rates of congenitally missing the anterior teeth for the students and the patients were as follows : the maxillary lateral incisor (0.6%, 1.0%), the mandibular incisor (1.5%, 2.6%), the maxillary canine (0.3%, 0.9%), and the mandibular canine (0.1%, 0.2%).

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With use of extracted human permanent maxillary anterior teeth with the root canals untreated, after root canal irrigating solutions (10%NaOCl, 15%EDTA) were filled in root canal, reaming and preparation of the root canal were done with reamers and K-files. The root canals were then irrigated alternately with 10%NaOCl solution and 3%H_2O_2 solution and the inner wall surfaces were observed with a scanning electron microscope. The results were as follows : 1. No specific differences about root canal enlargement were found between reamers and K-files. 2. Effects of using 10%NaOCl solution and 15%EDTA solution were observed only coronal one third of the root canal. 3. In order to increase cleaning effect of the root canals, abundant use of EDTA, NaOCl, and H_2O_2 appears to be necessary.

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