Investigations of the teeth of the primates are invaluable for the phylogenetic study of the teeth of the mammals. Furthermore, the fact that the milk teeth are more primitive compared with the permanent teeth makes the morphological study of the milk teeth of the primates essential for the phylogenetic study. Because of the foregoing viewpoint, the teeth in position of forty-eight skulls of rhesus monkeys, in possession of the department, were measured and examined morphologically. Rhesus monkeys belong to the cercopithecids of the primates and, their tooth formura is the same as that of the humans in both milk and permanent teeth. Morphologically, their teeth are closely allied to the humans. The results were as follows : 1. The development of the cingulum in the anterior teeth region was extremely little labially but rather advanced lingually. The development was prominent particularly at the central milk incisor and milk canine of the maxilla and at the milk canine of the mandible. 2. The development of the cingulum of the milk molar was not recognized lingually but was apparent buccally. Equivalents of the human molar tubercles were observed particularly at the first milk molar in the maxilla and mandible, not only at the mesial tooth neck but also at the distal tooth neck. 3. The occlusal forms of the milk molars in the maxilla and mandible showed bilophodonty as the molars of other cercopithecids. 4. The number of cusp of the milk molars was four in all cases, but the second milk molars of the mandible showed a trend for a slight degree of differentiation in the hypoconulid. 5. The form of the occlusal surface grooves was Type + for the first milk molar and mostly Type X for the second milk molar in the maxilla, and, in the mandible, Type + for the first milk molar and either Type + or X for the most of the second milk molars. Typc Y was extremely few. This differed greatly from the humans whose milk molars are mostly Type Y. 6. Supernumerary tubercles of the milk molar were extremely few. Occurrence of Carabelli's tubercles was 9.4% at the maxillary second milk molar, protostylid 2.1% and the sixth cusp 5.3% at the mandibular second milk molar. 7. According to the measurements of the crowns, the maxillary second milk molar was the largest of the milk teeth and the mandibular lateral milk incisor the smallest. Comparison by crown index of the rates of the mesiodistal diameter to buccolingual diameter of the crowns with those of the human milk teeth revealed little difference in the rates between them in the anterior portion. In the molar portion, however, the rate of the mesiodistal diameter of rhesus monkeys to the buccolingual diameter was extremcly greater characteristically in comparison with the humans'. 8. In the comparison between the mesial and distal buccolingual diameter of the milk molar crowns, the mesial buccolingual diameter was greater in the maxilla and the distal buccolingual diameter was greater in the mandible. Of the mandibular first milk molar in particular, the distal buccolingual diameter was significantly longer compared with the mesial buccolingual diameter. 9. In the relation of the size between the milk central incisor and milk lateral incisor, the milk lateral incisor was smaller in the maxilla, as in the humans, and the mesiodistal diameter of the milk central incisor was shorter in the mandible and the labiolingual diameter of the milk lateral incisor was shorter. 10. The second milk molar was larger in size than the first milk molar in both the maxilla and mandible in all cases.

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Present study was carried out to investigate the jaw muscles activated by an electrical stimulation to branches of the facial nerve innervating the facial muscles in the urethane-chloralose anesthetized rat. An electrical stimulation was applied to the branches of the facial nerve : the temporal, zygomatic, buccal, and marginal mandibular branch respectively. These branches were cut off in peripheral portion. Evoked EMGs were recorded at the anterior belly of the digastric, mylohyoid, and masseter muscle. Reflex discharges were recorded from the mylohyoid branch of the trigeminal nerve. Furthermore, afferent responses of the facial nerve were recorded by mechanical stimulation to the facial muscles. The main findings were summarized as follows. 1. When an electrical stimulation was applied to the buccal and marginal mandibular branch of the facial nerve respectively, evoked EMG was recorded from the anterior belly of the digastric muscle. In this case, the evoked EMG elicited by a stimulation of the buccal branch was greater and generated by a lower strength of stimulation than that in the marginal mandibular branch. In this evoked EMG, two types of reflex discharges, fast and slow reflex discharges were observed. Fast reflex discharges had latencies of 16.8-20.0 msec and disappeared in a short time. Slow reflex discharges had a latency of about 300 msec and lasted for a long time. Both reflex discharges increased in frequency and amplitude to maximum with an increase in the stimulus strength. No discharge was elicited by an electrical stimulation to the temporal and zygomatic branch. 2. These reflex discharges disappeared after pinching a point at the central side of the stimulating point in the buccal and marginal mandibular branch with a pincette. 3. Evoked EMG was generated in the mylohyoid muscle by an electrical stimulation to the buccal branch of the facial nerve. In this case, two reflex discharges, fast and slow reflex discharges similar to those observed at the anterior belly of the digastric muscle were recognized. 4. Reflex discharges were generated in the mylohyoid branch of the trigeminal nerve by an electrical stimulation to the buccal branch of the facial nerve. In these reflex discharges, fast and slow reflex discharges were observed also. 5. No reflex discharge was generated in the masseter muscle by an electrical stimulation to the buccal branch in most preparations. In only 2 cases out of 19 cases, small reflex discharges were recognized. 6. When tactile and pressure stimulation were applied to the surface of the facial muscle in the buccal region, afferent impulses were elicited in the buccal and marginal mandibular branch. In these afferent impulses, two or three types of units : fast, slow and intermediate adapting units were observed to exist in these branches. 7. The receptive fields caused to these afferent discharges were a narrow area on the surface of the facial muscles in the perioral and buccal region.

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Cariogenic challenge was effects in the experimental animals of the difference in timing of effecting cariogenic challenge. The groups with earlier cariogenic challenge showed higher caries scores. With aging, the caries score decreased sharply. On the second molar, what is called "post eruptive maturation" appeared to be continuing even at 37-day-old. With an increase in the intake of sucrose, the caries score increased. Sucrose intake during tooth eruption in particular affects the caries score. Sucrose intake during tooth eruption, even though minute in quantity, has a great influence.

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A study was made on some oral facters considered to be related to incidences of dental caries with three-year-old children in nursery school as the subjects. Positive correlation existed between the number of decayed teeth, the percentage of Streptococcus mutans to the total Streptococci in the dental plaque on the buccal side of the maxillary molar region, and Cariostat test. The plaque index for the labial side of the maxillary anterior teeth region did not show any correlation with the number of decayed teeth, the percentage of S. mutans to the total Streptococci in the dental plaque on the buccal side of the maxillary molar region, or Cariostat test. This plaque index proved to be inappropriate as an index for the oral environment. No correlation was either observed between dmft and the preference patterns for five varieties of snack. However, a strong preference for chocolate was observed in the group with a higher percentage of S. mutans to the total Streptococci in the dental plaque on the buccal side of the maxillary molar region. The group with Cariostat 2+ also showed a particular preference for chocolate.

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An epidemiological fact-finding investigation was carried out in September 1975 of tooth and gingival diseases in 1, 276 junior and senior high school pupils, aged 12 to 18, in the central Okinawa. The following findings of interest were obtained : 1. Significant differences in the average numbers of erupted teeth for the male and female were found across-the-board and in ages 14 and 17. The female tended to have earlier eruption than the male. 2. Significant differences in the average DMFT count were found across-the-board and in ages 12, 15, 16, 17, and 18. The female tended to have higher counts than the male. 3. Significant differences in the average FT count for the male and female were found across-the-board and in ages 16, 17, and 18. The female tended to have higher counts. 4. Significant differences in the prevalence rate of dental caries and the DMFT rate for the male and female were found across-the-board. The female tended to have higher rates. 5. Significant differences in the FT rate for the male and female were found in ages 16, 17, and 18. The female tended to have higher rates. 6. Significant differences in the FT teeth count rate for the male and female were found across-the-board and in ages 17 and 18. The female tended to have higher rates. 7. In the average DMFT count, DT count, and MT count for the male and female of Okinawa and of Kitakyushu, significant differences were found across-the-board and by age for both male and female. The male and female of Okinawa tended to have higher counts in each category than those of Kitakyushu. 8. In the DMFT rate for the male and female of Okinawa and of Kitakyushu, significant differences were found across-the-board and by age. The male and female of Okinawa tended to have higher rates in each category. 9. In the FT rate, significant differences were found across-the-board and by age, excluding ages 12 and 15 of the male, for both male and female. 10. In the OHI of Okinawa male and female, significant differences were found across-the-board and by age, excluding ages 14 and 18. The male tended to have higher rates. 11. No significant difference between the sexes was found in PMA index, P index, and M index for Okinawa male and female. However, in A index, significant differences were found across-the-board and in ages 14 and 15. The female tended to have higher rates. 12. In the OHI and PMA index of Okinawa male and female, a positive correlation was found between the male and female in each age group, excluding age 18 of female, for both male and female. On the basis of the foregoings, the female had higher incidence rates of dental caries than the male in Okinawa, and, at the same time, tended to have higher rates of treatment. The male tended to be worse in oral cleanliness and in adhesion of deposits. No great difference was observed in the state of gingiva between the sexes. Severer gingivitis however tended to occur more frequently in the female. Compared with Kitakyushu male and female, Okinawa male and female both had more dental caries, had higher incidence rates of dental caries, and tended to be lower in the rate of treatment.

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The artificial posterior teeth of the free-end saddle denture directly transmit through food the masticatory force to the denture base during mastication. A grasp of the occlusal surface form and functions of the artificial posterior teeth is therefore essential in containing the effects of the denture on the circumferential tissues within the physiological limits. Clinical selection and arrangement, however, of the artificial posterior teeth are often made on the basis of the past experiences, and the standards for selection are quite indefinite. Therefore, unilateral free-end saddle denture models of cantilever type were prepared with the artificial posterior teeth set for two and the changes in the effects on the anchor teeth roots with a change in occlusal surface form were measured quantitatively. Five different simulated models of occlusal surface form of the artificial posterior teeth were prepared for the experiment : 0°(10mmφ), 20°(10mmφ), 30°(10mmφ), 0°(6mmφ), 45°(6mmφ). However, the occlusal surface form of the anchor teeth was set for 0°(10mmφ) for all cases. The results obtained were as follows : 1. In the case of the unilateral free-end saddle denture, increasing the number of the anchor tooth from one to two reduced the burden on the distal anchor tooth to as little as 6-7%. 2. Arranging the artificial posterior teeth distally increased the burden on the anchor teeth. 3. When the artificial posterior teeth portion was loaded in the case of two anchor teeth, the load distribution was constantly about 40% on the mesial anchor tooth root and about 60% on the distal one. 4. In any range of the distributed load, from the model anchor tooth (α) to the model artificial tooth (δ), from the model anchor tooth (β) to the model artificial tooth (δ) and on the model artificial teeth (γ) (δ) alone, the trend of the burden on the anchor teeth was the same as that under concentrated load. 5. Of the artificial posterior teeth of the unilateral free-end saddle denture, cusp teeth exerted less burden on the anchor teeth than cuspless teeth.

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Recently, the light has been casted on the damage of the enamel in the direct bonding procedure ; one is, in the process of etching, the sound enamel surface is decalcified and dissoluted, and another is, as a result of bracket removal, enamel is removed with adhesive. For the purpose of defining what changes will be brought about on the etched enamel surface in oral environment, the etched enamel of human tooth, which was mounted to the lingual arch, was worn in the mouth of adult male. Its changes were monitored by scanning electron microscope after 10 days and 3 months, comparing with polished surface placed in the same specimen. The results were as follows : 1. The surface roughness of the etched enamel could be seen disappeared, and become almost same as polished smooth surface after 3 months. 2. The depth of enamel dissolution from polished surface to etched one was unchanged. These suggest that the recovery of surface roughness of etched enamel could be expected, but not quantity of dissoluted enamel. Taking these into consideration, as we have previously reported, maleic acid or pyruvic acid is more favorable as an etching agent in the sense that require less enamel dissolution in obtaining sufficient grip for clinical purpose.

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During the oral examination of 1, 013 grade school pupils in Kitakyushu city, a case each of supernumerary tooth and geminated tooth were encountered. Examination of color, morphology, size, and roentgenograms was made. The results were as follows : 1. The supernumerary tooth occurred in the right lateral incisor region of the maxillar. It was quite identical with the normal lateral incisor in color, morphology, and roentgenograms. 2. The geminated tooth was an extremely rare case, considered to be a union of the left second mild molar and the second premolar in the mandible. 3. Histogenesis has not yet been clarified.

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In the cleft palate patient, after the operative closure technique was performed, uneruptive teeth, missing teeth, crowding teeth and displacing teeth were found. The above factors always caused the following symptoms such as periodontitis, infra-occlusion, abnormal intercuspation, uncomfortable sensation of temporo-mandibular joint and a relative abnormality between mandible and maxilla. Osteoctomy, orthodontic and prosthetic treatment were always used to improve these symptoms. This was a case of infra-occlusion combined with cleft palate. In order to restore the height of vertical dimension to the normal range, the natural and artificial double arch denture was used.

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