The objectives were to analyze the curriculum of dental education and the problem-based learning in the United Kingdom and to prospect the future changes of our own education system. The General Dental Council (GDC) regulates the dental professionals and assures the quality of their practice. They also assure dental education in presenting a guideline such as The First Five Years. The system would work well in UK and could be introduced. The contents and the management of PBL were investigated on the visits to Liverpool and Manchester and the interview to the educators and students there. In experiencing the tutorial class, how the students join the class and study with group members was studied. There the curriculum has been integrated before the introduction of PBL, replacing the conventional discipline-oriented lecture-based ones. The basics of the human body were studied through the patient's case materials used in the medical school. The specifically developed dental packages, coupled with a guidebook for students or tutors, were also applied to the basic and clinical dentistry using the real patient's cases. Most of the students met usually accepted PBL, worked well as a member of the group and enjoyed the class. These indicated that PBL could be advantageous in the study of the dental practice in the integrated curriculum setting.

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Cytolethal distending toxin (CDT) of Actinobacillus actinomycetemcomitans is a protein toxin that induces irreversible cell cycle arrest, cellular distention and subsequent cell death in mammalian cells. In this study susceptibility to human cells (HeLa cell and normal fibroblast TIG-7) of the A. actinomycetemcomitans CDT produced by recombinant E. coli cells was estimated by morphological change of the cells and a ratio of cell death. When influence to cell morphology by CDT-treatment was examined, HeLa cells was round at 2 days and distended about over 5-fold in size at 4 days. In contrast, morphology of TIG-7 cells did not change at 2 days after CDT-treatment and showed slight distension at 4 days. But cell cycle arrest was observed in both types of the cells after CDT-treatment. When relationship between amount of CDT for treatment and cell number was examined, amounts of CDT did not affect the cell number of HeLa and TIG-7 cells. However, viability of HeLa and TIG-7 cells was obviously distinct, the viability of HeLa cells was less than 5% at 7 days after treatment and that of TIG-7 was about 20%. In addition, viable TIG-7 cells continued to be alive even after subsequent spread although the cells were not growing. These results suggested that CDT produced by A. actinomycetemcomitans might act as a factor that facilitates bacterial infection to the cells by inducing prolonged cell cycle arrest to host cells.

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Recently, composite resins for facing crowns have been widely used for natural colored prosthetic materials. However, over time the colors of these materials undergo changes. Therefore, color changes of 6 kinds of composites, which were immersed in filtered coffee, were examined in our previous study. The results of the experiment indicated that all the composites showed visible color changes after one week of immersion in coffee. Moreover, enamel paste showed poorer color stability than dentin paste. Similarly, non-polished surfaces were more discolored than polished surfaces.
In this study, we examined the surface hardness of the samples, which were used in our previous study, as the degree of cure. The relationship between color changes and surface hardness of composite resins were investigated.
As a result, polished surfaces showed less discoloration and greater surface hardness than the non-polished surfaces for all brands of resin tested because polished surfaces may have a higher degree of cure than non-polished surfaces. However, there was no correlation between color intensity and surface hardness of all resin brands tested.

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Schwannoma, alternatively designated as neurinoma or neurilemmoma, is a benign tumor of the neural sheath origin. It typically appears as a well-circumscribed solitary mass. Although the most frequently affected site is the central nervous system of the head and neck region, this tumor is uncommon in the oral cavity. Here we report six cases of Schwannoma of the oral cavity. Patients were referred to our hospital with intraoral swelling or nodules from 1989 to 1999. There were five females and one male, and the age range was 15 to 59 years with the mean of 27.7. Masses were found in the tongue in four cases and in the lip in two cases. All the tumors were surgically enucleated under local anesthesia. Histopathologic examination revealed that four tumors displayed Antoni A pattern and one of the other remaining cases displayed Antoni B pattern. The remaining one was found as a mixed type of Antoni A and B. No signs of recurrence have been observed during the postoperative follow-up.

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This clinical report presents resin bonded fixed partial denture and shape memory alloy for patients with cleft lip and palate. The minimal-preparation, resin bonded fixed partial denture may be considered to be one of the ideal choice of fixed prosthesis to replace a single missing tooth, especially in the anterior maxillary region.

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This study investigated the clinical results of 251 patients with primary squamous cell carcinoma in the oral cavity to make clear the usefulness and problems of the modality. The patients were treated in the former first Department of Oral and Maxillofacial Surgery, Showa University, School of Dentistry. They were devided into two groups according to the treatment period : the 1st period (-1990) and the 2 nd period (1991-).
The results obtained were as follows.
1. The overall survival rate in the 1 st period was 77.4% at 5 years and 71.8% at 10 years.
The rate in the 2nd period was 79.4% both at 5 and 10 years.
2. The 5-year survival rate of patients with the buccal mucosa, tongue, or the lower gingiva carcinoma was relative high. But the rate of patients with the upper gingival cancer was low.
3. The 5-year survival rate of T2 patients increased in the later period, although the rate decreased in T3 and T4 patients.
4. The survival rate of NO patients increased in the later period, although the rate of N1 and N2 patients decreased.
5. The survival rate of stage II patients increased in the later period, although the rate of Stage I, III, and IV patients decreased.
6. The survival rate of the patients who had undergone only surgery, or operation with chemotherapy had higher survival rate than patients who had been treated with operation, chemotherapy, and radiotherapy.
These results suggested that new treatment modality should be intensively developed for patients with advanced squamous cell carcinoma to upgrade their prognosis. It is also necessary to train talented persons with enough technique and knowledge.

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This paper reports a case of an inverted tooth in which the tooth crown erupted in the nasal cavity. The patient was a 22-year-old male with a chief complaint of a slightly strange feeling in the nasal cavity. Although the definite diagnosis was obtained by endoscopy, cone beam CT was useful for visualizing the eruption position and morphology of the inverted tooth, and its relationship with the surrounding tissue. Since the position of the inverted tooth was comparatively posteriorly located, it was extracted from the intraoral cavity under general anesthesia; as a result, we could get a good observation without any complication.

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