This review article is based on the ingredients of my lecture titled “Desirable way for oral biomaterial research in the JPS-considering Journal of Oral Rehabilitation Summer School 2006” at the JPS Advanced Seminer which was held with the general assembly meeting at March 4, 2007. How we explore the desirable way for oral biomaterial research in Japan was discussed with referral of the contents and discussion in the summer school.

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The purpose of this paper was to introduce The First International Clinical Prosthodontics Educators Workshop.
That workshop aimed at reconciling best evidence analyses of clinical information on the efficacy and effectiveness of prosthodontic interventions with the management of selected and assigned clinical scenarios. The International Journal of Prosthodontics (IJP) and the Institute for Advanced Dental Studies in Karlsruhe Germany were co-sponsoring this workshop on October30-November 1, 2006, in Karlsruhe. The 15 selected educators conducted a two and a half-day-day program for 36 participants selected from the international prosthodontic teaching community (22 countries).
The form of case histories selected and organized as teaching packages (2 scenarios, reading lists and pictures) for the participants, was sent for pre-workshop distribution by e mail. Morning presentations comprised faculty reviews of background material specific to diverse aspects of the clinical case histories. At afternoon sessions, participants broke out into small tutor-led groups to explore and debated the various treatment options for the case histories in the context of the mornings' reviews.
The Japan Prosthodontic Society should hold that kind of workshop in stead of classical lectures for faculty development.

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Purpose: Many studies have reported the relationship between facial morphology and stomatognathic functions. The steepness of the articular eminence is an important morphological factor to determine the mandibular movement or mandibular positioning. The present study analyzed the relationship between the condylar displacement during clenching and the condylar guide inclination related to simulated loss of posterior occlusal support.
Methods: Nineteen clinical residents (4 females and 15 males, 24-31 years old) with healthy natural dentitions were recruited as subjects. To change the posterior occlusal support, occlusal splints fitted to maxillary dental arches were cut in sequence from the posterior toward the anterior side. The condylar displacements during maximum voluntary clenching under every occlusal condition were measured using a mandibular movement analyzing system with six-degrees of freedom. The sagittal condylar guide inclination was also measured using the same apparatus.
Results
1. A greater loss of posterior occlusal support was associated with increased displacement distance of both condyles, however these values varied with the subject.
2. A significant positive correlation was observed between the displacement distance without splint and the relative displacement distance with splint (difference between before and after loss of occlusal supports).
3. A significant negative correlation was observed between the displacement distance without splint and the sagittal condylar guide inclination, and was also observed between the relative displacement distance with splint (above-mentioned) and the sagittal condylar guide inclination.
Conclusion: These results suggest that the sagittal condylar guide inclination is an important factor in condylar displacement during clenching.

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Purpose: The purpose of this study wasto investigate the coefficients of thermal expansion and shrinkage of an all-ceramic system (cercon^®smart ceramics, Degu Dent) utilizing tetragonal stabilized zirconia.
Methods: The coefficients of thermal expansion and shrinkage of the core material and the layering porcelains (dentin and enamel) used in this study were measured according to the ISO 9693 standard. Five specimens for the core material and ten specimens for each layering porcelain were tested. The core specimens were milled, sintered, ground and polished. Five of the specimens for each layering porcelain were fired two times, and the remaining five specimens were fired four times. The fired layering porcelain specimens were ground and polished.
The coefficients of thermal expansion and shrinkage were evaluated using a push-rod dilatometer at a heating rate of 5°C/min over temperature ranges of 25-700°Cfor the core, and 25-550°Cfor the layering porcelain. For each specimen, the coefficients of thermal expansion was determined to be between 25 and 500°Cfrom the plotted curve of expansion versus temperature.
Results: For the core material, the coefficients of thermal expansion and shrinkage showed almost the same value (10.8×10^-6/°C). For the layering porcelains, the coefficients of thermal expansion and shrinkage ranged from 9.3-11.1×10^-6/°C. The difference of the coefficients of thermal expansion and shrinkage between the core materials and the layering porcelains was-0.3-1.5×10^-6/°C. The specimens fired two times and the specimens fired four times exhibited almost the same value for each layering porcelain.
Conclusion: The core material and layering porcelains have a suitable relationship.

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Purpose: The degree of crushing and intraoral food flow was evaluated using peanuts by the occlusal forms of a removable bridge as indices to clarify the occlusal formative effect of maxillary molars on masticatory function.
Methods: The subject was a 29-year-old male without any gnathostomatic disorders and his removable bridge ((7) 6 (5)) was so made in interocclusal distance as to be 0.5, 1.0 or 1.5 mm from 0 mm standard having occlusal contact to antagonist. Then the subject was asked to chew 3 g of peanuts in a series of unilateral chewing schemes consisting of 5, 10, and 20 masticatory strokes each. The pool rate in the buccal oral vestibule and lingual proper oral cavity as an index of food flow was calculated as the weight of peanut particles accumulated in each side as a percentage of the total volume of recovered peanut particles. Also, the degree of crushing was calculated as the weight of peanut particles that passed through 10-mesh sieves as a percentage of the total weight in each side.
Results: As the interocclusal distance to the mandibular cusp increased with abrasion on the inside at maxillary buccal cusps, the pool rate of the buccal oral vestibule was significantly increased and correspondingly that of the lingual proper oral cavity was decreased. The degree of crushing indicated nonsignificances statistically among 0, 0.5, and 1.0 mm and significantly decreased in 1.5 mm as compared with 0 mm.
Conclusion: As the interocclusal distance to mandibular cusps from the maxillary inside of buccal cusps was increased, the pool rate of the crushed peanuts in the buccal side increased and the pool rate of crushed peanuts in the lingual side decreased, and the particles showed a comparatively low degree of crushing. It is clear that maxillary buccal occlusion has an effect on the crushing function and food flow.

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Purpose: The purpose of this study was to analyze the difference in educational effect on students who experienced both lecture-based learning (LBL) and problem-based learning (PBL) in a complete denture course. The analysis focused on differences between the two methods concerning self study, ability to understand clinical inference, and appraisal of class contents and tutors.
Methods: In the complete denture preclinical course, the class of 2003 received LBL in 3rd grade and PBL in 4th grade. PBL was planned to present five cases in five consecutive classes. Group discussion was carried out for each case, and a summary was required to be produced two times as a group, two times as an individual report and one time by group presentation. A questionnaire regarding the educational effect of LBL and PBL and assessment of tutors was administered. Factor analysis was carried out to classify the questionnaire items and each item was analyzed between LBL and PBL (Paired-t test).
Results: Factor analysis revealed that the questionnaire items could be classified into four components. Comparing lecture type and PBL:“study attitude”(4 out of 7 items), “clinical inference ability”(all items), “class contents”(5 out of 7 items) and “tutor appraisal”(2 out of 5 items) showed significant assessment with PBL. Eighteen of 27 items (66.6%) indicated the significant usefulness of PBL.
Conclusion: PBL improves the educational effect of self study and clinical inference ability, in comparison with LBL. However, since students are passive about taking the same system class repeatedly, a strategy to improve their attitude needs to be considered.

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Purpose: This study investigated the influence of intensity of occlusal contact, or occlusal height of an implant-retained single restoration on the stress in the crown surface and supporting bone.
Methods: A two-dimensional finite element model of the maxillary and mandibular first molars with supporting periodontal structures was created (Model M-M). One of the molars was replaced by a restoration retained by a thread-type implant to produce Model I-M (implant in maxilla) and Model M-I (implant in mandible). The models were isotropic and linearly elastic, except for the periodontal ligament with a non-linear material property to simulate the tooth movements. The tooth-to-tooth contact under the bite force was simulated by the vertical displacement of the mandible up to 0.24 mm from the initial occlusal contact. Non-linear contact analysis was conducted to calculate the stress in both the restoration and the supporting tissues.
Results: To obtain a restoration that shows the same stress in the occlusal surface as that in the natural molars under the maximum bite force, the occlusal heights in Models I-M and M-I were to be reduced by 0.10 mm and 0.11 mm, respectively. The restorations were not expected to occlude with their natural molar antagonists under bite force lower than 13.0% and 15.8% of the maximum force, respectively.
Conclusion: Reduction in the intensity of the occlusal contact, or decreased occlusal height of an implantretained single restoration, allows the establishment of an equivalent occlusal stress with the natural molars under the maximum bite force. This adjustment, either during fabrication or try-in procedure, can suppress excessive stress that may be created in the tissues. With this procedure, however, the restoration does not contact the antagonistic tooth under a relatively low bite force.

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Patient: The patient had esthetically unacceptable upper left central incisor crowns. The case was restorated using Empress (staining technique) for the upper central incisors on both sides.
Discussion: In making all-ceramic crowns, it is necessary to reproduce the shape and color near to those of the natural tooth. We should not overlook the importance of diagnostic waxing-up, provisional restoration, tooth preparation, gingival retraction and others, to achieve excellent appearance, function and biocompatibility.
Conclusion: It is effective to use the staining technique for an anterior tooth crown in order to obtain esthetically satisfactory results by the papilla being present in such cases as the distance from the base of the contact point to the crest of the bone is 5 mm or less.

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Patient: A 22-year-old female patient with defects of left mandibular molars and alveolar bone due to ameloblastoma visited our hospital with the chief complaint of occlusal instability and masticatory dysfunction. Four years have passed since the tumor extirpation, and no signs of recurrence have been found. Sufficient quantity and quality of bone was available for placement of osseointegrated implants. Superstructures were given occlusal contact with early contact of residual teeth simultaneously.
Discussion: Every regular examination showed that sufficient osseointegration between implants and bone and periodontal condition were maintained. Measurement of occlusal forces during maximum voluntary clenching by pressure-sensitive film demonstrated that total occlusal forces and distribution of occlusal forces of the patient were similar to those of healthy humans.
Conclusion: It is suggested that prosthetic treatment using osseointegrated implant in the region of tumor extirpation is one of the most effective treatments for recovery of the stomatognathic system.

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Patient: We initially planned to treat the patient with removable partial dentures in both the maxilla and mandible because the patient refused invasive operation. However, we could not achieve a satisfactory result, so implant treatment was selected following sufficient informed consent.
Discussion: When the implants were used with the removable denture, we have to consider various factors such as mechanical characteristics or the differences of the amount of tissue displacement between mucosa, teeth and implants and treatment plans for longitudinal predictability.
Conclusion: In this case, we could acquire the satisfactory occlusal support with implants, although removable partial dentures the patient hoped at first couldn't work well.

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Patient: A 60-year-old female presented with a chief complaint of poor adaptation of dentures. At the first examination, it was confirmed that she had symptoms of heavy dermatitis in the whole body, especially the hands and feet, and had a medical history of drug and metal allergy. As a result of patch testing, we diagnosed that these symptoms might be due to hypersensitibity reaction to some composition elements used in the dental alloys. After removing all the prostheses made of dental alloys and replacing them with new prostheses made of commercial pure titanium, the symptoms of metal allergy disappeared.
Discussion: The results of this case show that treatment using prostheses made of titanium may be suitable. In order to obtain a good prognosis, regular follow-up is important.
Conclusion: In this case, dental alloys may have been one of the causes of severe dermatitis and prosthetic treatment with titanium effectively solved the patient's symptoms of metal allergy.

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Patient: Adhesion pontic bridges, consisting of composite denture teeth and adhesion metal splint, were installed for missing lateral incisors for a patient with severe periodontitis.
Discussion: Peeling-off or falling-off of the adhered pontics and metal splint was not observed during 7 years after placement. This prosthetic treatment method might be advantageous to both dentist and patient, as it enables immediate esthetic recovery. Making an impression for fabrication of the metal splint was carried out after controlling the mobility of each abutment tooth by adhering pontics, which might have led to the excellent adaptation of the metal splint to abutment teeth and pontics. Furthermore, appropriate surface treatment for each bonding interface might have resulted in the durable bonding of pontics and metal splint to abutment teeth.
Conclusion: The current method provided satisfactory long-term results after placement equivalent to conventional fixed partial denture and adhesion bridge.

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Patient: A 37-year-old-male visited the hospital with aesthetic dissatisfaction and mastication functional disease due to multiple tooth loss as the chief complaint. As the patient had a strong gagging reflex, intravenous sedation or inhalation sedation was used, enabling full-mouth prosthetic treatment to be performed.
Discussion: Improvement of aesthetic dissatisfaction and recovery of mastication function were considered to have been achieved with fixed prosthetic restoration alone, allowing the specific occlusal relationship to be maintained. The procedure was made possible by controlling the patient's dental phobia and gagging reflex with sedation and performing the restoration prosthesis treatment in each block while the patient was sedated.
Conclusion: As the patient's gagging reflex exhibited reduced sensitivity following treatment, it was considered to have a significant psychogenic component; this must be taken into account in future treatment so that medical staff avoid instigating or exacerbating the patient's gagging reflex.

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