The relation between prosthodontics and regenerative medical therapy was taken up as a theme at symposiums in the 112th and 113th scientific meeting of Japan Prosthodontic Society. In this article, these two symposiums are summarized, and academic conference presentations in the scientific meeting of Prosthodontic Society and the content of scientific papers published in the past 21 years are listed by theme, and how the academic society members had worked on themes such as basic medical research and regenerative medical therapy are verified. As a result, it is clarified that reports on biological research and research of regenerative medical therapy carried out from the prosthodontic viewpoint have increased. in recent years. However, reports concerning biological findings on dental implants have not increased. It is shown that we have to think about the future direction again regarding the relations with recent regenerative medical therapy. In addition, the necessity of regenerative medical therapy in prosthodontic studies in the future is discussed including some personal opinions. The theme on which we have worked to date is not necessarily far from regenerative medical therapy, and research in the prosthodontic field will contribute to the development of regenerative medical therapy greatly if we appropriately adopt its concept and techniques. I hope that this article will have a good influence on the direction of research of academic society members, especially young members in the future.

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The patient, a 54-year-old male, consulted the Oral Surgery Department of Iwate Medical University Hospital with a complaint of a mass in the left oral base in June 1992. In September 1992, the patient was diagnosed as having cancer in the left mandibular base, and the tumor was excised by resection of the entire cervical region on the left side. Since radiation osteonecrosis in the left mandible and mandibular fracture were detected, segmental excision of the left mandible was performed in March 1993. Although the postoperative course was good without reconstruction, the patient consulted the Second Prosthetic Department to achieve functional recovery in February 1996. This patient had no occlusal contact between the maxilla and mandible because the mandible shifted to the affected side. After fixation of a mandibular prosthetic appliance for the defective mandible, a palatal plate for the maxilla in occlusal contact with the mandibular dentition and mandibular prosthetic appliance were fixed in November 1997. After fixation of a new mandibular prosthetic appliance and dentures for the maxilla with palatal ramp in April 2001, masticatory function was observed to have improved with control of the mandible.
Discussion: To prevent the mandibular shift and improvement of the masticatory function, a palatal plate with a palatal ramp in the occlusal contact region was fixed, and a balance of the masticatory muscles could be maintained. An evaluation of the level of improvement in the masticatory function and the pronunciation function indicated that the mandibular prosthetic appliance and palatal plate with a palatal ramp in the occlusal contact region increased the kind of food that the patient could take. Moreover, by enlarging the narrow Donders space, the pronunciation was improved.
Conclusions: Fixation of a palatal plate with a palatal ramp in the occlusal contact region without reconstruction of the mandibular bone was useful for the control of mandibular deviation to the affected side and improvement of the masticatory function.

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Purpose: Recently, the use of all-ceramic crowns has spread widely in clinical applications to meet the demand for both functional and esthetically-pleasing restorations. In making all-ceramic crowns, it is necessary to reproduce the shape and color near to those of the natural teeth. However, the color shades of abutments might influence the color of the copings which are made of material with high transparency. This study examined the influence of the color shades of the abutments on the final color of copings for three kinds of all-ceramic core materials: Empress, Empress 2 (IVOCLAR VIVADENT), and Procera All-Ceram (Nobel Biocare).
Methods: Copings with 0.5 mm in thickness were fabricated by using Empress (TC1), Empress 2 (100), and Procera AllCeram (white) core materials for an upper-right central incisor. Abutments were made by using six kinds of die materials of the Empress system (ST1, ST2, ST3, ST5, ST8, ST9), gold-silver-palladium alloy, gold alloy, and experimental black body. Copings were inserted in each abutment and the final color of the central part of the buccal surface was measured using a spectrophotometer according to the L*a*b* color system.
Results: Regardless of the color shades of the abutments, the chroma values of the copings rose in the order of Empress, Empress2, and Procera, and the values of lightness rose in the order of Empress, Procera, and Empress2. When the final color of each coping measured under the wet and dry conditions were compared, the difference in chroma was great.
Conclusions: Within the limitations of this study, the results suggest that the influence of the color shades of the abutments on the final color of the three kinds of copings is small in the order of Empress, Procera, and Empress2. In clinical and dental laboratory operations, it is hoped to observe and measure the color of copings and restorations under the wet condition.

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Purpose: Recently, there have been reports in favor of avoiding prosthodontic intervention as Shortened Dental Arch (SDA) in Northern Europe. However, many of these reports were conducted through interviews and questionnaires, and so the evaluation of the results lacked objectivity. Thus, this research analyzed the clinical status of SDA.
Methods: For the selection of subjects, seven patients (average age: 59±13.2 years old) who had had the free-end missing on both sides of the lower dental arches for over five years were chosen as the SDA group. As the complete dental arch (CDA) group, seven patients (average age: 61.3±9.6 years old) who had no clinical defects in their masticatory function, and who had no missing teeth other than the third molar, were selected. Measurement items in this study were occlusal contact areas for the mandible premolar, center of force, occlusion time, and interdentium. The Mann-Whitney U test was used for statistical analysis and the significance level was assumed to be 5%.
Results: The results were as follows: 1) The occlusal contact area of the mandible premolar of SDA was significantly large. 2) The center of force of SDA was significantly forward. 3) The occlusion time of SDA had a tendency of prolongation. 4) Interdentium of 32|23, 43|34and54|45of SDA were significantly wide.
Conclusions: There were differences of clinical parameters between SDA and CDA in this study.

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Purpose: The main objective of this study was to examine the influence of the thickness and its longitudinal change within the limited denture space on the stress releasing effect for installed implants during the healing period of a two-stage procedure.
Methods: As for the tissue conditioning material, Tissue Conditioner (Shofu, Kyoto, Japan) with the designated powder liquid ratio was used. The force transmitted to the implant with the material 5 min after the mixing was measured by a miniature pressure sensor in the position of the implant head (Kyowa, Tokyo, Japan). Measurements were repeated with the material preserved in the water for one and two weeks. Load of 2 kg was applied with a 3-mm diameter round tip using a static loading machine for 2 min to the center of the flat type denture model. The model consisted of denture, mucosa, tissue conditioning material and implant where the first three variables were changed as in the oral cavity. Influence of thickness of each variable was examined longitudinally.
Results: Force measured with any thickness of tissue conditioning material was smaller than that without the material. The stress releasing effect did not change with change of the longitudinal material property up to two weeks.
Conclusions: Within the limitations of our study, it was suggested that the stress releasing effect of the tissue conditioning material for the installed implant was not influenced by the thickness or change of longitudinal property.

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Purpose: The lower jaw is considered to be fixed during body exercise. However, its mechanism remains to be elucidated. The present study investigated masticatory muscle activity during of the back.
Methods: The subjects were 9 healthy dentulous patients. The maximum back strength of the patients was measured with a back-dynamometer. Muscle activities of the temporal, masseter and digastric muscles during exertion of the back and mastication of peanuts were measured. Muscle activities of the temporal and masseter muscle during maximum voluntary clenching and that of the digastric muscles during exertion of resistance against forced mouth opening were also measured, and maximum voluntary muscle activities were obtained. The relative percentage of each masticatory muscle against maximum voluntary activity was calculated from the data obtained, and muscle activities during exertion of the back, mastication of peanuts and maximum muscle activity were compared.
Results: Muscle activities of the temporal, masseter and digastric muscles during exertion of back muscles against maximum voluntary muscle activity were 32.1%, 26.4% and 97.4% respectively. Muscle activities of these muscles during mastication of peanuts against maximum voluntary muscle activity were 40.7%, 36.0% and 17.3% respectively.
Conclusions: Muscle activities during exertion of the back were 30% in the temporal and masseter muscle, and approximately 100% in the digastric muscles. The result suggests that the digastric muscles play a key role in fixing the mandible in all masticatory muscles including jaw-opening and closing muscles. People exert back strength not only in sports but also in daily life. This study demonstrates the stronger involvement of the digastric muscles in fixation of the mandible during exercise than during strong clenching. The results are of interest in terms of mandibular position, occlusal contact and the load on the temporomandibular joint (TMJ) since there is no wide mouth opening.

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Purpose: This study investigated the relationship between the degree of mandibular alveolar ridge resorption and the number of denture adjustments after insertion of dentures in complete denture wearers.
Methods: The subjects were 77 complete denture patients (34 males, 43 females, mean age 69.1±8.1 years). Using bite plates of Gothic arch tracing for new denture production, the width, height, and inclination toward the tentative occlusal plane of the mandibular alveolar ridge corresponding to the canine areas (C), first premolar areas (P1), second premolar areas (P2), and first molar areas (M1) were measured bilaterally, and the relationship with the number of denture adjustment was evaluated.
Results: The mean of number of denture adjustments was 4.4±1.8 times (male 3.8 times, female 5.0 times), showing a significant difference between males and females (p < 0.01). The alveolar ridge mean width was C: 9.7 mm, P1: 10.4 mm, P2: 11.5 mm, and M1: 13.0 mm respectively. The alveolar ridge mean height was C: 4.3 mm, P1: 4.6 mm, P2: 4.9 mm, and M1: 5.2 mm. The alveolar ridge mean inclination was C: 11.2°, P1: 13.5°, P2: 15.4°, and M1: 18.8°. The width and height of the mandibular alveolar ridge in C, P1, P2, and M1 were significantly larger in males than in females (p<0.05). The height of mandibular alveolar ridge was significantly lower in high number of denture adjustment than in low number of denture adjustment (p< 0.05).
Conclusion: Complete denture wearers showed a high relation between the number of denture adjustment and the mandibular alveolar ridge height.

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Purpose: The purpose of this study was to extract questionnaire items based on qualitative data from edentulous patients obtained by individual interview.
Methods: Forty-three patients (20 complete denture, 20 partial denture and three non-denture wearers) who had visited the dental hospital affiliated to Nihon University School of Dentistry at Matsudo voluntarily agreed to be interviewed about their denture use with ten questions structured by Triandis theory in an open-rended manner. Responses to interview were recorded by voice recorder and qualitatively analyzed into linguistic and coded items, i. e. fragmentation and editing of recorded data followed by linguistic coding. The coded items were then classified into one of the 4 domains of Triandis theory: intentions of their denture acceptance (I), social factor (SF), affect (A) and perceived consequences (PC).
Results: The analysis of qualitative data, description, fragmentation and editing, accumulated 722 linguistic items. These were summarized into 72 codes, and classified into twelve I, nine SF, nine A and 42 PC.
Conclusions: The 72 coded items, which summarized the edentulous qualitative data including the 4 domains of Traindis theory, are considered useful as questionnaire items of behavioral investigation. Further large-scale studies using this questionnaire will be needed to clarify the reasons for denture acceptance.

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Purpose: Three types of guide plane were compared to clarify the effect of guide plane setting conditions on abutment displacement which arises when an Akers clasp is inserted.
Methods: An experimental model with an artificial periodontal membrane made of hydrophilic vinyl polysiloxane impression material was created. Abutments given a guide plane with only a clasp body (G1), a guide plane whose span extended as far as the reciprocal clasp arm shoulder region diametrically opposite the retention area (G2), and a guide plane for the entire reciprocal clasp arm region (G3) were created, and an Akers clasp was made for each abutment. The amount of abutment displacement and the degree of rotation that arose in the abutment when the Akers clasp was inserted were detected with three laser displacement sensors for comparison.
Results: The amount of abutment displacement that arose when the clasp was inserted was higher with G1 than with G2 and G3 in the lingual and distal directions, and no difference was seen between G2 and G3. It was lower with G1 than with G2 and G3 in the buccal direction, and no difference was seen between G2 and G3. It was high with G1 in the mesial direction, and the abutment rotation was high, whereas they were low in the case of G3. A difference was seen between each condition.
Conclusions: Differences in guide plane setting conditions affected the abutment displacement that arose when an Akers clasp was inserted, suggesting that a difference in reciprocal action is seen depending on the setting conditions of the guide plane.

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Patient: The patient consulted our department with a chief complaint of aesthetic problems due to anterior tooth discoloration. Since improvement by bleaching was considered impossible, porcelain laminate veneer restorations were performed.
Discussion: Insertion took too long for the patient's satisfaction due to the repetition of color adjustment and recontouring. The veneer preparation area should be limited to enamel; however when dentin is exposed, it is important to treat with primer before adhesion.
Conclusion: In this case, establishing a selection criterion for bleaching, a combined approach was also considered. Although the preparation area is limited to enamel, phosphoric acid etching should be avoided when dentin is exposed. The treatment process should be arranged so as to reduce the manipulation period.

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Patient: The patient was a 48-year-old partially edentulous male with microstomia. His chief complaints were masticatory disturbance and aesthetic problems caused by missing teeth. After trayless impressions for diagnostic casts were made, sectional trays and a sectional record block were used for the definitive impression and maxillomandibular registration. Maxillary and mandibular acrylic sectional dentures were simultaneously delivered.
Discussion: Low caries activity, minimal occlusal force, appropriate plaque control, and simple designs for connecting portions of the two halves of the sectional dentures might lead to satisfactory results in this case.
Conclusion: No problems have been observed for approximately 6 years after delivery of the acrylic sectional dentures for this microstomic patient.

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Patient: The patient was a 70-year-old male with a chief complaint of poor adaptation of a mandibular unilateral extension base denture. The diagnosis was missing teeth of the mandibular bilateral second premolars, the first molars and the mandibular left second molar as well as poorly-fitting facing crowns in the mandibular bilateral canines and the first premolars. After inserting the facing crowns, a metal base denture was constructed using the altered cast technique. After 3 years, the metal base denture's masticatory function and appearance were successfully achieved.
Discussion: It was considered an achievement in this case to get maximum support from the residual ridge using the altered cast technique.
Conclusion: The metal base denture was constructed using the altered cast technique and successful masticatory function was gained.

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Patient: A 57-year-old female complained of aesthetic disturbance, dysmasesis and phonation disorder by attrition. She had severe attrition of almost teeth. To avoid metal color exposure and attrition of opposing teeth, hybrid ceramics were used for veneered crowns and fixed partial denture. Since the prosthetic treatment, the patient wears a night guard to prevent attrition of her teeth and prosthesis.
Discussion: There has been no specific trouble during the 4-year follow-up.
Conclusion: It is considered that using hybrid ceramics for veneering crowns and fixed partial denture and night guard help to prevent the attrition of opposing teeth and abrasion of prosthesis.

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Patient: The patient was a 60-year-old male with the chief complaint of loosening of the bridge on the upper right side. The diagnoses of the patient were detachment of the bridge ((7) 6 (5) 4 3 2 (1)(1)) and root fracture (51). A cobalt chromium plate with Mini-SG attachment was used at 4 3 2 to fix the bridge. The course of the patient was uneventful five years after the treatment.
Discussion: Judging from the condition of the detached bridge, the same type of fixed bridge was considered too weak to withstand the lateral force. Stabilization of the functional occlusion was achieved by using the attachment, followed by good clinical results.
Conclusion: The patient was satisfied with the comfort of the removable partial denture with attachment, and good functional results were obtained.

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