Purpose: The purpose of this article was to review the researches on prosthodontic materials and devices published by members of the Japan Prosthodontic Society.
Study selection: A total of 12 original articles published in the Journal of Japan Prosthodontic Society were selected. All were related to prosthodontic materials and devices, and published in Volume 49 of the journal in 2005.
Results: The research projects covered the fields of diagnostic systems, fixed prosthodontics, tooth-colored materials, titanium alloys, inorganic materials, and sports dentistry.
Conclusion: Overall, the reports suggest that considerable improvement in the outcome of prosthodontic treatment can be achieved if new generation materials and devices were properly selected and applied.

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Purpose: The purpose of this study was to compare the masticatory function between patients with myotonic dystrophy (MyD) and healthy individuals, and to clarify the severity of masticatory disturbances in patients with myotonic dystrophy.
Methods: Eighteen patients with MyD, consisting of 11 males and 7 females with an average age of 54.1 years, and twelve healthy individuals, consisting of 6 males and 6 females with an average age of 53.3 years were enrolled as the subjects of this study. The maximum bite force, muscle activity in the temporal and masseter muscles during one cycle of chewing, number of foods that were easy to chew, and the occlusal contact area were investigated, and the results in the MyD patients were compared with those in the healthy individuals.
Results: The maximum bite force, number of foods that were easy to chew and the occlusal contact area were statistically significantly smaller in the MyD patients than in the healthy individuals (P<0.01). On the other hand, the masticatory muscle activity was statistically significantly greater in the MyD patients than in the healthy individuals (P<0.01). The maximum bite force and occlusal contact area in the MyD patients were less than 25% of those in the healthy individuals, however, the masticatory muscle activity in the MyD patients was more than threefold of that in the healthy individuals.
Conclusion: These results suggest that MyD patients compensate for their poor masticatory ability by increasing their masticatory muscle activity while chewing, and that, therefore, their meal form requires careful consideration.

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Purpose: To determine the relationship between temporomandibular disorders (TMD) and the occlusal contact pattern, we conducted occlusal analysis in a prospective cohort study.
Methods: One hundred forty-six volunteers consisting of 98 males and 48 females with a mean age of 20.0±1.9 years selected from the dental students of Iwate Medical University were enrolled for the study. All the subjects were asked to fill out a self-administered questionnaire to screen their general and oral health conditions, and then clinical examination, including evaluation of the occlusal contact pattern, was conducted during the first year. A second clinical examination was repeated 2.5 years later to ascertain the incidence of symptoms of TMD. The natural course of TMD symptoms in the 128 subjects were as follows: 66 were classified in the symptom-free group, 18 in the symptom incidence group, 14 in the symptom remission group, and 30 in the symptom continuation group. Then, the occlusal contact patterns during lateral mandibular excursion were classified into five types: (1) canine protected occlusion and group function (CG; n=192), (2) bilateral occlusal guidance (BG; n=10), (3) working side molar guided occlusion (WM; n=45), (4) non-working side molar guided occlusion (NM; n=4), and (5) incisal guided occlusion (IG; n=5).
Results: In the second examination, 18 out of the 84 subjects (21.4%) who showed no symptoms at the time of enrolment into the study reported TMJ click and⁄or pain. Of the total, 23, 11, 1, and 1 subjects with symptoms of temporomandibular joint origin were classified as having the CG, WM, NM, and BG pattern of occlusal contact, respectively. With CG as the standard, the relative risk of TMD in subjects shown the WM pattern was 2.79 (95%CI: 1.16-6.70).
Conclusion: Since the group showing the working side molar guided occlusion pattern showed a high risk of future development of TMJ click and⁄or pain, lateral excursion guidance may be a contributing factor for the development of TMD.

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Purpose: The Procera system was introduced in Japan in December 2000, however, there have been few clinical evaluations of the Procera AllCeram crowns. The purpose of this study was to prospectively evaluate the clinical performance of Procera AllCeram crowns.
Methods: One hundred and one Procera AllCeram crowns were placed in patients' oral cavities at the Tsurumi University Dental Hospital from July 2001 to October 2002. The performance of these crowns was evaluated using the California Dental Association (CDA) quality assessment system at baseline and at all followup examinations.
Results: A total of 101, 97 and 67 crowns were examined at 1, 2 and 3 years after their fixation, respectively. During the three-year period, six crowns were removed because of fracture of the copings, fracture of the porcelain veneer, root fracture, or esthetic problems. Small incisal chips were detected in three crowns. All of the crowns examined were rated as satisfactory according to the CDA quality assessment criteria, except for the surface and anatomic form.
Conclusion: During the 3-year follow-up period, six crowns were removed, yielding a cumulative survival rate of 93.2%. All (100%) of the Procera AllCeram crowns were rated as satisfactory in terms of the clinical performance according to the CDA criteria, and to be useful for both anterior and posterior teeth. However, the observation period was short, and evaluation over a longer period of time is necessary for a more precise evaluation of these crowns.

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Purpose: The purpose of this study was to evaluate In-Ceram crowns after 5 years'use in vivo.
Methods: A total of 70 In-Ceram crowns were placed at the Tsurumi University Dental Hospital, Department of Prosthetic Dentistry, during the period from May 1995 to April 1996. A follow-up study was conducted 5 years later, from December 2000 to January 2001. We first examined whether the In-Ceram crowns were still functioning. In cases where the abutment tooth was missing, we asked the patients when and how it was lost. In addition, each crown was evaluated by two examiners according to the modified USPHS (US Public Health Service) criteria, which include marginal integrity, shade compatibility, secondary caries, and wear of the occlusal surface. Then, the examiners calculated the period of functioning of each crown from the date of placement to the present (or the date of failure). The survival curve of the In-Ceram crowns was analyzed using the nonparametric Kaplan-Meier method.
Results: A total of 57 of 70 In-Ceram crowns were examined after a mean of 60 months following their placement, and the remaining 13 were lost to followup. Fifty-two of the 57 In-Ceram crowns were found to be still functional, while the remaining five crowns were missing. Two of the five missing crowns had been removed due to fracture after 33 and 53 months, respectively. Another of the missing crowns had been removed because of periodontal disease after 29 months. The remaining two of the five missing crowns had been removed because of dislodgement of the dowel and core after 39 months in one case, and because a fixed partial denture including this tooth was fabricated after 55 months in the other case. According to the five categories of the modified USPHS (US Public Health Service) criteria, most crowns were assessed as Alpha, while both shade match and wear were rated as Charlie in 3.8% of the crowns. The cumulative survival rate was 91.2% (standard error: 0.038).
Conclusion: Out of the 70 crowns placed in 1995/1996, 57 In-Ceram crowns were available for followup at the end of an average of 5 years after their placement, and the survival rate of the In-Ceram crowns was 91.2%. Within the framework of the limitations of this clinical evaluation, the In-Ceram crowns were found to be clinically acceptable, not only for the anterior teeth, but also the posterior teeth.

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Purpose: The purpose of this study was to determine the optimum cutoff values on a 100-mm visual analogue scale (VAS) for assessing patients'level of satisfaction with their complete dentures, and to extend its use in the clinical setting.
Methods: Cross-sectional consecutive sampling was conducted to gather subjective ratings of existing complete dentures using both VAS and a four-point verbal descriptive scale (VDS). Eighty-two edentulous individuals (39 male and 43 female; mean age: 71.6±8.1years) participated in the study. The satisfaction ratings for existing dentures were measured using both the VAS and the four-point VDS at baseline. Agreement between the patient ratings on the VAS and the four-point VDS was analyzed by Spearman rank correlation coefficient, and the cutoff values were estimated by analysis of the receiver operating characteristics (ROC).
Results: There was significant agreement between the patient ratings on the VAS and the four-point VDS (overall: r=0.84, P<0.001; maxillary: r=0.75, P<0.001; mandibular: r=0.81, P<0.001). The cutoff points on the VAS were clarified for the overall (dissatisfied: 0–31; slightly dissatisfied: 31⁺–50; slightly satisfied: 50⁺–79; satisfied: 79⁺), maxillary (dissatisfied: 0–47; slightly dissatisfied: 47⁺–52; slightly satisfied: 52⁺–80; satisfied: 80⁺), and mandibular (dissatisfied: 0–36; slightly dissatisfied: 36⁺–48; slightly satisfied: 48⁺–83; satisfied: 83⁺) satisfaction.

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Purpose: To elucidate the factors influencing the masticatory muscle activities at maximum voluntary clenching (MVC) after successive use of occlusal splints, we examined the relationships between the changes in the amplitudes of the electromyography (EMG) and possible selected factors by multiple regression analyses.
Methods: The subjects were 25 patients with temporomandibular disorders (TMD) who underwent splint therapy. EMG activities from the bilateral masseter and anterior temporal muscles during MVC were recorded while the patients were not wearing the splint. The first measurement was performed on the day when the splint therapy was started and the second measurement was performed an average of 37.8±10.5 days after the start of the splint therapy. Stepwise multiple regression analysis was used to determine the factors related to changes in the integral values on the EMG.
Results: Pain on mouth opening, height of the occlusal splint and duration of use of the occlusal splint were selected as important correlation factors. The following correlations were found: 1) The EMG activities of the masticatory muscles at MVC decreased with increase in the height of the occlusal splint and duration of use of the occlusal splint, and 2) the EMG activities of the masticatory muscles at MVC increased with resolution of the pain on mouth opening.
Conclusion: 1) It was shown that increase in the height of the bite raising and duration of use of the splint were factors decreasing the EMG activities of the masseter and anterior temporal muscles at MVC in the intercuspal position, while resolution of the pain on mouth opening was a factor increasing the EMG activities of the masticatory muscles. 2) It was suggested that bite raising with the successive use of occlusal splints could have the effect of reducing the load to the temporomandibular joints and the workload of the jaw-closing muscles when the splints are removed.

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Purpose: The purpose of this experiment was to investigate the effectiveness of examining masticatory performance by measuring glucose extraction from chewing gummy jelly.
Methods: Twenty healthy subjects were asked to chew 2g of gummy jelly and 3g of peanuts for 10, 20, and 30 strokes respectively. The masticatory value as measured by the sieve method was then compared with the amount of glucose extraction from chewing gummy jelly.
Results: The relationship between the amount of glucose extraction and the masticatory value was positive (r=0.475-0.850). Both the amount of glucose extraction and the masticatory value were lowest for the 10 chewing strokes and significantly increased for the 20 and 30 chewing strokes (glucose extraction F=1179.6, P<0.01; masticatory value F=605.0, P<0.01). The standardized glucose extraction for the 10, 20, and 30 chewing strokes was 0.17, 0.34, and 0.49 respectively, and increased proportionally. The standardized masticatory values for the 10, 20, and 30 chewing strokes were 0.28, 0.35, and 0.37 respectively, and increased logarithmically.
Conclusion: From these results it was concluded that the masticatory performance as measured by the amount of glucose extraction from chewing gummy jelly is an effective indicator of masticatory function and has a high potential for clinical application.

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Patients: A 56-year-old woman presented with a severely resorbed edentulous mandible, complaining of poor retention and stability of her existing ill-fitting removable partial denture. The original maxillary right lateral incisor and canine were present. A conventional overdenture and implant-retained overdenture were selected for maxillary and mandibular rehabilitation, respectively. The existing mandibular denture yielded an unacceptable position of implant placement. After molding of the denture border and cameo surface was conducted, the existing denture modified using the neutral zone concept allowed proper implant placement.
Discussion: The position of implant placement affects the function and esthetics of an implant-supported overdenture. Preparation of diagnostic and surgical templates using the neutral zone concept facilitates proper implant placement for comfortable dentures. Correctly remolded denture borders and cameo surface allow proper implant placement.
Conclusion: The cameo surface for implant-retained or-supported overdentures needs to be prepared appropriately to obtain satisfactory implant position, in terms of esthetics, function, comfort, or patient satisfaction.

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Purpose: The aim of this article is to describe the procedure for preparing a disposable dust chamber for use in home-visit prosthodontic treatments, that is economical and can be made from materials that are easy to procure.
Methods: After cutting off both ends, the main body of a PET bottle (capacity:1.5 to 2.7 liters) is trimmed to a length of about 15-20 cm. A disposable glove is slipped over each cut end of the PET bottle. The finger and palm portion of the gloves at both ends are then cut off.
Results: Users can work on prostheses within this dust chamber, without dispersing the flying particulate waste produced by the grinding into the ambient air. After use, the chamber can be washed with tap water, and be reused after disinfection. This device also effectively reduces the noise produced by the cutting and grinding.
Conclusion: A low-cost handy disposable dust chamber that can be made easily is presented.

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