Gold-silver-palladium alloy, a dental material covered by medical insurance, hasbeen used as a prosthetic metal material in dental treatment for many years. However, the price of palladium with a content of 20% in the alloy rose markedly after 1998, due to temporary suspension of its supply from Russia, which is its major producer, and the market price of the alloy exceeded its standard insurance price. This paper reviews changes in the prices and supply-demand trends of goldand palladium, which are factors of the soaring price of the alloy, and providesan outlook on the future supply and demand of gold and palladium.

View full abstract

Today, in dental treatment based on the Japanese Social Insurance System, dental casting gold-silverpalladium alloys (including gold at 12% or more, including palladium at 20% or more, and including silver at 40% or more) are mainly used for crown-bridges, inlays, and retainers of removal partial dentures in Japan. However, according to the sudden rise in the price of palladium during the last two years, the relation between the treatment fee and the cost has lost the previous balance. This report was written based on this situation and some investigations. As the results, we concluded that it would be difficult to discover a new substitute for present gold-silver-palladium alloys, and that fact should be recognized as a good opportunity to look for a better material.

View full abstract

Gold-silver-palladium alloy has been in very extensive use as a substitute alloyfor a dental gold alloy in Japan. This alloy is predominantly silver in composition, but it has substantial amounts of palladium, which provides silver tarnish resistance. This alloy also contains 12mass% gold, and as much as 15mass% or more copper, to produce acceptable castings and have properties like a type 4 gold alloy. From the viewpoint of inflationary prices of palladium and occurrence of allergy, development of a low-content palladium alloy is expected. However, there have been some reports, such as that silver alloys containing less than 15mass% palladium do not have adequate mechanical property for prosthetic appliances, and that silver alloys that contain up to 5mass% palladium required more than 30mass% gold to restrain the tarnishing of silver. In this paper, the potential ofalternative alloys of gold-silver-palladium alloy is discussed.

View full abstract

Titanium is expected as a dental metal that will substitute for Au-Ag-Pd alloy, because of its corrosion resistance and excellent biocompatibility. However, titanium has the disadvantage of difficulty in processing; therefore, it has not been used generally in clinical dentistry. In recent years, new exclusive investment materials and casting methods for titanium were developed, and as a result the casting accuracy of titanium was improved to the level of clinical application. In addition, various processing methods other than casting were applied, and CAD/CAM system has already become in practice. As for polishing, which was another problem with titanium, some new methods were devised. Accordingly, technical problems impeding the clinical application of titanium are now being settled. Nowconsider what else prevents the diffusion of titanium in clinical dentistry, other than technical problems. Dentists did not learn in detail about titanium in undergraduate school, so they cannot easily use titanium, and the initial investment to process titanium is considerably expensive. To spread the use of titaniumas a substitute for Au-Ag-Pd alloy, it is necessary to publicize the advantages and disadvantages of titanium as a dental metal, toward dentists through undergraduate and postgraduate courses. Furthermore, prosthetic devices taking advantage of titanium should be devised.

View full abstract

Patients: Obstructive sleep apnea syndrome (OSAS) has been known to increase risk of other systemic diseases, and traffic accidents, due to daytime sleepiness. We report the case of a 42-year-old male diagnosed as having a severe-grade OSAS. Polysomnographic assessment revealed that the apnea index (AI) and the apnea-hypopnea index (AHI) before treatment were 33.4 and 48.5, respectively. A Harbst-type oral appliance connecting maxilla and mandible occlusal appliances was prescribed, to improve pharyngemphraxis during sleeping. Seven months after starting the appliance therapy, another polysomnographic assessment was carried out, and it showed that AI (4.5) and AHI (9.7) had remarkably improved with the therapy. No significant side effects on masticatory muscles and the temporomandibular joint were observed during the appliance therapy. Furthermore, delta sleep increased from 1.5 to 17.4% after the oral appliance therapy.
Discussion: Although various treatment modalities (e. g., nasal continuous positive airway pressure: CPAP) have been tried to improve the symptom, OSAS patients often complain of displeasing feelings and side effects due to the therapy itself. Fromthis point of view, oral appliance therapy could be a desirable treatment modality even for severe-grade OSAS, since it produces enough compliance owing to its less displeasing sensation.
Conclusions: We experienced a severe-grade OSAS patient whose sleep quality was effectively recovered by mandibular advancing appliance therapy.

View full abstract

Purpose: The purpose of this study was to analyze the effect of indirect retainers on the vertical displacement of lower unilateral distal extension removable partial dentures (U-RPD).
Methods: An available jaw tracking system (TMJAWGRAPH (R)) was modified to measure the jaw movement and the motion of aremovable partial denture, at the same time. Three markers were fixed in the U-RPD, mandible, and head, and allowed simultaneous 6 degree-of-freedom recording of their movements. The experimental denture could separate from direct retainersand indirect retainers. So, we could change denture form without changing occlusal contidion.
Results: 1. The vertical denture displacement in the most posterior point in the flange (MPFP) was different with the design of indirectretainers. Without indirect retainer, vertical denture displacement increased. There was no relationship between range of motion and the vertical denture displacement. 2. The vertical denture displacement in MPFP was not influenced by the indirect retainer rest position. There was a relationship between the indirect retainer rest position and the vertical denture displacement.
Conclusions: The vertical denture displacement during mouth opening was able to classify, as a whole, upper movement and rotation movement. The rotational movement had anaxis, which existed in direct retainer rest and in premolar. In this case, however, the axis had not related to the fulcrum line.

View full abstract

Purpose: The purpose of this study was to analyze tooth color changes of the elderly caused by aging and the color difference between teeth and commercial artificial teeth.
Methods: Sixty-nine subjects (38 males, 31 females, mean age 70.0±7.2 years) who had intact anterior teeth in the maxillary dental arch, volunteered to participate in this study. The tooth color of the following areas was measured: cervical, middle, incisal areas for the central incisor and canine, and cervical, incisal areas for the lateral incisor. The color ofeight commercial artificial teeth (total of 51 shades) was also measured. The tooth color and the proportion of subjects whose tooth color diverged from that ofartificial teeth were compared between two age groups: 60-69 years, and age 70 and over.
Results: The tooth color tended to decrease in values of L*, a*, and b* in age 70 and over group. A significant change was observed for a* value in the canine, and the b* value in the lateral incisor and canine. Of all measurements for teeth, 24.0% for L*, 8.1% for a*, and 3.8% for b* were not diverged from artificial teeth. With aging, higher proportions of subjects' teeth color diverged from the color of artificial teeth.
Conclusions: It was observed that a tooth color change caused by aging occurred among the elderly. It was shown that the number of the elderly teeth whose color diverged from those of theartificial teeth, increased by aging. In this study, it was suggested that a color with a dark and red tendency was needed for artificial teeth to match the color of teeth of the elderly.

View full abstract

Purpose: The purpose of this study was to investigate the adequate measurement points and the standard value in the polygon for an analysis method using the traces of standardized, panoramic radiographs, designed as an image diagnostic method for complete denture prosthodontics.
Methods: The subjects consisted of young dentulous volunteers, and complete denture wearers immediatelyafter new denture insertion. We measured angular and linear measurements on the crucial parameters in prosthetic therapy, such as the occlusal vertical dimension and the occlusal plane, which were based on anatomical landmarks on the tracesof standardized panoramic radiographs. We determined the mean value of the youngdentulous subjects and the complete denture wearers (one-way ANOVA and multiple comparisons, statistically). Moreover, we prepared the polygon for each gender, based on the data of the complete denture wearers. And we assessed those parameters of the old and new dentures of one edentulous patient for each gender.
Results: The measurements showed significance between males and females of the young dentulous subjects and the complete denture wearers, and between the young dentulous subjects and the complete denture wearers for each gender. And the occlusal plane was more parallel to Camper's plane based on the inferior margin of tragus than the one based on the superior margin as the posterior referencepoints. Moreover, it was suggested that we could assess the occlusal plane and occlusal vertical dimension of edentulous patients by the polygon based on the data of complete denture wearers.
Conclusions: In this study, we improved the analysis method using the traces of standardized panoramic radiographs. And it was suggested that the polygon based on the data of complete denture wearers for each gender could be applied to assess the dentures of the edentulous patient.

View full abstract

Purpose: The purpose of this study was to investigate and examine, statistically, the effective rate of clinical cases to design a crown by a dental CAD/CAM system, by using the method of tooth form data from the corresponding tooth located on the contralateral side of the mouth.
Methods: Patients' clinical records, X-rays, plaster models, and dental work orders of 1, 363 molar teeth from 567 patients, were examined to determine the possibility of using the method of tooth form data from the corresponding tooth on the contralateral side. Also, an investigation was conducted on the subject molar teeth, to determine statistical differentiations.
Results: 324 (23.8%) of the 1, 363 teeth were judged applicable for use of this method of tooth form data to design a crown. Significant differences were not found in the upper jaw (25.2%) and the lower jaw (22.6%); no significant differences were found between the left side (23.2%) and the right side (24.4%), either. However, there was a significant difference between the premolar (27.5%) and the molar (21.6%) teeth.
Conclusions: A statistical examination was conducted on the effectiveness of the method of using the tooth form data from the tooth on the contralateral side, to design CAD/CAM crowns, and the result suggested that this method was most effective for thepremolar teeth.

View full abstract

Purpose: The Dental Cadim^® (dental CAD/CAM system) measures the shape of the wax pattern by contact process, and milling of the metal block. The purpose of this study was to fabricate a metal coping from a titanium block by the Dental Cadim^®, and examine its processing precision.
Methods: The sample of the metal coping was fabricated by this Dental Cadim ^(R) system, and its processing precision was investigated. Next, only the process of milling was repeated, and the error in the milling was examined. The processing precision was evaluated by measuring the amount of gaps of the metal coping and the die.
Results: The error of A-type (acute angle type) was larger than the error of R-type (round type). The amount of gaps of the metal coping and the die was about 0.100mm, on average. The error in the milling wassmall.
Conclusions: 1. A metal coping with a post could be made adequately by this dental CAD/CAM system. 2. The shape of the boundary between the coping and post influences the processing precision in this system. 3. The error inthe measurement process was greater than the error in the milling process, and the error in the measurement process influences the processing precision.

View full abstract

Purpose: This study evaluated the prognosis of IMZ implant cases (271 patients, 972 implants) that had been placed over 13 years at two institutions: thehospital attached to the Nippon Dental University School of Dentistry at Niigata (Inst. 1); and Enomoto Dental Office, in Sanjo City (Inst. 2).
Methods: Of the 972 implants, 913 had been clinically examined, in 254 patients, withinthe past two years (recall rate 93.7%). The evaluation was performed focusing on: 1) survival rate, 2) maxillomandibular survival rate, and 3) implant survival rate according to implant sizes. Data obtained were analyzed using the Kaplan-Meier method and Life Table Analysis.
Results: The following results were obtained. 1. The cumulative survival rate was 96.3% for 5 years, 92.6% for 10 years, and 89.9% for 13 years, for the total of implants at Inst. 1 and 2. 2. Asto the association of implants with the natural teeth, fracture of the natural teeth occurred in 12.1% of connection cases at Inst. 1, and in 6.8% of connectioncases at Inst. 2. All the fractured teeth were non-vital. 3. Analysis of the total of implants recalled at Inst. 1 and 2 showed no significant differences in the survival rate between maxillary and mandibular implants (Breslow-Gehan-Wilcoxon test, p=0.61). 4. Although no significant differences in the survival rate were noted between implants 3.3mm in diameter, and implants 4.0mm in diameter (Logrank test, p=0.51), and there were also no significant diferences among implants 8, 10, 11, 13, and 15mm in length (Logrank test, p=0.45), the removal rate of implants was different according to implant sizes. Regarding the diameter of implants, the rate was 6.9% for 3.3mm, and 3.4% for 4.0mm, showing a higher survival rate with an increased diameter. Regarding the length of implants, the rate was 13.0% for 8mm, 4.4% for 10 and 11mm, 2.0% for 13mm, and 0% for 15mm, showing a higher removal rate for shorter length.
Conclusion: As the IMZ implant achieved a long-term high survival rate, this implant is useful for clinical application.

View full abstract

Purpose: The purpose of this study was to evaluate osteogenesis, histopathologically and histomorphometrically, around porous hydroxyapatite (HAP) blockson bone with or without expanded polytetrafluoroethylene (e-PTFE) membrane, as an application of the guided bone regeneration (GBR) method.
Materials and Methods: In the experimental group, HAP blocks were implanted on the parietal bone of rats and covered by e-PTFE membranes. In the control group, only HAP blocks were implanted between the parietal bone and periosteum. Tissue reaction and osteogenesis around HAP blocks were evaluated histopathologically and histomorphometrically. Some specimens were stained with tartrate-resistant acid phosphatase (TRAP).
Results: New bone had attached directly to HAP at 2 weeksafter implantation in both groups, and after that, new bone grew up. Newly formed bone was recognized in the upper area of the pore of HAP blocks in the experimental group, in comparison with the control group. The amount of newly formed bone in the experimental group was significantly more compared with the control group at 4 weeks, while the significance was not recognized at 8 weeks. The numberof TRAP-positive multinucleated giant cells increased until 4 weeks, and decreased at 8 weeks, in both groups. The number of TRAP-positive multinucleated giant cells in the experimental group was significantly more than in the control group, and it was suggested that bone remodeling was active.
Conclusions: These results suggest that the utilization of e-PTFE membrane as an application of the GBR method is effective for osteogenesis in HAP grafts on bone.

View full abstract

Purpose: The purpose of this study was to elucidate the relation between occlusal contacts and craniomandibular disorder (CMD).
Materials and Methods: Forty CMD patients cured by adjustment of the occlusal interferences detected by EMG biofeedback occlusal analysis, and 12 healthy dentate subjects as a control, were examined. The occlusal contacts of the subjects were examined at two different occlusal positions. One was the intercuspal position (ICP), and theother was the physiologic centric position (PCP), which was an extremely light tooth tapping position with the aid of EMG biofeedback. The occlusal contacts on each checkbite were traced on the lower teeth, and their areas were measured. The asymmetry index (AI) of the occlusal contact area was calculated before and after treatment in CMD patients and healthy subjects.
Results: 1.No significant differences were observed in the AI of the occlusal contact area at ICP between CMD patients and healthy subjects. 2.AI at PCP was decreased significantly after treatment (before: 54.6±33.1%, after: 15.1±12.5%, p>0.05). Al after treatment was not different from that (14.9±9.7%) of healthysubjects. 3.Bilateral balance of occlusal contact areas on first and second molars was significantly improved more than anterior teeth and premolars.
Conclusions: These results showed that the acquisition of bilateral balance of occlusal contacts is important to cure CMD. It was suggested that occlusal interferences on molars are more closely related to CMD, and that bilateral balance ofocclusal contacts is a normal occlusal contact pattern.

View full abstract

Purpose: The purpose of this study was to investigate the effect of teethclenching on grip force production characteristics.
Methods: Twelve healthy male subjects (age: 23.7±2.2year: mean±S. D.) were asked to exert maximal explosive grip force with their right hands for 2 seconds under thefollowing 2 conditions: 1. Maximum voluntary clenching of the teeth (MVCT), 2. Mandibular rest position (RP). The measurement was performed twice for each condition. Measurements were repeated after a 3-minute rest period. For 1 second after the onset of force production, maximal force (maxF), average force every 0.1 second (aveF), maximal rate of force development every 0.001 second (maxRFD), andtime to 90% of maximal force (T90%max) were statistically analyzed to compare the two conditions.
Results: maxFs during MVCT were significantly larger, by 8.4%, than during RP (p=0.0480). aveFs in all 10 recordings significantly increased with MVCT. The increasing rate of aveF during MVCT ranged from 7.9 to 36.1%(p<0.0095), and the maximum increasing rate was recorded at the first period (0-0.1 second). maxRFD was significantly increased, by 16.2%, in association with MVCT (p<0.0001). T90%max during MVCT was significantly shorter than during RP (p=0.0017).
Conclusions: Our results suggest that teeth clenching during grip force exertion may contribute to greater maximal force and quicker force production.

View full abstract

Purpose: Differences in lining surface roughness between direct and indirect methods, by the use of silicone soft lining materials, were investigated, and the influence of dental gypsum and a separating medium was evaluated.
Methods: After taking impressions of acrylic plates using silicone impression materials, 3 gypsum were injected, to produce gypsum models. After applying 3 separating mediato the gypsum samples, specimens were produced by pasting soft lining materials.Using a non-contact three-dimensional measurement machine, surface roughness of the acrylic plate, impression, gypsum before and after applying a separating medium, and soft lining materials were measured. Further, SEM observation of the gypsum and lining materials was performed. Lining by direct and indirect methods using 2 soft lining materials was performed in 21 lower complete denture wearers.Surface roughness by the direct method, and that of impression, gypsum model before and after applying separating materials, and lining surface before and afterapplying glazing materials by the indirect method, were measured.
Results: Nosignificant differences in surface roughness were noted among gypsum samples before applying a separating medium, and surface roughness of the gypsum samples after applying a separating medium was significantly lower than that before applying a separating medium. Surface roughness of soft lining materials was significantly low in the group in which vaseline was applied to gypsum, in comparison with other groups. Although surface roughness by the indirect method was significantly higher than that by the direct method, it showed a significantly lower valueafter applying glazing materials.
Conclusions: Although surface roughness of lining surface by the indirect method was higher than that by the direct method, due to the influence of plaster and separating medium, it was suggested that a relining surface by the indirect method could be smoother than one by the direct method, by applying glazing materials to the surface.

View full abstract