Although titanium has been a popular metal in dentistry, it was not actively applied in the clinic. Some of the reason were most importantly a hardened layer formed on the casting surface with a reaction between mold material and molten titanium that had different physical and chemical properties than titanium. Moreover, fit of prostheses is lost due to the removal of the reacted layer. On the other hand, internal defects are often observed by X-ray photography of titanium castings. Bubble-like defects formed by gas inclusion will lead to worse durability.
In order to obtain sound titanium castings, it is important to maintain surface transcription with high quality during the casting procedure and decrease casting error. A new investment may be a key to success. A development of titanium alloy seemed to be effective as prosthetic materials.

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Titanium is a difficult-to-machine metal, due to its high reactivity with abrasives. The cutting rate of alumina is significantly low. In contrast, at higher rotational speed and greater grinding force, the cutting rate of carborundum is much greater, but accompanied by severe loss of the tool. Since titanium has low thermal conductivity, the grinding temperature influencing titanium-abrasive reactions should be kept from rising. Relatively low rotational speed and small force are recommended. In addition, the tool should not be depressed against the work during grinding but moved over the work, otherwise unfavorable results are yielded: abrasive attrition, chip loading and oxidation of the surface, or grinding burn. Since polishing is also a procedure of cutting by abrasives, inhibition of titanium-abrasive reaction is an important key to efficient polishing. Recently, two finishing techniques were successfully applied in dentistry, electrochemical buffing and mechanical buffing with colloidal silica as abrasive. When the reaction-inhibition mechanism is clarified in these techniques, a new development will be possible.

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Pure titanium and titanium alloy have been developed to apply to general machinery for medical and dental use.
Titanium has some unfavorable characteristics when casting for use.
Evaluation of the casting and mechanical properties was done to determine if pure titanium can be applied to the metal framework.
The results were as follows:
1. External and internal casting defects occurred easily.
2. Reacted layer was formed on the surface of titanium at high temperature.
3. Manufacturing cost was high.
4. Titanium could substitute for gold alloy due to its mechanical properties.
Manufacturing cost and difficulty were the negative factors when developing titanium for use even if with the mechanical property was similar to the gold alloy. Application of titanium to dentistry should be done considering the mechanical and biocompatible characteristics such as low specific gravity and low allergic effect. So-called environmental hormone is drawing attention these days. Various alloys may be evaluated of their biocompatibilities before applying to the oral cavity in the very near future.

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Although titanium has been cast for over 50 years, it has only been recently that nearly precise casting has been attainable. Titanium is well known for its general biocompatibility and very low allergic potential. The difficulties with cast titanium for dental purposes include high melting temperature and high reactivity, low casting efficiency, inadequate expansion of investment, casting porosity, and difficulty in polishing this metal. Recently, improvements in processing techniques such as casting, computer-aided manufacturing, and spark erosion have made dental titanium restorations possible, and titanium is widely used in fixed restoration. It is expected that titanium will be applied to hard resin facing crown, ceramometal crown, post of the abutment tooth and machine-milled metal of CAD/CAM system. However, when titanium is applied with hard resin adhering metal and porcelain fusing metal, problems of strong oxidation of the metal surface and coarse oxidative adhesion arise. Therefore, how the treatment of titanium surface affected the adhesive strength between titanium and hard resin and the oxidation heat treatment affected the bonding strength for clinical applications were investigated. Because of fine mechanical strength and positive biologic properties of pure titanium, it is suited for the fabricated post of an endodontically-treated tooth. Since the CAD/CAM system utilizes a milling machine, casting is unnecessary; therefore, titanium can exhibit its original properties. The CAD/CAM system copes with pure titanium in a short time, and hard resin is adhered with it or porcelain is fused to it. Conventional soldering techniques do not work in titanium because of its passivated oxide layer and high reactivity. The laser welding technique using titanium to join the sectioned ends has demonstrated less heat affect and more accuracy than the conventional soldering technique.

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Titanium is a property that is easy to bond to polymeric material through a stable oxidation film generated in the surface. Many researches were carried out to apply this property of titanium to clinical prosthodontics. It was thought that titanium can be applied to resin veneered crown by the non-retention method, so a series of experiments on the bonding property between titanium and resin were conducted. The various surface treatments that combined alumina-sandblasting and heating to pure titanium were performed. The influence of these treatments on the wettability of the titanium surface were examined, and the influence on the bond strength between titanium and resin was also examined. From the results, the surface treatment of titanium that improves the bond strength to resin was found.

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This study was conducted to investigate the effect of surface treatment on bond strength of resin composite bonded to occlusal surface of abrasion-resistant plastic denture tooth. Nine different surface treatment methods for the occlusal surface were evaluated using the compressive shear bond strength test. Specimens without surface treatment have significantly lower bond strength than specimens treated with seven surface treatment methods (p<0.05), and showed interface failure after the test. Specimens treated with 5% hydrofluoric acid treatment +bonding agent treatment, sand-blasting treatment +bonding agent treatment, and sand-blasting treatment+5% hydrofluoric acid treatment+bonding agent treatment methods showed significantly higher bond strength than specimens treated by other treatment methods (p<0.05) and showed cohesive failure after the test.

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In the previous report, the relative position between two implants was measured during jaw movements, and mandibular flexure was evaluated as the change. In the present study, three-dimensional finite element models were constructed so that six titanium implants were placed in the right half of the mandible, and three models were prepared: 1) Connected: all implants were connected, 2) Anterior only: anterior three implants only were connected, and 3) Not connected: no implant was connected. The influence of the connection on the implant and the surrounding bone determined by linear static stress analysis of 3-D finite element model was discussed.
The results were as follows:
1. The inside loading value applied to the mandibular condyle was calculated from the implant deviation data of previous reports. The value was 20 N.
2. In three models the implant was deviated medial-backward and the deviation drastically increased from the Implant No.4 region.
3. The stress of 8 MPa around the implant in the “Not connected” model was observed, and that of “Anterior only” and “Connected” models was lower.
It was suggested that implant connection hardly affects the implant and the surrounding bone during mandibular flexure in jaw movements.

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The antibacterial activity of photo-cured denture relining resin against oral bacteria from the viewpoint of denture plaque control as investigated. Four kinds of photo-cured denture relining resins was used for the experiment. S. sanguis ATCC 10556, S. mutans ATCC 25175, S. mitis ATCC 3339, S. salivarius ATCC 25975, B. gingivalis ATCC 3327, and Candida albicans ATCC 18804 were used as test strains. Antibacterial activity of the photo-cured denture relining resin immediately after curing and after immersion in artificial saliva for one week were measured. An elute from the resins was measured by high-performance liquid chromatography.
Three relining resins showed antibacterial activity against the S. mutans, two resins showed antibacterial activity against the B. gingivalis and one resin showed antibacterial activity against the Candida albicans. However, all resins showed no antibacterial activity against the S. sanguis, S. mitis and S. salivarius. After immersion of resin into the artificial saliva, the resin showed no antibacterial activity. Urethane dimethacrylate, iso-butylmathacrylate, and hexandioldimethacrylate were identified by high-performance liquid chromatography. These monomers showed the same antibacterial activity as the settings of relining resin.
These results suggested that the antibacterial activity was produced by monomer of resin and relining resin did not have long lasting antibacterial activity.

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Eight elderly patients who were required to wear full or partial denture participated in this study (mean age: 81.1 years). The subjects were six patients with denture and two patients without denture at the first visit.
Hematological, immunological (NK activity, T lymphocyte subset CD 4 and CD 8) and biological analyses were made for all patients. Patients removed their denture for 10 days, and analysis was done three times:(A) immediately before removal, (B) on the final day of removal, and (C) 10 days after wearing the denture. Patients without denture were examined two times:(B) immediately before wearing newly-made denture, and (C) after wearing the denture for enough time to adjust it. The results were compared between A and B (n = 6), and B and C (n=8), respectively (paired Wilcoxon's test, p<0.05).
There was a significant decrease in CD 4/CD 8 ratio from A to B, and there was a significant increase in CD 4/CD 8 ratio from B to C. Thus the above suggested that the presence of denture should influence the parameters and there should be a relationship between masticatory function and immune system.

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The purpose of this study was to investigate the effects of various retainer designs on the characteristics of stress distribution and vertical dislodgment of the denture base. A mandible simulation model of unilateral distal-extension missing teeth (three teeth from the second premolar to the second molar) was used in this study. A conical crown, Akers clasp, and double Akers clasp were used as retainers.
The results were as follows:
1. The conical crown retained denture produced significantly less stress distribution and vertical dislodgment of the denture base than the two clasp designs.
2. The conical crown retained denture produced the most intense stress on the apical and distal surfaces of the most distal abutment, while the double Akers clasp design produced the least stress.
3. The Akers clasp design produced less load distribution of the denture base and greater vertical stress of the abutment tooth than the double Akers clasp design.
4. The bilateral denture design produced less load distribution of the denture base and greater vertical stress of the abutment tooth.
5. On condition of the bilateral denture design including clasps with a proximal plate, stress and load distribution were similar to those of the conical crown retained denture.

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The purpose of the study was to verify the significance of prosthodontic treatment for the elderly patients by our university's dental treatment system at home. Thirty-four patients whose dental practice was based on removable prosthodontic treatment and performed by the staff of our department were given questionnaires on satisfaction with the treatment and denture insertion. The results were as follows:
1. Seventy percent of the patients were in their seventies and eighties and almost half of them were edentulous.
2. ADL scores of the patients were low and most patients needed care.
3. The prevalence of cerebrovascular disease was fifty-six percent in the patients.
4. Ninety-four percent of the chief complaints about dental satisfaction of the patients was masticatory disturbance due to wearing uncomfortable dentures.
5. Forty-seven percent of the patients needed to have their dentures replaced.
6. Almost all patients answered that they were satisfied with the prosthodontic treatments offered at home.
From the results of this study, removable prosthodontic treatment is significant not only for the restoration of stomatognathic function and appearance but also for the improvement of quality of life for the home bound elderly.

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The purpose of this study was to examine changes of 1/f fluctuation of brain waves with before and after psychological stress load. A 10-minute mental arithmetic test was used.
As a result of giving a psychological stress load, it was suggested that emotional variation is related to changing the 1/f fluctuation spectral of a brain wave.

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A case of lichen planus of the buccal mucosa in a 52-year-old female is reported. Her teeth were cemented by a fixed bridge in a dental clinic three years earlier. A few days later, she had a constant pain in her oral mucosa that was worsening. She visited our hospital with this swelling, so the lesion was examined. Lichen planus was recognized in the biopsy specimen of the lesion. She had a medical history of metal allergy. Patch test for dental metal sensitivity was used to investigate the problem. Positive reactions were observed for tin, copper, chromium, gold, and palladium. Investigation was done by metal biopsy of the surface of the resin disk inscribed on her prostheses. The minute amounts of biopsy on the resin disk were analyzed by ESCA. It was found that her prostheses were made of Au-Ag-Pd and Ag-In-Sn alloys. These results suggested that this case may have lichen planus caused by allergy to dental alloys. Therefore, her metal prostheses were removed and a temporary restoration of resin for 10 months was done. Finally, a titanium prostheses was applied. Her condition has remained good without any allergic reaction. It seemedthat this treatment was successful because her lesion recovered.

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Secondary failure in adhesion at the denture base resin and self-curing resin interface is a common problem with repaired or relined denture. It is caused by insufficient bond strength of both materials. Various organisms, bacteria, and plenty of water penetrating the denture base resin are considered to be the important factors which decrease the bond strength of both materials. The purpose of this investigation was to determine the effect of water absorbed in the denture base resin on shear bond strength and bond durability between the denture base resin and self-curing resins. In addition, effects of some chemical and mechanical etching treatments of the denture base resin surface on shear bond strength between two materials were also studied.
The results were as follows:
1. Bond strength and durability of water saturated denture base resin and self-curing resin were not necessarily decreased in comparison with the use of dried denture base resin.
2. In case of using Unifast II, bond durability to the thoroughly dried denture base resin was markedly decreased.
3. Unifast II demonstrated the highest bond strength and durability to the denture base resin treated with 50μm aluminum oxide sandblasting.
4. Tokuso Rebase (Normal Set) demonstrated the highest bond durability to the denture base resin treated with methylene chloride.

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IPS Empress^® is an all-ceramic crown system which provides a color tone and light transmittance resembling those of natural teeth. However, because of the translucency of all-ceramic crowns, the color of the adhesive resin cements and the abutment teeth can affect the color of the final crowns.
This study examined the effects of IPS Empress^® on the layering technique and color of the adhesive resin cements on various background color by comparison and examination.
The color difference from the standard color was calculated, and it was judged to have color appearance when ΔE*ab≤2.0.
The conclusions were as follows:
1. For A 2 background, the color appearance to standard color were obtained using translucent type cements VW and VB (Variolink).
2. For Au background, the color appearance to standard color were all of translucent type cements, while for Pd background, opaque type cements YO (Variolink) insertion with better color appearance.
3. For H background, using translucent type cements Tr (LA cement) containing dentin color tone and opaque type cements VO (Variolink) with lower values of lightness yielded ΔE*ab≤2.0 with color appearance.
The above results suggested that appropriate intermediate cements used in the layering techniqueof IPS Empress^® decrease the influence of the background color, achieving a color tone approximating the target color.

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The purpose of this study was to investigate the effect of modification of clasp assemblies on connecting rigidity. Unilateral distal-extension removable partial dentures were constructed for this study with a simulation model. A cone-telescopic crown and 10 different clasps were used as direct retainers. The ten clasps included Akers clasp, double Akers clasp, Kratochvil type RPI clasp, and seven modified clasps. These modified clasps were made from three different types of conventional clasps to which a guide plate, enlarged bracing arm, positive rest with hook, and distal rest were added. Vertical loads were applied, and the stress on abutment teeth, load distribution, and dislodgement of the denture base were measured.
The results were as follows:(1) the partial dentures retained by a cone-telescopic crown and clasps with a distal rest generated large vertical and distal stresses on the abutment teeth;(2) modified Akers clasps with an enlarged bracing arm and/or positive rest caused less load distribution but large vertical movement of the denture base;(3) stress characteristics of the abutment teeth and load distribution of the denture base of the modified double Akers clasp and modified RPI clasp with guide plate, enlarged bracing arm, and distal rest were similar to those of the cone-telescopic crown; and (4) the cone-telescopic crown and clasps with amesial rest caused less vertical displacement of the denture base.

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The purpose of this study was to investigate the influence of various staining materials and heating rates on the surface texture and mechanical properties of castable ceramics (OCC^®) during crown fabrication.
The results were as follows:
1. Surface roughness and bending strength of the stained specimens were not influenced by the different kinds of staining materials and heating rates.
2. Surface gloss of the stained specimens tended to increase at a low heating rate.
3. Surface roughness of the stained specimens decreased, but bending strength was smaller than that of the sandblasted specimens.
It was found that the existence of a stain layer exerts a major influence on mechanical properties.
4. There was no relation between thickness of the stain layer and the bending strength.

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The purpose of this experiment was to investigate the possibility of quantitatively evaluating facial surface temperature which was necessary in establishing a diagnostic method of CMD by thermography. With the zygomatic arch as the standard, the surface temperature of the outer part of TMJ was measured andthe temperature difference between these two areas as well as the temperature difference between left andright sides of the same area of 20 normal subjects, aged in their twenties, were compared with 20 CMD patints.It was found that there was a highly significant positive relation between the zygomatic arch and the outer partof TMJ in their surface temperature for normal subjects. Further, though individual variation existed in bothnormal subjects and CMD patients the surface temperature of the outer part of TMJ and its bilateraltemperature difference were higher and larger for CMD patients than for normal subjects and a highlysignificant difference' was found between the two groups. Furthermore, the surface temperature of the outerpart of TMJ in relation to the zygomatic arch was significantly higher for CMD patients than normal subjects, and a statistically significant difference was found between the two groups. From these results, it wasconcluded that the zygomatic arch was an appropriate area for measurement, that the temperature differencebetween the zygomatic arch and other areas of measurement can be used as an effective index, and that it waspossible to quantitatively evaluate the facial surface temperature by thermography.

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The effect of water sorption on the ultimate transverse strength of a heat-cured denture base resin relined with four different direct denture reline materials was investigated. The relined specimens weretested after 1 day and 1 month of water immersion. It was found that prolonged duration of water immersionand an increase in the thickness of the reline material significantly (p<0.01) decreased the ultimate transversestrength of specimens relined with powder-liquid type direct reline materials. Specimens relined with pastetype reline material did not change the ultimate transverse strength after 1 month of water immersionsignificantly.

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For improvement of film thickness of final cementation, 2 brands (Shofu HY-BOND GLASS-IONOMER CX and GC Fuji-I) of Glass Ionomer Cement were milled and the experimental fine particlepowder was produced. Ohmae et al. reported the retention, total film thickness, and physical properties in aprevious study. In this study, the setting characteristics of these experimental cements, specific surface areaof particle, and disintegration rate were investigated. The results were as follows: Peak time of reaction ofexperimental cements using a differential scanning calorimeter were shorter than normal GICs. The startingpoint of dissappearance of fluidity of experimental cements using a thermomechanical analyzer were shorteras the perticle size became smaller. The specific surface area of experimental particle increased as theparticle size became smaller. The disintegration rate of experimental cements increased compared to normal GICs.

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The purpose of this study was to investigate the effects of changes in the anterior guide (AG) on EMG activity of the inferior head of the lateral pterygoid muscle (Lpt). The inclination of the sagittal condylar path (ISCP) in each subject was measured. Values were 20°in sub. 1, 32°in sub. 2, and 43°in sub. 3. Crowns in which the inclination of the sagittal incisal path (ISIP) was equal to that of ISCP (0°), as well as those with ISIP of-10, +10, +20 and + 30° from the ISCP were prepared. The subjects were instructed to perform protrusive sliding movement while wearing each crown. EMG of right Lpt was recorded with condylar movement simultaneously. Condylar movement and mean voltage of EMG (MV) were measured every 0.03 seconds.
In sub. 1, the MV did not change significantly with changes in the AG. In both sub. 2 and 3, distance and mean velocity of condylar movement increased and the MV decreased significantly as the AG increased. These results suggested that changes in the AG affected the activity of Lpt on protrusive jaw movement and the AG steeper than the ISCP contributes to smooth condylar movement. However, these differences of effect may have been caused by differences in the ISCP.

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The purpose of this study was to clarify the relationship between TMD and occlusal contacts on dental arch. Fourty TMD patients and 12 healthy subjects as controls were examined. TMD patients were cured by occlusal adjustment of the occlusal interferences detected by biofeedback occlusal analysis. The occlusal contacts of the subjects were examined at two different occlusal positions. One was the intercuspal position (ICP), and the other was the physiological centric position (PCP) that was an extremely light tooth tapping position with the aid of EMG biofeedback.
1. No significant difference was observed in the number of occlusal contacts at ICP between before and after treatment. The number at PCP was 4.2 before and 12.2 after treatment, increasing significantly after treatment (p<0.01).
2. No significant differences were observed in the asymmetry index (Al) of occlusal contacts at ICP among TMD patients and healthy subjects. AI at PCP was 54.3% before and 10.8% after treatment, decreasing significantly after treatment (p<0.01). AI after treatment was not different from that (10.1%) of healthy subjects.
3. In cases of palpation pains on one side, 21 (72.4%) out of 29 cases were found to be occlusal interferences on the same side observed palpation pain. Occlusal interferences were high frequently found to be in inclines that demonstrated a posterior direction of the occlusal force on mandible with signs and symptoms.
These findings clearly showed that the acquisition of bilateral balanced distribution of occlusal contacts at PCP is important for the cure of TMD. It was suggested that bilateral balanced distribution of occlusal contacts is one of the normal occlusal contact patterns and there is a close relation between the location of occlusal interference and prevalence of signs and symptoms of TMD.

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