Purpose : This study investigated the effect of immersion temperature on the flexural strength of a pre-coated E-glass fiber reinforced, UTMA-based composite resin. In addition, the effect of coating the fibers and the bonding agents on the flexural strength of the composites at two different temperatures was evaluated.
Materials and Methods : Continuous pre-coated glass fibers (impregnated everStick and preimpregnated Stick^TM-fibers) were placed parallel to the longitudinal axis of the specimen. The fibers were covered with a UTMA-based composite resin. The specimens were light- and heat-polymerized and then stored in a water bath at 37°C for 24 hours as well as at 70°C for 24 hours and for 7 days. After immersion, the flexural strengths of the specimens were measured and the fracture surfaces studied using SEM. The results were analyzed using statistical methods.
Results : After 24 hours at 37°C, the flexural strength values were between 603 and 676 MPa. There was no significant difference between the different types of glass fibers. At the high temperature (70°C), the flexural strength of the specimens containing pre-impregnated fibers deteriorated but the specimens containing impregnated fibers retained their flexural strength.
Conclusion : Within the limitations of this study, the results suggest that in the impregnated fibers, the bonding agent is evenly spread around the fibers. It is not possible for water molecules to diffuse into the matrix. However, further studies are needed to confirm the reasons why the flexural strengths of either the wetted (pre-impregnated) fibers or the composite resin decreased after 7 days' immersion at 70°C.

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Purpose : The purpose of this study was to investigate changes in postural control after the use of new complete dentures by evaluating gait and body sway.
Materials and Methods : Nine edentulous subjects who needed to have their complete dentures replaced participated in this study. Gait cycle and velocity while walking for 10 m and the locus of the center of gravity in a standing position for 60 seconds were recorded. To examine the influence of the use of new dentures, records were made when the subjects used their original dentures, immediately after the new dentures were inserted, and also after adjustments to the new dentures were completed. The following three experimental conditions were used to examine the influence of denture wear : dentures worn in an occluded position, in a non-occluded position, and dentures not worn. Two-way ANOVA with repeated measures was performed and then subjected to a post hoc analysis.
Results : All the variables were significantly influenced only by the use of new dentures (p<0.05). After the completion of the new denture adjustments, gait cycle decreased and gait velocity increased compared with those observed when using the original dentures (p<0.05). The locus of the center of gravity observed immediately after the insertion of the new dentures was significantly longer than that observed after the completion of the new denture adjustments (p<0.05).
Conclusion : The use of new dentures changed gait and body sway, and contributed positively to postural control.

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Purpose : A new device was made that can produce a high-speed jet of either water (water jet) or abrasives mixed with water (abrasive jet). This paper reports on the ability of this device to remove investment and metal oxides from cast alloy surfaces.
Materials and Methods : Two gypsum blocks, three investment blocks before and after heating, and three cast metal plates were tested with the newly produced device. The pressure of the jet was 4 or 8 MPa, and two types of abrasives (#400 and #1500 SiC and glass beads) were used. After treatment, the surface quality was observed with a charge coupled device camera. The concave depths of the investments were measured with a laser displacement meter and the alloy surfaces evaluated with a surface texture measuring apparatus. The concave depths of the investments and the surface roughness (Ra) were statistically analyzed with two-way ANOVA and Tukey's test using data from ten points.
Results : After heating, the investment was removed by a 4 MPa water jet ; the concave depth of the investments was from 0.7 to 8.2 mm. The gypsum was removed by the abrasive jet. The oxide films were removed by the 4 MPa abrasive jet using the abrasive agents.
Conclusion : This study examined the potential use of a new laboratory tool. It demonstrated that a water jet could remove investment after heating. Gypsum, adhered investment, and metal oxide were removed with an abrasive jet. This new device can be used effectively as a laboratory tool for removal of unwanted surface materials.

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Purpose : This study evaluated the bending strengths of five types of framework structures for implant-stabilized overdentures.
Materials and Methods : Five types of framework structures for implant-stabilized removable prostheses were cast using a Co-Cr alloy : conventional housing (Type A), housing with short skeleton (Type B), long skeleton only (Type C), housing with long skeleton (Type D), and Type D plus a metal backing connected by columns (Type E ; hereinafter referred to as the “double structure”). All castings were embedded in a heat-cured denture base resin. As controls, the same size resin blocks without frameworks were prepared. A bending test was used to test each specimen as it acted as a fulcrum on the implant. Breaking load, maximum stiffness, and strain were measured.
Results : The breaking load and maximum stiffness of the double structure were significantly greater (p<0.05), i.e., 1.5-4.5 times and 2-6 times greater, respectively, than for the conventional frameworks.
Conclusion : When the double structure framework was used for implant-stabilized prostheses, the bending strengths were greater than for the conventional housing design.

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Purpose : To clarify the relationship between the height of occlusal interference and stress responses by measuring the amount of dopamine released in the prefrontal cortex of rats.
Materials and Methods : Aluminum laminate (0.5, 1.0 or 2.0 mm thick) was fixed to the maxillary left molar to interfere with the occlusion of the rats. No laminates were fixed in the control rats. The amount of dopamine released in the prefrontal cortex was measured by microdialysis before and after fixing the laminate. After fixing the laminate, the dopamine was measured for 360 minutes in experiment 1. In experiment 2, it was measured for 180 minutes and later measured for an additional 180 minutes after the rats were given 20 minutes to eat a food pellet.
Results : In experiment 1, the amount of dopamine released in the prefrontal cortex was not significantly different among the groups during the 360 minutes following the operation to insert the laminate. The amount of dopamine released in experiment 2 increased only in the rats with an occlusal interference of 0.5 mm (p=0.04). Furthermore, a comparison of the amount of dopamine released before and after feeding within each group indicated that the only significant change was an increase during the 60 to 100-minute period after the 20-minute feeding session in the 0.5 mm group.
Conclusion : The amount of dopamine released in the prefrontal cortex of rats in this study was influenced by the height of occlusal interference. Low (0.5 mm) occlusal interference was more stressful than higher (1.0 and 2.0 mm) occlusal interference.

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Purpose : This study used a three-point bending test to measure the bond strength of porcelain to cast titanium and examined the effect on bond strength of one means of mechanical retention.
Materials and Methods : Retention beads (150, 200, 600 μm) were applied on the central portion of the pattern surface. After molds prepared from the patterns were cast with commercially pure (CP) titanium, the cast surfaces were air-abraded with 50 μm alumina powder. To investigate the effect of air-particle abrasion, cast titanium plates without retention beads were prepared and air-abraded with different alumina particle sizes (50, 125, 250 μm). Cast gold alloy plates air-abraded with 50 μm alumina were also prepared as references with and without 200 μm retention beads. Porcelain was applied on an area in the center of each cast metal plate. The three-point bending test was conducted at a crosshead speed of 1.5 mm/min. Fracture forces (F_f : N) and deflections (D_f : mm) at fracture were recorded. The data (n=5) were statistically analyzed.
Results : There were no statistical differences (p>0.05) in the F_f and D_f values of specimens air-abraded using different alumina particle sizes. Increasing the size of the retention beads significantly increased the F_f and D_f values of the specimens. The calculated bond strengths of porcelain to cast titanium were significantly (p<0.05) lower than to gold alloy.
Conclusion : The application of retention beads significantly improved the three-point bending strength of porcelain to cast titanium.

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Purpose : This study clarified the relationship between regular denture wear and neuroticism.
Materials and Methods : The subjects were 60 patients (28 males and 32 females) who underwent prosthodontic treatment using plate dentures made by the same dentist. Their mean age was 65.6±7.5 years. After adequate explanation of the purpose and importance of this study, psychological tests using the Cornell Medical Index (CMI) were performed with informed consent. The association between denture wear and neuroticism was evaluated.
Results : Fifty-five patients regularly wore their new dentures. The other patients (all were females) used dentures during meals but could not regularly wear them. The classification and distribution of the CMI neurosis areas were as follows : 34 patients (56.7%) were classified as Group I (psychologically normal), 20 (33.3%) as Group II (quasi-normal), 3 (5.0%) as Group III (quasi-neurotic), and 3 (5.0%) as Group IV (neurotic). The patients who could not regularly wear their dentures showed high values among the criteria for the discrimination of neuroses, i.e., inadequacy, depression, anxiety, anger, tension, cardiovascular system, fatigability, and frequency of illness. Many of them were classified as Group III (quasi-neurotic) or IV (neurotic).
Conclusion : Compared to patients who could regularly wear their dentures, those who could not regularly wear their dentures showed higher values for eight of the nine criteria for the discrimination of neuroses, which indicated marked neuroticism. These results suggested an association between patients who cannot regularly wear their dentures and neuroticism.

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Purpose : The purpose of this study was to investigate Merkel cell behavior under the condition of continuous pressure by a denture base.
Materials and Methods : A denture base made of 4-META/MMA-TBB adhesive resin was applied on the palatal rugae of golden hamsters, and the animals were sacrificed 2 and 3 weeks later.
Results : Immunohistochemically, an aggregation of CK 20-positive cells was seen at the tip of the rugae in the control groups. However, a significant decrease in CK 20-positive cells was observed in the experimental groups at each of the time periods.
Conclusion : These results suggest that the Merkel cells became apoptotic under continuous pressure and that the sensory system might have changed.

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Purpose : The purpose of this study was to establish an original Japanese version of the Visual Analogue Scale (VAS) and assess its descriptive statistics, reliability and validity as an outcome measure of complete denture prostheses.
Materials and Methods : Fifty-eight subjects (28 male and 30 female from 49 to 85 years of age ; mean age, 70.9 years) were recruited from edentulous patients who requested fabrication of new complete dentures (both maxillary and mandibular). General satisfaction and seven related items were selected for evaluation. Patients rated their existing prostheses at the first and second visits. Reliability was assessed with internal consistency and test-retest. Concurrent validity was assessed with association between general satisfaction and other items by simple linear regression.
Results : Significant differences were found between ratings of maxillary and mandibular dentures for general satisfaction (p=0.002), ability to masticate (p=0.004), ability to speak (p=0.013), stability (p=0.008), retention (p=0.001) and comfort (p=0.001). Distributions were overall skewed to the left for the maxillary and bimodal for the mandibular. Sufficient internal consistency and a correlation coefficient were obtained for each item. Significant relationships between general satisfaction and other items were found. However, the strength of explanation varied from 11.9 to 76.6%
Conclusion : The Japanese version of the VAS is considered to have sufficient reliability and validity for use as an outcome measure of patients' satisfaction with complete denture prostheses.

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Purpose : The goal of this study was to ascertain gender differences in sensory thresholds by measuring current perception threshold (CPT) values of the trigeminal and median nerves in healthy individuals.
Materials and Methods : CPT values were measured using a Neurometer^® (Neurotoron, Baltimore, MD, USA) when electrical stimulation of 2, 000, 250, or 5 Hz was applied to the left preauricular (trigeminal nerve) and thenar eminence (median nerve) regions in 20 healthy volunteers (10 males and 10 females with a mean age of 24.4 years). The day-to-day reliability of CPT was first verified in the trigeminal region by a test-retest method using an interclass correlation coefficient (ICC). The CPT values were then measured and statistically analyzed to evaluate whether the values were influenced by the electrical stimulation frequency and gender difference.
Results : Irrespective of the stimulation frequency, the ICC values were high (2, 000 Hz : 0.62, 250 Hz : 0.80, 5 Hz : 0.86), showing the high day-to-day reliability of CPT. The electrical frequency of the stimulation significantly influenced the CPT (ANOVA : p<0.0001) ; the mean CPT value during 2, 000 Hz stimulation was significantly higher than the value during 250 and 5 Hz stimulation (Bonferroni test : p<0.001). For median nerve stimulation, the mean CPT was lower for women than for men, but no significant gender difference was identified (ANOVA : p=0.11). Conversely, gender exerted significant effects on CPTs (ANOVA : p=0.02) for trigeminal nerve simulation. As to stimulation frequency, the mean CPT following 2, 000 Hz stimulation of the trigeminal nerve was significantly lower for women than for men (Bonferroni test : p<0.001).
Conclusion : The results suggest that healthy women are more sensitive to tactile or pressure sensations compared to healthy men, and that the effects of gender differences on the sensory threshold can be ignored with pain-related nerve fibers such as Aδ and C fibers.

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Purpose : This study evaluated the marginal fit of fixed bridges constructed using accelerated-type gypsum-bonded investment and compared them with fixed bridges constructed using conventional-type investment.
Materials and Methods : Four types of accelerated-type gypsum-bonded investment and one type of conventional-type investment were used. A three-unit fixed bridge was cast in 12% gold-silver-palladium alloy and Type III gold alloy using different types of investment. Each bridge was seated in the master die, and the margins were inspected via microscopy.
Results : The results failed to show any significant differences between the bridges constructed from either alloy using the accelerated gypsum-bonded investment and those constructed using the conventional investment. In most of the investments, the gold bridges had slightly smaller marginal gaps than the 12% gold-silver-palladium alloy bridges, but the differences were not significant.
Conclusion : The results obtained indicated that the fit of fixed bridges made in accelerated gypsum-bonded investment is similar to that of bridges made in conventional investment.

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Purpose : The Saxon test is a simple test for xerostomia that can be used for patients wearing dentures who are unable to masticate chewing gum. However, the test requires the use of thick gauze. The aim of this study was to investigate whether the Saxon test can be implemented by using gauze of different sizes or by shortening the measurement time.
Materials and Methods : The subjects were 24 healthy individuals (mean age : 23.9 years). The Saxon test was administered first with a gauze sponge (5×5 cm). Saliva was collected by having the patients chew the gauze for 2 minutes. The amount of salivary secretion was determined by measuring the increased weight of the gauze after chewing. Two modified Saxon tests (MSt) were administered : 1) 4×4 cm gauze was used, and the measurement time was set at 2 minutes (MSt 1). 2) 4×2 cm gauze was used, and the measurement time was set at 30 seconds (MSt 2). The relationships between the Saxon test and MSt 1 or MSt 2 were analyzed by regression analysis.
Results : The regression analysis of the Saxon test vs. MSt 1 resulted in the regression formula of Y=1.550 X ; vs. MSt 2, the regression formula was Y=2.568 X. There was a highly significant correlation between the Saxon test and MSt 1 or MSt 2.
Conclusion : The results of this study suggested that the Saxon test could be administered using different sizes of gauze and shorten the measurement times.

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Purpose : This paper proposes the application of haptic modeling to a virtual waxing-up system to be used for dental education and dental CAD systems.
Materials and Methods : A mandibular right first molar model was selected from the tooth crown model data library we had previously created from the three-dimensional coordinate data of plaster models enlarged four times. After partially damaging the occlusal surface shape of the tooth model, we reconstructed its original shape using a haptic modeling system consisting of a haptic force feedback device called the PHANToM^® and 3D modeling software called FreeForm^®.
Results : The FreeForm modeling system enables easier control of the functional shape of the occlusal surface than previous modification methods that handled the control points of various free-form surfaces with the 2D mouse. Additionally, the haptic interfaces were extremely useful for resolving visual ambiguities ; the sense of touch led to greater accuracy.
Conclusion : We affirmed that the use of this haptic modeling system can provide a significant benefit to dental education and dental CAD systems.

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Purpose : This article introduces the use of a measurement device that was recently developed.
Materials and Methods : This device was designed so that it can estimate changes in occlusal vertical dimension more precisely to measure the distance between the subnasal and the gnathion. It has several indicators and two scales. When positioned correctly, this device can measure, for example, the distance between the subnasal and gnathion on a patient or the distance of the interalveolar crest of the ridge of dentures. The authors performed an experiment using this measuring device to determine vertical dimension. Resin plates were used to raise the bite in a patient's mouth. The changes in the jaw position were measured by 11 clinicians using the device, and the measurements were statistically analyzed.
Results : The results of the experiment confirmed that the device is stable. There was no correlation between the number of clinical years of experience of the clinicians and the distance measured from the subnasal to the gnathion of the subject.
Conclusion : Stable measurements can be achieved with this measurement device.

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