Biomedical subjects

Shigezo Hirano

Publications and source records attributed to Shigezo Hirano.

7 recordsLinked to original sources

PubMed2006

Palatal coverage disturbance in masticatory function.

Oral sensorimotor function is essential for mastication. We hypothesized that palatal coverage would disturb mastication and sensorimotor function. Masticatory efficiency, which was expressed by the declination rate of particle size, and oral stereognosis ability (OSA) were measured for 20 dentate subjects. Both measurements were first performed without an experimental palatal plate. These measurements were then repeated with the plate on the day of the plate insertion, then again on the 3rd and 7th day. After 2 months, another series of measurements for the OSA test were performed without the plate with the same time-course. Masticatory efficiency significantly decreased with the plate. OSA score, which continuously increased during the experimental period, showed no difference between with and without the plate. Positive correlation between masticatory efficiency and the OSA score was found only without the plate. It was suggested that coordination between mastication and the sensorimotor function was disturbed by palatal coverage.

Adult↗

PubMed2005

Bonding properties of heat-polymerized denture base resin to Ti-6Al-7Nb alloy.

The purpose of this study was to evaluate the shear bonding strength and leakage of heat-polymerized denture base resin to titanium-aluminum-niobium (Ti-6Al-7Nb) and cobalt-chromium (Co-Cr) castings using four adhesive systems; three adhesive primers (Metal Primer II, Metal Link, MR. Bond) and one heat-polymerized adhesive resin containing 4-META (Metadent). The resin tab was heat-polymerized directly with or without the primer. Shear bonding strengths and dye penetration distances were determined before and after 10,000 times of thermocycling. The results were analyzed with three-way ANOVA and Tukey's comparison (p<0.05). Thermocycling significantly decreased bonding strength and promoted dye penetration. However, with the application of adhesive systems, post-thermocycling bond strength was significantly improved and dye penetration was inhibited. The bonding strength of Ti-6Al-7Nb was significantly smaller than that of Co-Cr, but the difference was marginal. These results suggested that the examined adhesive systems significantly improved the bonding efficiency of heat-polymerized resin to Ti-6Al-7Nb and Co-Cr alloys.

Acrylic Resins↗

PubMed2004

Occlusal pressure pattern analysis of complete dentures for evaluation of occlusal adjustment.

The purpose of this study was to investigate occlusal pressure patterns of complete denture wearers to evaluate progress of occlusal adjustment of dentures. Thirty three edentulous subjects volunteered to participate in this study. A computer-based device was used to measure occlusal pressure sequence while tapping with their new dentures. The following variables obtained from each occlusal pressure pattern were assessed: Peak Time; Duration from the onset of pressure to the maximum pressure, Unloading Time; Duration from the maximum pressure to the end of pressure, Contacting Duration; Duration from the onset of pressure to the end of pressure, Tapping Cycle; Duration from the onset of pressure to the next onset, Peak Ratio; ratio of Peak Time to Unloading Time. Recordings were performed after the occlusal adjustment at each appointment and continued until denture adjustments were completed. Variables were analyzed using ANOVA and Bonferroni. A significant decrease was seen in Peak Ratio as the occlusal adjustments progressed (p<0.05). Its coefficient of variation was constantly the lowest among variables. The coefficient of variation of Peak Ratio was significantly lower than others at the completion of the adjustment (p<0.05). It was suggested that Peak Ratio was useful for evaluation of occlusal adjustment.

Aged↗

PubMed2003

A new polyisoprene-based light-curing denture soft lining material.

OBJECTIVES: The purpose of this study was to investigate some clinically relevant properties of Clearfit LC, a newly developed polyisoprene-based light-curing lining material. Its properties were compared with those of other four commercial products. MATERIALS AND METHODS: Five soft lining materials, Clearfit LC, two plasticised acrylics (Super-soft, Soften) and two silicones (Molloplast B, Sofreliner) were used to determine water sorption, solubility, staining resistance, Shore A hardness and shear bond strength to denture base. Five specimens for each test were fabricated. The results of each test among the five materials were compared by one-way ANOVA and Scheffe's post-hoc test at alpha=0.05. RESULTS: One-way ANOVA of each test showed that the differences among five materials were significant (P<0.05). Clearfit LC showed the intermediate water sorption and solubility (10.07; 1.72 microg/mm(3)). It also showed the lowest color change in beta-carotene/olive oil solution and instant coffee solution (DeltaE=1.19, 5.48, respectively). The shear bond strength of Clearfit LC was 1.56MPa, and no adhesive failure was found. Its Shore A hardness value (56.2) was located between two acrylics and silicones. It was also found that the softer materials tend to failure cohesively. CONCLUSIONS: The polyisoprene-based lining material showed low water sorption and solubility, moderate softness, high staining resistance and satisfactory shear bond strength to denture base resin. It also provides clinicians sufficient working time due to its light-curing property. It would be an attractive alternative as a relining material.

Absorption↗

PubMed2002

[In vitro study on accuracy and repeatability of the T-Scan II system].

The T-Scan system has been used to analyze the distribution of occlusal loading forces, and occlusal contact variability. An enhanced version, the T-Scan II system, has been developed with clinical significance of its center of force. The T-Scan II system was also found to be clinically useful for measuring simultaneous occlusal contacts bilaterally. However, its improvement in accuracy and repeatability is still unknown. In the present study, the accuracy of time recordings, the liner relation between loaded forces and force recordings, the pressure sensitivity, and the variability of force recordings for repeated loadings, were investigated. The conclusions were as follows: 1. By regression analysis between the time and the time recording, the following equation was obtained: Y = 0.00357 + 0.9889 X R2 = 0.9964. The time recordings were proportion to the real time. 2. The force recordings were acceptably precise, especially for the moderately high level and default level, where a linear relation was observed. 3. The pressure sensitivity showed 6-61 g/cm2 for the high-4 level, 25-581 g/cm2 for the moderate-3 level, 56-1814 g/cm2 for the default level, and 146-3821 g/cm2 for the low-2 level. 4. The stability of force recordings for the repeated loadings was acceptable. A significant influence of repeated loading was found for the low-2 level; however, no significant difference was found between the repeated loadings, by post hoc analysis. On the contrary, the repetition of continuous loadings raised force recordings gradually, up to 120% at the fourth loading. The level of the force recordings stayed at the same level with no significant influence by repetition.

Bite Force↗

PubMed2002

[A clinical application of the T-Scan II system--usefulness for evaluating occlusal contacts of complete denture wearers].

The purpose of this study was to assess the reproducibility of the T-Scan II system and its clinical usefulness for evaluating occlusal contacts of complete denture wearers. The occlusal contacts of 13 dentate subjects, and 14 complete denture wearers, were recorded using a T-Scan II system during maximum voluntary clenching. The recordings for complete denture wearers were taken after each treatment for the new denture, and continued until the completion of all corrections. The recordings for complete denture wearers were analyzed using repeated measured ANOVA. In addition, the variables obtained with the system, the delta of the occlusal area and load, and the maximum-load time (MLT), which represented the time length taken to reach the occlusal load at the maximum level, were then compared between dentate subjects and complete denture wearers, using a t-test. The conclusions were as follows: 1. The standard errors values for both occlusal area and the load recordings for the dentate subjects were limited to within 10% of the means. 2. The values of the occlusal area and load significantly increased, and delta of the occlusal area and load significantly decreased, as the denture corrections were repeated. 3. The means of the MLT were about 0.3 seconds for dentate subjects, and 0.8 seconds for complete denture subjects. It was revealed that the T-Scan II showed acceptable reproducibility, and it was useful to evaluate occlusal contacts of complete denture wearers.

Adult↗

PubMed2002

Effects of a denture adhesive on masticatory functions for complete denture wearers--consideration for the condition of denture-bearing tissues--.

The purpose of this study was to examine effects of a denture adhesive on masticatory functions for complete denture wearers considering the condition of denture-bearing tissues. Sixteen edentulous subjects wearing well-fitting complete dentures volunteered to participate in this study. According to the condition of denture-bearing tissues, subjects were divided into two groups; "good group" and "poor group". Maximum biting forces, masticatory performance, and electromyography of the masseter muscle during mastication were recorded with and without a denture adhesive. Durations of chewing burst and cycle, and coefficients of variation for these variables were calculated using electromyography recordings. Data were analyzed by using two-way repeated-measured ANOVA and paired t-test in order to assess the effect of the use of a denture adhesive. The use of the denture adhesive increased maximum biting force and provided rhythmic masseter muscle activity during mastication for both groups. Masticatory performance was improved and duration of chewing burst was decreased only for "poor group". It was concluded that the effects of the denture adhesive on masticatory functions were observed overall for both groups, and more significant for denture wearers with poor denture-bearing tissues than with good denture-bearing tissues.

Adhesives↗