Biomedical subjects

Iwao Hayakawa

Publications and source records attributed to Iwao Hayakawa.

15 recordsLinked to original sources

PubMed2006

Physical properties of a new denture lining material containing a fluoroalkyl methacrylate polymer.

STATEMENT OF PROBLEM: A new fluoride-containing, methacrylate-based denture lining material has been introduced. Because of the fluoride content, this material is expected to demonstrate low water sorption and solubility and high stain resistance, but these attributes remain untested. PURPOSE: This study investigated a wide range of clinically relevant properties for a new fluoroalkyl methacrylate denture base liner product (Maxfit) and compared these properties with those of 3 other commercial products. MATERIAL AND METHODS: Four denture lining materials were tested: Maxfit, Kooliner, Tokuyama Rebase (fast set), and Denture Liner. Water sorption (microg/mm(3)) and solubility (microg/mm(3)) were tested according to International Organization for Standardization (ISO) Standard No. 1567. Stain resistance was evaluated by measuring color change (DeltaE) after immersion in 2 solutions (coffee and turmeric solution). Microhardness was determined using Knoop indentation testing according to American National Standards Institute/American Dental Association Specification No. 17. Relined denture fit was evaluated by measuring the gap (mm) occurring between the relined denture base and the cast after polymerization. Shear bond strength (MPa) to denture base materials (polymethyl methacrylate, cobalt-chromium alloy, and titanium) was tested according to ISO Standard No. 11405. Data were statistically analyzed using nonparametric Kruskal-Wallis (alpha=.05) and Mann-Whitney U tests combined with the Bonferroni correction (alpha=.008). RESULTS: Maxfit showed the lowest water sorption and solubility (8.0 +/- 0.1, 0.5 +/- 0.1 microg/mm(3), respectively). The color change from coffee immersion of Maxfit was significantly less than Tokuyama Rebase and Denture Liner, and significantly less than Tokuyama Rebase and Denture Liner in a turmeric solution (P<.001). Knoop hardness of Maxfit (8.66 +/- 0.51) was higher than Kooliner and Tokuyama Rebase (P<.001). The relined denture fit using Maxfit was not different from other materials. Significantly higher shear bond strength to denture base resin was noted for Maxfit compared to Tokuyama Rebase and Denture Liner (P<.008). CONCLUSIONS: The new fluoroalkyl methacrylate-based denture liner (Maxfit) showed the lowest water sorption and solubility, and superior stain resistance. In spite of the addition of the fluoride content, this product exhibited no deterioration in physical properties, such as surface hardness, fit of the relined denture, and shear bond strengths to denture base materials tested.

Adhesiveness↗

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

Antifungal effects of a tissue conditioner coating agent with TiO2 photocatalyst.

Tissue conditioners are susceptible to colonization by microorganisms. Therefore, the prevention of biofilm formation are important for oral hygiene. However, mechanical and chemical cleaning methods may cause clinical problems such as deformation or surface degradation of tissue conditioners. The objective of this study is to evaluate the antifungal effects of coating agents with a TiO2 photocatalyst. Photocatalytic antifungal effects on C. albicans biofilms and photodegradation effects of adsorbed protein were measured by colorimetric assays. Scanning electron microscopy was used to examine morphological changes in C. albicans. Viscosities of coating agents increased with incorporation of TiO2. However, both of coating agents with TiO2 were acceptable to the application by brush. The antifungal and protein degradation effects increased with the concentration of TiO2 in the coating agents. These effects also increased with radiation time. After 90 min radiation, the viability of C. albicans was reduced to 16.2+/-3.3 %. Scanning electron microscopy observation showed C. albicans remained on the coated surfaces even after 90 min radiation. These results suggest that coating agents with TiO2 photocatalyst can be effective for the maintenance of tissue conditioners when dentures are removed; during sleep.

Adsorption↗

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↗

PubMed2003

Effects of cyclic loading on viscoelastic properties of soft lining materials.

The cyclic loadings during mastication supposedly accelerate degradation of soft lining materials. The purpose of this study was to investigate the effects of cyclic loading on viscoelastic properties of soft lining materials. Two plasticized acrylics, two silicones and one isoprene-based monomer contained elastomer were selected. Cylindrical-shaped specimens, 10 mm X 10 mm phi, were prepared. Twenty specimens were subjected to cyclic loading in a water bath at 37 degrees C; another twenty specimens were without cyclic loading. The viscoelastic properties were measured using a creep-meter. The cyclic loading significantly decreased the heights of the two materials, the instantaneous elastic displacements of one acrylic liner and the viscous flows of three materials. The cyclic loading affected mainly delayed deformations. Therefore, cyclic loading was a useful method for evaluating the durability of soft lining material.

Acrylic Resins↗

PubMed2003

Impressions for complete dentures using new silicone impression materials.

This article describes a convenient technique for making impressions of complete dentures using two newly developed silicone materials. One of these materials, a heavy-bodied silicone material, is used for simultaneous molding of all borders. The material is available in automatic mixing systems, so it can be easily and evenly applied on the tray borders. The material is designed to have a low elasticity after setting so that excess material can be carved or deficient sites corrected with a small mix. The other newly developed material, a light-bodied silicone material, possesses better flow than the usual light-bodied silicones. In addition, since viscosity is controlled and adequate flow is maintained during seating in the mouth, mucosal detail is superior.

Compressive Strength↗

PubMed2003

Effect of denture adhesive on stability of complete dentures and the masticatory function.

This study examines the effects of denture adhesive on the retention and stability of complete dentures and the masticatory function. The authors estimated the stability of complete dentures from 3-dimensional (3-D) denture movement and rotational denture movement and additionally the masticatory function from cycle time and chewing time. Six edentulous subjects who participated in this study had old and newly fabricated complete dentures. Upper denture movement was recorded using a 3-D motion capture system while chewing 3 kinds of food (peanuts, fish paste, raisins). Both the new and old dentures showed that using a denture adhesive contributes to reducing 3-D denture movement, rotational denture movement and chewing time during chewing the various foods. The cycle time in new and old dentures was statistically unaffected by applying denture adhesive. There was no statistically significant difference in improvement in 3-D denture movement or rotational denture movement between the new and old dentures, for any of the foods. This study observes the overall effect of denture adhesive during use for both dentures. The results of this study suggest that denture adhesive contributes to reducing denture movement and so improves chewing function.

Adhesives↗

PubMed2002

A new approach to evaluating occlusal support by analyzing the center of the bite force.

The aim of this study was to create a standard for occlusal support in the diagnosis and evaluation of prosthetic treatment. In experimental occlusion, the maximal bite force of eight normal dentates was measured by pressure-sensitive film over the whole dentition using splints divided into nine pieces. The occlusal contact was altered by exchanging splint pieces according to the shortened dental arch concept. The occlusal load center (OLC) was located on a graph set up with reference to the size of the individual dental arch. The occlusal supporting index (SI) and the rehabilitation index (RI) were calculated from the locations of the OLC corresponding to each occlusal contact. Differences in numbers and distribution of occlusal stops could clearly be distinguished by the location of the OLC. Though the SI showed a strong positive correlation with maximal bite force, it is proposed that the number of occlusal stops, or occlusal units, provides the most effective index for quantitative parameters of occlusal support in clinical use. From the standpoint of bite force, analysis of the RI is suggested as a useful method of objectively evaluating the recovery of occlusal support with prosthetic treatment.

Adult↗

PubMed2002

Improving a self-curing dental resin by eliminating oxygen, hydroquinone and water from its curing process.

Self-curing dental resins are always manipulated in the presence of curing inhibitory factors such as oxygen, hydroquinone, water and another contaminants such as saliva and blood. The purpose of this study was to elucidate the effects of eliminating these curing inhibitory factors on resin properties. Several clinically relevant characteristics of an experimental resin cured in the absence of inhibitory factors (purified group) were determined and compared with the resin cured conventionally (control group). The purified group showed a significantly shorter induction period and higher reaction exotherm. It also showed significantly higher tensile strength and lower strain to failure. With regard to the amount of residual monomer, fracture toughness and fatigue strength the improvements were not significant. These findings suggest that the polymerization outcomes and mechanical properties of the purified group resin can be improved in general. Dental clinicians should pay attention to the storage and curing environments while manipulating the self-curing resin.

Benzoyl Peroxide↗

PubMed2002

[A study on evaluation methods of masticatory ability for complete denture wearers--correlation between evaluation using a questionnaire and masticatory performance].

The purpose of this study was to investigate the relation between evaluation by a questionnaire on masticatory aspects of 20 foods, and masticatory performance obtained using the sieving method, previously used in many studies. After replacement of upper and lower complete dentures made newly, 28 edentulous patients voluntarily participated in this study. The basal seat area of each patient was scored and divided into two groups, and masticatory ability was evaluated by two methods: using a questionnaire and the sieving method. The following conclusions were drawn from the data: 1. Evaluation of masticatory ability by both methods used in this study were not associated with gender, age, and evaluation of the basal seat area. 2. Evaluation using a questionnaire and masticatory performance showed significant correlation, and Spearman's correlation coefficient was 0.628 (p < 0.001).

Aged↗

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

[Fundamental study on the development of a measuring device using an accelerometer].

It is important to clarify stomatognathic functions. To diagnose them, some measuring devices, such as MKG and the Gnatho-hexagraph, were developed. Such equipment, however, is not widely diffused, due to cost. The purpose of this fundamental study was to obtain information on position using an accelerometer. This system consists of a micro dual-axis accelerometer and a peripheral interface controller. Two-dimensional acceleration, velocity, and movement can be calculated by a computer. We examined the accuracy of this system using a laser measuring device. The result was as follows: The accuracy of the system was 0.03 (p-p values) using acceleration of gravity and a frequency of 72.5 Hz. In the present study, mandibular movements during chewing raisins were analyzed using this system. The new system demonstrated its value for analyzing mandibular movements.

Acceleration↗

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↗