Hiroo Miyairi

Tensile behaviour of fibroblasts cultured in collagen gel

An in vitro morphological study on the relation of the stress field and the orientation of cells with the use of the time lapse video recording system was carried out. Specimens of thin collagen gel membrane, within which cells are proliferating, were examined under various mechanical conditions. Cell stretching, cell orientation, cell migration, cell proliferation and generation of tensile stress in collagen gel were recorded. It was demonstrated that fibroblasts generate tension and change their orientation along the tensile direction. A hypothetical mechanism for such phenomena is proposed, that is, fibroblasts generate tension and make tense collagen fibres, then cells stretch themselves along the tense fibres and increase tension in this direction. Thus, this mechanism works as a positive feedback loop which enables cells to make tensile stresses and align along them in accordance with the mechanical environment.

Deformation of restoration and fracture of luting cement film.

OBJECTIVES Functional occlusal loading can generate complicated stresses in the luting cement film between a restoration and its abutment. Such stresses may lead to cement fractures, which can promote cement dissolution and induce clinical problems. The purpose of this study is to determine the function of the cement film under loading, and to clarify the relationship between the deformation of the restoration and the cement fractures. METHODS Eccentric loads were applied onto model extension bridges which were cemented on brass dies with zinc phosphate cement. Strain measurements were recorded using of a strain gauge method, ultimate strength by tensile tests, leakage by dye penetration tests and cement fractures by ultrasonic microscopic analyses. Additionally, the bridges which were just seated on their dies without cementation were loaded, and strain measurements were recorded. RESULTS The cases for linear strain increment with loading showed high tensile strength and minimal dye penetration. The cases with non-linear strain behavior showed low tensile strength and considerable dye penetration. However, no fracture was observed in the occlusal cement film in both cases. The cement fracture first occurred at the opposite marginal region to the loading side. CONCLUSIONS One of the significant functions of the cement film is diminishing the deformation of restorations during loading. The deformation of the restoration affects initiation and propagation of the cement fracture considerably.

The study on Charpy impact testing method of CFRP

The Charpy impact test method has been widely used to investigate impact resistance of fiber reinforced composites because of its simplicity. However, when laminated composites such as CFRPs are to be tested, each specimen may have different thickness without a notch. This may result in incorrect material evaluation for impact resistance. In this paper, an instrumented Charpy impact tester was introduced in order to determine a proper Charpy impact test method for CFRPs and to investigate the effect of the ratio of the support-span length to thickness l/t on impact characteristics for both unidirectional and fabric CFRPs. Energy per unit volume u increases rapidly along with l/t in the range of l/t < 20 and l/t < 16 for unidirectional CFRPs and fabric CFRPs, respectively, both of which are influenced by interlaminar separation. However, the u values become almost constant over 20 l/t 40 for the unidirectional CFRPs and over 16 l/t 40 for the fabric CFRPs. It is found that those ranges are the proper range...

Shock absorption performance of full-face rider helmets

Full-face rider helmets are widely used these days, but the shock absorption and safety performance of them have not been discussed yet. So we examined the shock absorption performance and the safety of three full-face rider helmets (samples A, B, and C) of which the laminated constitutions of the FRP shell part were respectively different. The effect of the hybrid lamination, composed of aramid and glass fabrics, on the shock absorption performance has been discussed also. Testing was performed twice for the same impact site of a helmet hit flat and with semi-spherical anvils, according to the JIS-C shock absorption test method. The following results were obtained: The acceleration waveform measured at the forehead part of Helmet-A, which was hit on a semi-spherical anvil, behaved flatly while the part on the left side of the head behaved parabolically. In the case of Helmets-B and -C, which have an aramid fabric layer, they behaved conversely, such that a flat waveform was observed on the part on the le...

The most appropriate position and number for absolute anchorages for orthodontic tooth movements

Absolute anchorages proved to be very effective for orthodontic tooth movements. We used a 3D digitizer to record each tooth on pre-treatment diagnostic and post-treatment predictive setup models and then 3D coordinate system conversion was performed to make the coordinate values comparable. An arithmetic calculation of vector and moment based on the orthodontic forces and the tooth displacement under preliminary premises undertaken to decide the most favorable pOsition and number for absolute anchorages. Position-For two-dimensional and three-dimensional calculations, the most appropriate positions for absolute anchorages should theoretically be on the line of resultant force (2D) and the plane (3D) where the total moment effect tends to be zero. Number-As for the number of the absolute anchorages needed, it depends on the number of target teeth. Different combinations of target teeth provide different sets of results.

Locations of Bone Formation Change According to the Waveform of Loads

Cellular mechanisms of adaptive bone remodeling are reconsidered for the three major proposed hypotheses. Candidate cellular mechanotransduction mechanisms introduced are SA channels for the strain theory, flow mediated mechanotransduction mechanisms for the fluid flow theory, and voltage gated ion channels for the electric potential theory. The most simple and appropriate mechanism that explains how the bone cells detect the dynamic compression is given by the electric potential theory. The strain theory requires undiscovered cellular mechanisms and the fluid flow theory requires a possible but unobserved fluid flow to be appropriate.

Application to thinning palatal area of upper complete denture base by CF-cloth reinforcement

The acrylic resin denture base is used more than the usual metal denture base because of its low cost, ease of manufacture and ease of rebasing. Because the resin base is weaker than the metal base, the upper resin denture base is three to four times as thick as the metal denture base. So, a study was made to make the upper complete resin denture base thinner while maintaining the strength of the resin denture base currently in use. To make the palatal area of the denture base thinner carbon fiber (CF) cloth reinforcement was used. The resin denture base reinforced by the CF cloth was 0.7 mm thick and was evaluated for the mechanical properties of bending. As a result, it was found that both the stiffness and strength were improved by 10% or more compared with those of the ordinary resin denture bases.

Deformation and Shear Strength of FRP Adhesive Joints

The structural adhesives used in this study were a hard type polyester, a soft type polyester and an epoxy polyamide. The FRP adherend consisted of polyester matrix and reinforcement of glass mat/glass roving cloth combinations. The adhesive strength was obtained by using the tension shear test of single lap adhesive joints. The characteristics of adhesive strength were examined for the change in lap length, and the results were used to explain the deformation of adherend and the fracture pattern of layers. Furthermore, the peeling behavior of adhesive layers, the bending moment of FRP adherend and the influential factors on the adhesive strength of FRP adhesive joints were investigated.

Flexural Fracture and Mechanical Properties of Nonsymmetrical Sandwich Construction

Sandwich construction is composed of hard polyurethane foam(PUF) as core and glass-mat FRP(GRP) and aluminium(Al) as facing. The flexural fracture and mechanical properties of this nonsymmetrical sandwich construction are examined. The behaviors of flexural fracture of GRP/PUF/Al sandwich construction, which is loaded with GRP on tension side, are examined for flexural stress, strain etc. to consider the elasto-plastic deformation of GRP, and are numerically analyzed using a flexural load-deflection diagram of this sandwich construction. The flexural experiment has been made for comparing with the results of theoretical analysis on the mechanical properties of this sandwich construction. And this analytical method applied to the process of flexural fracture can be practical enough for the estimation of flexural strength and theoretical flexural load-deflection diagram.

A Study on the Reinforced Properties of Dental Plastics with Hybrid Construction

Acrylic resin is widely used as the denture base material, but a failure of the upper complete denture often happens during its use. Therefore, the denture base made of acrylic resin should be reinforced by something else. So, the authors have thought of improving the strength and rigidity by laminating the organic fiber reinforced plastics on the palatal surface of the denture base, which is called the canape construction. In this paper, the flexural strength, fatigue strength and the modulus of elasticity in bending of the canape construction were investigated as basic experiment. As the result, the flexural and fatigue strengths have been improved to 160% and 130% of the denture base acrylic resin, respectively. And the modulus of elasticity in bending has been improved 80%. Therefore, it seems that this new combination of materials using the canape construction might be applied well enough to the denture base.