Takeshi Murayama

Three-dimensional finite element analysis of cartilaginous tissues in human temporomandibular joint during prolonged clenching.

OBJECTIVE Bruxism, the parafunctional habit of nocturnal grinding of the teeth and clenching, is associated with the onset of joint degeneration. Especially prolonged clenching is suggested to cause functional overloading in the temporomandibular joint (TMJ). In this study, the distributions of stresses in the cartilaginous TMJ disc and articular cartilage, were analysed during prolonged clenching. The purpose of this study was to examine if joint degradation due to prolonged clenching can be attributed to changes in stress concentration in the cartilaginous tissues. DESIGN Finite element model was developed on the basis of magnetic resonance images from a healthy volunteer. Condylar movements recorded during prolonged clenching were used as the loading condition for stress analysis. RESULTS At the onset of clenching (time=0s), the highest von Mises stresses were located in the middle and posterior areas (6.18MPa) of the inferior disc surface facing the condylar cartilage. The largest magnitude of the minimum principal stress (-6.72MPa) was found in the condylar cartilage. The stress concentrations were relieved towards the superior disc surface facing the temporal cartilage. On the surfaces of the temporal cartilage, relatively lower stresses were found. After 5-min clenching, both stress values induced in the TMJ components were reduced to 50-80% of the stress values at the onset of clenching, although the concomitant strains increased slightly during this period. CONCLUSIONS It is suggested that both the condylar and temporal cartilage layers along with the TMJ disc, play an important role in stress distribution and transmission during prolonged clenching due to tissue expansion. Furthermore, our study suggests that a development of stress concentrations in the TMJ during prolonged clenching and risk factors for the initiation of TMJ degeneration could not be confirmed.

An in vitro evaluation of the adhesion of Candida species to oral and lung tissue cells

The analysis of the adherence capacity of fungi to surfaces of both oral tissue and different tissues would be of interest in the fungal dissemination as an oral and systemic pathogen. We developed an in vitro adenosine triphosphate (ATP)‐based assay technique to extract the cellular and fungal ATP separately, which allowed the quantitative evaluation of the adhesion of the yeast to monolayers of human gingival epithelial cells (GEC), gingival fibroblasts (GF) and pulmonary fibroblasts (PF). Seven oral isolates of Candida species (three of Candida albicans, three of Candida tropicalis and one of Candida glabrata) were used in the study. The adherent level of the Candida species varied depending on both the isolates and the cell origins, although all the Candida isolates had a significantly higher level of adherence to GEC than to GF except the single isolate of C. tropicalis. Whereas the adherent level of the five isolates to GEC was significantly higher than that to PF, the adherent level of the remaining two isolates of C. tropicalis to GEC was significantly lower than that to PF. These results suggest that candidal adherence to host tissue cells should be regulated in an isolate‐dependent and cell‐origin‐dependent manner, and that the phenomena may be involved in the colonisation and/or dissemination of the fungi.

Computer-aided redesign for improving recyclability

This paper presents a software tool assisting designers in redesigning products for improving recyclability. Taking a 3D-model of a mechanical product as input, this tool generates a disassembly sequence of the product automatically. Using the disassembly sequence, the tool generates some suggestions for improving the recyclability and gives them to the designer. The suggestions include: changing the materials of parts, integrating some parts into one part: changing some fixing methods, and reducing some parts used for fixing some other parts. The suggestions bring about the reduction of disassembly time as well as the improvement in the occupancy rate of recyclable materials. If the designer accepts the suggestions, the tool modifies the model according to the suggestions. An electric drill has been used to experiment with the tool.

Treatment of reliability for reuse and remanufacture

Summarized are approaches addressing reliability in reuse (without repair) and remanufacture. To support the design of a product whose life cycle involves reuse without repair, two types of reliability data (time to failure and quality-deterioration data) were used in the simulation of the material flow during the life cycle. For management of material flow, reliability models were developed and applied to predict quantities of returned products and reusable components for each time period. The predicted results can be used for production planning in manufacturing firms using reusable parts as well as new parts. A reliability model was developed and validated to better describe populations of systems that undergo repairs performed during remanufacture or maintenance. Remanufacturer waste streams of several products were analyzed to reveal remanufacture difficulties. A modified FMEA uses the results of waste-stream analyses and considers ease of detection and repair of failure in conjunction with waste-stream contribution of failure modes in design for remanufacture.

Disassembly sequence generation using information entropy and heuristics for component replacement

This paper describes a methodology of generating disassembly sequences for component replacement at maintenance stages, which are used for evaluating the ease of disassembly at product design stages. Information entropy evaluation and heuristics bring about the efficient generation of disassembly sequences. The disassembly is evaluated based on two criteria: disassembly time and disassemblability. The authors developed a software tool integrated with a CAD system and carried out an experiment for an electric drill using the tool.

Assembly partitioning by genetic algorithm for generating assembly sequences efficiently

This paper describes a method for identifying a subassembly or part to be removed from an assembly in order to generate an assembly sequence efficiently. In this method, the assembly is represented as a graph, and some cut sets of the graph are calculated by using heuristics and a genetic algorithm. Each of the calculated cut sets partitions the graph into two subgraphs, one of which expresses the subassembly or part to be removed.

Life cycle profitability analysis and LCA by simulating material and money flows

The authors propose a simulation-based approach to the evaluation of a products life cycle including recycling and reuse from the viewpoints of not only environmental impact but also the profitability of every companys business related to the life cycle. The flow of the material and money among the companies concerned with the life cycle are modeled and simulated. The simulation reveals whether each of the companies obtains a profit and how strong the environmental impact is. The simulation also shows the change in the environmental impact and profit with the passage of time. The modeling and simulation for a copier drum is presented as a validation example.

Mathematical model of reusability

Recently the reuse of products or their components has been recognized as an effective way to reduce solid waste and to conserve natural resources. To decide whether a product or its component should be reused or not, we need to evaluate its reusability adequately. In this paper, as a criterion for the evaluation, the authors define and model the reusabilities of a product and its component, based on reliability theory. The authors define the reusability of a component as a probability that a product having been used for a time period ends its life but a component included in it is reusable. Based on the definition, the authors develop a mathematical model of reusability, which is a function of use time. The authors made several graphs of the mathematical model, with changing values for parameters such as shape parameter of the Weibull distribution. As a result, it is found that the reusability of a component does not always decrease as the use time is lengthened. This is interesting because it goes against the general impression that the reusability decreases as the use time is lengthened. Next, the authors define and model the reusabilities of a product and a unit. The authors believe that the models of reusabilities are useful for deciding whether a product or its component should be reused or not and the models may be used for production management for reuse and remanufacturing.

Disassembly/assembly path search reusing solutions

It is important to generate and evaluate disassembly paths in product design stages for reducing the recycling and repairing costs of products. This paper proposes a method for generating the disassembly paths automatically by using CAD data. The method is efficient especially to generate the disassembly paths of the design objects got by modifying the original ones whose disassembly paths have been generated before. In the method, the disassembly paths of such modified design objects are generated efficiently by using those of the original ones. Based on the method, the authors developed a software tool integrated with a CAD system and performed an experiment using the tool.

Stability check and reorientation of subassemblies in assembly planning

Most assembly planning systems first search for a disassembly sequence by identifying a part or subassembly to be removed recursively, and then generate an assembly sequence by reversing the disassembly sequence. To identify a part or subassembly to be removed, some of them verify whether the part or subassembly can be removed without any interference. However it is computationally very expensive. The authors propose a method that has the advantage of reducing the verification times. This method selects the candidates for the parts and subassemblies to be removed prior to the verifications, by checking the stability of them. This method also uses a genetic algorithm and heuristics to select the expedient candidates.