Wyniki wyszukiwania - Biblioteka Nauki

1

System modelowania wybranych stanów mechanicznych żuchwy ludzkiej

100%

Chladek W.

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2000

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tom z. 59

1-108

PL

W pracy przedstawiono sposób kompleksowego podejścia do zagadnienia równowagi żuchwy ludzkiej. W warunkach naturalnych stan równowagi żuchwy zapewniany jest przez selektywne pobudzanie grup włókien odpowiadających poszczególnym mięśniom żwaczowym. W zastosowanym modelu podjęto próbę zastąpienia funkcji układu nerwowego "logiką" dostosowania się wartości reakcji więzów sprężystych do struktury przestrzeni obiektu dla zadanych obciążeń i przyjętych sztywności więzów. Etapem wyjściowym do modelowej oceny stanów mechanicznych żuchwy było zebranie danych dotyczących charakterystyk obiektów naturalnych, takich jak wielkości sił zwarciowych, kierunki działania sił w mięśniach żwaczowych oraz cechy geometryczne modelowanego obiektu. Aktywność mięśni zwierających i wielkość reakcji w stawach określono na podstawie analizy wartości wprowadzonego w pracy bezwymiarowego współczynnika "Wa". Współczynnik ten, odpowiadający stosunkowi wybranej składowej reakcji do siły okluzyjnej, umożliwia oszacowanie udziału rozważanej składowej w wysiłku układu stomatognatycznego, związanego z generowaniem sił zwarciowych. Obliczenia przeprowadzono dla sił przyłożonych w punktach odpowiadających położeniu kolejnych zębów po prawej stronie łuku zębowego. Wyniki badań modelowych przedstawiono w formie wykresów i tablic ujmujących aktywność więzów w kierunkach osi prostokątnego układu współrzędnych, dla różnych systemów podparć. Analiza wartości współczynników aktywności więzów uzyskanych dla modeli żuchw o budowie zróżnicowanej w sposób zgodny z formami spotykanymi w naturze wykazała odpowiedzi więzów na zadane obciążenia, logicznie związane z rozpoznanymi reakcjami rzeczywistych obiektów. Dowodzi to, że opracowany system pozwala, poprzez analizy numeryczne oparte na metodzie elementów skończonych, ocenić wielkość wybranych sił czynnych i biernych utrzymujących równowagę żuchwy w zadanym położeniu.

EN

The present dissertation shows a comprehensive approach to the human mandible equilibrium issue. In normal conditions the state of equilibrium is provided by selective stimulation of fiber groups corresponding to the individual muscles of mastication. According to the chosen methodology of the computational model, the nerve system is substituted with the response of elastic constraints, logically ocnnected with the object spatial structure and imposed loading. The starting point for a model assessment of the mandible mechanical states was the acquisition of data describing the properties of natural objects (e.g. the values of occlusive forces, directions of forces in masticatory muscles, geometrical features of the object modeled). The research of occlusive forces values revealed individual diversity, which makes an unambiguous description of the forces very difficult. The occlusive muscles activity and quantity of reaction in joints were derived basing on the analysis of values of the nondimentional coefficient "Wa" (introduced in the present dissertation). The coefficient (corresponding with ratio of chosen reaction component to (occlusive force) enables to estimate the participation of the considered component in the stomatognathic system effort (the effort of occlusive forces generation). The computations realized for the forces applied in the points corresponding with locations of successive teeth along the right side of dental arch. Results of model research are shown in graphs and tables expressing the constraints activity in directions of cartesian co-ordinates for different support systems. Analysis of constraints activity coefficients values obtained for mandible models with natural diverse structure proved the logical connection of constraints responses to imposed loadings with recognized reactions of real objects. It shows, that the system proposed is able to evaluate the value of chosen active and passive forces, which keep the equilibrium of mandible in the arbitrary position, using the numerical analyses based on finite elements method.

2

Influence of surface modification on friction coefficient of the titanium–elastomer couple

51%

Chladek W. , Hadasik E. , Chladek G.

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2007

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tom Vol. 9, no. 2

17-25

EN

This paper presents the results of a study of the friction coefficient of titanium–elastomer couple. The study was carried out with a view to potential future utilization of its results for constructing retentive elements of implanted prostheses. Changes in the friction force were recorded while removing titanium specimens placed between two silicone counter specimens made of Ufi Gel. The influence of the titanium specimen movement speed in relation that of to the counter specimens and the influence of clamping force on the friction force were assessed. Additionally, the surface roughness of titanium specimens differed; in one case, titanium was coated with polyethylene. The effect of introducing artificial saliva between the cooperating surfaces on the friction force and friction coefficient was analyzed as well. Based on the characteristics recorded, the possibilities of shaping the friction coefficient have been assessed, since it is the friction coefficient that determines effective operation of a friction couple through increasing the titanium specimen roughness. The artificial saliva being introduced between the specimens reduces considerably the friction coefficient through a change of the phenomenon model. An increase in the pressure force for the specimens of high roughness entails a reduction of the friction coefficient. The study carried out allows us to identify the roughness parameters, which in turn will enable obtaining the prescribed retention force for friction/membrane couplings.

3

Stress distribution in anchoring regions of posts cooperating with overdentures

51%

Chladek W. , Chladek G. , Krukowska J. , Lipski T.

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2005

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tom Vol. 7, no. 1

35-45

EN

The paper presents the results of model research of mechanical compatibility of selected overdenture structures. The tests based on finite elements method were conducted on flat models reflecting the areas of posts anchoring m a sagittal piane. The reference point was the structure of a prosthesis seated on ball-and-socket joints secured in tooth roots. As altemative solutions, dentures placed on two cylindrical implants supporting ball-and-socket joints were compared with a denture attached to a joint which consisted of a straight axis bar and an elastic clip as well as with a denture supported by a joint of elevated retention, built of a doubly bent axis bar and three elastic bar clips. Taking advantage of the MES Algor program functions, the diverse materiał structures of the systems investigated were modelled. Next. the reduced stresses and principal maximum stresses generated m osseous tissues, in the implants anchoring area. were determined. The value of the mechamcal stimulator decisive to the osseous tissue remodelling was assumed as au evaluatiou criterion. It was assumed that making use of patient's own tooth roots to attach implants IS an optimal solution which, in terms of mechanics, IS practically identical to the alveolodental ligament of a healthy tooth. The application of the other methods of implanted prosthesis attachment always creates a risk of undesirable changes, mostly in the upper area of post insertion into the osseous tissue. The least favourably, in the light of stresses comparison, looks the joint of a doubly refracted axis, where the probability of adverse changes of the osseous tissue in a short time is high. This indicates the necessity to carry on words in order to improve this solution characterized by good retention.

4

Experimental evaluation of occlusal forces

51%

Chladek W. , Lipski T. , Karasiński A.

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tom Vol. 3, no. 1

25-37

EN

The paper presents the results of measuring the occlusion forces in the group of 163 subjects being tested. In the research, the method based on the dependence of the plastic deformity and force intending the spherical penetrator upon each other in a metal sample was implemented. The results obtained allowed us to estimate the distribution of occlusion forces along the alveolar ridge and to define the dimensions of the maximum forces applied, while biting and gnawing. The biting force between the first incisors for different angles of parting mandible was also measured.

5

Estimation of stresses in layers of dentures' relining materials

51%

Żmudzki J. , Chladek W. , Krukowska J.

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2008

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tom Vol. 30, nr 1

21-24

EN

Purpose: Durability tests of materials relining dentures should be carried out in conditions reflecting the real loading that accompanies bite force transmission. The influence of geometry resulting from a denture foundation shape on real stresses in relining has not been so far found. Design/methodology/approach: Using FEM modeling, identified were the stress levels in relining layers in conditions reflecting biting loading for two opposite cases of bone foundation atrophy. Findings: The equivalent Huber-Mises` stresses have not reached their critical values, although tangential stresses on the interfacial where relining is bonded with denture base have reached 440kPa, which, for some of the commercial types of relining denotes the bonding strength. Research limitations/implications: The linear elastic mechanical characteristics were assumed. Hence, during further research, taken into account should be the “stiffening” of characteristics in the upper loadings range, which is typical for silicones. Practical implications: In case of a convex foundation the biggest danger will be caused by any bond defects occurring in the central area because in that area shear of bond has reached the highest values. Originality/value: Values of stresses components identified in this paper reflect the real shear conditions of relining bonding with denture base and might constitute a determinant for strength tests.