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Denture foundation tissues loading criteria in evaluation of dentures wearing characteristics

Kasperski J., Żmudzki J., Chladek G.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 43, nr 1

324--332

Purpose: Rationalization of rules determining shape of dentures functional characteristics requires knowledge of loading state of tissue denture foundation. Design/methodology/approach: During FEM numerical modeling there was made evaluation of loading state of denture foundation tissues pressed by a hard denture and relined by a silicone layer. Findings: Maximum shear is observed under mucous surface at bone on the side of process prominence. Soft tissues injuries and pain discomfort might result from exceeding both tolerances of pressure and shear, which maximum values are located in the opposite areas. Maximum pressure values are present in central areas at tips of edentulous ridges. The layers of relining material results in a decrease and balancing of maximum pressure values. It decreases tendencies of slip and frictional injuries occurrence by means of reducing tangential stresses on the mucous interface. Nevertheless, the transfer of part of loadings on ridges slopes results in increased shear inside of the tissue at the side of the convexity. In bone tissue at the tips of edentulous ridges there is observed decrease of principal stresses and the lack of significant changes of equivalent von Mises stresses. Research limitations/implications: One of the model simplifying assumptions was the assumption of isotropic linear elasticity of materials mechanical characteristics and denture adherence to its foundation. Practical implications: Recommended to relining are injuries occurring in the central area of bone convexities. If, in spite of a proper denture fit, there is still a typical ulceration at the side of the ridges convexity, use of relining increases shear of those area of the tissue, conducing development of a typical deep ulcer located usually from the bone towards the surface of soft tissues. Originality/value: Tangential stresses and loads on mucous surface are not the only one criterion of evaluation and diagnosis of mucous membrane loading state.

Estimation of stresses in layers of dentures' relining materials

Żmudzki J., Chladek W., Krukowska J.

Archives of Materials Science and Engineering

2008

Vol. 30, nr 1

21-24

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.