An evaluation of the influence of orthodontic adhesive on the stresses generated in a bonded bracket finite element model.

The objective of this study was to evaluate the stresses generated in the bracket-cement-tooth continuum by a tensile load case when the physical and geometric properties of cement are varied. A 2-stage approach was used. In the first stage, a validated 3-dimensional finite element model of the bracket-cement-tooth system was constructed that consisted of 15,324 nodes and 2971 finite elements. Bracket base geometry was held constant; the physical properties (elastic modulus; Poisson's ratio) and geometry (lute thickness) of the cement varied. A simplified 2-dimensional model was then developed to investigate the localized effects of the cement lute thickness and the shape of the lute periphery on the stress distribution in the system. Small increases in stress were recorded under load within the cement as the rigidity of the cement increased. Similarly, Poisson's ratio values above 0.4 appeared to have a small influence on the major principal stresses in the impregnated wire mesh layer when a tensile force was applied. Variation in lute thickness was shown to have an influence on the distribution of major principal stresses within the cement lute. Increased stresses were recorded at the lute periphery as the lute dimensions increased. The morphologic features of the lute periphery also appeared to have had a significant effect on the performance of an orthodontic adhesive. Acute cement-enamel angles resulted in an increased chance of singularity development and attachment failure. The physical properties and thickness of the cement lute and the shape of the cement lute periphery contribute to the stress distribution within the bracket-cement-tooth continuum and, therefore, the quality of orthodontic attachment provided.

Modeling of viscoelastic behavior of dental chemically activated resin composites during curing.

Shrinkage stresses generated in dental resin composites during curing are among the major problems in adhesive dentistry, because they interfere with the integrity of the restored tooth. The aim of this study was to find a mechanical model to describe the viscoelastic behavior of a two-paste resin composite during curing, to aid our understanding of the process of shrinkage stress development. In this study, stress-strain data on Clearfil F2 during curing were obtained by a dynamic test method and analyzed using three mechanical models (Maxwell, Kelvin, and the Standard Linear Solid model). With a modeling procedure, the model's stress response was compared with the experimental stress data, and the material parameters were calculated. On the basis of the modeling and evaluation results, a model for describing the viscoelastic behavior of the shrinking resin composite was selected. The validation results showed that the modeling procedure is free of error, and that it was capable of finding material parameters associated with a two-parametric model with a high degree of accuracy. The viscoelastic behavior of the shrinking resin composite, as excited by the conditions of the test method, cannot be described by a single mechanical model. In the early stage of curing, the most accurate prediction was achieved by the Maxwell model, while during the remainder of the curing process the Kelvin model can be used to describe the viscoelastic behavior of the two-paste resin composite.

Asymptotic analysis of the stress field in adhering dental restorations.

Polymer-based composites are widely used in restorative dentistry as alternatives to metals and ceramics to fill cavities in teeth. They adhere to the walls of the cavity in the tooth, thus forming a composite body consisting of dentine, enamel, and composite resin. Geometric discontinuities along the interfaces between these materials can induce singularities in the stress field, which in turn lead to premature failure of the restoration. In the present investigation, a complex stress function technique is employed to derive the order of the stress singularity. It is shown that the order of the singularity depends on both the material properties of the restorative material and the local geometry of the cavity. It is also shown that the singularity in the stress field can be avoided through careful design of the cavity shape. The results presented correlate well with experimental results reported in the literature.

A finite element analysis of the stress at the restoration-tooth interface, comparing inlays and bulk fillings.

A finite element investigation comparing bonded inlays and directly placed restorations is presented. The stress build-up due to the contraction of the restorative composite and the composite luting cement was computed using a finite element model accounting for the time-dependent, elasto-visco-plastic behaviour of the composite. In addition, the stresses generated in the restoration due to occlusal loading were computed. It was found that inlays, in general, generate higher stresses during curing, particularly along the interface between the cement and the dentine at the base of the cavity. This is probably due to a reduced capacity for stress relief through viscous flow during the early stages of the curing reaction. Under occlusal load, restorations placed using both techniques perform similarly, from a purely mechanical point of view.

Computation of the elastic properties of a resin impregnated wire mesh by the means of a homogenisation procedure.

The present paper presents a homogenisation technique applied to the problem of calculating equivalent material properties of a resin impregnated wire mesh. Although this type of material can be expected to possess, in general, a four-fold axis of rotational symmetry, it was found that a transversally isotropic model approximates the material behaviour to within 3.5%. It is therefore concluded that a transversally isotropic model is adequate for representing the resin impregnated mesh in structural calculations.

Identification of the Constitutive Behaviour of Dental Composite Cements During Curing.

This paper is concerned with the qualitative and quantitative description of the constitutive behaviour of dental composites during the curing process. Both generalized Kelvin- and Maxwell-models are studied and the parameters characterizing these models are determined by the means of an identification procedure based on the matching of model calculations to experimental data. This procedure is illustrated by means of an example. It is found that the Maxwell-model fits the experimental data better than the Kelvin Model.

Adaptive finite-element approach for analysis of bone/prosthesis interaction.

The study uses the finite-element method to analyse the stress field in a perfectly bonded hip prosthesis arising from loading through body weight. Special attention is paid to the accuracy of the numerical analysis, and adaptive mesh refinement is introduced to reduce the discretisation error. The finite-element procedure developed is especially well suited to analyse the behaviour of a bonded interface as it is capable of calculating accurately the stress at the nodal positions while satisfying the natural discontinuity in the stress field at this location. An orthotropic material model is used for the representation of the behaviour of the bone, and an axisymmetric geometry with non-symmetrical loading is adopted for the analysis. The results demonstrate the usefulness of adaptive mesh refinement and the significance of adopting anisotropic material modelling in the context of tissue/prosthesis interaction.

An adaptive finite-element approach for the analysis of dental restorations.

The present paper deals with the problem of stresses generated during the setting process of polymer tooth fillings. A finite element procedure capable of accurately predicting the stresses along an interface between two different materials is presented. Adaptation of the finite element mesh is carried out based on a simple error estimator. The procedure is tested against benchmark problems and then applied to polymer tooth fillings. The results of the study are relevant in understanding and improving the behaviour of dental restorations.