Biomedical subjects

R H Kuijs

Publications and source records attributed to R H Kuijs.

10 recordsLinked to original sources

PubMed2005

A comparison of fatigue resistance of three materials for cusp-replacing adhesive restorations.

OBJECTIVES: To investigate the fatigue resistance and failure behaviour of cusp-replacing restorations in premolars using different types of adhesive restorative materials. METHODS: A class 2 cavity was prepared and the buccal cusp was removed in an extracted sound human upper premolar. By using a copy-milling machine this preparation was copied to 60 human upper premolars. In groups of 20 premolars each, direct resin composite restorations, indirect resin composite restorations and ceramic restorations were made. All restorations were cusp replacements made in standardized shape and with adhesive techniques. Cyclic load (5 Hz) was applied starting with a load of 200 N (10,000 cycles) followed by stages of 400, 600, 800 and 1000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to 2,10,000 cycles maximum. In case of fracture, the failure mode was recorded. RESULTS: No differences were seen in fracture strength between the three groups (Wilcoxon P = 0.16). No differences were observed with regard to failure mode above or below the cemento enamel junctions (chi2 P = 0.63). The indirect resin composite and ceramic restorations showed significantly more combined cohesive and adhesive fractures than the direct resin composite restorations, which showed more adhesive fractures (chi2 P = 0.03 and 0.002). CONCLUSIONS: The results of this study suggest that ceramic, indirect resin composite and direct resin composite restorations provide comparable fatigue resistance and exhibit comparable failure modes in case of fracture, although the indirect restorations tend to fracture more cohesively than the direct restorations.

Acrylic Resins↗

PubMed2005

Can internal stresses explain the fracture resistance of cusp-replacing composite restorations?

The aim of this study was to explore and compare the results of occlusal load application to cusp-replacing composite restorations, studied by means of finite element (FE) analysis and in vitro load tests. A three-dimensional (3D) FE model was created with a set up similar to an in vitro load test that assessed the fatigue resistance of upper premolars with buccal cusp-replacing resin composite restorations. Occlusal load was applied to two geometries (with and without palatal cuspal coverage), and the tooth-restoration interface and composite material stresses were calculated. Subsequently, safety factors were calculated by dividing the material strength values by the obtained stresses. The highest safety factors were observed for the restorations with cuspal coverage. This was consistent with the load test, in which cuspal coverage led to higher fracture resistance. Furthermore, the FE analysis predicted that failure of the tooth-restoration interface is more likely than failure of the composite material. Correspondingly, the load test showed predominantly adhesive failures of the restorations. Although the described test methods did not lead to a complete understanding of the failure mechanism, it can be concluded that the FE analysis provides additional information with regard to the differences in fracture behaviour of these types of restorations.

Adhesiveness↗

PubMed2004

[Research methods in dentistry 5. The finite element method].

The finite element method is a commonly applied experimental research technique. The method comprises computer simulation of constructions under load and of internal mechanical processes, which enables the study of effects of geometrical and material variations. The analysis shows internal stresses and, consequently, predictions can be made of possible failure. In dentistry, the method is applied in disciplines, such as orthodontics, oral and maxillofacial surgery, implantology en restorative dentistry.

Computer Simulation↗

PubMed2003

A three-dimensional finite element model of the polymerization process in dental restorations.

Restoration of dental restorations with resin composite is hampered by shrinkage of the material during the polymerization process. In this study, we simulated the polymerization process in a detailed three-dimensional finite element model of a human upper premolar with a cusp-replacing restoration. It was analyzed how the stress patterns changed during polymerization and it was assessed whether immediate failure of the restoration is likely to occur and if so, which locations within the restoration are at highest risk and what the clinical implications of these findings are for clinical practice. It was found that the stresses increased rapidly during polymerization and decreased again in the post-polymerization phase. At the interface, tensile stresses relaxed to a higher degree than the shear stresses. Stress values in the composite material and at the interface with the tooth tissue were lower than the reported strength values suggesting that immediate failure is unlikely. The safety factor against mechanical failure of the interface, however, was relatively low indicating that the interface between the composite material and the tooth tissue is at a higher risk for failure than the bulk of the restoration. Stress relaxation was less effective in areas where the interface surface was irregular. In common practice, irregular interface surfaces are used to increase the retention of the restoration. This study indicates that the increased retention may be compromised to some extent by higher shrinkage stresses. The fact that stresses considerably decreased during the post-polymerization period suggests that mechanical loading should be limited during the first few hours after restoration.

Bicuspid↗

PubMed2003

Does layering minimize shrinkage stresses in composite restorations?

Polymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young's modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp.

Chemical Phenomena↗

PubMed2003

[A finite element model of a cusp-replacing adhesive restoration].

This article describes the development of a three-dimensional finite element model of a premolar, based on a micro-scale computed tomographic data-acquisition technique. Using the model shrinkage stresses were analysed during and after the polymerisation process of resin composite. The stress patterns generated were three-dimensional. The results of this study indicate that failure of the interface is more probable than failure of the composite material. The described procedure is a relatively easy method to produce a highly detailed 3-D finite element model of a premolar with an adhesive cups-replacing restoration.

Bicuspid↗

PubMed2003

[Minimal invasive treatment of cuspal fractures of premolars].

This article describes the cusp-replacing adhesive restoration as a minimally invasive alternative for crowns after cuspal fracture of premolars. To demonstrate the importance of this treatment option for daily practice, the results of an incidence study of cuspal fractures are reported. Subsequently, the development of clinical guidelines and procedures as applied in a clinical study of adhesive cusp-replacing restorations are described.

Bicuspid↗

PubMed1998

[Layer thickness of dental adhesives. Relation between layer thickness and viscosity].

OBJECTIVE: To investigate the viscosity of two dental adhesives in relation to the adhesive layer thickness. DESIGN: In vitro study. METHODS: The viscosity of several dental adhesives has been determined with a reogoneometer. Both a high and a low viscous adhesive was used to restore class II preparations. These restorations were sectioned and the thickness of the adhesive layer was measured on several defined locations. A statistical analysis was performed. RESULTS: The high viscous adhesive resulted in a thinner layer along the cervical outline of the restoration. With both materials pooling occurred at the line angles of the preparation. On the flat surfaces of the preparations there was a layer of even thickness. CONCLUSION: The differences in thickness of the adhesive layer as often seen on radiographs cannot be explained solely by the use of adhesives with a different viscosity.

Dental Cements↗

PubMed1996

Consistency of resin composites for posterior use.

OBJECTIVES: The aim of this study was to compare a large set of resin composites suitable for application in stress-bearing areas on the basis of their consistency. METHODS: A variety of posterior resin composites were tested using an apparatus that was originally designed for determination of the consistency of elastomeric impression materials (ISO 4823, 1992). The consistency of a standardized volume of resin composite was tested in a dark room at 23 degrees C by loading the samples during 60 s with 1625 g. After loading, the circumference of each sample was determined by a digitizer. Results were analyzed using Tukey-HSD multiple comparisons test and Student's t-tests. RESULTS: The consistency of different brands of composites varied considerably. P50 was the material with the thinnest consistency. Significant differences (p < 0.05) in consistency were found between the same brands of material which were applied directly out of the syringe or out of a preloaded tip. Loading a Centrix tip with one composite out of a syringe resulted in a thinner consistency of the material than when taken directly from the syringe. SIGNIFICANCE: A ranking of posterior resin composites is presented to enable a material selection based on consistency.

Bicuspid↗

PubMedDate not supplied

Generation of 3-D finite element models of restored human teeth using micro-CT techniques.

PURPOSE: This article describes the development of a three-dimensional finite element model of a premolar based on a microscale computed tomographic (CT) data-acquisition technique. The development of the model is part of a project studying the optimal design and geometry of adhesive tooth-colored cusp-replacing restorations. MATERIALS AND METHODS: The premolar was digitized with a micro CT scanner with a resolution of 13 microns. Surface contours were fitted to the various materials, after which a 3-D finite element mesh was constructed to the contours. To demonstrate the potential use of the resulting model, it was applied to a cusp-replacing resin composite restoration. RESULTS: The stress patterns generated in the composite material were truly 3-D. Stress concentrations were found at the surface where the load was applied and in the vicinity of the dentin-composite bonding surface, where the interface had its complex geometry. CONCLUSION: The described procedure is an easy method to produce a highly detailed 3-D finite element model of a premolar with an adhesive cusp-replacing restoration.

Bicuspid↗