Evaluation of adhesive interfaces on dental prosthetics
Laboratory bond strength measurements are a widely used method of evaluating commercial dentine bonding systems. Therefore, a thorough understanding of the stress patterns involved in bond failure is an important factor in evaluating usefulness of a specific bond strength testing method.
Right: A photograph of a stick type test specimen, with the corresponding finite element analysis (FEA) model (far right). The FEA model shows the stress field developed in a test specimen of composite bonded to animal dentine, areas of greater stress are shown in brighter colours. Half of the hourglass shape is shown for the model, a photograph of the specimen is overlayed on this.
Researchers at Sheffield have investigated three standard specimen designs, commonly used in the microtensile bond strength testing method, namely stick, dumbell and hour glass. Three types of study have been performed:
- The microtensile strength measurement itself on each of the specimen designs
- A microscopic examination of the failure surface, to identify the failure mode, and
- A finite element analysis model of the bonding system
In this way the actual and predicted bond strength and failure mode have been compared, and shown to be in good agreement. Studies further indicate that there are no major differences between the three designs in the stress distribution in the adhesive layer.
Left: Low magnification SEM image showing a specimen with cohesive fracture of the resin adhesive material. Both sides of the fracture are shown, above on the dentine side, and below the composite side.
Researchers engaged in this work are George Cardew, Naeima Betamar and Prof. Richard van Noort.
Acknowledgements: We are grateful to 3M ESPE for the donation of the materials used in these studies.