Stability of surface texture of soft liners after fatigue testing

The surface properties of relining materials in the short and long term are crucial for the health of the oral tissues. A very common problem associated with the use of soft relining materials is the colonisation with microorganisms and fungi on the surface. Relining materials are subjected to mechanical and thermal cycling in the oral environment, which may change the surface texture and make them more susceptible to microbial colonisation. Objectives: Evaluation of the changes on the surface of soft relining materials after different mechanical cycling periods. Methods: 3 silicone and 2 acrylic based commercially available soft relining materials were used in this study. A stainless steel block for detail reproduction was used on the basis of the apparatus recommended by the ISO 4823:1992 test method for preparing a standardised surface. The specimens were subjected to mechanical cycling in the form of compresion for different periods in 37°C water. A control group from each material was only subjected to water immersion. Cyclic loading was carried out with a strain of 16.6 % and a frequency of 1.6 Hz. The specimens were then duplicated and compared with the controls using surface microscopy and SEM. Results: No difference was observed after 10000 cycles. When the number of cycles was increased to 200000, degradation of the surface and loss of substance and detail was observed. Conclusions: The chemical constitution of the soft relining materials seemed to affect their potential of preserving the surface texture after mechanical cycling. This study supports the hypothesis that mechanical cycling influences the surface degradation process leading to changes of the surface texture and smoothness.