Background. Prosthodontists use silicones and pigments for extraoral prostheses. Degradation leads to deterioration of optical properties. In vitro work showed that UV and oxidation are potential contributors but the cause is unclear. Objectives. Due to the absence of compositional studies, the aim is to determine the chemical change in two silicones and one pigment after photodegradation. Methods. A pilot determined the analytical techniques suitable for the materials. The main study used UV sources to age samples in different gas environments. Colourimetric measurements were performed at frequent intervals. After degradation, analytical results were compared with those from the pilot study. Results. IR and NMR spectroscopies provided compositional information. The chemical structure dictated the degradation process. For the silicones, the crosslinking reactive sites were the least stable and seemed to be associated with colour degradation. Conclusion. An understanding at the molecular level will result in better solutions to this problem.
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