Overview
SIST EN ISO 7491:2001 (ISO 7491:2000) specifies a standardized method to determine the colour stability of dental materials after exposure to light and water. Colour stability is a critical property for restorative and prosthodontic materials where long-term aesthetics and clinical acceptance depend on resistance to fading or discoloration.
This standard is used in conjunction with material-specific standards that define specimen preparation and references. It describes the test environment, radiation source, specimen mounting, exposure duration and visual comparison procedure.
Key Topics
- Radiation source: A xenon medium-pressure lamp with colour temperature 5 000 K to 10 000 K and an illuminance at the specimen of 150 000 lx (deviation ±10 % permitted). Equivalent light sources of comparable performance are acceptable.
- Ultraviolet filter: Borosilicate glass filter with transmittance <1% below 300 nm and >90% above 370 nm to replicate realistic daylight spectra while limiting short-wave UV.
- Water bath conditions: Circulating water (grade 2, ISO 3696) at (37 ± 5) °C with a water depth of (10 ± 5) mm above specimens to simulate oral hydration during exposure.
- Specimen holder: Opaque holder (preferably metal) for discs up to 50 mm diameter; design permits clamping or partial covering of specimens for side-by-side comparison.
- Exposure procedure: Specimens are exposed in the water bath with the UV filter in place for (24 ± 1) h to xenon irradiation. Half of each specimen is shielded so exposed and unexposed regions can be directly compared.
- Colour comparison: Visual assessment by three observers with normal colour vision (verified). Observations are made under diffuse daylight conditions or a D65-equivalent lamp, at 1 000–2 000 lx, with viewing distance 200–300 mm and exposure to the sample limited to about 2 s.
Applications
- Quality control and batch release testing of dental restorative and prosthodontic materials.
- Material selection during product development and formulation optimisation to improve long-term aesthetics.
- Comparative studies and conformity assessment for regulatory submission and certification.
- Research into ageing, pigment stability, and effects of light and water on dental polymers, composites and prosthetic materials.
Related Standards
- ISO 3696 - Water for analytical laboratory use (specifies water quality used in test).
- ISO 4892-2 - Methods of exposure to laboratory light sources - Xenon-arc sources (illuminance and lamp requirements).
- CIE Publication 15.2 - Colorimetry (D65 reference and viewing conditions).
Keywords: SIST EN ISO 7491:2001, ISO 7491, dental materials, colour stability, xenon lamp, UV filter, water bath, visual assessment, D65, quality control.