ISO/TR 28642:2016

Overview

ISO/TR 28642:2016 - Dentistry - Guidance on colour measurement provides practical guidance for assessing and interpreting colour (shade) in dental tissues and materials. The technical report identifies three main topic groups - colour compatibility, colour stability, and colour interactions - and describes both visual and instrumental methods for evaluating shade conformity and interconvertibility of monochromatic and polychromatic dental specimens. It also gives guidance on reporting, observer colour-vision screening, and interpretation using colour-difference metrics (ΔE) and 50:50 perceptibility and acceptability thresholds.

Key Topics

• Visual and instrumental assessment: Recommendations for using spectrophotometers, spectroradiometers, colourimeters, imaging systems, viewing booths, and hand‑held shade lights. Emphasis on spectral measurements for flexible illuminant/observer calculations.
• Measurement settings: Considerations for illuminant, standard observer, geometric conditions, illuminance, visual angle, background, and surround - all critical to repeatable shade measurement.
• Colour-difference metrics: Use of CIE formulae (e.g., ΔE variants) to express colour distance; interpretation via 50:50 perceptibility and acceptability thresholds.
• Observer competency: Screening and qualification methods for human observers, including Ishihara, Farnsworth‑Munsell 100 hue, and dentistry‑specific colour discrimination tests; guidelines on testing intervals.
• Test methods and reporting: Protocols for visual judgments and instrumental evaluation; standardized reporting items (illuminant, object, observer/instrument details).
• Appearance attributes: Recognition that translucency, opacity, gloss, and colour shifting (blending and physical translucency) influence perceived shade and must be considered in assessments.
• Coverage error: Definition and use of coverage error to evaluate how well shade guides represent natural tooth colours.

Applications

• Clinical shade selection: Improving dentist and technician communication and achieving better aesthetic outcomes.
• Material development and QC: Manufacturers can assess colour stability, aging, staining, and inter-material compatibility.
• Research and standardization: Use in sensory studies, perceptibility/acceptability testing, and development of new dental shade guides.
• Education and training: Establishing competency testing for clinicians and lab personnel performing visual shade matching.

Who should use this standard

• Dentists and prosthodontists
• Dental technicians and laboratories
• Dental materials manufacturers
• Color scientists working in dental research
• Standards developers and regulatory bodies

Related Standards

• ISO 1942 - Dentistry - Vocabulary
• ISO 11664‑1 - Colorimetry: CIE standard colorimetric observers
• CIE publications cited for colour-difference formulae (e.g., CIE Pub No 15.3)

Keywords: ISO/TR 28642:2016, dentistry colour measurement, shade matching, ΔE, perceptibility threshold, acceptability threshold, spectrophotometer, shade guides, colour stability.