Abstract
Aim: To evaluate the reliability and reproducibility of the Spectromatch-Pro digital colour system (Spectromatch Ltd. UK) in the reproduction of simulated skin-silicone colour samples; and to determine threshold Delta E (∆E) (CIE L*a*b*) of perceptible and acceptable colour differences for maxillofacial prosthetics. Method: A two phase quantitative research design. Phase 1: tested; (i) the reproducibility of the spectrophotometer for eight subjects (n=48) scans; from four ethnic groups White, Chinese, Asian and Black. (ii) minimum silicone-skin sample thickness for colour scanning; and (iii) reproducibility of simulated silicone-skin samples formulae recipe. Phase 2: Determine the perceptible and acceptable colour match difference between colour silicone-skin samples and human skin for 8 subjects'; from baseline colour scan, an in-built colour L*a*b* gradient scales 0-8 at 0.5 ∆E increments were formulated. Silicones samples (n=776) were processed; perceptible and acceptable colour difference (∆E) assessed by (n=12) colour assessors. Results: The spectrophotometer skin colour scans for White, Chinese Indian and Black ethnic groups demonstrated positive correlation (r=0.99). Scanner reproducibility for the eight subjects, Mean ± SD, ∆E maximum (1.43 ± 0.63), to minimum (0.47 ± 0.21); colour formulae silicone sample achieved an acceptable colour match of 0.43 ∆E to 1.36 ∆E. The minimum silicone sample thickness (mm); for light to dark skin tones was 8 mm (White 6 mm; Black 8 mm). Pigment formula-sample reproducibility (Mean ∆E and SD) maximum (1.36 ± 0.29), minimum (0.43 ± 0.16). The acceptable colour difference threshold for skin simulated medical elastomers for four ethnic groups 1.54 ∆E, White 1.61 ∆E; Chinese 1.87 ∆E; Indian was not detectable; and Black 2.33 ∆E. Perceptible and acceptable colour difference (L*a*b*) CIE for L* (Light/dark) for all subjects 1.68 to 3.18 ∆E; for a* (red/green), the scores were below 2 cut off point (not acceptable); and for b* (blue/yellow) 1.58 to 0.51 ∆E. Conclusion: This study has established the reproducibility of the Spectromatch digital colour system; and objectively defined the perceptible and acceptable (∆E) thresholds (1) for facial prosthetics (Mean ∆E 1.54), (2) the relationship to human eye sensitivity and the perceptibility / acceptability for silicone-skin colour match for maxillofacial prosthetics.