Colourfast pigments in silicone hand and maxillofacial prostheses

Abstract

This study addresses the clinical problem of long-term discolouration of silicone hand and maxillofacial prostheses. Seven (7) pigment hues, considered essential for achieving a suitable tissue colour-matched prosthesis, were compared for their colourfast property, across three selected proprietary formulations. In all, a series of 21 pigments, were tested for colourfastness. The pigments, presenting as suspensions (PS), pastes (PP) and dry pigments (PD), were exposed, over nine months, to ultraviolet light, elevated temperatures and varying concentrations of salinity. Colour change of the pigments was measured and expressed as Commission International de l'Eclairage (CIE) (L*, a*, b*) units. Pigment discoloration was significantly attributed to ultraviolet light. Pigmented and clear silicone samples showed a "yellowing" (+Δb*) effect. Lighter pigments became darker (-ΔL*) in shade. Pigment samples at the elevated temperature of 50°C showed significant but small colour change (ΔE, 0.77 to 3.63). Only the master blue pigment (PS-4) recorded a higher ΔE, 6.26 at 50°C. At a moderate temperature of 35°C, both pigmented and clear silicone test samples remained relatively colourfast. Comparison was made to control samples, stored in darkness, at 26°C. The pigments were generally colourfast (ΔE<6 units) to saline solutions of 0.15M and 5.0M concentrations. Only the monastral red (PD-3) pigment recorded a ΔE of 9.33, in 0.15M normal saline, simulating the vulnerability of this pigment to the salinity of human sweat. Pigment hues were systematically ranked according to colourfastness. Pigment suspensions were more colourfast than pigment pastes.