UV/Vis Spectroscopy Protocol for Pigment Degradation in Maxillofacial Prosthetics Elastomers

Objectives: Establishing a standardised protocol for UV/Vis spectroscopy pigment degradation studies in maxillofacial prosthetics, which will aid in further research.
Methods: A Translucent maxillofacial elastomer (A-223-30, Factor II, Inc., Lakeside, AZ, USA) was cured as two 1mL circular samples of 35mm diameter and 1mm thickness: without pigments and other with 9.68 μL of Bright Red TECH-P112-50 added (Technovent,UK). For the spectroscopic measurements, a Lambda 900 UV/Vis/NIR spectrometer equipped with an integrating sphere (PerkinElmer,UK) was used over the range of 350-750nm having a white diffuse reflectance standard (Spectralon®,Labsphere,USA). The data was expressed as Reflectance(R) and was processed with the software PerkinElmerUVWinLabV.6.0.4/2011 (PerkinElmer,UK). The samples were exposed to two sunlight simulators and spectroscopically profiled according to the time sequence: Sun-2000ABET Solar Simulator (ABET Technologies,USA) at 1,2,3,4,5,6,8,10,12,14,16,18,20,25,30,40,60,90,120,180,240,360,420,480,600,720,840,1200,1440 minutes. For 2880,4320,5760,7200 and 8640 minutes, the solar simulator employed was the Q-Sun Xe-1 (Q-Panel Lab Products, Westlake, OH, USA), calibrated dry according to ASTM D 7869-13.
Results: The Translucent A-223-30 maxillofacial silicone spectra presents a plateau over the visible range (from 400-700nm) and Reflectance(R) of 0.85, and after exposure to 8640 min. of sunlight simulators, the spectra keeps its plateau shaped aspect, and has a lowest Reflectance value of 0.70 at 400nm and maximum of 0.79 at 700nm. The Bright Red has a broad spectral reduction in Reflectance, as a result of the strong absorption in the green regions of the spectrum, with minimum of 0.54 at ~ 500nm. Upon UV exposure, the characteristic visible absorption characteristics are seen to rapidly degrade, initially on a timescale of ~ 300 minutes, followed by a slower degradation over a period of 8000 minutes, until a final Reflectance of 0.74 at 500nm is reached.
Conclusions: This suggestion experimental protocol for spectroscopic profiling of maxillofacial pigment degradation may aid the understanding of when and how the discolouration process occurs in extraoral maxillofacial prostheses. From our findings, the Red pigment presents the faster colour decay.